Ditching a helicopter: (incl pictures)

[HeliEng]

I have just been looking at another post with a picture of one of Bristows Pumas in the sea, and it got me thinking.

Realistically, how long can you expect a float equipped aircraft the stay afloat for? Whether it be an R22 Mariner or a Super Puma.

Also, are the floats designed to save the aircraft ie:- Stop it sinking all together, or is it just to give crew and pax an extended amount of time to get out?

Would be interested to hear what you guys have to say, and also to know whether there is any data regarding this issued by the manufacturer.


"Some days you are the pigeon, some days you are the statue!"

[ 08 November 2001: Message edited by: HeliEng ]

[widgeon]

see post on lightning strikes for link to AAIB report on Puma strike and ditching. We worked with Apical to certify emergency floats for AS350 that allow you to take off again after landing on water ( I think it did one full rotation at start up before the TR took over !) . I don't recall too many reports where they have been able to recover the aircraft after ditching , if the sea is dead calm the floats should keep the helicopter floating but how often do you sea a calm sea ?.

[Lu Zuckerman]

Pop out floats were invented and developed by the US Coast Guard Rotary wing Development Unit in Elizabeth City, North Carolina. We had them installed on our HO3-Ss (S-51). We never had the reason or opportunity to use them but in the developmental stages they landed with the floats deployed and they also landed (but very gently) to test the immersion switches. Naturally, after landing they had to take off again but the landing and takeoff were conducted in a protected area with minimal wave action. If you recall I had posted on another thread my experiences with this type of helicopter and how easy it was to get into ground resonance when operating off of a pitching and rolling flight deck. If the landing were made in the open sea things would be very difficult especially on the 3-S because it had a three bladed rotorhead and tricycle landing gear which made it very unstable. I would think that it would be very difficult to takeoff once having landed with the floats deployed for the same reason the 3-S had difficulty in starting up on the flight deck. The reason (Please everybody, do not jump on me telling me there is no such thing) is gyroscopic precession. The wave action will cause the fuselage to pitch and roll while the blades are rotating. This differential of movement will introduce a perturbing force into the rotorhead and it will respond 90-degrees later. The next movement may be in a different direction causing the rotor to precess in a different direction. This could cause instability in the rotor system. I doubt if ground (water) resonance would come into play because of the flexible as opposed to a hard surface but it would make it difficult to maintain control.

All of this is IMHO

[HeliEng]

Sorry to be a pain in the a*se, but that still doesn't answer the question of whether the float system is there to save the aircraft or extend escape time.

What statistics show is something totally different. That does not show what they are intended for.

Do the manufacturers not provide this kind of information?????

Sorry again!

[widgeon]

AS350 description and operations manual chapter 25 section 62 para 1 , scope states.

In the event of a ditching the emergency floats provide sufficent bouyancy to enable the personnel to be evacuated and the aircraft to be recovered.

Obviously variants like sea state and time to get a suitable recovery craft to the airframe come into play. This documents for this type suggest floats are intended for both purposes.

[HeliEng]

Thank you very much.

That was what I was looking for.

Cheers for your help

[Cyclic Hotline]

The primary design and certification goal of installing an Emergency Floatation system is to allow the safe egress of the occupants.

Salvaging the aircraft is a bonus (or maybe not, depending on your point of view!), if it occurs. The majority of aircraft that survive the initial ditching and remain afloat, always seemed to be generally sunk or severely damaged in the salvage attempt.

I do recall a few succesful float-jobs off the top of my head. Quite a few 212's over the years (Worldwide), an S61 that was towed back to Aberdeen undamaged, (another one that spent a few days in the water and was rebuilt by Sikorsky, yet another that sank and was at the bottom of the Amazon for a couple of weeks, and was rebuilt). A B214ST off Peterhead that was relatively undamaged, BV234 that ditched and then sank(?), and I know there are more. Check out Bill Kellogg's experience at; http://www.justhelicopters.com/picture_gallery.htm

Federal Aviation Regulations.
Part 29. Airworthiness Standards:
Transport Category Rotorcraft

Sec. 29.801 Ditching.

(a) If certification with ditching provisions is requested, the rotorcraft must meet the requirements of this section and Secs.29.807(d), 29.1411 and 29.1415.

(b) Each practicable design measure, compatible with the general characteristics of the rotorcraft, must be taken to minimize the probability that in an emergency landing on water, the behavior of the rotorcraft would cause immediate injury to the occupants or would make it impossible for them to escape.

(c) The probable behavior of the rotorcraft in a water landing must be investigated by model tests or by comparison with rotorcraft of similar configuration for which the ditching characteristics are known. Scoops, flaps, projections, and any other factors likely to affect the hydrodynamic characteristics of the rotorcraft must be considered.

(d) It must be shown that, under reasonably probable water conditions, the flotation time and trim of the rotorcraft will allow the occupants to leave the rotorcraft and enter the liferafts required by Sec. 29.1415. If compliance with this provision is shown by buoyancy and trim computations, appropriate allowances must be made for probable structural damage and leakage. If the rotorcraft has fuel tanks (with fuel jettisoning provisions) that can reasonably be expected to withstand a ditching without leakage, the jettisonable volume of fuel may be considered as buoyancy volume.

(e) Unless the effects of the collapse of external doors and windows are accounted for in the investigation of the probable behavior of the rotorcraft in a water landing (as prescribed in paragraphs (c) and (d) of this section), the external doors and
windows must be designed to withstand the probable maximum local pressures.

[ 09 November 2001: Message edited by: Cyclic Hotline ]

[Jed A1]

Helieng, there are two answers to your original question.

Firstly, emergency pop out floats are just that. For use in emergency to keep the helicopter afloat for long enough to enable the pax and crew to exit. Generally speaking (as there are many different types of installation) you should expect the helicopter to stay afloat for approx 20-30 mins, in clam water's. Acouple of minutes in rough water's. If the ditching has occurred near to the beach, a vessel or offshore installation then you may just have enough time to recover the aircraft.

The pop out floats have a nasty habit of slowly deflating. Hoses, connections and the floats themselves slowly leak after being inflated. The air bottles used to inflate them have one shot of air to inflate once. Usually one float will deflate faster than the others (due to Murphy’s law) and cause the aircraft to list or even roll over.

Great care has to be taken when alighting the water with regard to forward, sideways speed and wave action to ensure one is not ripped off. See above for outcome. All this at a time when the excrement has already hit the air-conditioning.

The second answer to your question is with regard to fixed floats as per the R22 Mariner. These are either of a rigid plastic or rubber construction or inflatable (with the ability to top up the inflation). Fixed floats are designed to be in constant use for many take off's and landings. Great fun at start up, trying to keep the yaw under control. Great fun taxying (although not recommended). I don't know of any twin machines using fixed floats (I stand to be corrected) but reasonably popular with single machines, B206, H500, H300, R22 etc. Used extensively by Tuna spotters.

[Lu Zuckerman]

Here is some more useless or extraneous information regarding ditching. In 1949 when I was attending aircraft mechanics school in Elizabeth City, NC the Coast Guard was developing a standardized ditching procedure. Several years prior to this, the Coast Guard had sold 13-14 HOS-1s to Western Union to be used for line patrol. They proved to be too expensive and were returned to the CG. Each of these helicopters was flown to an altitude of about 1000-1500 feet and autorotated to touchdown in the water. The helicopters were landed at different fuselage attitudes relative to the surface. In most cases after landing the helicopters were rolled to the right in order to separate the blades from the rotorhead. In those days the Sikorsky blades had a singular tubular spar much like a flagpole that had different decreasing diameters from the root to the tip. The blades had internal ribs and were covered in fabric. I believe that this maneuver was performed to prevent rotor incursion or to prevent exiting passengers from being struck by a rotating blade.

[Nick Lappos]

I hate to yet again be the gadfly to put pins in Lu's credibility, but on water operations in helicopters is very normal, very natural and very safe. Rotor starts, takeoffs and landings are normal water operations for many helicopters, and gyroscopic precession problems are a mythological problem, like glowing helicopters and 18 degree rigging problems. I have many water landings in boat-hulled helos, and know of lots of normal water-borne operations in many types.

Regarding the original question from Helieng, the several posters who said emergencies only are correct, at least for the Sikorsky S-76 and S-92. They are designed to let folks egress safely, and any more float time is for bragging rights.

Those floats that allow normal operations are so stated in the flight manual as allowing amphibious operations in Chapter 1 of the manual. I know of no pop-out floats that allow amphibious operations. :D

[Lu Zuckerman]

To: Nick Lappos

“I hate to yet again be the gadfly to put pins in Lu's credibility, but on water operations in helicopters is very normal, very natural and very safe. Rotor starts, takeoffs and landings are normal water operations for many helicopters, and gyroscopic precession problems are a mythological problem, like glowing helicopters and 18 degree rigging problems. I have many water landings in boat-hulled helos, and know of lots of normal water-borne operations in many types”.

I was operating on a float equipped helicopter (HTL-1) most likely before you took your first airplane ride. That helicopter was very stable on the water and it was able to shut down and start up and then take off with no problems. The HO3-S on the other hand was highly unstable because of a high CG and the fact that the pop out floats were mounted on tricycle landing gear. As I indicated previously we had problems in operations off of the back end of an icebreaker. Under the stated conditions and with this helicopter you have no standing because you were never exposed to this type of operation with this type of helicopter.

Regarding your experience with boat hulled helicopters; these aircraft were made for water operations. While at Sikorsky I watched the first tests of the S-52. They had a small model and they shot it into a child’s wading pool while taking high-speed motion pictures of the models behavior when it hit the water. The model was equipped with a weight that could be raised on a shaft to simulate changes in vertical CG. I asked why they had to perform the tests under various CG conditions. The engineers replied that they had to get CG right in order to maximize the stability of the helicopter when it was in the water. The HH3 has a much lower vertical CG by comparison to the S-51 and the lateral stability is much greater than the S-51. I would think that the S-51, which was susceptible to going into ground resonance on the flight deck, would also be subject to rotor perturbation due to the movement of the helicopter as a result of wave action. Your boat-hulled helicopters are immersed along their waterline and this provides the major buoyant support while the sponsons provide lateral stability while helicopters on floats ride much higher on the water. Many other helicopters that have pop out floats are partially immersed in the water and can’t recover or take off as the tail rotor is in the water. The S-61s at least those that were made by Agusta had sponsons that were much bigger than the standard S-61 to improve lateral stability and add additional buoyancy. These helicopters were used in offshore work.

Regarding gyroscopic precession please tell me what would happen if you move the fuselage in relation to the spinning rotor disc. It seems to me that when the fuselage is displaced it changes the swashplate angle in relation to the rotor disc causing a pitch input that would result in a change in the disc attitude. If the wave action is erratic the disc could be moving all over the place. If the helicopter were on land this would be ground resonnance.

Over

[Nick Lappos]

Lu,
You wax on so much you get all muddied. The entire point of your first post was about how much you knew about the (mythological) precession and how it made water operations a bad idea. You start in again at the end of your last post. This is not a factor, and (parden the pun) you are all wet here.

Furthermore, if you felt that I "have no standing" in matters like water operations because you RODE as a PASSENGER in a water landing, that makes you all hot air, as you have never flown anything, let alone an amphibious helicopter.

It is a shame that you can't separate the great number of things you do know from the even greater number of wrong things you THINK you know! Please don't ask any questions on precession, you will only hurt yourself trying to screw it all up.

[ 10 November 2001: Message edited by: Nick Lappos ]

[Lu Zuckerman]

To: Nick Lappos

“You wax on so much you get all muddied. The entire point of your first post was about how much you knew about the (mythological) precession and how it made water operations a bad idea. You start in again at the end of your last post. This is not a factor, and (parden the pun) you are all wet here”.


“Furthermore, if you felt that I "have no standing" in matters like water operations because you RODE as a PASSENGER in a water landing, that makes you all hot air, as you have never flown anything, let alone an amphibious helicopter”.

Response:

Once again you have taken my statements out of context and twisted the meaning. I stated that boat hulled helicopters are very stable in the water because of the large wetted area of the fuselage and the fact that they have sponsons. I also stated that the HTL-1 was very stable on the water and that you could shut down and start up on the water and by inference the boat hulled helicopters including the CH-47 could do the same. However I stated that the HO3-S was unstable on the water because of it’s landing gear configuration and as a result was susceptible to movement of the fuselage because of a very high CG. Because it was a three bladed helicopter you would not want to shut it down and then restart for the reasons quoted in another thread dealing with the possibility of resonance. Using the term resonance I am implying that the helicopter would move all over the place during start up due to temporary imbalance of the rotor system until it came up to speed. When I made the statement about you having no standing I specifically stated that you had never flown an S-51 off the back of a pitching and rolling flight deck.

Oh by the way, I have several hundred hours of stick time in S-51s, S-55s, HO5-Ss and the HTL-1.


“It is a shame that you can't separate the great number of things you do know from the even greater number of wrong things you THINK you know! Please don't ask any questions on precession, you will only hurt yourself trying to screw it all up”.

Response:

Nick did you ever hear of the word imagery or maybe they never used the word at Georgia Tech. Imagery among other things is defined as creating images or pictures in your mind. I have to use this process every day as a RMS Engineer. Here is an example.

Picture a spinning articulated rotor disc. The disc as a whole has rigidity in space ala a gyroscope. The blades can respond individually to gusting or some other external force and flap up in response to the gust load. When the blade flaps up the pitch coupling will extract pitch from the blade and it will return to its’ in track position. If the external aerodynamic forces are continuous the entire disc will respond and you can get flap back / blowback and the pilot must take corrective action by application of a countering cyclic input. If we are addressing Bell or Robinson helicopters the swashplate and disc are parallel to each other and on any other helicopter depending upon phase angle the swash plate will deflect in a different direction than the disc. However this is the normal state for the swashplate in relation to the disc. If the blade moves in relation to the swashplate there will be pitch flap coupling.

Now lets’ reverse the situation. On the water the blades are rotating through a fixed tip path and they exhibit rigidity in space. If the fuselage is displaced sufficiently it will move in relation to the spinning disc. If the fuselage moves then the swashplate and pitch rods will move with it as a single unit. With the blades rigid in space the pitch rods will move in relation to the blades causing a pitch change. Because of the wave action and the frequency and amplitude of the wave action as well as the directions of the waves in relation to the fuselage the pitch input can vary in both amplitude and direction causing the rotor system nutate. The amount of nutation and the frequency of change can cause the rotor to be unstable. If the offset interlock is sufficiently strong the disc movement can be reflected in the movement of the fuselage. The S-51 due to the nature of its’ rotor design had minimal offset interlock. If the helicopter is stable in the water this action will be minimal however if the helicopter is not stable then this movement will be quite noticeable. This is why I likened it to ground resonance. To my knowledge the only helicopter with an articulated rotor system that was mounted on floats was the US Air Force H-19 and having never worked on or flown in it I can’t say how stable it was and how it responded to being started up on the water. There may be others but but I have no knowledge of these helicopters.

We can take the argument one step further. Let’s assume that the offset interlock is strong enough to allow the disc to reflect fuselage movement. The constant movement of the disc will result in the onset of gyroscopic precession causing the disc to respond 90-degrees after the input of the upsetting force. As the wave direction and intensity varies the disc will end up chasing itself like a dog chases its’ tail.

Over

[ 10 November 2001: Message edited by: Lu Zuckerman ]

[ 10 November 2001: Message edited by: Lu Zuckerman ]

[tigerpic]

i love a good discussion! especially if i'm right! lol :D

[Nick Lappos]

HeliEng,

You can't have it both ways, a lively forum and a quiet nap.

When someone posts their thoughts, and they are simply wrong, if there is no challenge, this forum will turn into a dumping ground for unchallanged theories and misleading information. We are not talking about what color to paint your living room, where the "wrong" color does not exist except in opinion. We are talking about how and why the machines we fly behave the way they do. Facts must predominate.

Where someone posts a wrong fact, it should and must be challanged if it is important enough. The object of this forum is to help folks decide what to do and how to fly their machines, not to let you rest easy.

I don't particularly like to argue, either, BTW.

Let the group decide - is this forum to be a simple unchallanged place to park any idea, however valid and flawed? Should readers be lead to believe (in this specific incidence) that a float landing is made dangerous by gyroscopic precession? Please, let the group call it. If the neighborhood decides that, I can live with it, elsewhere.

:)

[Heliport]

Nick

You are right to challenge flawed theories, and to correct misleading information.

Forums inevitably attract a wide variety of people, and there is nothing to prevent anyone continuing to push their pet theories even when those theories have been discredited in everyone's eyes except their own.

I think you can rest assured that a test pilot's views carry a great deal of weight on Rotorheads!

I suspect most people are more interested in what helicopters actually do in practice, than in what according to some pet theory they should, but don't.

More of your excellent contributions, please!


Heliport
Moderator

[ 11 November 2001: Message edited by: Heliport ]

[HeliEng]

Nick,

Looks like once more I have been misunderstood.

I don't 'want it both ways' I enjoy a lively forum, with many different contributions, arguements and challenges. What I find a little tiresome is your CONTINUAL challenging of Lu's arguements.

No-one likes arguing, but it seems as though you can NEVER agree.

For me (and this is an opinion) these forums are best when you have inputs from many people with different viewpoints, and backgrounds. When I open a thread and the order goes, Lu, Nick, Lu, Nick, Lu, Nick and so on, I personally switch off, I close the thread and go to the next one.

None of this is meant to offend either yourself or Lu, and I am sorry that my previous post has been so mis-interpreted, as to provoke your last post.

[Lu Zuckerman]

To: Heliport

“You are right to challenge flawed theories, and to correct misleading information.
Forums inevitably attract a wide variety of people, and there is nothing to prevent anyone continuing to push their pet theories even when those theories have been discredited in everyone's eyes except their own”.

Response:

You are totally correct in what you have stated however Mr. Lappos has only challenged my theories by telling me I’m full of crap to put it mildly. He has yet to offer any technical reason as to why my theories are false. I would suggest that you dig up my posts on this thread and see if I had asked him to respond on a technical basis. The only time he ever offered a technical answer regarding the 18-degree offset on the Robinson rotorhead. His explanation was that pitch flap coupling allowed the rotor system to behave as if it had a 90-degree phase angle and that all blade motion in response to cyclic input would take place within 72-degrees as opposed to 90-degrees on other helicopters and I am not fullky convinced of this and that is why i will have the test performed. Mr. Lappos can only disprove the theory about the rotor system being effected by wave action when the helicopter is on pop out floats when he offers the technical reasons why my theory is flawed.

“I think you can rest assured that a test pilot's views carry a great deal of weight on Rotorheads!
I suspect most people are more interested in what helicopters actually do in practice, than in what according to some pet theory they should, but don't”.

Response:

How about the views of a Senior Reliability Maintainability and Systems Safety Engineering consultant that has been in this field since 1968. What about the experience gained while in this field working on the Apache, The Cheyenne, The A-129, The EH-101, The AH-1J, The B-214 and all of the other Bell Helicopters in use at that time. How about my experience in the US Coast Guard working as a maintenance technician on Bell and Sikorsky Helicopters and, how about attending close to 18 Helicopter factory schools. I would think that that is worth something. I don’t place myself above Mr. Lappos and I really don’t care if he challenges me. However what I don’t like is when he responds on a very personal level and then he does not provide the technical material that counters my claims.

[ 11 November 2001: Message edited by: Lu Zuckerman ]

[ 11 November 2001: Message edited by: Lu Zuckerman ]

[hoverbover]

Why do I love flying helicopters?

Because they are unpredictable and each time you fly you learn something new! Im also afraid that the helicopter never read any books on what it should and shouldnt do, and never bothered reading the rules,just like a dog ,it will bite you if you provoke it.You fly helis by the seat of the pants,and a boffin may be able to give you all the numbers in the book, but could he get it off the ground????

I see people like Nick Lappos doing things with helicopters I can only dream about, they have been there and done it got the T shirt, and some have paid the ultimate price so that idiots like me can read the RFM and know the helicopters limitations without having to take the risk. My hat is off to you and your kind, you are the gods of our industry.

Regards
Hover Bover
PS
Lu this is not a swipe at you, just the way I see it, and why you will probably find one hell of a lot of support for Nick, after all he probably has done it all and more, and pilots know that.

[ 11 November 2001: Message edited by: hoverbover ]

[Nick Lappos]

hoverbover,

Don't go on so, test pilots are very human and screw up more often than they care to admit. We have a fun job, but in the end it is the users like you that are King, because all we in the manufacturing and governmental testing work for is to get you in a safe, efficient machine.

The real "Gods" are those who use the machines every day, in the North Sea, in rescue squadrons at godforsaken places, in police work, wire stringing, military missions and the like. I stood at the seawall at Peterhead in Scotland and watched the S-61's and 76's go out in a gale with the wind blowing the rain sideways at me, and I was driven to tears with the thrill of knowing that those guys do it EVERY day and EVERY night, and they make it look easy!

Now, regarding Lu's insessant bull about floats and precession being different that boat hulls, I will not debate with him, he is like the science fiction creature who thrives on the things you use to stop him. In his case it is pedantic debate about his crackpot theories that feeds him!

I hereby quit discussing this with him.
Folks out there, his assertions about precession and water landings are pure poppycock, period. No debate, email me if you want more logical thoughts as to why, I don't share these thoughts with Lu, as it will make him step on some Japanese trains like Godzilla, and I don't want that to happen! ;)

[Hoverman]

Nick
You contributions to the forum are highly valued, for obvious reasons. And of course it's helpful when you point out theories/statements which are incorrect.
Whether you choose to enter into a discussion justifying your opinions is a matter of choice for you as far as I'm concerned.

Lu
You ask "How about the views of a Senior Reliability Maintainability and Systems Safety Engineering consultant .... How about my experience as a maintenance technician on Bell and Sikorsky Helicopters etc"

Hoverbover has already answered that question far more eloquently than I could.

I enjoy many of your posts, particularly the anecdotes. The problem is that you don't seem able to let your theories drop, and try to squeeze them into unrelated threads. (This one was about floats/ditching!)

You know as well as I do the effect that has had on so many contributors. They get fed up!
This doesn't happen with anybody else, but it constantly happens with you.

Let's try a new approach...
I get the feeling that people have now had enough of the 'problems' of gyroscopic precession and 18 degree rigging theories, and don't want either topic brought into other discussions so often, or at all.
Do you get the same impression?
What about letting them drop?

[Lu Zuckerman]

The following was extracted from the article about the rollover of the Super Puma in the North Sea.

The passages are not in the order of their occurrence in the article. I changed their order for journalistic juxtaposition.

“The rotor blades were still turning as the Super Puma helicopter rolled and it is understood one blade struck the co-pilot, breaking his leg”.

“According to a spokesman, the West Navion was pitching and rolling between four and five meters. A westerly wind was blowing at 33knots-gale force seven to eight – and visibility was 4,000m.

"If it was sitting steady on the deck I can only imagine it was pitch and roll that caused the problem."

This may very well be a case of dynamic rollover but is there a possibility that the pitching and rolling effected the stability of the rotor system?

We had a similar situation on an icebreaker with our S-51s. What kept it from rolling over was that it was tied down during start-up and released as the piliot pulled collective. If the movement of the helicopter was violent enough we would release and the pilot would clear the deck by pulling collective.

This will be my last input on this subject.
Of course my fingers are crossed.

[sling load]

Lu,
I don't understand how you call yourself an RMS Engineer when you don't have an Engineering Degree. Are you a member of a professional engineering institute or association?

I should call myself a Helicopterologist.

[widgeon]

i think some people have not understood the name of this thread is starts with a D not B.
LOL

[Lu Zuckerman]

To: sling load

True, I do not have an engineering degree. I majored in Industrial Design with a minor in general science. I did take several courses that were a part of the Engineering curriculum but not enough to be called an engineer. After leaving school my first job was with Sikorsky and after completion of a fourteen-month training program I was given the title of Field Service Engineer. Ever since that time I have been working in various aspects of the engineering field and in every one of those jobs I was considered to be an engineer.

Regarding professional organizations I have belonged to many of them. If I wanted to take the time and expend the effort I could attain professional status as a Reliability Engineer, a Maintainability Engineer, A Safety Engineer or a Quality Assurance Engineer. At my age and experience level the obtaining of professional status does me no good.

Now, I will ask you the same question. Why do they call aircraft mechanics in the UK and most likely in OZ and NZ Engineers when they do not have an engineering degree?

[heedm]

Lu got me thinking when he mentioned the rotor disk staying in plane but the fuselage rolling and pitching with the waves causing the swash plate to change it's orientation with respect to the rotor disk. I think he's right that it causes disk movement, but I see it increasing stability and rotor clearance rather than generating any problem.

This discussion only requires a response from the rotor due to a change in swashplate orientation. It doesn't require any mention of gyroscopic precession, aerodynamic precession, Newton's Laws, etc.

Consider a Jet Ranger on floats that rolls left. The rotor disk wants to stay in plane but the swashplate at 3 o'clock (from above) rises. This causes blade pitch increase at 12 o'clock which causes the disk to tilt to a new plane with the tips highest at 9 o'clock and lowest at 3 o'clock.

