Why do military helicopters crash rather than autorotate?

[ifresh21]

Hi,

This is a question I have wanted to ask for a good while. This forum isn't specifically related to military flying, but hopefully some of you guys have knowledge about that.

A while ago, I was watching black hawk down. In the movie, blackhawks get shot down at low altitude and crash. Crew members die. It is based off of real life and similar crashes happen often. I also heard that if the tail rotor on something like an AH-64 gets shot and malfunctions, the helicopter will crash.


My question is, why can't the pilots autorotate down to a fairly soft landing? I know in the R-22 they say if there is a tail rotor problem, enter an autorotation. Why would a helicopter have to crash because of just a tail rotor failure?

Thank you in advance for help

[Non-PC Plod]

Ifresh, in theory you may well be able to autorotate with a tail rotor failure if the aircraft gets it at a convenient time. "Convenient" would normally mean at an altitude which gives you time to think, at cruise speed to help maintain directional control, in a lightweight aircraft, using low power, over a nice big soft field.
I regularly teach this malfunction in the simulator in a benign environment, and even then most people will crash the first couple of times.
A heavy aircraft full of troops at low altitude over a built up area with people shooting at you is the worst environment I can imagine to get a tail rotor failure. Barring a miracle, it is always going to end in a world of hurt. When you are hovering at heavy weights, the engines are producing a huge amount of torque. If the tail rotor departs, there is no anti-torque reaction and you will start to spin rapidly. Its inconceivable that you could turn the engines off and lower the collective quickly enough to maintain control. Even if you can, its only going to help if you are over a nice big flat level area with no bad guys in it.

[Ian Corrigible]

Besides which, military rotorcraft no longer crash: they only suffer 'hard landings.' Which probably reassures Joe Public and the beancounters more than the grunts in the back. :E

I/C

[TXSIK]

high disk loading

[Fareastdriver]

There are a lot of things around a tail rotor that can cause enormous trouble if the get damaged. A drive failiure is the standard emergency procedure but that is easy. More important things that can go wrong are:

Severe blade damage. This can cause the a tailrotor blade to fly so far out of track it hits the pylon or causes such an imbalance that the tail rotor assembly is torn from its mountings. Whether it is restrained by the controls or not it will just be a chunk of metal thrashing around the back and a conventional autorotation will be unlikely.
Control wire damage. The control cables on all aircraft are tensioned so to avoid any slack in their operation. 2nd World War gun cine film demonstrates an untold number of aircraft that suddenly go into an uncontrollable roll when one of the aileron cables is severed. The same effect will cause a helicopter to spin uncontrollably if a tail rotor cable is cut. Some helicopters have a centering device to prevent this if this happens;---- unless the device itself is hit.
Ground Proximity. I know of one case with a Puma where they had a tail rotor failiure in the hover and managed to shut down the engines and carry out a controllable landing. However, that manoeuver had been practised in a simulator; without that training they would have be unlikely to get the same result.
Low level with high speed you have a multitude of problems where you may just, if you are lucky, get away with it.

That cannot be forcast.

[Mungo5]

Hollywood also has an affect too. Lots of smoke and beeping followed by "terrain terrain" is far more cinematic that a nice entered auto and landing.

Drama.. it's all in the drama.

[Fareastdriver]

I forgot that. The seat cushions in helicopters are highly inflammable and wherever the helicopter is hit the seats catch fire and clouds of smoke comes out of the cabin.

[Gomer Pylot]

Don't believe much of what you see in the movies. They play by movie rules, which have little, if anything, to do with real life. That said, when people are shooting at helicopters with high explosives and incendiary rounds, bad things can happen, and lots more than just the tail rotor can be damaged or blown completely away. There are lots of things on military helicopters that are far more flammable than seat cushions, including fuel and ammunition among others.

[albatross]

Open Joke"
Autorotation is not the solution to every problem. Would that it were it would make life so much easier.:E
I know of one bright lowtime lad who - having the engine chip light come on - rolled the throttle smoothly to idle and Auto'd to a perfect landing in a very, very small swamp amongst the trees - 1 mile from a very nice field with farms, farmer's daughters, telephones and roads and all that good stuff.
Sometimes, however, there is only time to call "#$%^ brace, brace, brace!" and hang on for dear life.:ooh:
"Close Joke

[ifresh21]

Thanks for the replies

Btw, the movie is based off real life

[212man]

Btw, the movie is based off real life

I think you'll find most people here know that! ;)

[Rotorwashed]

at such low level, and high weight, it would be near impossible to enter an auto rotation.

In Michael Durant's autobiography, he says that when the tail rotor failed, the helicopter started spinning so quickly that the centrifugal force made it impossible for the co-pilot to cut the throttles almost immediately.

[ironchefflay]

often its the "dead mans curve" that mil helicopters tend to operate in or around making autorotation impossible no matter the damage etc

Height-velocity diagram - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Height-velocity_diagram)

[MikeNYC]

Besides which, military rotorcraft no longer crash: they only suffer 'hard landings.' Which probably reassures Joe Public and the beancounters more than the grunts in the back. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif

Like this one?
http://www.thedenverchannel.com/2010/0630/24098112_640X480.jpg
This photo, from a source, shows the wreckage of the Apache helicopter on the side of a mountain near Pikes Peak. The Army referred to this as a "hard landing."
Army: Helicopter Crash On Pikes Peak Caused $26M In Damage - Denver News Story - KMGH Denver (http://www.thedenverchannel.com/news/27133488/detail.html)

Gotta love their definition of a "hard landing"...

