Ditching a helicopter: (incl pictures)

[HeliEng]

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 ]

[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.

[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

[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!