Since the helicopter rolled left, this new disk position would attempt to roll the helicopter back to level.

Seems to me that this generates stability.


Matthew.

[sling load]

Lu,
Yes in Australia and the UK Maintainers are called Engineers, but the term is to do with the Licence they are issued Licensed Aircraft Maintenance Engineer, or LAME, its a carry over of the old ways, like the days when flying boat skippers were piped on and off the "vessel". If you call them mechanics they would probably smack you in the face and turn you into a hand puppet. The term Engineer has stuck instead of saying the full title, only difference is they don't design things, they fix them.

[Lu Zuckerman]

To: heedm

What you say may be true but you have taken a snapshot in time. The helicopter does not just roll in one direction. As the trough of the wave passes the helicopter will roll in the opposite direction and if the helicopter is at an angle to the trough the helicopter will also pitch as well as roll. Once it rolls and pitches in one direction it will move in the opposite direction. This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage. This is not stability.

[Nick Lappos]

heedm,

Lu is all wet yet again!

The rolling deck has motions that are small potatoes compared to the rates needed to create big rotor forces, and the swash plate does not get driven by the rotor, only an ignoramous could tell you that. If the swash plate moves because the rotor is "following" the deck motion, what happens to the sticks in the cockpit, which must move with the servos, and therefore with the swashplate. The sticks and swashplate are held in position by the big servos, which take thousands of pounds of force to move them backwards against the pilot's stick.

The answer that Lu is too ignorant to know is that the rotor stays at the same angle to the aircraft mast, and it develops some forces (very small), as it is moved about in space by the deck motions. Most decks have periods measured in many seconds, and motions of about 3 to 4 degrees (extreme deck motions for helos not using Haul-Down rigs is about 8 degrees - check the max deck angles in most operator procedures manuals). A rig or a large ship takes about 5 to 10 seconds to roll through that angle, so the roll rate is about one degree per second, maybe two. Compare this with a gentle hover cyclic wiggle, where you can generate 30 or 40 degrees per second roll rate.

Now you see why I must answer Lu's drivel, because he is so close in his crackpot drivel that he almost, almost makes sense.

Please, please, please watch yourself with Lu, it is almost like talking to one of those shopping cart fellows down town, the ones who think Nixon came back as Socks the Cat. :rolleyes:

[Lu Zuckerman]

To: Nick Lappos

“The rolling deck has motions that are small potatoes compared to the rates needed to create big rotor forces, and the swash plate does not get driven by the rotor, only an ignoramous could tell you that. If the swash plate moves because the rotor is "following" the deck motion, what happens to the sticks in the cockpit, which must move with the servos, and therefore with the swashplate. The sticks and swashplate are held in position by the big servos, which take thousands of pounds of force to move them backwards against the pilot's stick”.

Response:

Once again Nick you have let your alligator mouth overload your hummingbird ass. Nowhere did I ever say that the rotor developed feedback forces sufficient to overcome the forces developed by the servos. In fact it is because the servos hold the swashplate in the last commanded position that creates a resistance that when the blade moves in relation to the swashplate that resistance causes the blade to move against the pitch rod. Do the sticks move during pitch flap coupling? The answer is no. It is the same thing here if the rolling motion causes the disc to try and maintain its’ position due to gyroscopic rigidity and the disc moves in relation to the fixed control system then there will be a resultant pitch input.
Get you head out of your ass, not everybody flies a helicopter with a rotorhead that is six feet across with a very high moment of inertia and a high level of offset interlock nor, do they operate off an LHA or an aircraft carrier. There are smaller helicopters and there are smaller ships that have a very rapid roll rate. If you have ever been on a ship passing through the Davis Straits you would know. In that area the water flows from three different directions and on a ship that does not have bilge keels the roll and pitch rate are fantastic. So much so, we almost lost both of our helicopters over the side. One other point is that some helicopters operate on floats and are subject to unrestrained wave action. In the case of ships with rapid roll rates and helicopters operating on floats there can be large changes in the disc position. Everybody knows what you do and your level of expertise and because of that they have a great deal of respect for you. Hell for that matter I have a lot of respect for you but when you tell me and everybody else that my experiences operating off the back end of an icebreaker are false and the words of an ignoramus then I take offence. I keep telling you don’t get so personal.


“The answer that Lu is too ignorant to know is that the rotor stays at the same angle to the aircraft mast, and it develops some forces (very small), as it is moved about in space by the deck motions. Most decks have periods measured in many seconds, and motions of about 3 to 4 degrees (extreme deck motions for helos not using Haul-Down rigs is about 8 degrees - check the max deck angles in most operator procedures manuals). A rig or a large ship takes about 5 to 10 seconds to roll through that angle, so the roll rate is about one degree per second, maybe two. Compare this with a gentle hover cyclic wiggle, where you can generate 30 or 40 degrees per second roll rate”.
“Now you see why I must answer Lu's drivel, because he is so close in his crackpot drivel that he almost, almost makes sense”.

Response:

Read my response above especially the part about alligators and hummingbirds. Coming from a person of your stature people will begin to believe what you say about me. But as I stated before your opinions don’t effect me.

PS READ THE LAST FEW POSTS ON THE NORTH SEA CRASH THREAD.

[ 15 November 2001: Message edited by: Lu Zuckerman ]

[ 15 November 2001: Message edited by: Lu Zuckerman ]

[heedm]

Lu, when you first posted to this thread, you asserted that the helicopter's response to wave action caused a rotor response that is 90 degrees out and generates instability. I showed you that it is 180 degrees out and serves to reduce the motion caused by the waves. You then responded to me by suggesting I was only looking at a snapshot in time. Not so.

I isolated one movement but just as easily could have generalized to any deviation of the helicopter's vertical axis. Combining pitching with the rolling may confuse you, but to the helicopter it is still just a movement away from the vertical axis. As Nick mentioned, the roll rates that the helicopter can generate are much greater than those experienced due to wave action. The rotor won't lag in it's "correcting" position, it will respond to each and every deviation of the helicopter's vertical axis.

Stability is when a system that is disturbed tends to return to it's state prior to the disturbance. What I have described IS stability.

I don't doubt that what you have told us about the icebreakers and some earlier floats is true. I just don't think you've found an appropriate explanation for it. Everything you've said wrt the icebreaker sounds like the natural rebounding frequency of the float was resonant with either the helicopter's vibrations or with the deck motion (I assume the former).

As far as floats vs hulls, the vertical c of g you mentioned is a small part of the story. What's important is how the center of buoyancy moves when the helicopter pitches and/or rolls.


Nick, I think you misunderstood Lu's initial assertion, which I believe is valid. The swashplate's orientation doesn't change with respect to the servos or the fuselage. It does change with respect to the earth, as the fuselage moves. The rotor disk does not want to move when the fuselage rolls or pitches due to it's angular momentum (make this easy and consider either a teetering or a fully articulated rotor). Thus the rotor disk and the swash plate change their orientation with respect to each other....same effect as putting in a control input, but without any change in the orientation of the flight controls with respect to the pilot.

Thanks for the warnings wrt Lu, but you will find I tend to stick to the discussion rather than getting personal.

Matthew.

[Nick Lappos]

Heedm,

I do not misunderstand Lu, unfortunately. Even though he now denies what he posted, his drivel of 14 November said, "This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage."

That clearly describes a non-commanded rotor motion, does it not? That is the heart of Lu's drivel, that the rotor has a mind of its own, and the precession causes rotor motions that possibly roll over the Puma.

I have landed on dozens of such rigs, and unfortunately investigated several roll overs that were caused by a combination of the slope of the boat and the wind. No strange forces from Jupiter, and Nixon is still dead. Talking dynamics with Lu is like calling the Psychic Hotline for advice.

[RW-1]

Gee, missed this thread somehow as I was busy.

I am so loving this ....

It leaves no room for error in my past predictions of LZ.

Whatever the topic.

:D :D :D

Back to what I was doing ...

[heedm]

Nick, I believe a small uncommanded rotor motion occurs. It doesn't create any problems, instead it makes the helicopter more stable in the water with rotors turning than without.

Ignore what was said about gyroscopic precession. Just consider the swash plate moves with the fuselage and the rotor disk will tend to maintain the plane it is spinning in.

This puts a different relative orientation between swashplate and rotor disk.

This is not psychic, it's physics.

"I have landed on dozens of such rigs, and unfortunately investigated several roll overs that were caused by a combination of the slope of the boat and the wind."

Check my posts, I'm not saying this uncommanded rotor movement is causing problems. I say it's small and it slightly helps matters.

Matthew.

[Cyclic Hotline]

You called! :)

[Jiff]

Nick,
Imagine this scenario, the Helicopter in question has an underslung rotor system, is on floats and is pitching back and forth and rolling left and right. Doesn't an underslung system allow the fuselage to behave like a pendulum?, which means Lu's statement "This constant fuselage displacement will cause the rotor system to constantly change in relation to the fuselage." is correct. Although the rotor system is moving in relation to the fuselage the rotor system is effectively not moving but maintaining its position in space and the fuselage is the item that is moving.
Now what about a helicopter with a rigid head?, Lynx for example (no I haven't seen one on floats either), I think because of the rigidity between the rotor system and the fuselage if a wave tried to roll the helicopter then we would see an excellent demonstration of precession i.e. it would either pitch forward or backwards respectively.
And while were at it can we stop the personal attacks / insults?
Jiff

[nomdeplume]

Jiff
I understand your last comment - but only up to a point.
But I have much more sympathy for Nick Lappos.
It must be a pain in the butt (as our American cousins might say) for a Test Pilot who voluntarily gives his time to contribute to the forum to be constantly contradicted by the ramblings of a geriatric engineer (mechanic) who's isn't and never even has been a pilot.

I know Lu calls himself "a consultant", but the guy who just sold me a new kitchen also told me he was a "consultant". (I always thought they were called salemen, but you learn something every day).
Anyone can call himself a "consultant" - it means the square root of you know what!

[Nick Lappos]

for the group-

The difficulty I have with Lu is mine, and I will wrestle with it. His posts are so misleading, and he is so unwilling to either think or understand that I am completely exasperated!

Imagine the ship is tossing like those movies Lu evokes, with vast pitch and roll motions like a bucking bronko. OK now forget that, it is wrong. Any pilot who lands on that deck without haul-down is nuts, and will be unemployed shortly.

The typical deck landing in commercial service never involves deck angles beyond about 8 degrees (commercial guys, please post the operating limits for deck landings from your ops manuals.) The typical period of motion for a large rig boat is several seconds, usually about 10 seconds or so. For a rig, it is often 20 seconds or so. This makes the deck motion actually very slow in roll or pitch rate, and the contribution of the dynamic motions very small.

The rotor will not wave around or depart from its commanded path due to these motions, no matter what Lu thinks. Even if underslung, the rotor is not free to wave around independant of the aircraft without a swashplate input, unless the angular motions are very fast.

Having investigated the roll-over of several aircraft, I can assure you the results are disappointingly static in nature, a combination of wind velocity (which will move the rotor) deck slope and where the pilot left the stick. For a broad sided helicopter in a cross wind of 35 knots with gusts that are higher, and with a deck roll that compounds the aircraft lean, all it takes is an unattentive pilot to allow a roll-over. The problem with Lu's assertion is that he believes the rotor does its own thing, and that wanders around. He has it backwards! As the aircraft rolls, the rotor follows the aircraft. With a cross wind, the rotor produces strong roll moments that add to the roll tendency that the deck is producing. A pilot would try to put roll cyclic in to keep the rotor disk parallel to the horizon, at the peril of those on the deck under the disk. The pilot is stuck - try to keep the aircraft glued to the deck, but hurt someone around the machine, or risk a roll-over. That is why most operators don't allow large deck angles.

A cure is to ask the ship to turn into the wind, so the roll angle is not aligned with the crosswind, but pilots are reluctant to impose on the ship operations (unless they are in the Navy, where the air boss helps the ship captain decide).

OK, that above is the kind of answer I expect from LU, something based on a blend of experience and common sense, not mumbo-jumbo. Should any pilots with experience want to disagree with what I said, I would (and have) listened, and I always admit when I am mistaken. I want to learn from this forum, too, and I always do. That is what I expect from the posters that I respect - good honest intellectual discussion. :D

[heedm]

Nick, your argument seems to be of the order, "I'm a test pilot and have lots of experience so listen to what I say." If your argument is cogent, it doesn't matter what your resume reads.

Please tell us how the underslung rotor keeps it's rigidity in space with the fuselage rolling and there is no change in orientation of the swashplate with respect to the rotor disk.

Matthew.
(experienced helicopter pilot)


Edited to indicate I am a pilot with experience.

[ 16 November 2001: Message edited by: heedm ]

[rotorque]

Currently operating BK117, marine pilot transfers in OZ

We have a limit of 3 degrees at night and 5 degrees during the day. Concidering all the information at hand - wind, swell etc, we can stretch the day limit a bit, but we do not budge on the 3 degrees at night - not so much because of aerodynamics, its more to do with visual cues on approach etc. We turn the ships onto a different course to reduce the rolling if needs be.

[Nick Lappos]

Thanks rotortorque for the info. At 3 degrees night and 5 day, little rollover potential is there.

Now heedm, please compare 5 degrees to the picture Lu made of rolling tossing ships in a storm, and understand one reason why I dismiss his argument.

Regarding the reason why the underslung rotor doesn't move appreciably relative to the fuselage, please do not think I say it because I am a test pilot! The rotor cannot move appreciably differently from the swashplate because that is how it is connected mechanically. Please picture the pitch change links as you oppose the fuselage and rotate the disk through a new tilt angle - do they impose a pitch change on the blades? Of course they do, and that pitch change is going to force the rotor to follow the fuselage. Only a very fast fuselage rotation that matches the rotor's natural frequency will cause other motions. And the size and speed of typical ship motions do not cause the "dreaded rotor behaves with a mind of its own Lu Zuckerman syndrome".

The real culpret in this roll-over scenario is exactly BACKWARDS from Lu's assertion. The rotor is stuck with the fuselage, so in a rolling motion with a strong wind, the rotor is forced into an angle relative to the wind that creates strong roll-over forces. This can be considered as if the roll of the ship in a 35 knot cross wind causes the rotor to make a lateral quickstop maneuver because the rotor MUST follow the fuselage. The rotor's strong stability relative to the rolling motion is the problem, and Lu is yet again exactly ass-backward!

It does not matter if the rotor is underslung or not, nor does it matter if I am a test pilot or not, these are facts, not opinions. The problem we all have is the democratic principle, where if enough idiots vote that there is a green cheese moon, it must be true. The fact that Lu can email, and that he can spout theories, does not make him correct, nor does it make his discussion worthy. What is most difficult for me to face is that I could post 100 accurate descriptions of the physics and aerodynamics of the situation, and he will squirm out into another corner, squirt some ink of incredible colors, and be off and running!

In short, to avoid roll-over on a tossing deck, stay off wildly tossing ones, keep the rotor level with the horizon (at the peril of the people around the aircraft) and try to avoid situations where the cross wind and the roll are in the same direction.

Also, try not to believe that mysterious rotor dynamic misbehavior is the culpret, because you will be a worse pilot - an ignorant one - and more likely to have an accident. Also, believe nothing someone tells you just because they are a test pilot, or a consultant engineer! :)

[Lu Zuckerman]

To: Nick Lappos

“A cure is to ask the ship to turn into the wind, so the roll angle is not aligned with the crosswind, but pilots are reluctant to impose on the ship operations (unless they are in the Navy, where the air boss helps the ship captain decide)”.

On a Coast Guard icebreaker (at least in my experience) the Captain will not accommodate a pilot during the landing of a helicopter when in the icebreaking mode. While in this mode the ship can be rolling +/- 18-degrees (maximum) and at the same time, pitching up and down several degrees. Because of the inherent dangers involved in landing along the centerline of the flight deck (approaching over the stern) the pilots would land athwartship trying very hard not to contact cable stays and a large boom. And they would be flying sideways and forward in order to maintain their position in relation to the moving flight deck. The danger in landing in either direction was that there were no wheel brakes on the helicopter and the parking brakes, which were set upon touchdown, were ineffective. Because of this the ground crew had to attach tie downs and chocks to restrict any further movement. If the helicopter had to be restarted in this position under the stated conditions there would be a severe instability due to the helicopter moving on its’ oleos and the imbalance of the rotor system during start up. It was the same when the helicopter was aligned with the ship centerline but there was less chance of losing the helicopter over the side. Now these are my experience and they differ from the rules and regulations that exist at this time. Most likely they occurred prior to the birth of most of the pilots on this forum.

Another point to consider, is that if during the landing sequence, the icebreaker hit large/thick pack ice and became stalled in its’ forward movement the pilot would crash on the other helicopter on the deck. Or in the case of our ship, also hit a very large fuel tank that we were transporting to the Alert weather station. Perchance we were the pathfinders that would lead to changing the rules to those that presently exist.

[Jiff]

Nick said,

Regarding the reason why the underslung rotor doesn't move appreciably relative to the fuselage, please do not think I say it because I am a test pilot! The rotor cannot move appreciably differently from the swashplate because that is how it is connected mechanically. Please picture the pitch change links as you oppose the fuselage and rotate the disk through a new tilt angle - do they impose a pitch change on the blades? Of course they do, and that pitch change is going to force the rotor to follow the fuselage. Only a very fast fuselage rotation that matches the rotor's natural frequency will cause other motions. And the size and speed of typical ship motions do not cause the "dreaded rotor behaves with a mind of its own Lu Zuckerman syndrome".

Response,

So when I walk out to the hanger and stand on a step ladder and grab the end of the 206 blade and move it up and down from bump stop to bump stop, I see no change in pitch angle. Please re read my previous posting on this thread and I invite someone to tell me why I'm wrong.

Jiff

[Lu Zuckerman]

Jiff:

Using your example there will be minimal pitch change at low collective because the pitch horn/pitch link connect point is on or near the teeter axis. If the collective is raised and you teeter the blades there will be some pitch change because the pitch horn/pitch link connection are no longer coincident with each other. This is the same as pitch coupling.

[Lu Zuckerman]

A point to ponder:

Let’s talk about everybody’s Favorite subject GYROSCOPIC PRECESSION. If you have a gyroscope with three degrees of freedom and you move or rotate the entire gyroscope the rotor will maintain its’ position in relation to the local horizon. If you take one of the degrees of freedom away and rotate the assembly the rotor will nutate or precess 90-degrees after the input of the changing force. The first type of gyro is used in an inertial navigation system or autopilot. The second type is used in a directional gyro. Now, let’s apply the second type of gyro to the rotor system of a helicopter. The rotating disc is the same as the spinning rotor on the gyro. The rotor disc can be commanded through control input to change its’ position relative to the local horizon. If the rotor moves with the helicopter due to the application of a local force the disc, which is maintained in position due to gyroscopic, rigidity will respond to the external force because it also exhibits precession just like the rotor on the gyro. There does not have to be relative movement between the fixed pitch link and the pitch horn to make the rotor move in this manner. As I explained to Jiff above, when the collective is at the low pitch position the pitch horn/pitch link are coincident with the flapping axis and there is no coupling. However, according to the laws of physics the rotor should nutate or precesse 90-degrees after the input of the external force. This may or may not apply to single rotor helicopters.

Propellers on fixed wing aircraft exhibit this gyroscopic turning moment but the movement is in the outer areas of the blade and the major resistant force is the crankcase bearings. On the V-22 when it is in the aircraft mode and the attitude changes the prop rotors respond by precessing as they are mounted in rubber. Any precessional movement of the prop rotor is corrected by the servo system.

Now if Nick sees it any differently let him explain it without mentioning my mental capacity or my age.

[ 16 November 2001: Message edited by: Lu Zuckerman ]

[ 16 November 2001: Message edited by: Lu Zuckerman ]

[heedm]

Nick, I doubt if this has caused any confusion, but I've always been thinking of a helicopter floating, not one on a ship. I guess it's because the post is titled, "Ditching". It shouldn't matter, though, because all we require is something external to the helicopter that moves the fuselage.

As far as who I believe, I trust in the experience of people like yourself, but I still like to see reasons rather than just trusting expertise.

In my original post on this thread I said, "Consider a Jet Ranger on floats that rolls left. The rotor disk wants to stay in plane but the swashplate at 3 o'clock (from above) rises. This causes blade pitch increase at 12 o'clock which causes the disk to tilt to a new plane with the tips highest at 9 o'clock and lowest at 3 o'clock."

With all the knowledge and experience in this group, I'm surprised that none of these "experienced helicopter pilots" noticed that the blade pitch actually decreases at 12 o'clock. Thus, the rotor disk flies itself to follow the fuselage's motions.

I didn't put that error in there to prove anything, it was an honest mistake. It turns out to be a good example of why not to blindly trust experience, but rather to demand rational explanation.

I was wrong. I'm sorry if I misled anyone.


Matthew.

[Jiff]

So, if the jet ranger rolled, the disk would fly its self back to its original position relative to the fuselage but there would be no precessive forces applied to the fuselage, assuming the collective is at its minimum i.e. zero pitch.
This means that a helicopter with an underslung system would have no added stability or instability effect from the rotor system while it was bobbing about on the sea?

Back to the Lynx on floats, because of the rigid head the fuselage would experience precessive forces as it rolled or pitched?

A quick thought,
Here we are discussing helicopter aerodynamics and forces, just stop and think for a moment what the pioneer's of this industry went through!

Jiff

[sprocket]

I venture in with trepidation,

heedm: If the helo rotor is at operational RPM and is then rolled to the left by a wave, then I cannot see what would change the blade pitch. The pilot is presumably holding the rotor controls in a neutral position
There will be a ‘tendency’ for precession to occur and may tilt the airframe in the water accordingly. The size and frequency of the waves in this scenario will affect the outcome.
If the wave came from the fore or aft direction then the airframe may tend to tilt left or right, as well as in the direction of the wave tilt. That would be destabilizing.

In your example, the top of the mast and hub-trunnion are going to be putting the main input force into the rotor. The swashplate will follow but not change it’s angle relative to the mast.
That would mean there is no aerodynamic input or result. In fact the swashplate will be working to stop the blade pitch changing.

The only stabilizing effect (that I can see) is the gyroscopic rigidity of the rotor (its resistance to angular change) and that may only help if the helo experienced one wave.
If the rotor is slowing to a stop (as would be the case after a successful autorotation)without a rotor brake in a turbulent sea, then the rotor will start flailing about as it loses aerodynamic control and then move independently of the fuselage.

[Nick Lappos]

heedm,
Your last post hit the nail on the head. I think we see it the same way now.

Sproket,
Try not to think about gyroscopic precession, its effects are small at the roll and pitch rates we are talking about here. The rotor will automatically fly itself back to the position commanded by the flight controls, even if the aircraft and mast are rolling around due to wave forces (which are the same wether the aircraft is floating or on a ship). The reason is that the swashplate will hold its position relative to the mast, and as the mast is rolled and pitched, it will send the proper control inputs via the pitch links to the rotorhead. In reality, there is no precessional force, and no unusual rotor behavior due to the rolling (as long as the rates are in the few degrees per second range).

The Lu bugaboo about unstable rotor behavior that he pushed in his earlier posts is backwards, as the rotor is actually too stable relative to the airframe, so it develops aerodynamic forces due to the wind that accompanies the waves. It is the combination of the wind and the wave slope that eventually could roll the aircraft, not funny gyro or unstable rotor forces.

Lu, I have NEVER used your age against you, nor will I. I have strong respect for tolerance regarding age, race and sex, and I resent your slur in that vein. Your posts are simply inane, not due to age, due to your inability to realize what you do not know, and your inability to learn. These are not age issues, I think. I have lots of respect for your experience, and your breadth of knowledge. It is you that destroys your own credibility when you venture so far from what you know, and when you keep pressing the same old bull into every post.

I absolutely refuse to answer your posts, I will be glad to discuss issues with any other ppruner. :D

[Lu Zuckerman]

To: Nick Lappos

OK, but before you withdraw yourself from my "inane" comments please answer my post on Weather and other nasty stuff.

[heedm]

For gyroscopic precession to occur, a moment has to be applied to the rotor disk. This does not appreciably happen by moving the fuselage or mast with a teetering rotor, or with other types.

A rigid rotor would have a moment applied by the fuselage rolling and/or pitching, but the amount of rotation added to the rotor disk is so small compared to it's existing roll that the effect would be difficult to observe.

Matthew.

[thjakits]

HeliEng,
I hope you are still sane! I am new to the gang so for the moment I still "enjoy" the fight between the two "masters".
Here some info on floats as far R22, R44, Bell-47´s.

