Ditching
 

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 ]

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 ?.

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

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!

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.

Thank you very much.

That was what I was looking for.

Cheers for your help

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 ]

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.

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.

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

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

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 ]

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 ]

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

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.

:)

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 ]

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.

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 ]

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 ]

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! ;)

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?

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.

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.

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

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?

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.

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.

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.

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:

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 ]

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.

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.

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 ...

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.

You called! :)

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

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!

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

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 ]

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.