I have to look it up in the manual for the R22, but the R44 float-equipment(permanent+pop out´s) are to be used for emergency use only, although the floats are very tough (even the pop outs, which look like the permanent ones but are thinner). That of course includes training. However if you have to land on water because there is no where else to land on permanent basis, the Robinson is not for you. The R22 is okay to land in water, even close to max gross w. But it is quite interesting - don´t try this in heavy seas (preferably in fresh water only!!).
For tuna-checkouts I take students for full touch downs in the R44, however with 2persons on board only and half fuel. The R44 sits awfully deep in the water (which is good when the engine went, bad for training)
As they are to be used for emergency only, this is okay as it gives the helicopter lots of stability once in the water, although with a full load mostlikely you will have water in the cabin. However you probably will float for ever without rolling.
Not so good for training as the R44 airfilter sits very low and even when it is sealed with tape, you better watch out that you do not get any water in there(bad news for the engine!!).
R22 will roll sooner or later except in calm sea. However most pilots make successful emergency-autorotations.Just for the record:
As far as I know the reason on ALL of this e-autos was lousy maintenance......
Other than that, in a Robinson you really do not need Floats, they are the most reliable machines I know (I have about 6000 hrs total, of that about 4000 in R., in all kinds of "interesting" terrain...),they just slow you down (except the pop-outs).
According to the manual of the R44 you can take off again, even on the pop outs, repeatetly.
Last: most helicopters (tuna ops) that go in the sea undamaged, get light to heavy damage on recovery to the tunaboat, due to the movements of the boat and the available recovery gear.
Probably this does not answer all your questions, but it gives you some idea about floats on light helicopters at sea.
To Lu Z.:
What about the Hughes (MD)-500 models, are they fully articulated? They had loads of them in the tuna spotting business on floats, as far as I know no trouble with ground resonance (Although they are out of business now as they can not match the R44 with the easy of maintenance and economy of operation and endurance...). Contrary the few Schweizer 300´s that where tried out where terrible (3 blades...).


Fly safe,

3top
:cool: null

[Nick Lappos]

3 top,
You hit on the principal difference between floats for everyday use, and emergency floats - the amount of flotation. For Sikorsky, we have a rule that the floats must allow safe water entry, they must keep the cabin fully dry, and they must allow full egress for all occupants. The aircraft can settle down where no self respecting pilot would lift it back off again, for instance.

You may find that the R-44 floats will allow takeoff at reduced weight and CG, and would be a problem for lift-off at full weight, mostly because of the amount of bouyancy.

[ 18 November 2001: Message edited by: Nick Lappos ]

[Bladestrike]

Any of you learned fellows know at which RPM gyroscopic procession starts to become an issue? I'm thinking about blade sailing on startup/shutdown and where the moment applied by the wind will have its affect.

[HeliEng]

Just about sane!

The topic has wandered somewhat, and many of the issues discussed have gone totally over my head :eek:

I was speaking to a colleague, who recommended that I add an addition to my initial post. What purpose do the floats on an S-61 serve? The aircraft is designed to amphibious anyhow, so why have the floats in addition?

(Try not to argue over this one guys!)

"Answers on a postcard to......."

[heedm]

You're likely to start an argument just by mentioning gyroscopic precession. For the record, GP is an effect observed on a rotating body whose geometry has constraints. Some rotors fit in those constraints, others don't. The phenomenon that causes the GP effect is the conservation of angular momentum. That applies to anything that spins, no matter at what speed it spins.

When you apply a force to a blade, it causes the blade to rotate about it's flapping axis. If the blade is already rotating about a vertical axis, then the resultant spinning is a sum of the two.

When the rotors are up to speed and only relatively small forces are imparted to the blade, the result is predictable: gyroscopic precession (or something close).

When the rotors are not up to speed and you have something that imparts a relatively large force on the blade, all the spinning motions are conserved but it may not appear to be like gyroscopic precession.

Consider the rotor just started moving and a gust of wind hits the helicopter causing the forward moving blade at 3 o'clock to rise. The immediate result of the two spins is that the blade will want to spin in a disk that is almost vertical but with the top of the disk leaning slightly forward. The forward leaning is due to the very slow rotor speed. If the blade was allowed to spin 360 degrees in this disk, the maximum displacement would be at the 12 o'clock position, where the tilted disk is highest. This is the result that you expect from the GP explanation. With the rotor stopped, the immediate result of the gust would be for it to spin in a vertical disk.

Notice I mentioned only the sum of the two spins. In helicopters with elastomeric bearings, control geometries that respond to blade position, etc. other forces are imparted on the blades, which may cause yet another spin to occur, which can change the "gamma" to something other than 90 degrees. This doesn't contradict the angular momentum argument, but it gives much more to talk about. It does contradict the gyroscopic precession argument, but only because the rotor doesn't fit within the constraints of what defines a gyroscope anymore.

If you accept gyroscopic precession as a reasonable explanation as to why rotors behave the way they do, then gyroscopic precession occurs at all rotor speeds. Since the blades are normally mechanically restricted on the flapping axis, the immediate result of blade movement doesn't appear to be due to gyroscopic precession.

If you don't accept GP as a reasonable explanation, it doesn't matter. The blade behaves the same way no matter what words you apply to the physics. If you talk about rotational dynamics instead, you would be much more accurate, but very few people would understand you.

For those that want a straight answer.

The faster the rotor is moving, you'll see the maximum displacement of the blade further forward in the rotor's direction of spin.


Matthew.

[Cyclic Hotline]

The pop-out floats on the S61 were installed to improve the lateral stability of the aircraft in the event of a ditching. As you note, the S61 is designed and approved for amphibious operations.

Due to the high C of G on the helicopter they are prone to capsizing in anything above a moderate sea state (Rotor shut-down in 3 foot seas has been demonstrated). These floats were initially designed for use with the small sponsons installed on the SH-3 (military S61) series utilised by the US Navy.

S-61 floats were mandated by the CAA in the late 70's/early 80's and were retrofitted to all commercial S61's along with some other very practical modifications learnt from previous accidents/incidents.

If you look here (http://209.196.171.35/images/sinking61.jpg) you will see a very interesting image of a ditched S61. Unfortunately, in the picture you cannot see that the top of the cockpit is missing, following a blade strike on landing that significantly altered the cockpit arrangement!

The aircraft was flown off the rig and ditched in the water, where, unable to shut it down (no throttles, power, etc.) it was abandoned and cruised around the rig uncommanded, for some quite considerable time before running out of fuel. Fortunately it never contacted anything else out there!

Hence you have the very unusual image of an S61 running on the sea, in what would have to be described as a pretty reasonable swell.

After it ran out of fuel, it sank!

[Lu Zuckerman]

To: Bladestrike

“Any of you learned fellows know at which RPM gyroscopic procession starts to become an issue? I'm thinking about blade sailing on startup/shutdown and where the moment applied by the wind will have its affect”.

Most helicopters, other than the Robinson, that have the capability to flap or for the blade to move in relation to the rotorhead have some type of centrifugally operated locking device that will not unlock until the blade has achieved sufficient rotational velocity and centrifugal forces to sustain the input of cyclic pitch with the resultant movement of the blade. Sikorsky helicopters at least those that I am familiar with have similarly operated locks to restrict flapping and drooping. Some Hughes helicopters do not have locks that restrict flapping but they do have a device that restricts drooping movement. This device supports the static weight of the rotor blades and distributes that weight of the blades evenly. If one blade flaps and stalls out or aerodynamically, is forced to droop, the kinetic energy is translated to the ring support and is absorbed by the resistance of the other three or four blades to move upward. This device is not normally in use once the blades cone up. If in the process of maneuvering one blade hits this stop it will simply shift the ring position in relation to the mast centerline.

I would suspect that those helicopters that are equipped with the centrifugally operated devices are capable of cyclic input and be susceptible to gyroscopic precession once the devices are activated. It is not to say that at speeds lower than the speed necessary to release the locking devices the gyroscopic precession is not present however, the blades are not capable to sustain lift and they could stall out contacting personnel or the fuselage.

On our B-47 (HTL-1) we had no such devices and unless the blades were restrained they would be free to move all over the place both from wind passing over the flight deck or, because of the ship pitching and rolling. This led to a one-time experience. The ship was rolling in heavy seas and the blades were moving all over the place. Prior to our going aboard the icebreaker we removed the springs from the centrifugal clutch. This meant that just as soon as the engine started the blades were moving at engine speed (via the transmission). This was the first time we started the helicopter since coming aboard. The blades were dipped down relative to the local horizon and when the engine started the blades immediately aligned with the local horizon. The forces were so great that the helicopter almost flipped over. Following that experience I would hold the blade tip in the neutral flap position and when the engine started I would pull my hand back. I also learned something from that experience and that was to move my hand back a bit faster as I got hit with the following blade. This model of Bell had restraining cables (Sprague Cables) in the rotorhead which limited the amount of teeter both in the non driven condition and the flight condition.


Now I will take cover.

[ 18 November 2001: Message edited by: Lu Zuckerman ]

[thjakits]

To The Cat:

Lu, how did you get the Bell 47 started in the first place, when the clutch springs where out? I have been flying Bell 47´s on tuna boats and when it happened that the clutch pads would get sticky overnight I had trouble to start at all as the starter would have a hard time to pull all that mass through up to a speed where the engine would fire. I don´t say it is not possible, but I wonder you did that on purpose. I burned more than one starter like that.

3top :)

[thjakits]

To HeliEng:

GP, you will always have GP as soon as you try to move the spinning axis of ANYTHING rotating (ever wondered what kind of forces you put on your cars hubs once you do 55 or 120 or so? Spinning wheels and you constantly try to tilt them by moving forward. how about something faster like a Formula 1 or CART race car......)

GP is kind of hard to UNDERSTAND, we all know the effects, but did you ever grasp the "WHY"? (When I look it up I think I get it, but.......)
There is good explanation in an old "flighttraining"-mag and a different one in an as old ArmedForces flight instruction book.
If you want I can find out details about the publications.....

3top :cool:

[Lu Zuckerman]

To: 3top

I can understand the problem you outlined. We never had it. Even though the springs were removed we never had a problem with the shoes sticking to the clutch drum. It might be that your lube oil was viscous and the shoes stuck due to the adhesion between the shoe face and the drum. It may also have been a factor of humidity. Where we were even though we were operating in the Arctic Ocean the humidity level was quite low. Regarding the condition of our lube oil, we changed it every 25 hours. The Coast Guard also insisted on the use of high quality lubricants. Our rotor heads were lubed with Texaco grease and were lubed every 5 hours and our engines were lubed with Texaco aviation oil. We also rotated the rotor backwards much like they do on Hughes 500s and Bells to see if the rotor spool is stuck to the casing.

[HeliEng]

3top,

If it does not put you to too much trouble, I would be grateful if you could get hold of the details of those publications. I will try and get hold of copies.

I do not have a problem understanding WHAT happens, it is WHY!! Perhaps that is my fault for not just being able to accept it like others can?

"Some days you are statue, some days you are the pigeon!"

[Nick Lappos]

Gyroscopic precession is a mysterious force, until you look at the fundamental physics behind it. The best way to figure it out is to look it up in a Physics text, or an Engineering Mechanics text.

The underlying principles are basic. The gyro has a fixed angular momentum due to the spinning mass. This is a set quantity, and(like linear momentum) must be preserved. If you try to rotate the gyro, you are adding to the angular momentum (because the rotation of the whole gyro in another plane induces a change to the total angular momentum). The faster the rotation you impart, the more the momentum change that you request. As a total system, the momentum must be constant, when you disturb the angular momentum balance, the extra rotation 90 degrees out results.

One way of describing it is to picture a wheel spinning free in space. Imagine it in front of you spinning with its axle pointing at you, rotating clockwise (top to the right). It is happy to spin there, undisturbed, until you push on the top rim (12 o'clock position)in a direction away from you. The wheel is rigid, of course, so each part of it cannot move relative to any other. Because you start it moving away from you, the piece of the wheel at the top has two components of its velocity, one to the right, and one directly away from you. This means that you have tried to disturb its velocity, relative to the rest of the wheel. Because the rototion you called for (top away, bottom toward you) has no rotational speed at the sides of the wheel (the 3 and 9 o'clock pieces of the wheel see no translation due to your push), the mass has the confusing need to have more energy at the top and bottom (more total speed) than it does at the sides (3 and 9 o'clock) The "precession" of the gyro is simply the motion that the gyro makes that rotates this 3 and 9 o'clock part to EXACTLY match the 12 and 6 o'clock part. The speed of rotation imparted on the wheel is proportional to the force you exert on the wheel, and its angular momentum (speed of rotation, basically). The slower it spins, the faster the precessional speed to make up for the larger disturbance you caused.

Try this site for one stab at the explanation: http://sprott.physics.wisc.edu/demobook/chapter1.htm

[Dave Jackson]

>You're likely to start an argument just by mentioning gyroscopic precession.,< ~ Heedm

OK! http://www.unicopter.com/7up.gif

Gyroscopic precession has *virtually* nothing to do with a helicopter's rotor.

Gyroscopic precession is little more than a simplistic means of describing the basic end result at the rotor, after the application of a cyclic input. (i.e. 90-degrees later ~ basically). It is no good for explaining the 'how'.

The simplest argument against the use of 'gyroscopic precession' is to look at its algorithm. Mass and rotational velocity are the predominant variables. The relative mass and rpm in a gyroscope are humoungeous. The relative mass and rpm in a rotor disk are negligible.

The helicopter's rotor disk 'flies' to position. The eventual demise of the sinusoidal swashplate will result in rotor blades that can fly to position in 12.3-degrees or 123-degrees.

[Lu Zuckerman]

To: Dave Jackson

As much as you and many others insist that gyroscopic precession has nothing to do with helicopter rotors I would suggest that you contact the training departments of Sikorsky, Boeing, Bell and even Robinson. I have the training text for the first three and they all address gyroscopic precession as the motivating force in changing disc position. They also address a phase angle of 90-degrees. Robinson on the other hand provides illustrations showing that the pitch horn is offset by 18-degrees from the teeter hinge and they address gyroscopic precession as being referenced in the text. The problem is the illustration they use is that of a Bell system which does not have an offset between the pitch horn and the teeter hinge and the supporting text states that there is a 90-degree phase angle still talking about the Robinson head. I personally believe that they would have a very difficult time in describing how the Robinson system can respond like a Bell, which has a 90-degree phase angle, and the Robinson has a 72-degree phase angle. According to what Nick Lappos stated the mechanics being trained would have to be a graduate engineer or physicist in order to understand the mechanics of the system. That is probably why in Frank Robinsons’ response to me he indicated that we wouldn’t understand how it works.

Now do you know where my confusion stems from?

Regarding the demise of the sinusoidal swashplate it has already happened. The Lynx does not have a swashplate but it does have an isolation bearing that separates the rotating elements of the flight control system from the stationary bits. The Lynx has an offset similar to the Robinson (15-degrees) and with out the electronic flight control system the blades would dip down to the left with forward cyclic. There could be a thousand different ways of eliminating the swashplate but those systems would be so complex as to be rife with single point catastrophic failures.

[ 19 November 2001: Message edited by: Lu Zuckerman ]

[Dave Jackson]

Lu

The results of gyroscopic precession and aerodynamic precession are the same, but the result of gyroscopic precession is easier to see. It therefore is a quick way to explain precession to mechanics and pilots who have to work with it but do not necessarily have to know its 'innards'. If a pilot or mechanic want to fully understand precession then to continue to explain it in terms of gyroscope precession becomes a problem.

I am not saying "that gyroscopic precession has nothing to do with helicopter rotors". It plays a role, but its direct roll is a very small one and its indirect role is exactly that ~ 'indirect'.

A gyroscope (gyroscopic precession) functions because of high mass and high rpm. Aerodynamic plays no significant role.
A rotor (aerodynamic precession) functions because of aerodynamic forces. Mass and high rpm play no significant role

Direct role:

I believe the magnitude of gyroscopic precession's direct role in aircraft is dependent upon the rigidity, mass and speed of the device. A propeller will have a reasonable amount of gyroscopic precession, whereas a teetering rotor will have very little.

Indirect role:

Nick mentioned "The wheel is rigid, of course, so each part of it cannot move relative to any other.". What he is saying [I think :) ]is that a force at one location on the rigid wheel is creating forces at all locations on the rigid wheel. If a force at 90-degrees azimuth results in an upward force of 5 lbs at that location then there will be a force of -5 lbs at 270-degrees. There will be a sine(45) * 5-lb force at 45 and 135-degrees. There will be a 0-lb force at 0 and 180-degrees, etc,etc. The culmination of all the upward forces is at 180-degrees, and this is the high point. . The culmination of all the downward forces is at 0-degrees, and this is the low point.

Nick is talking about a singular force being distributed around the circumference due to the rigidity of the circumference. As he said, he is describing gyroscopic precession.

The helicopter rotor does not have this rigid ring at its circumference. It also does not have a singular force at one location. The pitch of its blades is providing a force directly to all the locations.

For these reasons, I believe that aerodynamic precession is a cleaner description.
_______________

In addition :)

Gyroscopic precession and aerodynamic precession only give the same results because the swashplate and gyroscopic precession produces a sinusoidal curve. When the swashplate (pure sinusoidal curve) is replaced, gyroscopic precession must fly out the window. This is because the new pitch controllers will be able to put into the blade any pitch at any azimuth they want to. I.e. no longer pure sinusoidal.

In the case of an intermeshing or coaxial helicopter, it may be possible to add a little additional short-term pitch to the lower blade as it passes through the downwash of the upper blade.
_______________

Phase lag, Gamma, offset and delta-3 are subjects for other future threads.

[Lu Zuckerman]

To: Dave Jackson

Not being a graduate engineer I find it difficult to follow Nicks' example. Did he or did he not say that when the force was applied to the upper portion of the spinning wheel that the wheel reacted 90-degrees later. If he did not say there was a reaction then the axis of the wheel had to be rigidized so that no movement is allowed. The normal explanation using the bicycle wheel is to have it mounted on an axis that allowed the person conducting the test to hold the spinning wheel in space. Under this condition when a force was applied to the axis the wheel would move in a direction 90-degrees after the input. Another experiment is for the individual to sit on a chair that is free to rotate. Holding the spinning wheel in the same manner and applying a lateral force the spinning wheel (gyro rotor) will cause the individual to rotate on the chair.

I don’t understand your comparison of a spinning gyroscope rotor to a helicopter rotor by saying that the gyro spins at a high rate and therefor has more “angular momentum” (if that’s the correct term) than a helicopter rotor which weighs ten thousand times more than the gyro rotor but is spinning much slower speed. Some time back I described the Cheyenne rotor system. It is controlled by a gyroscope (control gyro) and is installed above the rotorhead, and is positioned in relation to the rotor by applied force to the swashplate. Unlike any other helicopter there is no direct linkage from the pilots controls to the rotorhead. The movement of the control gyro initiates all pitch change. Now this control gyro weighs considerably less than the rotor system that it controls but never the less, it is a gyro. It is not traveling at a great speed but for its’ size it can generate a great deal of nutating forces. Gyros and rotors can be of any size and can rotate at any speed. If they both are properly designed, speed of rotation and mass make no difference.

[Joker's Wild]

The question is, "does gyroscopic precession have a direct role in the workings of a rotorhead".

In my current aircraft, if I wish to move forward, I of course apply forward cyclic. However, if one looks at how the swash-plate moves when I apply forward cyclic, they will see something quite different to what they might expect. The swash-plate will not tilt forward, but rather, will tilt to the right. But because the designers know it will take 90 degrees in the direction of rotation before a result of this control input is realized, the aircraft moves forward.

I'm not an engineer or a physics professor, but I certainly believe gyroscopic precession plays a direct role in how a helicopter rotor head works.

[heedm]

"This is the thread that never ends, Yes it goes on and on my friend..." ;)

It seems that the same group of people join in this subject whenever it starts. We mostly get closer to agreement each time, and the understanding of the underlying physics increases.

Nick's right when he talks about summing the spins. The energy argument is a little mixed up, and it actually applies to special cases only. One important point, the angular momentum is not constant, it is conserved. If you apply a moment to a spinning object you change the angular momentum in magnitude, direction, or both.

In the past I've found that many don't accept some of the jumps in a rotational dynamics based description of gyroscopic precession, or they don't have the background to understand it. If you want a fairly complete attempt at explaining gyroscopic precession, I put one on page two of the Helicopter Dynamics: Gyroscopic Precession (http://www.pprune.org/cgibin/ultimatebb.cgi?ubb=get_topic&f=11&t=001342&p=2) thread. I warn you, it's long.


Don't believe what Dave says about a gyroscope requiring high mass and high rpm. Gyroscopic effects happen on all rotating systems. Read my previous message in this thread.


The biggest problem with gyroscopic precession is that the term is used completely inaccurately when describing helicopter flight. It is not a force. It is not an explanation of why a force applied to a spinning object appears to manifest itself 90 degrees later. It is an example of that apparent 90 degree lag.

When you spin a top, if the surface it's contacting offers little friction, then the top spins about one axis until that axis leans from the vertical. Once it leans from the vertical, gravity tries to pull it over. Instead of falling over, the top continues to spin about it's axis, but the axis rotates in space, or precesses.

That's what gyroscopic precession is.

The top precesses rather than falling over because the force of gravity causes a moment about the contacting point of the top. Since the top is spinning, that moment adds more spin to it, but about a different axis. When these spins are added, the result is the top wants to spin about it's axis while leaning 90 degrees away from the direction that the force was applied. Gravity continues to act on the top, so the top continues to "fall" 90 degrees away from the direction the force was applied. The result is the precession.

Lu. I think you're right about the 18 degree left roll in a Robinson. I was watching one the other day, and he couldn't fly straight, always banked left. He probably understands physics, unlike the few other pilots who have flown Robinson helicopters. :D


Matthew.

[Dave Jackson]

Heedm

>"Don't believe what Dave says about a gyroscope requiring high mass and high rpm. Gyroscopic effects happen on all rotating systems."<

I agree with the above.

A clarification of the comment to which you refer is;

The relative mass and rpm of a gyroscopic is high visa-vie the relative mass and rpm of a helicopter rotor.
The relative aerodynamic activity of a gyroscopic is low visa-vie the relative aerodynamic activity of a helicopter rotor.


Do we agree on this?

[ 20 November 2001: Message edited by: Dave Jackson ]

[heedm]

Dave said,
The relative mass and rpm of a gyroscopic is high visa-vie the relative mass and rpm of a helicopter rotor.

The rpm of a gyroscope is higher, but the mass of a typical helicopter rotor is higher. What really matters is the magnitude of the angular momentum. Angular momentum is a function of rpm and the distribution of mass about the center of rotation (moment of inertia). Without being given specific examples, it's hard to say which has a higher angular momentum, but the one with the highest will be the hardest to stop.

Try stop a gyro with your hand. Now try stop a helicopter rotor with your hand. Which one was easiest? That one had less angular momentum.

Higher angular momentum only means that when you apply a force, it has less of an effect than if you applied that same force to something with lower angular momentum. That is why a gust of wind hitting a rotor that is slow during startup can result in much more blade motion.

The relative aerodynamic activity of a gyroscopic is low visa-vie the relative aerodynamic activity of a helicopter rotor.


When I think of a gyroscope, I think of something that has been designed to not interact with air. However helicopter rotors are designed specifically to interact with the air. Therefore, I agree, but I don't see how this is significant.

I've heard you mention your aerodynamic precession theory before. I don't think you're wrong, I just think you're giving another name to something we already understand. If you follow through my very long post where I describe why an apparent 90 degree lag takes place, I think you'll find that the theory behind it is the same for gyroscopic precession and aerodynamic precession.

I say we stop confusing people. Don't use the term precession. It is absolutely wrong. Don't use the term Gyroscopic Precession, it's not theory, it's just an example of something that behaves similarly. From now on to avoid confusion, let's talk about non-relativistic rotational kinematics.

Matthew.

[ 20 November 2001: Message edited by: heedm ]

[Dave Jackson]

Heedm

>"...the mass of a typical helicopter rotor is higher."<

Respectfully, I think that your are loosing sight of the word 'relative'. If a helicopter had a rotor, where the weight was proportional to that of a gyroscope, the helicopter would never lift off the tarmac. Heck, it probably would have sunk into the tarmac.
_________________

>"I think you'll find that the theory behind it is the same for gyroscopic precession and aerodynamic precession ."<

I have always agreed with you on this. In fact, during the previous set of postings I did the math to verify it.
________________

The following is another reason for using 'Aerodynamic non-relativistic rotational kinematics' in preference to 'Gyroscopic non-relativistic rotational kinematics'.

The swashplate and also the basic Bell, 2-blade, teetering (normal to span) rotor exhibit exactly the same characteristic as a gyroscope. I.e. 90-phase offset.

All rotorheads with a flapping hinge offset have a phase offset that is less than 90-degrees. 'Gyroscopic non-relativistic rotational kinematics' cannot represent this (at least not easily). 'Aerodynamic non-relativistic rotational kinematics' (blade flying to position) can.

Would you agree to this?
_______________

We can't be having Lu's ~ England/USA/Australia/& all point between ~ communication problem. We are probably next door neighbors. :)

[ 20 November 2001: Message edited by: Dave Jackson ]

[Kyrilian]

Dave,
Perhaps you need a quantitative way to describe your definitioin of 'relative'. How about the Lock number (gamma = rho*c*cla*R^4/Ib where rho is density, c is chord, cla is the lift curve slope, R is rotor radius and Ib is the blade moment of inertia)? So what you're arguing is that gamma is much larger than 1 (and I think a reasonable number for argument's sake would be 8--more for most articulated and teetering rotors, and less for rigid rotors).

[heedm]

Edited stuff in italics

Dave, I was a bit confused about what you meant by the relative mass and rpm. The only significant comparison between the two of which I'm aware is angular momentum. I think helicopter rotors have more angular momentum than the average gyroscope.

There are many other relationships that include mass and rpm. Rotational Kinetic Energy is one of the obvious ones. I didn't consider including more concepts to be useful.

As far as what type of non-relativistic rotational kinematics to use, drop the terms "gyroscopic" and "aerodynamic" and I'll agree with you.

The flapping hinge offset is described by basic physics quite easily. This is a very small part of the explanation. There are aerodynamic and control geometry effects that have a much larger effect on gamma. I alluded to this in my long post on gyroscopic precession. The natural frequency of the blade becomes less than the 1/rev of a blade with the flapping hinge coincident with the center of rotation. Because of this, the blade wants to flap in a full cycle in less time it turns through a complete revolution, so when it's finished a 1/4 cycle (max displacement) then blade has rotated less than 90 degrees (gamma less than 90).

Were it not for a driving force that is mechanically in phase to rotation of the blade (via swashplate) then the blade's motion could be quite erratic.

I live in Comox. I was in Vancouver two weeks ago, wondered if I should look you up. Two kids screaming in the back and then being rear ended by some greaseball who figured smoking cigarettes was more important than stopping at red lights reaffirmed my belief that although Vancouver is a fun, beautiful city, the best view of it is the one in the rear view mirror.

Matthew.

[ 20 November 2001: Message edited by: heedm ]

[Lu Zuckerman]

To: Dave Jackson

“The swashplate and also the basic Bell, 2-blade, teetering (normal to span) rotor exhibit exactly the same characteristic as a gyroscope. I.e. 90-phase offset”.

“All rotorheads with a flapping hinge offset have a phase offset that is less than 90-degrees. 'Gyroscopic non-relativistic rotational kinematics cannot represent this (at least not easily). 'Aerodynamic non-relativistic rotational kinematics' can.

On the typical Sikorsky with the possible exception of the S-76 the pitch horn leads the blade by 45-degrees. The control servos are offset from their direction of control by 45-degrees. When the pilot pushes forward cyclic the fore and aft servo will move down. This causes the swashplate to dip 45-degrees ahead of the longitudinal centerline. With the swashplate in this position, the advancing blade will have maximum control input and will (pick one), fly as an individual blade down over the nose or, it will dip down over the nose as a part of a collective assembly called a rotor system, with this movement, caused by gyroscopic precession. In either case, the opposite blade will be doing exactly that, move in the opposite direction. Other helicopters have different relationships between the pitch horn and the positioning of the servos but in any case when you add up the servo offset and the pitch horn lead it adds up to 90-degrees.

[Dave Jackson]

Thanks Kyrilian

The Lock number could be a perfect way to scale the rotor.
It might also be usable for scaling the gyroscope, by using '1' as a constant for 'density x lift curve slope'
______________

Heedm

>"As far as what type of non-relativistic rotational kinematics to use, drop the terms "gyroscopic" and "aerodynamic" and I'll agree with you.

I'm happy to drop the term 'gyroscopic'. It is a good one for holding a spinning bicycle wheel in your hand and saying "Wow". It is also a valid analogy for describing a basic teetering rotor head, which is used in conjunction with a 90-degree offset pitch horn and a swashplate.

I believe that the analogy with the gyroscope starts to lose its validity as delta-3, flapping hinge offset and rigid rotors are introduced. It will probably lose more of its validity as 'smart materials' are incorporated into the rotor blades. An expert in the field has stated that the swashplate is no longer totally compatible with many current rotorhead designs.

The helicopter rotor is an aerodynamic device. I believe that the best way to describe its operation, is aerodynamically (I.e. the blade flies to position), now and even more so in the future.

So what have you got to say to that? :eek:
______________

Lu

Why introduce the control system for 'warp drive' into the argument when we are still try to put the simple gyroscope to rest. :rolleyes:

[Lu Zuckerman]

To: Dave Jackson

“I'm happy to drop the term 'gyroscopic'. It is a good one for holding a spinning bicycle wheel in your hand and saying "Wow". It is also a valid analogy for describing a basic teetering rotor head, which is used in conjunction with a 90-degree offset pitch horn and a swashplate”.

Response:

Why do you feel that a Bell rotor system emulates the qualities of a gyroscope just because it has a 90-degree pitch horn? Yet you totally discount the Sikorsky and all of the other multi blade helicopters which have a precession angle of 90-degrees. The Bell is a two-blade system and it is designed with a 90-degree lead on the pitch horn. The Robinson has a 72-degree lead on the pitch horn and it too is a two-blade system. The reason it has a 72-degree lead is because the pitch horn can’t cross the cone hinge. If it did, it would have severe pitch flap coupling to such an extent that it would be uncontrollable. That is why I feel so strongly about the R-44 as on it the pitch horn has crossed the cone hinge causing a reversal to the normal pitch flap coupling.

If you remember in past posts I acknowledged aerodynamic precession as an alternate theory to gyroscopic precession but whether you think aerodynamic or gyroscopic precession the precession or phase angle is 90-degrees. How in engineering or plane talk do you prove aerodynamics over gyroscopic precession when the resultant to the pilots input takes place 90-degrees later in the direction? What law in aerodynamics or blade theory dictates that from an aerodynamic standpoint the blade will respond in 90-degrees?

[ 21 November 2001: Message edited by: Lu Zuckerman ]

[heedm]

Dave said, "I believe that the analogy with the gyroscope starts to lose its validity as delta-3, flapping hinge offset and rigid rotors are introduced. It will probably lose more of its validity as 'smart materials' are incorporated into the rotor blades."

If you apply a moment to a rotating body, the result must be a vector sum of the original angular momentum and the impressed angular momentum. Doesn't matter if there is an unusual control geometry, aerodynamic effects, etc. Gyroscopic precession is actually an illustration of that effect. Many basic helicopter texts use gyroscopic precession to mean that effect. If you use this latter definition, then it's valid as long as the rotors are turning.

"The helicopter rotor is an aerodynamic device. I believe that the best way to describe its operation...."

I try to talk only about the motion of the rotors due to a force being impressed upon them. Yes, some of those forces are generated aerodynamically. How they are generated does not change the effect they have on the system.

Rotors are also accelerated by an internal combustion engine. Should that be in a theory on why rotors lag by 90 degrees? :D

I really don't care what you want to call it. To me, rotational dynamics says it all. So does many other terms. I don't see that specifying the origin of these forces creates any deeper understanding of the concepts, rather it may confuse.

I'm sure given the budget we could build a model of a rotor system that generates "lift" through magnetism or something other than aerodynamics. It would exhibit a 90 degree lag as well.

Matthew.

[ 21 November 2001: Message edited by: heedm ]

[Dave Jackson]

Lu

>"Why do you feel that a Bell rotor system emulates the qualities of a gyroscope just because it has a 90-degree pitch horn?"<

I don't.

The following statement is from an aerodynamist, who's name I've forgotten. "For blades freely articulated at the center of rotation, or teetering rotors, the response is lagged by exactly 90-degrees in hover".

The pitch horn does not make the rotor emulate the gyroscope. The pitch horn only aligns the cyclic control stick with the rotor.
____________________

>"Yet you totally discount the Sikorsky and all of the other multi blade helicopters. "<

I don't discount the Sikorsky. Its only that I, you and perhaps a few others are having difficulty understanding the basics, so it is probably a little premature to introduce additional complexities.
____________________

Re the Robinson helicopters:

Lu, we are currently having trouble with one attribute of the rotor. The rotor has dozens of attributes. It is therefore a little premature to come to conclusions on the Robinson's rotors. The best we can do, at this point in time, is speculate.
_____________

Re non-relativistic rotational kinematics :)

Nick explained gyroscopic precession a couple of days ago. Heedm went to even greater lengths in explaining it a couple of months ago. How can you keep asking for an explanation when it would appear that you are not attempting to delve into what they are saying?

I feel that this has to be understood before phase lag and delta-3 can be considered. You may wish to re-digest what they have said.

[ 21 November 2001: Message edited by: Dave Jackson ]

[Dave Jackson]

Heedm

This is getting perversely pleasurable. http://www.unicopter.com/sexyface.gif


>"If you apply a moment to a rotating body, the result must be a vector sum of the original angular momentum and the impressed angular momentum."<
>"I don't see that specifying the origin of these forces creates any deeper understanding of the concepts, rather it may confuse."<

Why talk about "impressed angular momentum' when one can eliminate the middlemen, go right to the source and just say 'thrust'?
________________

>"Yes, some of those forces are generated aerodynamically. "<
>"Rotors are also accelerated by an internal combustion engine. Should that be in a theory on why rotors lag by 90 degrees? "<

There is only one force that is of interest. It is the only one that is variable and it is aerodynamic. The "original angular momentum" is an uninteresting constant. Or at least the RRPM better be a constant or there are serious problems.
__________

As previously mentioned, we are talking about the same thing. I prefer looking at it aerodynamically and use aerodynamic algorithms, where as you prefer to look at it dynamically and use dynamic algorithms. Are these fair statements?

[connavar]

Phewww!!! Getting a bit off track there guy's! only just found this one but what fun it is.

I dont want to take away anything from anybodies wonderful arguements but one thing is in my mind getting back to the original question.

Sod all this gyrosopic precession bull***t, but if you had to ditch would you really give a toss what was going on with the rotor head / disc / fuselage. Id be out of the bloody thing like a shot and certainly wouldn't hang around to find out who's theories or experiences were correct.

HeliEng - How many times you been ditched and how is yor floatation equipment!! :o

[tgrendl]

Dave, Heedm, Nick, Lu

Great work once again throwing all the ideas up on the table and letting them battle themselves out.

Being what I would call "slow" I look for the simple proofs to validate an idea or to help me along in the understanding of a concept.

On a bell head asking whether it's a predominantly gyroscopic effect or an aerodynamic one would simply require spinning the aircraft up sans blades. Do the control inputs still have the same efect on the tips of the grips?

The building blocks of understanding that are happening here really are good.

Cheers from the high desert :)

[Lu Zuckerman]

To: Tgrendl

“On a bell head asking whether it's a predominantly gyroscopic effect or an aerodynamic one would simply require spinning the aircraft up sans blades. Do the control inputs still have the same effect on the tips of the grips”?

All things being normal there would be no effect, as the grips would not deflect. The same thing would be true for any other helicopter. There is no aerodynamic effect because there are no airfoils. Because there is no aerodynamic effect there is no gyroscopic precession.

Gyroscopic precession is a function of a force being applied to one side of the disc or an imbalance of forces across the disc. In this case the force is a resultant of the differences in aerodynamic lift across the disc. Although the advancing blade has its’ rotational velocity plus the relative wind it has less pitch than the retreating blade. Whatever pitch is taken from the advancing blade it is added to the retreating blade thus it generates more lift even though the relative wind is moving in the same direction. This differential of forces (greater lift) will be applied to the retreating side of the disc and the imbalance of forces causes the disc to raise 90-degrees after the application of the force. This in turn causes the entire disc to dip down over the nose and rise over the tail. Some individuals will look at this as a pure aerodynamic function, which causes the blades to fly to the commanded position, and gyroscopic precession be damned. I will totally believe that theory if someone can convince me that there is a law or rule or theory in aerodynamics that explains why this phenomenon takes place in 90-degrees as opposed to 35-degrees or 125-degrees.

In the case of retreating blade stall the force imbalance is greater on the right (advancing) side and the imbalance is much greater by several orders of magnitude so as to cause the disc to flap / blow back with minimal warning.

To: Dave Jackson

You have a marvelous capacity to evade certain discussions (read argument) by using a lot of engineering platitudes.

[ 21 November 2001: Message edited by: Lu Zuckerman ]

[Dave Jackson]

With apologies to connavar, and probably many others.
_________

tgrendl

[(aerodynamic) vertical thrust] = [(dynamic) impressed angular momentum]
Without the blades, there is no means of applying the above to the rotor.

This is the story;

The aerodynamicist will collect a large number of variable, such as; pitch, angle of attack, RRPM, forward velocity, air density, chord, airfoil profile centrifugal force etc., etc. etc. He will then calculate [the height that the blade will fly to], at the azimuths of interest.

The dynamicist will simply come along and steal from the aerodynamicist [the blades vertical thrust at all azimuths], which is a byproduct of the aerodynamicist's hard work. He will then blend this thrust into the rotor's rotational momentum, which he also stole from the aerodynamicist, and then calculate [the height that the blade will be forced to] at the azimuths of interest.
:)

[ 22 November 2001: Message edited by: Dave Jackson ]

[Dave Jackson]

Lu said
>"You have a marvelous capacity to evade certain discussions (read argument) by using a lot of engineering platitudes."<

You can't have it both ways!!!!!!

Either;

Accept an overly simplified explanation ~ by blind faith.

~or~

Understand the mathematical proof ~ by reading and comprehending.

Your choice.

[ 22 November 2001: Message edited by: Dave Jackson ]

[Lu Zuckerman]

To: Dave Jackson

It is very easy to prove aerodynamic precession by using a Bell analogy indicating that in 180-degrees of rotation the rotor has aligned itself with the swash plate. Now, try to justify that theory by addressing a multi blade rotor system where the rotor never aligns itself with the swashplate.

In the Bell analogy the pitch horn leads the blade by 90-degrees and you can justify the theory since when the swashplate is tipped down over the longitudinal centerline the advancing blade is disposed over the lateral centerline which is 90-degrees ahead of the longitudinal centerline. On the Robinson when the swashplate is tipped down over the longitudinal centerline with forward pitch the advancing blade is not over the lateral centerline but it is advanced 18-degrees ahead of the lateral centerline when it has maximum forward pitch input. Now, address this using aerodynamic precession.

As you said, you can’t have it both ways.

[Dave Jackson]

Lu posted 21 November 2001 19:39

>"Some individuals will look at this as a pure aerodynamic function...... I will totally believe that theory if someone can convince me "<


Lu posted 21 November 2001 23:19

>"It is very easy to prove aerodynamic precession"<

[ 21 November 2001: Message edited by: Dave Jackson ]

[Lu Zuckerman]

To: Dave Jackson

>"Some individuals will look at this as a pure aerodynamic function...... I will totally believe that theory if someone can convince me "<

This is what I said:

Some individuals will look at this as a pure aerodynamic function, which causes the blades to fly to the commanded position, and gyroscopic precession be damned. I will totally believe that theory if someone can convince me that there is a law or rule or theory in aerodynamics that explains why this phenomenon takes place in 90-degrees as opposed to 35-degrees or 125-degrees.


>"It is very easy to prove aerodynamic precession"<

This is what I said:

It is very easy to prove aerodynamic precession by using a Bell analogy indicating that in 180-degrees of rotation the rotor has aligned itself with the swash plate. Now, try to justify that theory by addressing a multi blade rotor system where the rotor never aligns itself with the swashplate.

No more evasion. Please address my comments in detail.

[Thomas coupling]

Jesus christ will you 2 drivel off elsewhere so that the subject matter can resume. Are you two applying for the most boring conversation award, or what?

Lighten up will ya? :rolleyes:

[heedm]

Dave said, The aerodynamicist will collect a large number of variable, such as; pitch, angle of attack, RRPM, forward velocity, air density, chord, airfoil profile centrifugal force etc., etc. etc. He will then calculate [the height that the blade will fly to], at the azimuths of interest.

Thank you. We agree. Since NONE of our discussions mentioned pitch, angle of attack, forward velocity, air density, chord, or airfoil profile then obviously we weren't discussing this from an aerodynamics point of view.

Aerodynamics is "The dynamics of bodies moving relative to gases, especially the interaction of moving objects with the atmosphere." (The American Heritage® Dictionary of the English Language, Fourth Edition)

We weren't discussing anything about aerodynamics. What we were talking about were the effects of forces that we all took for granted, forces that are generated aerodynamically.


Dave said, "Why talk about "impressed angular momentum' when one can eliminate the middlemen, go right to the source and just say 'thrust'?" Because the two are different. You add thrust to angular momentum the same way you add oranges to anecdotes...you can't. Besides, thrust is an intermediary. The thrust produced by the blade is mostly used to hold the helicopter off the ground. A small part of the thrust is used to create a moment on the blade which imparts angular momentum to that blade, which is summed with the angular momentum the blade already has, .... are you getting it now?

Dave said, "There is only one force that is of interest. It is the only one that is variable and it is aerodynamic. The "original angular momentum" is an uninteresting constant. Or at least the RRPM better be a constant or there are serious problems."

You may find it uninteresting, but just like high school geometry, you can't do without it. The mass of planets doesn't change considerably, but if NASA ignored that uninteresting constant, those rockets just wouldn't get anywhere.

Also, there is not only one force that is variable. Drag is variable. Weight is variable (remember weight is a vector, it's direction changes as the attitude of the blade and/or helicopter changes). Depending on how you choose to label all the interactions the rotors have with their environment, there can be many more changing forces. Of course, it doesn't matter how you label them, they all have to be considered no matter how much they interest you.


Yes, we do agree on most of this stuff. You still seem to hold aerodynamic precession as a very special concept. I'm not sure exactly what your theory is, and as Lu was wondering, how it explains what the apparent lag is. A more general theory from a dynamics point of view (keep in mind that aerodynamics is a subset of dynamics) does explain that apparent lag, and it doesn't need to know the air density to explain it.

_______________________

Lu said, "I will totally believe that theory if someone can convince me that there is a law or rule or theory in aerodynamics that explains why this phenomenon takes place in 90-degrees as opposed to 35-degrees or 125-degrees."

Read that long post on the Gyroscopic Precession thread that I keep mentioning. The reason it would happen is written there. BTW, the reason for it is neither aerodynamic nor gyroscopic.


_______________________

Connavar you're right. Don't think about this kind of stuff when you're ditching. Right now, I doubt if any of us involved in this conversation are ditching, so I guess that's okay with you.

I ditched once. We got out like a shot, never got wet, and the helicopter slowly sank. We sat back, thought about it, and salvaged a helicopter worth at least $20 million dollars. I guess thinking does pay off. Hey, my employer still hasn't paid us for that salvage.


_________________

Thomas coupling if you're having problems with the big words I'll be happy to translate for you.

You also asked us to lighten up. Okay.....a three legged dog walks into a bar and says, "I'm lookin' for the man who shot my paw." :)

Matthew.

[ 22 November 2001: Message edited by: heedm ]

[ 22 November 2001: Message edited by: heedm ]

[Peter Knight]

Hi guys,just felt a need to throw in a couple of comments.I've never worked on two bladed heads so most of my experience comes from 3,4 and 5 bladed heads. The comments i've been reading about pitch horn offset seem to miss the point as i understand it which is that the pitch on the blade will reach it maximum deviation 90degs before the effect is felt.so the pitch horn offset can be ignored because it is the position of the blade centre line that is important as the response is at 90degs to this.
Somebody mentioned the control spider on a lynx (sorry forgot who) and said that with system the sinusoidal nature of the swashplate can be overcome, this however is not the case.The end result of the spider is exactly the same as a swashplate. Another point made about the lynx head is that it is rigid and will suffer the effects of procession more so than fully articulated head,although the head is semi-rigid the articulation is achieved in the flex of the titanium sleeves and central star,so the blades still flap,lead and lag the same as any other helicopter and so shouldn't feel procession more or less than any other helicopter.
If i've misunderstood any of the above comments i'm sure somebody will put me right

[heloplt]

I put forth this input just to confuse the issue....whilst doing conversion training for new CH-47 Chinook pilots at Fort Sill, Oklahoma....a USAF crew flying their H-3 Sikorsky made a water landing and made mock of the fact that Chinooks could not do that. Much to their chagrin....we splashed down next to them and cruised circles around them.

Point being....unless you have fixed floats or a boat hull, that is not a recommended maneuver. Emergency floats are notably unreliable and should be considered just that....emergency use only.

If used in salt water...which usually connotes the presence of waves...the quicker one exists the aircraft the better...and in light of the current issue of underwater breathing apparatus to Navy/Coast Guard aircrews....I think there is a message there!

Also...one commercial operator I have worked for asked for us to ensure a "float failure" after the crew and passengers were out of the aircraft should we land in salt water. Pilots were encouraged to wear a knife for just such eventualities. Seems insurance value of the aircraft was enhanced if it was submerged permanently.

[Grey Area]

Gentlemen, especially believers in precession. A point to ponder for you.

The Autogyro (yes I’ve flown those as well). The control of the rotor in simple autogyros is direct movement of the teetering hub; this input is in phase with the disk movement.

Lets look at the forces applied when commanding the disk to tilt forward.

1. An upward force is applied at the BACK of the disk (6 o’clock).

2. A tiny movement of the disk causes the advancing blade to experience an instantaneous reduction in effective pitch angle reducing the angle of attack. The disk begins to move, does it:

A. Tilt up on the side of the advancing blade (3 o’clock [for example]) following the laws of precession?

Or

B. Tilt forward.

Given that we already know that the controls are rigged in phase we know that the effects of precession are not noticeable to the pilot and the disk tilts forward.

Now imagine if you used a swashplate instead. Where would you want to reduce the pitch if you wanted the disk to tilt forward (teetering, undamped head)?

GA

PS. With over 1500 helicopter deck landings I can assure you that the disk follows the helicopter, which follows the deck, at normal rotor speeds no matter what the pitch or roll. Why? Because if it didn’t it would experience a change in its’ attitude relative to the control orbit which would return the disk to its’original position as though the pilot had commanded the disk to level itself with respect to the aircraft. However gust of wind, or turbulence, especially with a vertical component alter the induced velocity and disturb the disk, at low rotor rpm the blade sail can be quite significant and tip strikes on the deck are not unheard of.

PPS Heedm – In response to an earlier post of yours, the Robinson you saw hovering tilted to one side was experiencing an effect called “Tail Rotor Roll”, more or less all conventional single rotor helicopters experience this, it has nothing to do with gyroscopes.

[Heliport]

Thomas Coupling
Long time, no post.
Good to hear from you again.

How about starting a lighter thread?
:)

[Jed A1]

Glad to see we’ve got back too the original question.

Interesting comment about “ensuring” float failure! My view is that given time pop out floats will deflate anyway leading to the airframe capsizing.

Anybody who has done Helicopter Underwater Egress (Escape) Training will know that a float failure is assumed hence the emphasis on evacuation of the helicopter whilst inverted underwater.

As an aside one of my friends was doing his HUET revalidation yesterday. Somehow he managed to split his head open whilst evacuating upside down. He is now flying today with a dispensation for not having revalidated his HUET and a second dispensation for flying with a pre existing condition. He looks quite comical. Anybody who sees a rather large captain landing on a tropical platform with what looks like a turban on his head will know who I’m talking about.

A suggestion to any pilots out there who don’t undergo HUET training as part of their job is, I would highly recommend attending a course. I saw an advert recently in a flying magazine offering such courses to private pilots. It may have been Flyer Magazine and through Biggin Hill Helicopters for less than GBP100 but I’m not too sure. Not only does such a course teach you how to evacuate a helicopter upside down underwater but it also teaches preparedness for such an incident and gives you the confidence and respect needed to handle life threatening incidents like this. These courses will be held around any major offshore flying base. In the UK, Great Yarmouth, Aberdeen, Fleetwood and Hull all have facilities to do this training. Money well invested.

[Nick Lappos]

I thought I'd toss in my 2cents about gyroscopic precession and helicopter swashplate rigging angles. Kirilian laid out the factors that describe how a rotor does not obey the gyroscopic precession rules (because it is not a gyroscope in any real way). The swashplate rigging angle is affected by many factors, and is never really 90 degrees in any helicopter!

Before all the mechanics jump up and describe (accurately) that their helicopter is rigged exactly at 90 degrees (forward stick makes the swashplate tilt exactly to the right), let me clarify one point:

The rigging of the helicopter is the offset put in to phase the cyclic exactly to match the motion of the aircraft. The test of perfection is that the pilot moves the cyclic forward and the nose goes down, with no roll at all (and vice-versa). Well, that never really is achieved! We compromise in two important ways:

1) Speed changes the rigging angle (we call it Gamma) so that there is a big change between hover and Vne. As I recall, high speed needs less Gamma, hover needs to most. The difference for the S-76 was about 10 degrees, for the Comanche it is even more! We usually compromise at a Vcruise setting and let it go. The S-76 flew with 3 different sets of mixing bellcranks, and we picked the "best" set to match our opinions. For Comanche, with the Fly By Wire, we tune the Gamma to match each flight condition.

2) There is a rotor tilt for short term, medium term and long term that is different. The short term is seen in big stick inputs done fast, and washes out quickly. This one is usually under-mixed, since it is seen only in abrupt, unusual maneuvers (unless you are dogfighting in a Comanche). The BO-105 folks know this one when they pull load factor and there is a big need to retrim roll.

The meduim term slow response is there as the "constant" term and is the one we address with mechanical mixing in most helos. This is the one that sets Gamma. You find this if you ask for 5 degrees per second roll rate, and look to see if any pitch retrim is needed.

The longest term is the roll and pitch retrim needed for changes in airspeed, which we do not set up mechanically, we let the auto-pilot or pilot worry about this. This one sets the S-76 and Robinson stick somewhat to the right as speed increases, about 1" or so from hover to cruise. Don't be confused by this one, at any point in the flight, if the pilot pushes the stick forward, the nose goes down with almost no roll, even though the stick is moving with airspeed in a slightly rightward direction.

Let me forwarn LU, I will answer no questions he asks on this subject, as he has read all this before and has NEVER understood a word of it. If any other ppruners have a question or disagreement, fire away! :D

[Thomas coupling]

Hi heliport, will think of something suitable....have been participating on our own (police/HEMS)forum which we are trying to get off the ground (identical to the PPrune infrastructure). Won't give the link unless someone wants to join...
Hang in there HP :D

back to sleeeeeep, now

[Lu Zuckerman]

To: Everyone else but Nick because he won’t answer

Nick sez:

“Before all the mechanics jump up and describe (accurately) that their helicopter is rigged exactly at 90 degrees (forward stick makes the swashplate tilt exactly to the right), let me clarify one point”:

Response:

I know of no helicopter that when the cyclic is displaced forward the swashplate tilts to the right.
Regarding mechanics that accurately describe their respective helicopters as having a phase angle or rigging angle of 90-degrees. Sikorsky mechanics other than S-76 mechanics can make that claim Hughes and Apache mechanics can make that claim Aerospatial mechanics can make that claim, as can many others.

Nick sez:

The rigging of the helicopter is the offset put in to phase the cyclic exactly to match the motion of the aircraft. The test of perfection is that the pilot moves the cyclic forward and the nose goes down, with no roll at all (and vice-versa). Well, that never really is achieved! We compromise in two important ways:

Response:

You use the term rigging and rigging angle interchangeably. Rigging angle (your usage) can change. (See below) but the helicopters rigging is constant once it is set. If it changes you are in deep trouble.

Nick sez:
1) Speed changes the rigging angle (we call it Gamma) so that there is a big change between hover and Vne. As I recall, high speed needs less Gamma, hover needs to most. The difference for the S-76 was about 10 degrees, for the Comanche it is even more! We usually compromise at a Vcruise setting and let it go. The S-76 flew with 3 different sets of mixing bellcranks, and we picked the "best" set to match our opinions. For Comanche, with the Fly by Wire, we tune the Gamma to match each flight condition.

Response:

You use the term “rigging angle”, as something that is dynamic and it may be an accurate choice of words. However those of us that are not used to the term or the term Gamma will visualize the rigging of the helicopter flight controls as being dynamic. I do not mean dynamic in that it moves in response to pilot input I mean that they might think that the controls are dynamic in respect to speed changes. The pilot will adjust his controls to compensate for speed changes or in compensation for external forces acting on the rotor system. I can accept that.

Regarding the S-76 flying with three sets of bellcranks I think you should clarify the reason for doing so. From what I understand, there was a goof-up on the gearbox casting and the servo attach fittings were not in the proper place as compared to other Sikorsky designs. The basic Sikorsky design places the Fore and aft servo 45-degrees ahead of the longitudinal axis and the left lateral servo 45-degrees after the longitudinal axis and the right lateral servo 180-degrees out from the left lateral servo. All Sikorsky helicopters up to the S-76 had their servos mounted as described above. Please do not include the Blackhawk. The three different mixing units were developed to obtain the optimum response from a given pilot input. In concert with the servo mounting relative to the two axes on other Sikorsky helicopters the pitch horns led the blades by 45-degrees. This meant that the blade over the right side of the helicopter would be at the lowest pitch and the blade over the left side would be at maximum pitch. The two blades in-between (assuming a four-blade system) would be at the collective pitch setting when the pilot pushed forward cyclic. As a result, the disc would dip down over the nose. I choose to believe it is gyroscopic precession and others like you say it is aerodynamic precession. It works either way.

I have a few other question s but they won’t be answered so why ask.

[Dave Jackson]

Heedm

>>""Why talk about 'impressed angular momentum' when one can eliminate the middlemen, go right to the source and just say 'thrust'?"< Because the two are different."<.

True, but force (or torque) changes the state of rotational inertia and rotational inertia is a component of angular momentum.

>"Also, there is not only one force that is variable. Drag is variable. Weight is variable."<

True again, but for conceptual simplicity, it is easier to consider them as being constants.

>"You still seem to hold aerodynamic precession as a very special concept. I'm not sure exactly what your theory is, and ..... how it explains what the apparent lag is."<

Phase lag is one of the reasons why I like this hypothetical aerodynamic precession. For me, it is easier to aerodynamically envision the relative phasing between the control plane and the tip path plane, when considering a blade that is flying to position in less than 180-degrees.

If phase lag is to be discussed, others might prefer that it be on a new thread.

I agree with all you say 100%. Well; not to go overboard [as in ditching], lets say 99.9%.
Whatever. This discussion is certainly thought provoking and educational, for me at least.
_____________


In a hypothetical world, one could have a teetering rotor, with absolute rigidity between the blades (to resist coning), and no mass.

There is no 'original angular momentum' in this hypothetical world since the rotor has no mass. If the engine stops, the rotor will immediately stop revolving, since there is nothing to oppose the drag.

In this hypothetical aerodynamic world, it will still be possible to fly the rotor disk to position, whereas it will be impossible to move it to position by gyroscopic forces.

Now; if helicopter designers can continue to reduce the mass of helicopters far enough, gyroscopic precession will take its last flight - out the window. ;)
_____________

Nick

Thank you ~ again.

Your explanation of Gamma is very timely. I have been reading and rereading documents on Gamma in the Sikorsky ABC. As you know from flying the craft, it had an in-flight variable Gamma from less than 20-degrees to greater than 60-degrees. The graphs show the results of different Gamma at different forward speeds. It has been difficult to understand, but interesting.

Your current description of Gamma and forward speed is making things easier. Thanks.

Now back to rereading your posting. :)

[heedm]

I'll respond to everyone in one post.

Nick, thank you for that practical discussion. While I enjoy getting into the theory, I don't lose sight of the fact that the pilot makes the finesse corrections as the flight parameters change. I don't mind going head-to-head with you on physics but for cockpit knowledge, I bow to your training and experience.

You said, "Kirilian laid out the factors that describe how a rotor does not obey the gyroscopic precession rules...." Was that the Lock's number post, or did I miss something?

I agree that many factors will affect this angle, but no matter how many factors there are, basic physics still applies. If the rotor flapping hinge is coincident with the axis of rotation, then an angle of precisely 90 degrees is measured between a maximum force and maximum displacement. If the hinge is offset, then the angle will reduce.


Jed A1, I do a two day HUET and EBS course every 3-5 years. I've always been comfortable in the water, but I learnt on day one that I would have not escaped an upsidedown ditching without the training and confidence that that course gave me. You're right to recommend it.


Grey Area, first of all, I was kidding about that left turning Robinson. Part of a long discussion.

Secondly, the forward movement of the stick in the autogyro with a teetering head doesn't directly put an upwards force on the disk at 6 o'clock. It's a teetering head, so when a blade is at 6 o'clock, the hinge is normal to the force. Consider what would happen with the blade at 6 o'clock but the rotors not turning. What I believe does happen is the forward movement of the stick causes less pitch at the 3 o'clock and more pitch at the 9 o'clock. The process from here follows the apparent 90 degree lag discussions.

Kyrilian what is the gamma that is in Lock's formula? The way gamma has been used here is that it is the phase angle between blade pitch and blade displacement (don't know the precise definition of that angle).


Matthew.

[ 23 November 2001: Message edited by: heedm ]

[eden]

Hi there - Just wanted to be post 100 and ask one thing .........

Who's talking about ditching now? or is it just something that rhymes with it ........?

energy driven eccentric nirvana

[heedm]

Dave, not leaving you out, just didn't get your post before I started mine.

If you can email those articles on the ABC, I'd really appreciate it. If they're not on the computer yet, just point me in the right direction.

Problem with your massless rotor is if you attempt to fly it to position, you will apply a force to the blade. A force applied to massless matter (not possible, but I'll follow it through) will cause infinite acceleration, and your attempt to fly to position will result in catastrophic failure.

Matthew.

[Nick Lappos]

heedm,
The lock number that kirilian posted is the term that describes the relationship between the flapping inertia of the blade and the aerodynamic damping it gets (the force feedback) as it flaps. This lock number gives us a feel for the flapping frequency of the rotor blade, which tells us how much we must lead the desired motion to get the proper output. While Lu does not know of any helicopter that has a 90 degree swashplate angle, that is because he gets all wrapped up in how long the pitch arm is (in degrees of rotation) so he gets fouled up in the math. Let's face it, if the pitch horn from the blade was long enough to wrap around the swashplate two times, it would have a 720 degree lead or lag, and that would get that someone's panties in a bunch. Really, the issue is how much ahead of time does the pitch change need to reach the blade to get the blade to hit peak flapping when we want it to. The lighter the blade, and the skinnier it is, with the flattest lift curve slope, the easier it jumps up into position, and the less we have to lead the controls (rig them earlier). The heavier the blade, and the fatter it is (so the air above it slows down its attempt to flap up) and the steeper its lift curve slope, the more we must telegraph the control input to get the disk to obey. While this is all really not purely gyroscopic precession, it is physics (and Dave Jackson, I'll take your advice here anytime!).

We in the industry tell everyone it is gyroscopic precession to keep the troops in line and fool them, but it really is the phase angle between the forcing function (the controls) and the rotor flapping resonance (the disk tilt).

The phase angle for the S-76 is about 56 degrees, which would make Newton roll over in his grave, gyroscopically. Most helos would not be rigged (yes, Lu, rigged, rigged rigged, get used to it) at 90 degrees if we tried to perfect their controls, but pilots are wonderfully adaptive fellows, and quickly get the phase angle just right even if the manufacturer did not. The Benson and De Cierva gyrocopters are examples, where the cyclic stick is directly attached to the swashplate, so pushing forward stick achieves something approximating a left roll, I think (any gyrocopter pilots here to help me out?). Ouch, but it works.

This is similar to a motorcycle, where the way to turn left at speed is to tweek the handlebars rightward, and cause the bike to lean left to make the banked turn. Not natural, but easily learned and quickly second nature.

:D

[ 23 November 2001: Message edited by: Nick Lappos ]

[Thomas coupling]

Eden glad to see you around and about. How are you?

;)

[Dave Jackson]

Heedm

>'If you can email those articles on the ABC, I'd really appreciate it. If they're not on the computer yet, just point me in the right direction."<

Xeroxes of these articles were obtained from the American Helicopter Society. A list of the ones I have can been seen on web page: http://www.synchrolite.com/0891.html .

Your E-mail address is not available, so a Private Message has been sent via PPRuNe. If you do not get this message, send me an E-mail at [email protected]


>'A force applied to massless matter (not possible, but I'll follow it through) will cause infinite acceleration, ...."<

The blade is being flown to position in air. If the ascending flap velocity were to exceed the commanded rate, the angle of attack will move to above the blade and force it back down.
_________

Don't want to take words out of Kyrilian's mouth, but to save time;

Lower case gamma is Blade Lock Number.
Upper case Gamma is what Nick is refering to. I think the symbol Delta-psi is also used.

[ 24 November 2001: Message edited by: Dave Jackson ]

[ 25 November 2001: Message edited by: Dave Jackson ]

[sling load]

Lu,
If your concept of understanding still dictates that rotors behave the way they do due to gyroscopic precession, tell me what would happen to a four bladed rotor rigged with a swashplate in a total vacuum, with cyclic and collective inputs. Im interested to hear your response.

[Lu Zuckerman]

To: Sling Load

Most likely nothing. There would be no response to collective input nor, would there be any response to cyclic input. Whether you believe in aerodynamic precession or, gyroscopic precession in order to make either work you need to be in a field of air. You already know how blades move if you subscribe to aerodynamic precession well if you subscribe to gyroscopic precession you need a differential of lift which creates a nutating force on the rotor system which has the characteristics of a gyroscope rotor. With the differential of lift being greater on the left side (American design) then the force differential will cause the disc to dip over the nose and raise over the tail with forward cyclic.

Now, I’ll give you a question. Please explain aerodynamic precession in the case of retreating blade stall. If the retreating blade stalls and falls due to the lack of lift what makes the advancing blade and therefore the entire disc raise over the nose? I say the entire disc is effected by the extreme difference in lift across the disc and the disc responds due to gyroscopic precession. What do you say?

[Grey Area]

Lu,

“There would be no response to collective input nor, would there be any response to cyclic input“

I really would expect a reliability engineer to look at the problem in depth not just fire off a line off the top of the head. As you couldn’t be bothered to think it though let me.

In a vacuum the aerodynamic forces will be non-existent, however there are forces that could change the state of the system, namely, friction in the various hinges. A control input pushing upwards would be opposed by friction in the feathering hinge - in the case of elastomeric or other rigid systems this resistance could be significant. The movement of the control orbit can therefore move the blade. As the blade experienced a displacing force and there are no aerodynamic forces damping forces one could expect precession. The magnitude of the forces involved would be very small therefore the response of the disk would be very slow. Interestingly, as there are no aerodynamic damping forces the disk could well overshoot it’s commanded position, although in an articulated head with a hinge offset a damping force will still be created as a result of the cyclic flapping of blades through the plane of rotation. In the case of a collective input one could expect momentary coning would occur before the disk slowly resumes an un-coned state due to inertial effects.

In summary, in a vacuum one can expect some sort of disk response to cyclic inputs but only momentary movement in response to collective input.

GA :)

[Lu Zuckerman]

To: Grey Area

It would be sneaky of me to say that if Sling Load indicated that we were in a vacuum situation that I would assume a frictionless environment but I didn’t think of that. Based on what you have stated in your post you are indicating that the blades would move not by aerodynamic forces due to the lack of air but solely due to gyroscopic precession. Did I get your statement correctly? If that is what you indicated then upon your return to Jolly Old you will be taken directly to the tower and summarily beheaded.

Down with aerodynamics and, up with physics.

[Grey Area]

Yes.

[JoePilot]

Stick forward: max +ve rate of pitch change at front, opposed by moment of intertia about longditudinal axis, resulting in and upward flapping tendancy during a blades' passage through the front half of the disc. So it would reach a high point on port side (hide behind the term Gyroscopic Precession if you like). The forward stick displacement would require an accompanying stick force to the right.(the force you need to be continuously increasing pitch at the front).

The new resulting plane of rotation would set up a differance from the control plane equivalent to pushing the stick to the left ..... and around and around the problem would proceed :eek:


(this is just a lite look at one aspect)

[JoePilot]

It's Lu's presence which does this.

Educating Lu is drain on the pilots.

Whatch out Lu's 'stick time' is increasing all the time. He's almost a pilot now.

Appology in advance to thread owner...

[sling load]

Lu,
I wouldn't say the disc drops due to gyroscopic precession, there is a difference in lift between the retreating stalling blade and the still advancing blade, which at high speeds is approaching compressibility and the problems that brings. At that condition, lift is not equal across the rotor and our old friend dissymetry of lift comes into effect. In any case, the disc will rise and slow the aircraft down and if the pilot is a total idiot and pushes cylic forward without changing collective ,the condition will worsen and roll.

Im not an engineer Lu, only a student of the subject, but I admit when Im hooped on something and don't understand it.

Grey Area even saw that.Mechanical linkages work in vacuums too Lu.

The point of the vacuum was to remove the affect of aerodynamics from the rotor,
if you beleive that a rotor works like a gyroscope, then aerodynamics play a minor role in rotor behaviour, is that what you understand?

[ 24 November 2001: Message edited by: sling load ]

[Lu Zuckerman]

To: Sling Load

“I wouldn't say the disc drops due to gyroscopic precession, there is a difference in lift between the retreating stalling blade and the still advancing blade, which at high speeds is approaching compressibility and the problems that brings. At that condition, lift is not equal across the rotor and our old friend dissymetry of lift comes into effect. In any case, the disc will rise and slow the aircraft down and if the pilot is a total idiot and pushes cyclic forward without changing collective, the condition will worsen and roll”.

First of all, let’s disregard compressibility as retreating blade stall can occur under several different sets of conditions. I agree that there will be a lift differential. At this point our opinions start to differ. The roll will occur prior to the disc rising over the nose. At the onset of retreating blade stall there is a pronounced vibration followed by a roll to the left (American design). If at this time the pilot has not taken corrective action the disc will not just rise over the nose it will flap (blow) back quite violently and in some cases the blades will contact the tail boom (cone).

The major difference between us is how we view the reasons for roll and blow (flap) back. You say that is a pure aerodynamic response and I agree that aerodynamics is involved. As I have stated previously this is an alternate to gyroscopic theory and I can accept that. However, I believe that the differential of lift or, differential of forces acting on the disc which has gyroscopic characteristics causing it to precess. The roll is aerodynamic but it is the precursor to the flap back, which I believe is the result of gyroscopic precession.

The same condition exists but to a lesser degree when transitioning and the helicopter rolls and the disc blows back. Under these conditions the pilot can take corrective action by applying forward cyclic.

[connavar]

Saw a classic example of Gyroscopic Procession in Sydney during Mardi Gras once!! :D :D :D

[Grey Area]

Lu,

:mad: :mad: :mad: :mad:

YOU HAVE GONE TOO FAR! Friendly banter is one thing you have just crossed the line!

Your last post was DANGEROUSLY ill advised, there is no similarity between retreating blade stall and transition at all. Your comment could lead to confusion and God forbid someone continuing to advance the cyclic in an incipient retreating blade stall, YOUR ADVICE WILL KILL THEM!! As someone who has taught recovery from incipient RBS and has had the misfortune to lose control (and luckily regain) as a result of RBS I can categorically say you are talking out of your backside.

PLEASE FIND OUT WHAT YOU ARE TALKING ABOUT, YOU ARE BECOMING A FLIGHT SAFETY HAZARD!

This is not a point for discussion Lou.

:mad: :mad: :mad: :mad:

GA

[Lu Zuckerman]

To: Grey Area

You missed the point of the comparison. In order to accept my reasoning you have to accept the theory of gyroscopic precession. If you can’t accept that, then substitute aerodynamic precession.

Transverse flow effect:

When the helicopter is in the area of transverse flow effect two things happen. One is the helicopter will roll to the right and the rotor will blow back. These actions are relatively benign and the pilot can correct for these effects by input of cyclic control. The blowback is caused by a differential of lift across the disc with the greater lift being on the right side. This lift differential will in effect be a perturbing force on the rotor (which has gyroscopic characteristics) and cause the disc to tilt up over the nose and down over the tail. This disc movement if I understand it correctly in effect changes the angle of attack on the blades and the disc responds by tilting to the right.

Passage through the transverse flow field will cause the helicopter to vibrate just below effective translational lift. This effect can also occur during landing when the helicopter passes through the effective translational lift.


Retreating blade stall:

In retreating blade stall the retreating blade(s) are generating less lift than the advancing blade(s).

This lift differential is a perturbing force on the right side of the disc and is acting upward causing the disc to respond as a gyro rotor and the resultant of this upward force is the tilting of the disc up over the nose and down over the tail. The differential of lift will cause the helicopter to roll to the left, which is a precursor to the flapping back or blowing back. In this area there is a pronounced vibration just prior to the blow / flap back.

In both cases there is a differential of lift causing the disc to tilt up over the nose and down over the tail. In one case, the helicopter rolls right and in the other the helicopter rolls left. The roll is the result of aerodynamic forces while the flapback / blowback is the function of lift differential across the disc and the upward perturbing force results in a gyroscopic response.

In the case of the actions resulting from transverse flow effect the movement of the helicopter and the rotor is benign and the pilot can counter these actions with cyclic input. In the case of retreating blade stall the roll is pronounced and there is a lot of vibration. If by that time the pilot has not taken corrective action the disc will flapback violently and most likely chop off the tail boom.

Hopefully you can see that the actions taking place are similar if not identical. The corrective actions by the pilot are different and there is a major difference in what happens to the rotor relative to its’ response. Each condition should be taught in the flight training program and it should be obvious to any pilot that he / she will not experience retreating blade stall at translational lift speeds and therefore, understand the corrective actions that must be undertaken for both situations.

[Grey Area]

Lu,

All the major Test Flying Schools (ETPS, USNTPS, EPNER), Eurocopter, AugustaWestland etc plus the major text books, Gessow, Prouty et al disagree with you, so do I.

[Hoverman]

Lu
What about Grey Area's more important point?
Professional pilots/instructors are able to make their own asessments of the value or otherwise of your theories, but the site also has lots of inexperienced/low time pilots.
Since you often give your views on how a pilot should react in a particular emergency/problem, don't you think you should point out you are not a pilot?
Perhaps you could add a 'health warning' to your 'Cat' signature?
I mean this as serious suggestion in the interests of flight safety.

[Lu Zuckerman]

To: Hoverman

“What about Grey Area's more important point?
Professional pilots/instructors are able to make their own assessments of the value or otherwise of your theories, but the site also has lots of inexperienced/low time pilots.
Since you often give your views on how a pilot should react in a particular emergency/problem, don't you think you should point out you are not a pilot?
Perhaps you could add a 'health warning' to your 'Cat' signature?
I mean this as serious suggestion in the interests of flight safety”.

To my knowledge the only “ADVICE’ I have offered relative to the recovery from an emergency situation was the recovery from a zero G incident and those instructions were quoted from the Robinson POH for the R-22 and the R-44. Regarding those instructions I added that “IF” there is in effect an 18-degree offset when the pilot followed the POH instructions he could possibly add to the right roll developed by the tail rotor during the zero G incident which is counter to the POH instructions. It seems that there is a degree of “confusion” between some Robinson instructors as to exactly how the cyclic is to be handled during zero G recovery.

Regarding the 18-degree offset I have Contacted Canadian Helicopters in Ontario and they are considering my request to perform the test. Once the test is performed we will know who is right regarding this condition.

Regarding my not being a pilot all the reader of any of my posts has to do is read my Bio. It will indicate that I have no ratings. Nor does it indicate what type of helicopters I fly. If you read some other posts you will see that some individuals address some really intricate problems relative to helicopter aerodynamics and they are not pilots.

Here is another point regarding the supposed 18-degrree offset. It is not dangerous and the pilot can if it exists correct for it with cyclic input. The only place where it would be dangerous is in recovery from a zero G incident and then it would only be dangerous for an inexperienced pilot.

[voljet]

Lu

And so do I disagree with you - vehemently! As one who has experienced retreating blades stall, real time, in the classic case of trying to outrun a CB some 40 years ago (in a Sikorsky S51), I know that the first solid manifestation of the phenomenon is a violent pitchup of the nose FOLLOWED by a tendency to roll to the right. However, your not-so-ever alert young pilot - well-trained and anticipating the possible condition - was able to mimimize the roll with reduced collective and increased throttle - just as taught. I think you're caught up in the proverbial whirlwind of theorists talking to professionals who know, or have experienced, better, and you ought to cut bait before someone from ETPS or Patuxent River gets hold of you.

[voljet]

To anyone still here. Should have read my first post TWICE before hitting the button. Obviously the rolling tendency was to the LEFT, not the RIGHT. Apologies to all.

Voljet

[Lu Zuckerman]

To: Voljet and everyone else.

I stand corrected. I got it twisted around. The FAA Rotorcraft Flying Handbook Page 11-6 states: At the onset of retreating blade stall the helicopter will experience a low frequency vibration followed by the disc pitching up and the helicopter rolls to the left. Sorry if I got everyone upset.

On a personal note, you must be near my age if you were flying S-51s. My experience on those helicopters was between 1949 and 1952.

[sling load]

Lu,
Further to my mind experiment with the vacuum, put the same rotor head in a heavier fluid than air, say water. If the rotor were to turn at the same speed as the rotor in air, and the vacuum, do you beleive the rotors will still respond as a gyroscope?

The forces acting on the blade will be greater and the stesses on the blade to overcome this stress would probably be so great as to destroy the blade. For a blade to be at its lowest point at the twelve o clock position, the blade would have to have its pitch changed much earlier than 90,(three o'clock)in order to give the blade time to overcome its stresses in time to acheive its lowest point at twelve o'clock.

This point could be at 100 degrees or 112.22 degrees,who knows, but it would have to be worked out for the stresses it undergoes. Do you think that the same rotor turning at the same speed in a heavier fluid than air is still a gyroscope?

Its a matter of designing blades with the fluid that you and I know as air, and the phase angle alone does not dictate automatically that it is a gyroscope. All spinning objects have the properties of a gyroscope, but aerodynamics or fluid dynamics, play a major role.

Nick or Grey Area, I would welcome your comments on my 'mind' experiment.

Im not an engineer, but studying the stuff at Uni.

[Lu Zuckerman]

To: Sling Load

The situation that you describe is purely hypothetical however you do acknowledge that there would be increased forces that would damage the blades or, to totally destroy them. If we were to take this point one step further and say that the resistive forces were not present and the rotor could turn in water at 250-400 RPM then the cavitation would be so strong as to eat the blades within a moment or so.

I copied a part of one of my posts on the Phase Lag thread. It was in response to a claim that centrifugal force played no part in the operation of a helicopter rotor system.

“It’s is very nice to refer to engineering texts as a frame of reference but you have to understand that the author is making his own point and then he is creating the mathematics to describe the condition. However this situation would never be encountered in real life. While in school it gives you the ability to envision various situations but once you leave school you should close your text books and do it the way your employer tells you to do it”.

My point is that in setting up these hypothetical situations you have to take all things into consideration as well as that they must be demonstrable in order to prove the point of the hypotheses.

I don’t have the knowledge or technical background to properly answer your question. If you had indicated that it was a gyroscope under water then I would say that precession would take place and that the water might have a dampening effect and that there might be cavitation taking place which would increase the frictional forces on the surface of the spinning rotor and possibly cause pitting on the rotor which in turn would increase the frictional forces and on and on and on and........

[voljet]

Lu, the Cat

Mine was about a decade later, when the Canadian military was still using them as the RW conversion trainer at the Canadian Joint Air Training Centre in Rivers, Manitoba. I still have the 'winged S' imbedded in the palm of my right hand - but the old girl holds a big part of my heart - if you were good to her, she was more forgiving than any of the many types I've flown since - she did the sweetest downwind 'nap' autos I've ever seen, including 47s, 12Es and 206s. Maybe we could swap tales sometime.

Cheers, Voljet

[heedm]

Sling Load, without trying to guess at the precise final outcome, I think it's safe to say that you're right that the density of the fluid changes the dynamics.

Consider a gyroscope demonstration. You push down on the disk at 3 o'clock, 90 degrees later, at 12 o'clock, you see that part of the disk go down. When the disk moves, it must also move air. Which puts in a force downwards at 6 o'clock. Since the result of that forces appears to happen 90 degrees later, then it causes the disk to tilt slightly to the 3 o'clock. The net effect of all this tilting is that instead of tilting to the 12 o'clock, the disk tilts between 12 and 3 o'clock. The denser the air, the further from the 12 o'clock.

How much the disk tilts to the three o'clock depends on how strong the second order force is. Throw this experiment into water, and that force gets much stronger.


Now lets go on to helicopter rotors. If they're behaving like a gyroscope, then the result of a force appears to lag by precisely 90 degrees. Put the helicopter into water, and that hasn't changed. What has changed is that there is more than just one force on the blades.

If the helicopter doesn't act like a gyroscope, then the phase angle will still be affected by air density. The theories involved don't change, just the magnitudes of some of the forces on the blades.

Matthew.
[email protected]

[helmet fire]

Great thread, pity i had to work and miss most of it.

Lu, Re retreating blade stall - we have been here done this. Last time we discussed this you agreed that:
a. The rotor disc does not become suddenly unstable.
b. The tail boom is in no danger of being struck.
c. the stalled blade in fact only has a portion of it stalled dependant upon its rotational position.
d. The blade does not rise up over the nose of the aircraft. this is not what causes the pitch up.
e. The stalling blade is still producing lift, despite sections of it being stalled.

Your repetition of this line of arguement merely adds credence to Nick's propostition that you have a hard time learning - it appears you have forgotten all the ground we made at that time.

The RBS thread was unfortunately closed so I cannot give you the examples. Did the Robinson Course thread also get closed? I cannot find it. Why did it get closed? We were making headway there too.

Basics (IMHO - I am not an aerodynamicist) for some of the stuff being discussed:
1. The blade disc will follow the fuselage with stick nuetral on a deck in motion. The disc is always attempting to align itself to the control position during positive G operations.
2. Didn't we previously agree that the rotor disc does not exhibit gyroscopic tendencies (or minimal at the most) because (amongst other things) it is not a rigid dis, rather the blades are free to flap independantly? This includes the Bell system. Lu: we agreed to the fact the Bell system allows individual blade flap in the Robinson thread.

3. Ditching is bad. Avoid exploration of the theories!

Good ditching stories: There was a B214ST ditching on video, I think it was from Northern Australia on a lloyd machine. old mate pulled off ditching. Pax egressed succesfully. Copilot used personal knife (not specially designed provided one) to cut life raft from aircraft. During vigourous knife application, poor bast ard copilot managed to spear left side float. Loud farting noise occurs as aircraft starts slow left roll. Captain yells expletive, decides to exit the right side of the cockpit and does beautiful 1/2 pike from his door opening as aircraft completes left roll and visits the ocean floor.

On the other extreme, a Russian KA26 Kamov ditched off Vladivostok due transmission problem. Floats worked, crew egressed and were rescued, ship sailed on, much vodka was drunk. 2 or 3 weeks later, said aircraft washes up on beach. New trannie fitted, and back to work it goes!

So I guess that the answer to "how long" will a float equipped aircraft last is like everything else in aviations - the answer is ...it depends!... :cool: :cool:

[sling load]

Heedm,
Yes, that is exactly the point of the hypothetical. The dynamics of a rotor in flight are very different from the vacuum and the water example.

In the vacuum the blades will probably respond sooner as there are no forces other than the linkage and friction. My point is, the rotor could be rigged at different phase angles to suit the design of the rotor system, I understand that rotors have the properties of a gyroscope, but gyroscopic precession in itself is not the explanation in total. Aerodynamics is the dominating force.

I had quite a lengthy hour and three quarters! discussion with a physicist on this subject (a relative) and he doesn't support the gyroscopic precession dominance at all. He stated the aerodynamics would overwelming be the dominant effect.

I have done aerodynamics at uni, but we havn't got into the helicopter aerodynamics,thats a way away.

I have disagreed with Lu on this before on so many other posts, and he knows that, all I can say is, I beleive Mr Robinson knows far more than Lu, and that he should address his concerns with them, or, go to the issuer of the TDC the FAA and explain it to them. Hes had some of the industries experts like Nick in total disagreeance with him and yet, this stuff still keeps him up all night. Mind you, my relo got quite excited about the discussion and it got my brain frazzled for a while, :)

[paulo]

A curiosity question from fixed wing jockey.

I was pondering the other day the issue of ditching in a Helo.

Is there any standard approach to this? So you've auto-rotated down, splash, and you're goint to bail, but then there's those rotors still spinning above you, and you're sinking. Sounds a bit like a fish-bait scenario.

I remember studying the advice for fixed wing. Apart from not landing on the front of the wave or swell, it more or less said "cross your fingers".

[RW-1]

Ditching in a heli is a bit easier, depending upon the situation. You still have to look at swells, etc.

We look at it from two standpoints:

Whether we have power for it or not.

With power, most checklists have us come into a hover and the pax exit the aircraft, then we move off a short distance and put it in (gets pax away from the rotors).

Power off all remain with the craft.

As for your concern about the rotors up top, etc. At water entry typically lateral cyclic is applied in either situation, which will cause the blades to contact the water. Everyone waits until all motion has stopped before leaving the aircraft.

Since a majority of heli's have a high CG (engines and transmissions up top), most will then continue to roll inverted when submerged, one should be prepared for that. In my mil training, you grab a referance point and hold on to it if possible, and work your way thru your pre planned exit route hand over hand, never taking both hands off of the frame, etc.

For training did the dunker 4 times, 2 day, and 2 sim night with darkened goggles.

First runs everyone goes out thru their own exit.
Second runs everyone files out thru "Main cabin door"
(have to brief this among everyone just before they dunk you)

Dunkers were certainly one of the fun things about training, serious business, but fun never the less :D

[Thomas coupling]

Paulo: Options are very limited.
Most ditchings are uncontrolled where the pilot becomes a passenger. If you do have any available control/power over the helo, then the above is true. Get rid of your pax because the chances of you getting out safely are slim. Be very careful about "lateral movement" of the cyclic prior to going in.
If you offer the retreating blade into the water first, there is a good chance that the gearbox and or engine(s) will smack you in the back of the head:eek:
If you are mister cool and think you have your wits about you you might be tempted to offer up the advancing side first which dismounts the heavy metal behind and above you...rearwards:p

If I was to put it into the water again for my second time then I would kick the doors offprior to landing and settle it gently onto the water, then prey!
If you aren't ex mil, I won't go into the abandon aircraft drill, but if you do a lot of over water, i would suggest a 'dunker' course (£180+) at Fleetwood or similar for the experience which you will come to rely on and never forget!.
When most choppers ditch (controlled) they role over and sink nose first, putting you inverted pointing away from the surface and in the dark...nice...

Stay feet dry....

[Lu Zuckerman]

Back in 1949 the US Coast Guard attempted to determine the best method of ditching a helicopter. Having access to twelve surplus HOS-1 helicopters the pilot took them up in succession and dumped them into the Albamarl Sound just off Elizabeth City, NC. After all of the ditchings were completed the final report indicated that the helicopter should enter the water in a normal attitude and then the pilot would move his cyclic to the left causing the retreating blades to hit the water. In a previous post it was indicated that the gearbox may hit you in the back and this may be true in today’s helicopters. In the test helicopters the blades were not as robust as the blades on today’s helicopters and in the ditching process the blades just disintegrated upon hitting the water.

[chopperdr]

paulo: best trick, have emergency floats installed before going out over water, and then do not be afraid to use them at the first sign of trouble. repack/ recharge is cheap considering the consequences.
chp dr

[bcp]

Just a thought, some of the experts out there might be able to help more....

What about in the auto (assume engine failure) at the last moment before contact with the water giving the chopper aft cyclic to try and get the tail rotor in the water first to try and slow down the main rotor a bit to reduce the problem mentioned above about the gearbox smashing through to the pilot.

[Lu Zuckerman]

Dipping the tail rotor in the water would slow the main rotor down for a mili second at which time the tail rotor and gearbox would be torn away from the tail cone and the drive shaft would suffer a great deal of damage..

There was a case where a pilot mistook a river for the active runway and he set his H-300 down in the water. When the tail rotor hit the water the drive shaft wound up torsionally, severely shortening it and the diaphragm couplings stretched to make up the difference caused by the torsional shortening of the shaft. The diaphragm couplings then separated from the gear drive and the tail rotor gearbox and the helicopter came to rest on the river bottom. As an aside the pilot sued Hughes for the damage to the drive line..

[Whirlybird]

Thomas, or anyone,

Do you have any details of where to do a dunker course. It sounds like a really good idea. Just reading this thread sends shudders through me - I've read about what to do and I remain unconvinced about any of it. I think some practice would be sensible.

Please could you e-mail me any info, as I'm off to the US tomorrow and may not have internet access for three weeks; it'll save me remembering and hunting for this thread when I get back.

Thanks a lot, and bye for now.

[offshoreigor]

WRT Ditching:

There are three primary considerations:

1. Flight Conditions ie. IMC/VMC
2. Time of Day, ie. Day/Night
3. A/C Type.

Condition 1 and 2 will determine the flare height and amount of flare at the bottom, ie Night or IMC would dictate a flare at approximately 150' with 10 degrees of flare. Day VMC would require a flare at 100' upt to 25 degrees of flare(over land) but over water, the IMC tequnique is recommended do to loss of visual cues.

Condition 3 will determine the touch down. In the S76, it is recommended that you hold 10 degrees nose up until touch down with the floats deployed through 500'. In the 212 it is recommended that you actually drag the T/R through the water, this has nothing to do with slowing the blades, rather it provides a certain amount of stability to the A/C while deploying the floats after touch down.

Depending on the sea state/ Wind combination, the use of these techniques can lead to a successful ending. Having never ditched (full on auto to water) its hard to say, but having ditched in training (waterbird training in CYAW) it is the way I'll go.

Cheers :eek: OffshoreIgor :eek:

[chopperdr]

inflating emergency floats after touchdown,is for the float systems i have personally installed or been involved with testing, not considered standard procedure, emergency floats should be inflated before contacting water.
chpr dr

[Helinut]

Whirlybird,

The Civy dunker courses are done at Marine Colleges around the UK. They started doing them for the offshore industry. Living in Wales your best bet is Fleetwood Nautical/Marine College. I know of other courses at Aberdeen, Yarmouth, Southampton (Warsash). They do them in the military too, of course, but you normally have to wear a funny colour flying suit.

[Robbo Jock]

I did the Royal Navy dunker course at HMS Dolphin (as a civvy travelling out to Grey Funnel Line ships) many years ago and I can heartily concur with Thomas Coupling - it is an experience which you will never forget. Four dunks, last in the dark with darkened visors down: wait until you're upside down (less chance of the 'fish bait' scenario, Paulo) then exit through a defined exit in a set order. Scary. Having 'died' twice, I'm none too happy about helos over water ever since (not good for a North Sea wannabe!! :) )
But, it has focussed my mind on getting out of anything in an emergency. All these years later, whenever I get in an aircraft (airliner or light aircraft) I make damn sure I know how to get off it again in a hurry, operate emergency exits, etc. Some years after the dunk, I got on an airliner with a colleague who'd been on the same course as me. Just after we'd sat down I asked him where the nearest emergency exit was. Without looking or hesitation he pointed over his shoulder at it saying: "there and I'm going that way". He, like me, had automatically, nearly subconsciously, looked as soon as we'd found our seats. The training worked.

[offshoreigor]

Chopper Dr:

If you deploy the floats on a 212 in flight, you are in for a very big suprise!

Furthermore, if you are doing an auto in a 212, you probably have your hands full so to take your hand of the collective and reach over and pull the lever it may be a little distracting. This system is designed for a water contact deployment, hence the water sensors.

Cheers :eek: Offshore Igor :eek:

[RobboRider]

There have been a number of posts talking about whether or not the gearbox will come forward with blade impact. This same topic came up on a news group a while back, particularly in relation to Robinsons. This was especially pertinent because the flight manual says roll left while the various mathmatical types on the NG suggested this would force the gear box forward into the cabin.

I wrote to Robinson for clarification and one of their engineers wrote back and said that there was no likelihood of the MR Gbx coming forward as the blades were shown to disintegrate first. The roll to the left was to make sure the pilots door was uppermost to make egress easier.

[[email protected]]

Robborider,

Having rolled over in an R22 on land, to the left, I can heartily endorse the Robinson advice - the rotor blades will disintegrate/distort on initial impact leaving you in a broken but substantially intact helicopter.

[Helo]

If you have to ditch a helicopter and have a choice of rolling it right or left, which side should you chose?

I've heard some say rolling to the left to reduce the chances of the retreating blade entering the cabin (with a counter clockwise rotor). Is this true, and if so, does the benefit from that outweigh the problem that would cause when you're flying from the left seat?

Thanks for your comments

[Barannfin]

I think it would really depend on your helicopter, and who your passengers are. I know in the robbies that the blades would certainly not survive their contact with the water no matter which side you put them in, and that it is easier for the pilot to get out if you roll left. But if there is someone you care about in the left seat you'll probably want to roll right, as you likely have much more exp./familiarity with the helicopter. just my 2 cents.

[CTD]

If you must roll, roll so the blades break off at the back.

[Nick Lappos]

It's a loaded question. Why roll? Settle into the water, let the blades contact when they will, keep the aircraft upright to allow better orientation for those getting out. Open the doors/windows before water entry.

[Irlandés]

Here's another angle to it. Before ditching should you undo your seatbelts? High time pilots confident with their autorotation skills might undo seat belts before, knowing they can put her down gently and so not have to undo seatbelts under water which I'm told is not as easy as one would imagine. I've heard stories of people completely unable to get their seatbelts open under water. On the other hand if you make a mess of it and go in heavy, you'll probably wish you had your seatbelt on. My own opinion is keep them on, and after surviving touchdown pray you have the presence of mind to get yours and your passenger's (should he/she need help) undone. My instructor however seems to prefer the first method. Obviously has more confidence in his autorotational ability than I do in mine. :rolleyes:

Any ideas?

Irlandés

[GLSNightPilot]

I'm with Nick on this one. Why roll if you don't have to? I plan on my floats keeping me dry, should worse come to worst. You do have floats on your ship while flying over the ocean, don't you?

Unfastening the seatbelt isn't that hard, & you should have plenty of time to get them undone, if you do the auto correctly. I've gone through the 'dunker' training, & if you stay calm, it really isn't that bad. Easy to say, probably harder to do.

[sycamore]

A few points to consider from way back ;
use all of the collective on "landing", for control and it also gets rid of the rotor energy as you ditch,
the tail-rotor might break,so you will lose yaw control and might roll either way,even if pre-planned,
the doors may provide some rigidity to the fuselage ,so,it may not be a good idea to open them too early.They will also prevent water coming in and may provide a bit of buoyancy time.
keep the as/c as level as you can as blades striking the water can turn the a/c over,before they break.
having briefed the pax. prior to flight-Do not release your harness until the a/c has settled,you may end up upside down or get flung around and unconscious/injured,
release your harness as the water fills the cockpit/cabin to your chest BUT dont let go of the strap on the out-board side,as it provides you with an orientation point/reference,as you will lose all sense of orientation ,if the a/c turns over.Release doors/em.exits,take a deep breath at the same time and grab a door-frame to pull yourself out-let go if you are free;if not try another route-if you release your harness too early you will float up,whichever way that is!I know as I`ve done it in the Dunker-from the cockpit ,under the pilot`s`seat and out thru` the cabin!:p ;;Want to try it at night??

[RobboRider]

A couple of comments about some of the posts:
The question of which way to roll (or not) arises fairly regularly on rec.aviation.rotorcraft and as a result of varying opinions I contacted robinson helicopter company and got the lowdown on their opinion.
I can't speak with any knowledge on other types though.

The theory of some maths whiz pilots was you should impact the blade so the forces would transmit to the MR gearbox and dislodge it backwards, not forwards into the cabin. This would mean a right roll (in counter clockwise turning blades). Some others said "no, the impact needed to be on the left side after a left roll". The maths was a bit over my head when they started getting so contradictory.

Robinson's answer was. "We have tested the theory and none of it applies. Robinson blades bend up and distort or break and the MR gearboxes never dislodged." So they maintain the roll to the left as dictated in their handbook is purely to provide easier exit for the pilot as the aircraft submerges.

I guess if you have a passenger then which way to roll is dependant on whether you think they they will find it easier to get out than you will.

I suspect that some other types of helicopter with beefier blades may have more strict guidelines on rolling to avoid MR gearbox dislodgment.

Floats:
It would be nice to think that the situation would never arise where you would be over water without floats. But reality is there are planty of times where the only place you can land may be wet. A lake, creek or river in a heavily tree covered area, tracking along the coast and have to turn back into the wind and suddenly find your glide distance is a few metres short of the beach etc. In Oz is quite legal for private ops to be over water and out of auto distance provided you have lifejackets on.

Seatbelts:
On one of my many dunker courses we were shown a video with footage and interviews with people who had been in ditchings and their comments were interesting.

Firstly seatbelts. One guy undid his first for the same sort of arguments put forward above. When he touched down with what he thought was a zero speed auto he was slammed into the dash as the real zero speed was reached very rapidly. He was hurt but not enough to stop him getting out. His comment was that your perception is distorted because you are just so busy and stressed. He said he would never undo his belt again till everything stopped in the water.


Water entry and time to get orientated.
Two separate pilots told of how the cabin instantaneously filled with froth. Not a second to get organised and it was completely disorientating because all those suggested things like seeing which way the bubbles rise or things float was no help at all. In full daylight and "clear water" theywere completely blinded by bubbles. Sounds like you need to treat every ditching as the equivalent of a night ditching.
The average time I heard quoted at each course I did was less than 10 seconds from engine problem to swimming clear of the aircraft. Doesn't leave any time for much at all.

My advice 9 for what its worth) is do as many dunker courses as you can. Besides they are great fun.

[clearance]

Seatbelts...

If there is a chance of the aircraft rolling over, undoing your seatbelt prior to entering the water is not advisable. When the aircraft rolls inverted or part thereof, being strapped into your seat provides you with a great orientation/reference point in which to find the appropriate exit point (The window/door that was on your right will still be on your right while upside down) As a HUET instructor so many people try to get out the 'other side' when put upside down, so my advice is not to undo the seatbelt/harness. :)

[Nick Lappos]

This is a great thread, like so many on pprune!

A comment on the question of transmission coming unglued - This is a weakness of some designs, but not a pervasive helicopter problem. Most helos keep the gearbox in place when blades contact objects and break off. The exception seems to be the 2 bladed Huey family, whose transmission does unseat when blade strikes occur.

I strongly suggest that a roll will help disorient the occupants, and also make blade-water contact occur at higher rpm (more energy, more damage). Keep the aircraft level as long as possible, pull off the rpm with collective and settle in. Do not release belts until aircraft motion had stopped, a slight head injury makes you an unconscious sinker, not a conscious swimmer.

On the way down before water landing, spot the belts, and even lay your hands on the release. This muscle memory trick is important for performing the act while shockingly cold, blind, underwater and scared. If you rotate the aircraft during water settling, the sharp roll and even upside down aircraft are very disorienting, up is hard to identify, and you are much more likely to go down with your ship.

[RW-1]

Nav procedures would be to maintain the aircraft upright and allow to settle, I wouldn't roll IMO.

Belts release is after all motion has stopped. Certainly after water contact.

As for those familiar with ditching, I already have a point of referance selected for exiting (not to hard in a robbie, but one could have several for a CH-53E).

Anyone else use HEEDS? If I'm going over long patches I take mine with me. :D

[Edited: Thomas has a point, I've been trained. You would need to know how to use one. While I do not believe in the ditch situation that you will get the bends from ascending too fast with HEEDS, not enough time for nitrogen to build (I'm a diver as well) but if you didn't exhale during ascent, he is correct, you could damage yourself, etc.]

I know similar units are available in most diving shops, not too expensive either. If one were faced with a real situation, the ability to breathe for 5-6 minutes after going in can make a real difference in how you react.

I'd also advise if anyone has the ability to attend a class whch includes a dunker, to do so, darn, I remember my 9D5 rides, fun, but a good learning experience.

[Edited: USN requires a dunker ride every 4 years, don't know if that has changed since I left.]

[Thomas coupling]

Concur with most of the above:
Seat belts: definitely keep locked.

Disorientation hand remains on QRB, and (if pax) other hand on escape handle(door handle) - DONT LET GO until all motion has ceased.

DO NOT inflate Mae West inside cockpit!

Most light twins (2-3 tonnes) are estimated to sink at 8'/second
:eek: Most roll over (due to high C of G) and rotate through the fore/aft plane (i.e. nose dive)

Dunker is the most valuable form of insurance and should be repeated often (2-3 yearly?).

DONT buy STASS or HEEDS from your corner shop and stick it in your pocket while flying over water!!! You MUST do a training course for this as it is compressed gas at depth. Use it without training and pulmunary embolisms will get you if drowning doesn't :eek:

If you think sea floats will keep you upright in anything other than mill pond conditions...think again:D

Autorotating into water with the engine(s) off will almost certainly take your TR out, unless of course you flare too early:D

A powered approach to the hover then settling vertically into the water just after the swell is the aim...and that requires precision

[Helo]

Thanks guys .... as usual a great discussion with people who know infinitely more than me!! :)

[Arm out the window]

I've never ditched, but the accepted teaching when I learned to fly rotary was to get the rear doors open, then to zero-speed into the water, hold it upright as long as possible, and then if there was a choice, roll it so that the advancing blade would hit the water, supposedly reducing the likelihood of the transmission ripping off its mounts and taking out the passengers strapped onto the centre rear cabin wall (this was in B204/205s).
Sounded fair to me at the time.

[Hughes500]

Guys

I always have a spare air system attached to my life jacket, it gives you about 2 mins of air for about £200. Having experienced cold water sudden emersion and having seen test results you are unlikely to hold your breath for more than 20 seconds !!

I am always shocked at the number of people who cross water with no life jackets or emersion suits, I have even heard emersion suits are too expensive ! and this from someone flying a new squirrel - what price your life ? Shame to auto in and get out and the drown waiting to be picked up !;)

[ShyTorque]

All good stuff; the only further advice I can give is

1) Do underwater escape training as often as possible. Even once is very worth while because it can quickly dispel some pre-conceived ideas of what to expect! Many people say afterwards they would probably have panicked in the real situation, having experienced being upside down under water in the trainer's controlled conditions.

2) Preferably ditch on land. If not, always ditch near a lifeboat.:D

[Thud_and_Blunder]

Shy,

I'm one of those sad blokes who'd say that once was enough! I can remember every last terror-filled red-helmet-wearing second of every dunker run I ever did, from the first in Vernon in 1976 to the last not too long ago. Until the advent of STASS I was able to control the panic long enough to endure each of the sessions - knowing that I'd have to wait between 1 and 3 days for the inevitable sudden dump of brine from the sinuses at predictably inopportune moments.

STASS finally did my head in. I could hyperventilate fast enough to suck one of those ******s dry in 20 secs flat. Dunker trips became sheer purgatory - something to be marked in blood-red ink on the planner.

I agree that the dunker was essential training, but I reckon the first session lasted me a full flying career; the remainder only served to make me miserable at grimly predictable intervals.

I now fly as far from the sea as I can manage, and despite the best efforts of the water authorities in the W Mids I reckon I could probably get out and walk over most of the river/reservoir surfaces hereabouts (shades of the river in Ankh Morpork).

Top advice on ditching otherwise, folks. I also used to brief the preference for power-on ditchings (eg single HYD fail with incipient loss of the remaining system) where the heli hovered to drop crew/pax/dinghy then moved downwind to ditch. Crew/pax boarded raft then brought sea-anchor inboard and drifted onto pilot's position.

[SASless]

Nick forgot one important point in his well laid out ditching procedure....."The Captain shall be the last person out of the aircraft." My usual briefing concludes with that final bit of information...closely followed by the statement ....."and If I pass you on the way out....consider yourself promoted to Captain!"

On a serious note....always keep in mind that there may be more than one way out....or that your primary exit may not be open.

I usually brief my copilot to please to remember to jettison his door just prior to contact with the water.....it might be a deviation from the standard procedure....but I would much prefer to have one large open exit for sure ...than have to get two pilots out the itty bitty windows on a Bell 212. I can assure you I will discard that sorry invention of Bell's if I am the non-handling pilot. By the time you strap on all the Heed Bottles, Life Jackets, Head sets....and other items ....combined with my growing girth.....the thought of squirming out one of those tiny windows seems challenging. All the radio calls, altitude calls, checklist readouts and such....don't mean a thing if you do not exit the aircraft. More people drown in less than four feet depth of water.....measured from the top of aircraft floats to the top of the cabin ceiling.....when inverted.....just because they did not find a way out when the aircraft rolled over.

Doing the dunker training is nice....but one needs to carry that over to the actual aircraft being flown....to develop a mindset and habit pattern to fall back on in times of dire stress. You do for real...what you do in training.

[Randy_g]

I would be very careful when directing someone to jettison a front door on a Bell medium while still in flight. A Canadian registered 212 was destroyed (and all onboard were killed) in the Maldives, due inpart by the copilot jettisonning his door too soon.

When briefing any passengers who may be riding up front (forestry officials), I always caution them about when to jettison the door in the event of a ditching. I tell them to wait for water contact, that way I ensure that there is no confusion.

Cheers

http://randyspics.tripod.ca/gifs/naughty.gif Randy_G

http://randyspics.tripod.ca/gifs/bear_eating_picnic_md_clr.gif

[SASless]

The advice was "just before water contact".....I guess I could have been even more specific....and said after all forward movement....or something...but assume and rightly I believe...that just before contact... even if at 100 knots....it doesn't matter what happens. This presupposes an uncontrolled or power off type ditching...otherwise one has plenty of time to discuss what procedures will be used. This brief is for that event when all goes wrong and you find yourself heading for Neptune's Locker without a formal invite.....and survival becomes the issue and not semantics. For example....remember the video of the H-3 spinning across and off the deck of the frigate that Nick provided us a while back......at some point popping the emergency exits and worrying about if they wind up in the moving bits becomes the least of your concerns. That is the situation I discuss with my Co.....it is more a survival procedure rather than an emergency drill. Controlled ditchings are quite a different thing from uncontrolled or uncommanded ditchings.....one is an emergency procedure...the other is a crash. When I am crashing....all the rules are out the window.....except one....survive however possible.

[3top]

another 2 cents,

R-44 transmisions don´t move - confirmed. I saw one where they tried to "ditch" into trees. The ship disintegrated (the only thing in one piece and untouched was the T/R, anything else was "affected":) ) However the engine and transmission stayed together, although a little twisted due to the frame getting his share. It was pretty violent ( Frozen student, the instructor couldn´t get the student to loosen his grip, so they where fighting over control - although subconsciously [I flew with the student before and after, if I would say, whisper, yell "I have control" he would let go immediately.], taking of from a river bed, the helo turned right and rolled over (already in the air!! and went into the trees like that (half upside down) - Robinsons are tough mothers!!

After about 3000hrs on tunaboats, I saw some helos in the water and heard of others: They always stay afloat (no helis without floats on tunaboats...), but most times they roll over because of the sea - total loss once immersed in salt water....
One pilot got killed - drowned - in a old B-47 - just a belly strap. no shoulder-harrness, got knocked out - helo upside down, but floating...

As a result I don´t like to fly over water without floats.

If I had to go in without [floats], I would take the machine to water contact or a foot above and keep pulling the collective until the rotor stalls. At this point most off the inertia is gone.....I´d try to keep it level all the time. Rolling is just disorienting...

I hope I never need to check this one out in a real situation! (But it helps to "plan" a course of action in your mind now and then.....

In my job we do tourist flights along the Panama-Canal. Although we always wear life jackets (so do the passengers), we do not use floats on most helicopters (majority of the ride over land...) however as for most of the ride there are no emergency landing spots on land, I rather take my chance at the shores of the Canal, than going into up to 200ft trees!!

:D3top:D

[ShyTorque]

Thud,

I know what you mean about the Dunker, some folks never get used to it. One of our largest pilots came out still wearing the seat harness, complete with bent fixing bolts and penny washers.....he just about killed everyone else "on board" fighting his way out! :D

[mikhar]

Im not a helicopter pilot but love everything about helicopters, I just had to say this was a real interesting topic and I enjoyed reading it.

Mikhar

Cheers!

[Red Wine]

Whilst we would all like to think that we will be able to control the machine once on the water, it will all of a sudden be a boat [for a short time anyway]....and a top heavy boat as well. And boats arn't designed that way..... even ships capsize.
Stats will show that a rollover is the likely outcome....just reviewing the Oz history......very likely.

Jettisoning your doors windows etc before touch down....Not this soon to be wet duck.....My concern would be to get the boat where I want it, not to worry about my flying door and my still revolving tailrotor!!....I can recall a Police Twin in NSW that had a cowl enter the main disc...crash!!

Good quality recurrent HUET training will highlight most traps.......and seat belts MUST be on [and ontight]....2 years max.

Interesting comments on STASS/HEEDS/AIR POCKET [or similar]......whilst the Air Pocket uses the rebreathing system and is relatively safe/idiot proof........the others certainly need a training course.
Despite the advertising blurb on HEEDS/STASS...I have sucked the bottle dry in 30 secounds under pressure....don't bank on the 2 minutes quoted around the traps.

Above all........keep your feathers dry.....:confused:

[Baily]

A really good useful thread - many thanks to you all. I've printed the whole thing off as it makes a very useful discussion document and thought provoker.

Life rafts?

One further question if this thread is still active. I privately own an R44 which I use for a bit of business travel but much more for simply having fun.

I cross water in it quite a lot. The channel to France, The Isle of Man, the Med to Majorca and have taken it across to Holland & Germany by the longer sea routes. It does not have floats! However I always wear an immersion suit and I have one for a passenger, We always wear life jackets over the suits and I carry a 6 man raft in the back. I think the raft is probably most useful psycologically as I am never sure that in a emergency we would be able to get it out and to manage it. What do you think? What is the best procedure for the raft and barring floats is there anything else I should have to increase my and my passengers safety.

Thanks.

[Irlandés]

Hey Baily,
when you say the 'longer sea routes', do you ever lose sight of land? Just curious.

Irlandés

[Baily]

Irlandes

Well yes. Spain to Majorca and area south of Rotterdam to Lydd for example - Your point?

[Nigel Osborn]

Baily,
With those distances over cold water, I would definitely invest in pop out floats.
When I used to ferry 206s across the Bass Strait, ( nearly as bad as the North Sea), without floats, the liferaft sat on the back seat where it was highly unlikely the front crew could reach it if we were sinking. I bought 2 single seat liferafts which we slipped onto our belts, so that if we had to jump out quickly the liferafts weren't forgotten and came with us.:D

[Barannfin]

Well I wouldnt get rid of the life raft because there are some situations where you could do a pwr on ditch. Passenger could jump out with the raft as you hover. I dont know stats very well, but rescue times increase dramatically when rafts are used because of visibility.

[Red Wine]

Look at the scenerio in sequence......

A problem.......ditch
Escape............HUET / HEEDS Training
Survive 1............Cold Water Suit.....Yes as uncomfortable as they are.
Survive 2..........Good quality dual chambered jackets.....
Survive 3..........Individual good quality raft[s]....2 smaller are better than one larger.
Rescue 1........407 Sat Beacon...or at least a 123.5/243 basic beacon.
Rescue 2....Flares, Heliograph, Water Dye.....
Rescue 3....A litre bottle of fine single malt scotch.

[Thats for the SAR crew that will have to winch you out after taking such an aircraft across that streatch of water....ggrrr]

[Barannfin]

Red wine, am I at least on the right track about the life rafts? Just dont want to be spreading any misinformation.
thanks again.

[moosp]

Dunkers?

As a private helicopter flyer operating near and over water I would like to do a dunk course. Anybody know of a commercially available dunker in Asia (HKG/SIN/KUL/TPE)?

I hear there is one in SIN for the oilies but I believe you have to be part of the oil industry to attend a course. Any info?

Hoping to Plunge.

[ppng]

MOOSP: Try calling the Hong Kong Government Flying Service (sorry, I don't have any contact details, but there is a website). Their pilots do regular 'dunkers' - in SIN, I think - and you may be able to 'buy a seat' on a routine course.

[rotorspeed]

A few points further to Baily's post concerning over water flight without floats in the R44.

I did quite a few 50nm plus over water trips in my single Squirrel, which did not have floats either. Easy to say one should have them, but in the end of course there are cost, payload, speed, range issues to balance in deciding where the inevitable compromise lies.

I remember talking to some Castle Air guys a few years ago who ditched a non-floated 206 in the Channel. One clear message was that you would never get your liferaft out of a stored position (ie like back seat), so I used to fly with a compact 4 man type attached to my waist with a belt. In the Squirrel of course you've got space beside the seat and big doors. I reckon that this way my raft would come out with me.

Liferaft needs to be compact to do this - can't see much point in a bulky 6 man raft in a 4 seat R44, particularly as it will compromise having it available at all.

Wearing a modern immersion suit was not too inconvenient, life jacket of course, and I would also hang an EPERB around my neck. Someone mentioned bubbles on ditching - interestingly that I found was the biggest problem on the dunker test so I kept a pair of swimming goggles loosely around my neck too!

Finally I would make very sure I kept to a route someone knew and in RT contact, with the ability to give a position virtually instaneously if it all went quiet.

Well that's the theory anyway. No doubt all togged up you do feel more confident and so fly better too. Reckon I'd get out of out of the aircraft OK which of course would be lost - as a floated one probably would too. Whilst one or two sensible pax might make it out I believe the chances are pretty poor for children or a full load so would avoid taking this.

Having said all that, I now fly a twin and must say, whether at night or over water, I feel a lot more comfortable! The stats may suggest you're little better off, but that doesn't take into account the significantly more relaxed cockpit environment of knowing you've got two of more than just engines!

Great use of the forum. Any stories of actual ditching experience? That's where we'll all learn most.

[Baily]

Many thanks again.

I'd not thought of individual rafts, that sounds like a very good idea. I already have an EPIRB stored in a pocket in the immersion suit and I have done a very useful (but unpleasant - never did like getting my head underwater) dunker course at southampton. Floats would be nice but are not practical to retrofit on an early (non hydraulic) R44.

I'm now going to boil down all I've learnt from this thread into some clear intructions to myself for overwater flying and to enable me to give good briefings to any passangers.

[moosp]

ppng

Thanks for the idea. I know that GFS use the SIN facility. I'll give them a bell and see if they would consider a paying guest on one of their forays to Lion City.

[chopperdr]

sirs: concerning rafts and access to them upon ditching, apical industries has developed and received faa certification for a raft system that deploys when the emergency floats are deployed. the rafts themselves are contained within the floats bags and then are fired seperatley from the floats themselves, so as not to inflate until a.c is on the water. to date the system is available on the md 902, shortly on the a119, and in testing for the bell 407, 412, eurocopter 350, 120,130.

[hihover]

Interesting thread, as are most in the Rotorheads forum.

Story:

On one of several visits to the dunker, I was sampling the variety of seats. Strapped in the back of a "Lynx" with the seat athwartships, I felt that the egress would be simple... right up to the point that I tried to release my harness. I had a lungfull of air, I had a reference point, I had divers close by, but the stress that set in immediately was overpowering. I tried as hard as I could to rip this harness buckle open but it was not going to unlock. Panic... you bet I did.

A friendly diver who was behind me reached over, calmed me down, and tried to open the buckle. Not a chance, this thing had locked and was not going to play the game. We were now at about 30 seconds in the water and I was fighting the desire to breath in.

The diver calmly reached for the harness anchor point and unclipped the whole thing, releasing me from the seat and allowing me to surface.

The point that was forced home to me, was that, even under controlled circumstances, panic, disorientation, stress and a bit more panic, set in very quickly. I could easily have unclipped the harness at the anchor point, but I didn't have the presence of mind. I can only imagine how difficult the exercise would have been if I had just autorotated to ditch, with parts still splashing around me, and possibly with an injury and a passenger to take care of.

Bottom line for me... if I am flying a single-engine helicopter without floats, I fly around anything bigger than a puddle.

[BlenderPilot]

A couple of years ago I knew of an R44 that was flying between Cancun and Cozumel (carribean) had engine failure, auto'd into the water, no floating devices for heli or pax, the thing just sank inmediately in about 30 FT of crystal clear water, the pilot came out alone and noticed his pax (3 germans) were still in the helicopter, he then dove down, unstrapped them, and they all swam to shore, the pilot says the germans biggest concern was their wet cameras around their necks.

[TomBola]

I've just been offered a job as a helicopter pilot in UAE. It's on a rotation, but the pay seems quite low compared to other overseas jobs I've heard about and the 8:4 schedule isn't very attractive. I've also heard quite a lot of rumours that there is a very high turnover of pilots out there. Is there anybody out there with recent experience of the place who can tell me if the rumours of pilot turnover are really true, and if so, what's the reason? I'd quite like to go, but I don't want to find myself out of work again in a few months.

[Islander Jock]

My reason for the above question is that as a HUET instructor our organisation is constantly being bombarded by companies demanding that we practice this competency as part of the course.

My thoughts on the matter are that a helo will, in a well controlled autorotation situation with correctly functioning floatation and a relatively calm sea, remain upright. However if one of the favourable circumstances above are removed then in all probability the airframe will roll over.

The only scenario I can imagine of a helicopter sinking upright would be a controlled autorotation and failure of the floatation to inflate. My question though is whether or not it is feasable to sink in this attitude given the high centre of gravity? Also is it feasable that a main rotor blade striking the water would transfer torque forces through the airframe and twist it at least onto its side?

It appears that the design of the METS HUET system is driving the training competencies rather than what is statistically shown to be the oucome of a ditching.

Would appreciate views from anyone with HUET training or crews with ditching experience. Also where I can find any authoritative statistics on the subject.

[Lu Zuckerman]

I do not know if any records were kept or if they were if they still exist but in the summer of 1949 the US Coast Guard ran a series of autorotation and ditching of a large number of Sikorsky HOS-1s. The pilot Cdr. Mc Dermid (spelling may not be correct) intentionally crashed the helicopters into the Albemarl Sound at the Elizabeth City, NC Airstation. He hit the water in various attitudes to determine the best way for the pilots and crew of other helicopters to evacuate from the fuselage. In most cases he intentionally moved the cyclic in order to dissipate the energy of the blades by hitting the water. From what I understand he would move the cyclic in all directions to determine the most effective way of dissipating the rotational energy of the rotor system.

:eek:

[Brother]

If the autorotation is successful, the sea is calm and all the floats inflate, the aircraft will remain upright for a while.

Sinking is generally caused by the sea state rolling the aircraft over, or a float bag slowly deflating and causing a rollover.

One of the large Gulf of Mexico operators who have recently lost some aircraft, all which have had successful autorotations, is looking into ways of increasing the longevity of the aircraft floating so that they increase the chances of aircraft recovery.

In the cases which occurred recently, the aircraft was lost, and the operator believes that improved floats or supplementary floats could prevent hull losses.

Brother

[Ascend Charlie]

All the ditchings I have seen on film or TV have rolled to one side and floated for a while. Think back to that footage of the Hueys ditching beside the aircraft carrier when Saigon was lost. Big splashes as rotors thrashed about, fuselages floated long enough for crews to exit if they were conscious.
Two ditchings around NSW involved a twin and a single, both had the same story, roll onto right side, float, sink.

I have no doubt that HUET courses saved lives in those 2 cases. It is great training for the basic principles, which can then be applied to each situation. Very few helos in Oz have floats, so we can expect them to follow the laws of physics and put the heavy bits (transmission, engine, rotor heads) under the empty light bits (cabin, fuel tank) and thus be upside down.

Helicopters: a triumph of science and technology over common sense..

[Straight Up]

On the two HUET courses I've done (one at Sale in Vic, Aus, and one run by the Royal Navy in th UK) we were told that if the floats work, it'll stay upright and you can get out (sea state permitting).

If the floats don't work/are not fitted to aircraft/high sea state, it will roll over and either float belly up or sink, either way you'll need the HUET training.

The pictures etc that we were shown at the naval dunker (to keep us amused until it was our turn), showed a lot of belly up aircraft.

I think Ascend Charlie has it spot on with the heavy bits at the top, and light/empty bits at the bottom. Not sure how it would work for Wessex style aircraft, with the engine down low in the nose, and some transmission up top.

[bigdog1971]

I have been told of a urban myth that a Blackhawk with external wings and jugs, will stay upright for a few minutes before it rolls or sinks, (providing your entry was not to rough).

But hey my hat goes off to that hard B@rstard who deliberately ditched all those Sik horseys into the ocean........

-----------------------------
If it don't hover Don't Bover........
:eek:

[Lu Zuckerman]

To: bigdog 1971

But hey my hat goes off to that hard B@rstard who deliberately ditched all those Sik horseys into the ocean........

Several years later that same pilot was promoted to Captain and was the Skipper of the Coast Guard Air Station in San Diego. The US Navy had commissioned several PBM-5As and they turned them over to the Coast Guard to test them to destruction. The Captain would walk through the hangar and pick out a crew from the available personnel.

He would then take the PBMs to the roughest water and make all types of open seas landings including stalling the aircraft out and coming straight down. He accomplished what the Navy wanted and destroyed both aircraft. After his demonstration the Navy scuttled plans to build more PBM-5As.

Needless to say the crew was not too thrilled to be picked out for the tests.

:cool:

[Islander Jock]

Thanks for the responses folks.

If I may ask you to be a little more direct. In your knowledge or experience, would you forsee a circumstance where a helicopter would / could sink vertically?

Straight Up,
we have a brief summary of the RAN Wessex ditching in the Bass Straight in 1993. Reports were that after inflight vibration was felt, both the airspeed and altitude were reduced whilst trying to reach the coast. Upon a fairly catastrophic transmission failure it was reported that the airframe rolled almost upside down and struck the water in a nose down attitude. There apparently was no pause on the surface and at least two survivors escaped via the gaping opening at the rear of the cabin where the tail boom had torn away.

[Thomas coupling]

As an ex waterbird Instructor (S61) and now current dunker victim, stats then and now show that helos will remain upright up to sea state 1 without floats and SS3 with floats. If SAS is kept in, it will increase the risk of a tip strike with the swell as the tip path plane hunts for the level attitude. Because of the lack of a water anchor the helo will float beam on also increasing the chance of a tip strike.
Unless the a'c is designed to float for prolonged periods (S61 / Sea Sprite etc), you will most certainly sink within seconds without floats. In a calm SS there is a good chance it will sink vertically without toppling, especially if the lower section fills with water quickly. But the sea is never calm!!! So it is almost a certainty that it will (a) roll over inverted and (b) dive nose down after it is fully submerged [For light helos it is estimated that it could sink up to 8'/second....all in the dark, too:eek:

If in doubt...do the dunker...Duty of care and all that for the establishment, tremendous confidence for the crew.

[moosp]

Islander,

Does your HUET company offer courses for walk in private (H) pilots or are you just for the offshore/commercial world? I have been looking for a course in Asia/Aus for a while.

Email me if you feel the moderators might think it advertising.

Thnkx

[Islander Jock]

Thomas coupling,

thanks for the info. Much appreciated.

moosp,

will email you later with details.

[aspinwing]

Having ditched a Wessex 1 in Sea State 1 in which the bags did not inflate:mad: :mad: :mad: :mad: on water entry; I can assure you that it did roll to the right - causing a blade tip hit the water and wrap around the cockpit - until inverted and then sink nose first.

The RN dunker training was almost a perfect simulation.:) :) :)

BTW: it was a Friday the 13 th.

[MBJ]

A colleague of mine called Art Swain gave an SAR demo off Lyme Bay which ended up with rapturous applause from the crowd on the beach when the engine stopped at the end of the display. Calm sea - floats popped as advertised and he climbed into his dinghy from the wheel strut dryshod.

Colin Bates did a great demo some years back of a 206 on floats autorotating into the water - nice stable floating platform on flat calm water.

BUT if one of the floats doesn't inflate or bursts, it'll roll, a blade will hit the water and you won't know if it'll dig in or flip the aircraft over onto its other side. In any event lots of thrashing about.

If in doubt do the dunker!

[heedm]

I'd say the best answer to the question is that it might float upright. But it also might flip over. With odds like that I'd say egress training is necessary for any who do extended overwater flights.

I ditched an H46 under controlled conditions (power on landing...in-flight fire). As it took on water, it also began to roll. If left alone I think it would have been on it's side or inverted prior to the last piece of metal going below the surface.

Without floats...you're on your own. With floats, if they work you should be okay in advertised sea conditions and entries.

[John Bicker]

A bit that was missed here is that most flight manuals include in the procedure for ditching sans floatation to roll the aircraft prior to losing control effectiveness to intentionally stop all the flailing bits lest it sit there upright with the blades skipping around on the surface once it sinks to that level and you exit to resurface amongst them.

Full touchdowns with floats is best learnt watching ducks land!

[Draco]

a well-known british pilot and instructor tells a great story about ditching following and engine failure...

the bags inflate.....

the heli sits there happily while the nearest destroyer launches a cutter to pick up VIP Admiral passenger and the crew...

the cutter comes alongside...

the sailor on the cutter uses a boathook to make contact with the heli...

boathook goes through bags...

time to go swimming, including said Admiral :D

I don't suppose that sailor got promotion that year. Probably fiction, but did make me laugh.:)

[GLSNightPilot]

The usual thing in the Gulf of Mexico is for the autorotation to go fine, the helicopter floats with no damage, until the boat gets a line on it & pushes the throttles forward, whereupon the helicopter turns turtle. Max speed on the floats is probably < 5kts, closer to 1, but the boat captains are impatient with that speed, & almost always the helicopter ends up upside down, with the blades spinning, then cutting the tailboom. I saw one B206 that had just had an engine decel just after takeoff, the pilot put it in the water with absolutely no damage, and by the time it was back on the platform helideck the blades were about 3' long, it had no tailboom & no skids, & was a total wreck. The CG is very high, & the helicopter will roll in a heartbeat. I can't imagine one sinking upright, since the CG will be much closer to the head even with the fuselage filled with water, but I guess anything is possible. I certainly wouldn't want to bet my life on its sinking right-side-up.

[Oracle]

A quick summary of comments:

1) Wessex types were notorious for losing float bags on anything other than a flat entry at low speed. We lost a Wx5 off Norway at night and although the bags inflated as advertised, the force of the impact (Inadvertant Flight into Water at high speed at night) tore one off and the other soon deflated - it sank like a brick, both crew lost, sadly. If the ditching it controlled and level (in good/moderate sea conditions) the Wx would sit fat, dumb and happy as long as you didn't do anything daft like engage the rotor brake, which oftens turns the higher c.g. aircraft turtle - not recommended practice - let the blades coast to a standstill or hit the water - it's always safer and I have even know crew members who jumped out before a controlled ditching (UH1) to then get back in again afterwards once the blades started to trim their hair some on the surface! There were several Wx recovered successfully/undamaged after controlled ditchings.

2) BELLs tend to ditch nicely if well controlled on entry and as long as the floats aren't manually deployed in flight beforehand. This is because many of the flot bags (skid mounted) have lengths of plastic inside to stop the bags from adhering to themselves in the heat etc. The AB205/UH1 thus would dump 6 to 8 feet of plastic sheeting into your tail rotor during final autorotation (unless your timing was immaculate!). The 412 is better and has been recovered successfully several times after controlled ditchings. The only failures being when rescue craft have subsequently puntured the floats by 'coming alongside' under the stationary rotor disc thinking that the floats are bloody fenders! Best to get everyone over the side into as many liferafts as you have as quickly as possible, and then be recovered from the liferafts - saves the aircraft in many cases and stops people sitting in the ditched machine waiting for the inevitable to happen!
3) The S76 floats well and has great float gear - as demonstrated by many. It will also block the pilot's door from opening however and is most effective at stopping the aircraft if inflated (accidentally) during ground taxy! More difficult to puncture than the Bell/Wx, the spread and size of these puppies will normally keep everyone's feet dry! (As opposed to the wasp/scout with it's flotation level 1 feet below the surface!).
4) Blackhawk. This Beast is a 22,000lb lead sinker - so unless you have flot gear fitted (which few have), don't expect it to keep you on the surface in the event of a ditching. The ESSS stubs and tanks would likely detach anyway (they're only only Glass-fibre) and would probably just ensure a nice level glide down to the sea-bed! I would recommend underwater escape bottles as a standard (as in the USN) for any pilots flying the Beast offshore!

So - recommendations are, in a controlled ditching, let the floats work automatically if they do so, or operate at the last minute otherwise, don't use the rotor brake at all, get into the liferafts IMMEDIATELY and remain attached to the aircraft (if still afloat, that is!) until rescue arrives. Then keep the rescue tug/boat aways from the flotation gear - so that you get a bonus for saving the aircraft for salvage! ALERT DISASTER CONTROL run a very good HUET course in Singapore and might help with any queries.

:D

[Arm out the window]

I'd be interested to hear of people's experiences of having to use pop-out floats in anger.
I'm now flying B206's fitted with these, and would like to see what other users reckon about things like:
- the best time to activate them in an auto
- how the aircraft flies during and after activation
- what they're like when you hit the water
- any other observations or thoughts on the matter.

I've operated with fixed floats a few times in a 205, and remember being particularly surprised at the huge shove of forward cyclic that was required on auto entry to stop the pitch-up. Obviously that wouldn't be needed with pop-out floats if you activated them in the latter stages of the flare, but what other things might come in to play?

[Nigel Osborn]

I haven't popped a 206 float in the air, only once in a As350, but I have done a few circuits with the floats blown up and it felt very similar to fixed floats. i.e. no problem. The As350 flew normally, so basically it made little difference.
The tendancy is to blow the floats too low. Obviously if you can hover, then blow them in the hover. However general practice if in auto is to blow them early, by 350 to 500 ft or so, then you have plenty of time to get the machine sorted out so that you can concentrate on the landing.:O

[spinningwings]

Very good question...and no doubt lots of semi correct answers (including mine)...in my view be aware of the A/C gross wt at the time of needing them....there is considerable disturbance to the airflow thru the rotor with floats "popped" in autorotation...such that 206s on fixed floats require considerable autorotation RPM re rigging when fixed floats are installed/removed.

Thus were I in the A/C and it were heavy I might 'pop' the ******s a good bit earlier than if the A/C were light because the weight of the A/C would put the auto rpm at the higher end of the green...with the A/C at lighter weights (solo) the auto rpm would be at the lower end and any disturbance to the airflow in my opinion would be undesireable ....... having said that we assume that both sides WILL appear at the same time on command (???) a plan to consider might be to pop them after flaring to zero/zero the A/c above the water and then let it settle in the water hopefully upright hoping the pax if there are any don't rupture them opening the flaming doors.... good luck talk to your Chief Pilot ...cheers :)

[chopperdr]

Sirs: regarding float inflation, would suggest that the floats be popped below float vne, the emergency float systems i have installed and worked on certification testing would normally be popped well before the flair, usually around the 1000ft mark, this allows the floats to inflate and settle, then the pilot can concentrate on a smooth auto. as for a/c weight, the floats are designed to provide floatation on max gross a/c, one should also check if the floats are certified as ditching or emergency floats, there is difference.if you wish there is very good promo video available from apical industries showing real full on autos of many different helicopters, let me know if you would like one and i will pass your info onto apical.

[widgeon]

and gentleman Jim is the pilot on many of the videos , i think Andreas filmed the 105 ones.

[Arm out the window]

Thanks for your informative replies.
The video you mention sounds like it would be well worthwhile getting hold of, chopperdr.
I'll ask around at work and see if anyone has a copy; if not, I would be keen to get hold of one myself.

[Run-on Landing]

I seem to remember watching a TV programme (Tomorrow's World on BBC, I think) a good few years ago that featured devices in development to prevent helicopters capsizing completely after ditching, but haven't heard anything since.

I had a look on the internet and found the following web site and also found out that the CAA had conducted trials in 2001 into escaping from a side-floating HUET.

http://www.bmtfm.com/devices_to_prevent_helicopter_to.htm

Anyone heard/know any more? Comments? Opinions?

[[email protected]]

Interesting - but will the extra weight/drag and its effects on the C of G both longitudinally and vertically on the aircraft be acceptable.

I think you would have to vastly increase the thickness of the engine bay doors to provide sufficient buoyancy to stop the aircraft rolling over.

The area around the engines is subject to high temperatures which will have to be taken into account - also if the blades make water contact at significant RPM during the ditching, they will probably tear the transmission and possibly the engines off anyway.

If someone makes it law it will happen - if not then don't hold your breath (no I mean do hold your breath cos you'll be upside down)

[zalt]

I hear that the side floating option came out well in the HUET trials (as the water pushed people up to the windows) compared to up-right submerged and inverted..

Talk of a design study on the mods required for a in-service aircraft.

[GLSNightPilot]

Even if you put flotation in the doors, or even around the engines, I'm not sure it would prevent the aircraft from rolling over. The vertical CG is so high, I think it might roll on over, especially if the seas are up. That's why dynamic rollover is something to be considered in a helicopter - the CG is way up there, & it's relatively easy to get it outside the skids, or wheels.

[NickLappos]

I always find it interesting how the safety garus can sometimes look into the wrong end of the telescope. I recall the droll Boy Scout rule for packing eggs - pack eggs at the bottom so when they break, they don't get eveything wet!

Nothing can be nothing more depressing than making aircraft safer by making them float better when a critical failure occurs. It is even more depressing when the normal flotation system is expected to fail and let the aircraft capsize! So we enhance safety by putting a second flotation system on the aircraft!

OK enough sarcasm. How about we just require the normal floats to keep the aircraft upright? How about we require the design to have enough redundancy to assure that ditching was a very remote probability?

[GLSNightPilot]

Nick, I have to agree with you. To me, the flotation is just to give me time to get out of the helicopter. Once I'm out, I'm still not happy - I've seen sharks the size of my helicopter swimming around out there, & everything in the water can swim better than I can. I'd far prefer something that kept me safe and dry so I didn't even have to think about floats.

But what is the cost? You can design in so much redundancy that the aircraft isn't economically viable, and no one can afford it. Consider that the vast majority of the aircraft operating in the US GOM are single-engine, the C+ costs us more to operate than a 214ST, and the S92 is likely to be so expensive I'll be surprised if 10 ever operate here. Somehow, the costs have to come down and the oil companies have to be convinced to spend some of the exhorbitant profits they're making. In the meantime we're hanging our a$$e$ out, and nobody seems to care.

[James Roc]

I've heard conflicting opinions on the best and most safest way of ditching a Heli in the sea and surviving following an engine failure and would like your opinions on the matter. Is it best to back cyclic and use the tail rotor to slow the rotors down or sideward movement and let the main rotor hit the water first?

[flyer43]

By far the best idea is to have two engines. The chances of ditching are dramatically reduced!! Altrernatively, you should avoid flying single engine machines over water.................

[B Sousa]

Unfortunatley Flyer thats not an option for some. I have often pondered my little Bell Baby getting quiet after many hours of overwater between Florida and St Thomas. The water gets a bit deep there, but warmer than up near UK Land.
As to ditching there are too many variables to think about to have one pat answer. Calm seas, vs. Rough seas, Engine failure vs, partial . One will just have to decide at the time based on whats available.
For sure its easier to utilize pop-outs and attempt to get the thing upright with blades stopped so you can exit and take all your toys with you.
That opens another bucket of worms as to what your going to have for survival, as the heli heads for the bottom..

[S76Heavy]

First, make sure that you have done a HUET course, so you have a chance of escaping when it goes belly up (not a question of IF but WHEN). Even with floats, they will buy you time at best.

Then it depends on sea state, wind, type of helo and its CoG. I have been taught that if you anticipate a rough landing it's best to stick the tail in to absorb most of the impact forces.
What it does to the main rotor and wheter they will come crashing throug the cockpit, I don't know. But to nose is is certain disaster.

Furthermore, If you're machine has hydraulic controls, make sure you don't position the controls in such a way that your left leg gets physically trapped. To survive you need to be able to exit the aircraft..so think also about wearing a helmet.

And finally, you need a bit of luck. And survival kit to keep you alive outside of the aircraft in a hostile environment like the sea.

[Lu Zuckerman]

Back in 1949 the US Coast Guard ran a test to determine the best way to autorotate into the water. They used surplus HOS-1s. I saw several of the landings and ditchings and I believe there were a total of ten or twelve ditchings. They used the data to standardize the method of ditching for USCG and USN pilots. If you are really interested you might contact USCG Headquarters (Aviation section) in Washington DC to see if they kept the records.

The tests took place at the CGAS Elizabeth City, North Carolina sometime between July and December of 1949.


:E :E

[Rich Lee]

There are many considerations involved in ditching a single (or twin) helicopter at sea following an engine(s) failure. This assumes that the helicopter is not equipped with utility or pop-out floats (a high risk configuration beyond the autorotative distance to land).

Do not forget to open a door(s) or window during the descent and prior to touchdown. A door on a closed cabin helicopter is very difficult to open until pressure is equalized between the outside and inside of the cabin. Should you forget this step you may only be able to open the door when the helicopter is so deep that you or your passengers may find it difficult to swim to the surface.

Use as much rotor energy as possible as you settle into the water. There are debates as to the best way to do this but in my opinion holding full up collective and settling vertically is more effective than an aft cyclic, tail entry method.

Understand sea state and recommended methods for landing in calm or swelling seas. An autorotation into a six foot swell moving at the helicopter creates considerable difficulty for the pilot.

Understand proper methods and use of available instruments and lights to judge flair height. Water is every bit as forgiving as concrete when dropping in from 50 feet.

Use personal flotation devices appropriate to the water temperature and distance from land. Always have them on, not stowed. What you are not wearing will probably not leave the aircraft.

A thorough brief of crew and passengers to include an exit drill or at the very least an exit discussion. This brief must at the very least include methods to open a seatbelt, methods to open a door and when to leave the aircraft (remember the pilot may not be alive or able to give an exit command or instructions).

Use a raft and overwater survival kit. An easily reached breakout knife in case you forgot to open the door is also helpful.

[B Sousa]

As to the above post in reference to the U.S. Coast Guard. You can start here: www.uscg.mil

[Jcooper]

I've heard that if you use lateral cyclic to stop the blades the force of them stopping so quickly can rip the MR gearbox into the cabin. Any truth to this? It was discussed concerning an r22

[Aesir]

I have always heard that you should use right lateral cyclic upon touchdown in CCW rotating helicopters, so that if the gearbox is gets ripped loose its going to move aft and away from the cockpit!

[Lu Zuckerman]

In my post above about ditching the HOS-1s I do not believe they experienced a transmission breaking loose. On that helicopter type the blades had a main tubular spar and ribs and were covered in fabric.

There was greater danger if a blade hit the ground in a roll over the balancing weights (lead shot) would spray out as if shot from a gun.


:E :E

[ShyTorque]

Landing across the swell (along the length of a wave) is supposed to be smoother and should prevent a nose-down surf into a wave trough.

Manufacturer's ditching advice for the S-70 as I recall, (no floats on ours then), is to deliberately roll the aircraft over (to the right?) in a positive and controlled fashion before the rotor slows to the point where it's no longer flying.

I think this is to make events more predictable than if the rotor is left to it's own devices in the final few moments. The drag of the water will stop the rotor very quickly so the next part, the crew evacuation, can begin asap before the aircraft sinks too deep.

[Thomas coupling]

From memory as a waterbird instructor:

Normally, you won't have time to do anything else but land as gently as possible at the bottom of your engine off, in a single. Any thought about landing cross swell, etc will not be an option because you won't be able to time the moment of impact!

With a twin, unless it is fuel contam when both engines stop, you'll have time to consider most of the variables.

Aim of the game is to reduce touch down speed to a minimum! Everything else is secondary.

Picking your touch down point to be across swell is by far the best. never attempt to land into or behind the swell, you'll lose all semblance of control.

IF you have the wherewithall then consider tail first to cushion the landing - but this can be a harsh option if you are able to land with little or no fwd speed where you can simply 'plonk' it onto the water, almost vertically.

There are some schools of thought about putting the advancing blades in first so as to encourage the MGB to depart aft should it feel like it!! [opposite and equal reaction]. But one needs to remember that this action could deposit the MGB in the crew cabin aft too!!

Of course any fancy manouevres need only be considered in a sea state 3 and above. Below this, simply flare it to a full stop immediately above the relatively calm sea and overpitch vertically.

Get rid of as many emergency exits, JUST PRIOR TO ENTRY, any earlier and they could go thru the main / tail rotors and spoil your perceived flight path! Relying on emergency doors after entry into the water is dodgy to say the least because you may have buckled the airframe and the doors may jam.

Once on the water, and in a sea state >2, expect a blade tip strike and consequent roll over due to swell.

ALWAYS attempt to land as close as possible to the wind direction accepting cross swell landings.

DO HUET often and pay close attention to what the instructors tell you. A HUET course in the Uk is only £180/person and worth its weight in gold.

[Devil 49]

Everybody I've ever talked to who'd done this "actual," flared and pulled pitch higher than they thought they were. The water's a very poor surface to judge altitude from. I'd guess that all the fancy talk of rolling left, right, landing on the crest, etc. is not realistic- falling from 10+ feet with decaying RPM is going throw the timing and effect off.

SO- I'd do a HUET for sure.
I'd want floats.
I'd have my vest and survival gear on at all times.
I'd prebrief everybody and hope they're adequately trained.
With small seas running, I'd go into the wind and ZERO forward motion at touchdown, and parallel the swells if they're significant, with ZERO forward motion at touchdown.

ZERO forward motion, I think is the prime consideration. It's important enough that I'd ditch with power if ditching was certain rather than risk the trend to fall from height. It'd be tough, but sometimes there are no good answers, only some better than others.
Hitting with forward momentum will tend to bring the heavy and rotating stuff into the cabin and that's very bad.
ZERO forward momentum, more than rolling left, tail first etc. is my aim. Hitting with minimum vertical impact would be next consideration.
Having the doors open is a nice thought. The pilot flying probably won't have time, and the pax will probably be involved in cinching tight, etc., so be prepared to jettison underwater and/or kick panels out...

[Vfrpilotpb]

We disscussed this in a thread about three months ago, and I mantioned my pal who put down a B206 into the salty stuff between EGNH and the IOM,
to quote the man

" I just had enough time to get out of the already unlatched door, after splashdown by undoing the belt at that moment, I then kicked away from the heli which was turning over and showing its skids"

So time is definatly " Tempus Fugit" possibly time to relate on your insurance policy:ok:

[dzeroplus]

If you are in the fortunate position to find a company (not many companies have fixed floats) to do a float endorsement and the company conducts touchdown autos to the water, this will assist in judging approach speeds, flare heights and picking swells etc.

HUET courses are worth more than their weight in gold.

Lifejackets that double as survival vests with a minimum of ELB, mini flares, fluorescent marine dye marker, floating torch, good quality fixed bladed knife and a small oxygen bottle (spare air) for those vital extra seconds.

[James Roc]

I'll bear all of the above in mind, thank you...James

[Islander Jock]

Just wondering if one of the rotorheads can steer me in the right direction for some info.

During a HUET course I was conducting today one of the students asked me about whether any specific data relating to maximum sea state that say an S76 or AS365 could expect to remain upright upon ditching was available. Those two types are fairly common here in Angola. I could not really answer it with any info based on authoritative sources except for what I have read and that is that on emergency floatation, most helicopters will be fairly unstable.

Things like the control of the landing/impact on the surface, whether or not pax panic and rush to one side, whether the airframe remains headed into wind and waves and whether all the floatation cells function correctly are some of the factors I could come up with.

Anyone know if there is any documented study of this subject?

Thanks in advance

IJ

[B Sousa]

As to exact Studies Im no help.I do think by using the internet you may find some information that will be of use. I suggest downloading a free Search Tool that utilizes many Search Engines at once. www.copernic.com
Site I would look to may be the Navy or Coast Guard. They live on the water and that is a big concern of theirs. Try www.navy.mil or www.uscg.mil
Having a few hundred hours overwater its also been a concern of mine albeit I flew different helos. In conversations items that came up were will they rip off in Autorotation/ Hitting the water etc. Experience of a room mate on one day out of 365 where he had calm water and close to shore. He had an engine failure in a B206 and put it down perfectly in the water off St Croix. They towed it to land.

Good Luck and if your in Angola, the water is probably prefered over walking through the Minefields.......

[Aesir]

The BHT-222U-FMS-12 says that the emergency flotation should keep the helicopter stable in up to Sea state 6 which is 25 kt wind and waves up 2.5 to 3.4 m height.

I presume that the B-222 is unusally stable compared to many other helicopter types due to the emergency float layout. The main floats are positioned outboard on the stub wings under the wing end cover.

http://www.helicopter.is/agm_sling%20HIA_resize_resize.JPG

[Helinut]

It's a very int eresting question and I would like to know if anyone finds any major statements of the basic stability performance of offshore helos. On the whole I think it is one of those areas where manufacturers do what the aviation regulators require (i.e. not much). The military sounds like a good source - if it is accessible!

If you look at real ditchings, the way that the helicopter enters the water will always make a big difference to the outcome, pretty much regardless of the water stability of the thing when it is turned into a boat.

[chopperdr]

if anyone is interested apical industries has an excellent video available of various full on autos of emergency float equipped aircraft, mostly light single turbine, the heaviest being 902.
also keep in mind their is a significant difference between a ditiching float system and an emergency float system with regards to bouyancy requirements.
as for water stability the float style itself will have a significant effect of the ability of the airframe to remain upright. tri-bag systems have a much greater footprint and provide greater stability.
dr

[Aser]

Is it possible to download any video about this thread... ?¿

[chopperdr]

sirs: if you would like a copy of the video, send me a email and i will direct it to the people at apical. they would be glad to get one out to you.
dr

[Thomas coupling]

I'm surprised one of the canadian mil pilots hasn't come forward with this topic, they are the waterborne experts during their training.
Anyway, I'm sure I mentioned it somewhere yonks ago, it may even be in this thread, but can't be bothered to read thru it, so here goes:

I was a waterbird instructor for my sins during my exchange with the RCAF. It was our job to throw S61's at the water from all angles and even try to fly away after!

Bearing in mid that the S61 has a 'boat hull', if anything is going to remain stable on the water, this is the a/c to be in. I would suggest that anything else is less stable and will suffer the following consequences, more readily:

It is assumed that there is going to be no attempt to take off again!

1. Integrity of airframe affected depending on design. This means that water will flood the a/c faster or slower, depending on how well the a/c has been put together! Large quantities of water sloshing around the insides of the a/c will exacerbate uncontrolled instability, eventually leading to a top heavy a/c 'tipping' over.
2. If the rotors are still turning (quickly), they will strike the swell in anything >SS3. This could result in tipping the cab over or serious structural damage (not a problem if you intend to scrap the airframe after).
3. Water ingress will very very quickly affect the electrics. The most obvious problem being unable to communicate with the passengers/crew. This is by far the most serious issue especially when/if the cab turns over!
4. If the flot bags don't deploy evenly, the cab will sit skewed off to the swell / sit at an awkward angle and further exacerbate the eventual overturn.
5. If the drogue shute isnt deployed, the a/c will sit side onto the swell and within minutes, she will turn over in anything >SS4/5.
6. The worst I've heard of is SS6 and the a/c remained upright and pointing in the right direction for long enough to be recovered. The swell though was a long one and not too choppy.

The worst thing is thinking about all those people down the back while you are doing everything in your power to keep the ***er from tipping over! If she goes....God help the pax! At least you've got jettisonable doors and STASS and HUET training and correct gear and radio and ELT and and and.....

Don't go there.

[TheWayWeWere]

Well, if you say that no other CF Sea King pilot has jumped in, that saves me reading all the posts. I just read the first page and this last page.

We did receive good training on putting the bird in the water and also taking off from the water. In most cases of ditchings, the reason that put you down there, meant you were going to stay on the water. However, I can recall that one crew did have a ditching and then a take-off sequence but after all these years, I can't remember what caused them to go in. However, they managed to take off and fly to shore.

The Sea King is great for taking off and landing on water - at relatively low sea states. But in most North Atlantic sea states, once you were in the water, if at least one engine could keep the rotor still turning, you might have some chance of keeping it upright in low enough sea states and if you still had enough outside visual reference (depending on day/night wx) to know which way was up. I remember a lot of our missions being at night and in higher sea states. Even with the rotor turning and flying rpm, the Sea King had a limited range of off-level before it was beyond the range at which it could be levelled, even at full power.

If both engines quit or were shut down, all bets were off. Being so top heavy meant it was likely to turn turtle pretty quick. But even then, the combination of the airframe float design and the inflatable bags would keep it floating for some time - in some cases hours, and in some cases a couple of days before slow leaks took their effect.

I was never more greatful than when I was given the privilege of taking the Underwater Egress training or whatever that course was called. It included being strapped in a fuselage, turning turtle and escaping, first in daylight, then blindfolded (night), then finding doors jammed requiring alternate exit, then having to work back into the cabin and removing an immobile patient out the door before exiting yourself. And it was good clean fun!

Another posting to follow . . .

Shipborne ops were conducted on rough water. The hauldown system locked the aircraft on the deck. That meant that you could handle ship motion up to something like nine or ten degrees of pitch and up to 31 degrees of roll while locked in. The landing gear wheel on the "upside" of a high roll would actually come off the deck but the hauldown probe in the belly had you securely locked into the beartrap so the bird could not roll right off the ship's deck. It didn't feel too comfortable though.

You would only experience that until the ship took a steadier course in preparation for engine and rotor start-up. Then the pitch and roll had to be quite a bit less - I can't remember the numbers now. There has been some discussion about blade movement, precession and all that. In practical terms, we had to do a rapid rotor engagement and the same for braking the rotor on shutdown. We would start one engine while it remained disengaged from the rotor. When aircraft and systems checks were done, we started the second engine and ran up the rotor together. The Sea King had droop stops to prevent the blades from drooping too low when at low rpm, until the rpm could be increased to normal. One of the things the deck crew had to watch for when we disengaged the rotor was to see if all the droop stops were working. If not, we had to quickly wind the rotor up again and try another disengagement.

There was a posting that mentioned floats were only used on smaller helicopters.

The CF used floats on Twin Hueys (Bell 212). They were huge ungainly looking things - big, black, long cigar shaped, inflated bladder type floats, with the bows tapered upwards.

They also used similar looking things on the Kiowa (Jet Ranger). If the situation required start-up/shut-down on the water, you had to paddle away from shore so that you could spin around doing a 360 until the tail rotor became effective. In flight you had to anticipate slowing your roll rate in a turn because of the weight and momentum created by the floats being heavy and at a distance from the longitudinal centre line of the aircraft. On shut down it would turn as well when the rotor lost effectiveness.

[Islander Jock]

G'day all,

Can anyone point me in the direction where I can get some up to date statistics on ditchings involving RW aircraft in the oil and gas industry.

We have some info that we give in our HUET courses but I have some doubts as to its accuracy given that the information only applied to ops in GOM and North Sea and is now quite dated.

Thanks
IJ

[JimL]

A good first port of call would be a paper written by the RHOSS committee entitled CAP 641 Report of the Review of Helicopter Offshore Safety and Survivability; this can be found at:

http://www.caa.co.uk/publications/publicationdetails.asp?id=138

You should be aware that you might have to be careful with any searches that you do (and any information that is returned): ICAO and most States do not require an engine failure to be reported; if that engine failure is then followed by a ditching (landing on the water) which does not result in injury or damage beyond a certain threshold, it will not be recorded as an accident or in some cases an incident.

[Islander Jock]

Another request if I may,
Does anyone know where I can find a photo of the Puma sitting upright on floats. Not sure if it was of the one being referred to in the most recent posts.

Just need it for HUET training purposes.

Thanks.

IJ

[Islander Jock]

G'day all,
I posted this request on the ditching thread but thought I'd just give it a quick try as a separate topic.

I really need a photograph of a helo on emerg floats in the drink. Preferably Puma/S76/B212 or 412. Just upgrading our HUET training presentations and I'm not sure the locals understand what I am talking about when referring to emergency floatation systems.

There was a good piccie some time back of a Puma in the drink will all floats activated and the cabin high and dry. But despite my best efforts of searching I cannot locate it.

Any help would be greatly apprciated :ok:

Cheers
IJ

[JimL]

Islander Jock,

Check your PMs.

[dedhead]

IJ,
As above,check your PM's.
DH

[Heliport]

If anyone has any photos, or links to photos, please post them here as well.

Thanks

[SilsoeSid]

Found this Lynx pic here (http://home-3.tiscali.nl/~mwdeba20/lynxaida.htm)

http://home-3.tiscali.nl/~mwdeba20/pics/lynxfloat.jpg

[Islander Jock]

Thanks everyone for replies so far.
Looks like I now have exactly what I need. :ok:

[Spunk]

nevertheless, you've got one more pm... :D

[John Eacott]

IJ,

There are a few of a ditched Sea King where the floats aren't doing a great deal of good:

http://www.eacott.com.au/gallery/d/1249-1/824+Sea+King+051+ditched+and+inverted.jpg

http://www.eacott.com.au/gallery/d/1251-1/824+Sea+King+051+ditched+and+inverted+with+diver.jpg




;)