[minigundiplomat]

High disk loading primarily caused by operating at heavy op weights on the edge of the envelope, with external inputs at very inopportune times in difficult terrain/surroundings.

Of course, RPG and small arms passing through the cockpit can provide a distraction at the time too.

Hollywood portrayal of such events is bolleaux. Most of the incidents you refer to are during the critical phases of an operation and involve putting the aircraft and crew in situations you'd rather not. However, crews take as many precautions as they can and actively minimise the time spent in the more hazardous areas of the curve.

Most of it is down to luck after that. Can't comment on tail rotors, don't like them, dont have one.

[rotornut]

Don't believe much of what you see in the movies

How true. It seems whenever they show a pilot flying a 206, he's usually in the left seat. And the sound is usually from a Bell 47 except in Blue Thunder and a few others.

[B.U.D.G.I.E]

Some would say it's because they have military pilots in control. :sad:

[PlasticCabDriver]

And don't forget that, whatever the emergency, however minor or major (makes no difference anyway, all the CWP captions will be on and a overly loud warning horn will be sounding like an hyperactive foghorn), the single Immediate Action is to grab the cyclic in both hands and wrestle with it, and make no attempt at all to fly the aircraft or do any drills. Spinning round and round a few feet above the ground for longer that you might think strictly necessary is in the Subsequent Actions.

[lelebebbel]

Also, refer to this scene from the movie "the day after tomorrow" for a highly realistic depiction of a typical in-flight emergency:

5hFE1itGJQw
(http://www.youtube.com/watch?v=5hFE1itGJQw&feature=related)

[grumpytroll]

you're at 100 feet agl flying at a low airspeed in a very hot environment in a heavy UH60. Lots of power being pulled already. a shocking blast runs through the aircraft. immediately it begins to spin violently because the tailrotor has stopped at a high power setting. you pause however briefly to try and assess what has happened and what to do about it. because you are spinning violently, it is difficult to get your hand on the power control levers, pull them to idle and the get them past the idle detent to off. In the mean time the pilot on the controls has lowered the collective to save rotor rpm so you are descending at a rate of several hundred fpm. Also since the blast hit your tail area, possibly a large amount of weight relative to your W and B has been removed from the aircraft causing the nose to drop violently due to the out of balance condition. in the meantime since you are over a hostile area and trying to locate a landing area amongst buildings, cars etc...

its easy really

[topendtorque]

And the sound is usually from a Bell 47

really good to hear that something of intrinsic value and quality is being preserved.
tet

[wickednorthernwitch]

ifresh21

In the "movies" made in Hollywood about WW2 they would have you believe that the Americans won the war single handedly without any help from the allies.

Shame they didn't do the same in Iraq or Afghanistan and saved a lot of British lives.

[Lonewolf_50]

ifresh21, have you stopped beating your wife? (That is a rhetorical question, used to make a point).
Why do military helicopters crash rather than autorotate?
What you did was assume an answer in the phrasing of your question. Some people call this "begging the question," but let's just call it ignorance at work.

On the basis of what evidence do you frame your question?

Here is another way to ask that question.

Do military helicopters crash rather than autorotate?

That is another very ignorant question.

You can autorotate and still end up at the bottom with a difficult landing that results in a crash. This happened to a colleague of mine whose tail rotor quit in a Navy SH-60B.

You can also be over terrain that works against you. You can also cock up the flare and landing. Lots of things can go wrong during a forced autorotation, particularly one involving the loss of tail rotor function.

The other problem with your question would be ...

Are the operating environments identical, or similar enough to make a comparison? This has been addressed by a number of responses to you.

Based on what you have posted, you have neither the background, nor the actual intellectual capacity, nor the curiosity, to explore the question in any depth.

You have a movie made in Hollywood. (?????????????)

WTF?

Do you actually fly helicopters?

[grumpytroll]

"Besides which, military rotorcraft no longer crash: they only suffer 'hard landings.' Which probably reassures Joe Public and the beancounters more than the grunts in the back."

I would love to know the actual source of the above statement. I googled this apache crash and other crashes and found dozens of articles all of which refer to specific incidents and quote from official sources and they all use the term "crash" to describe what happened. I'm certainly willing to be educated. As far as i know the term "hard landing" has specific descriptors to describe an event but not the final outcome. ie. "the aircraft experienced a hard landing which led to the crash." Sometimes a hard landing results only in damage to the landing gear. I wouldn't consider it a crash. Or would you want to describe a fender bender in the parking lot at your local grocery as a crash?

GO

[ironchefflay]

the curse of PPrune strikes again!!

[rotornut]

really good to hear that something of intrinsic value and quality is being preserved

Right on. I asked a film guy why they often used the sound of a Bell 47 even on turbine helicopters. His answer: Because of the great sound!

[alouette3]

I have an ongoing bet with my better half. Every time a helicopter shows up in a movie billed as a thriller, I bet that it is going to crash and burn within the next few frames.
A prime example would be ' Broken Arrow'.Several good and decent helicopters were harmed unnecessarily in the making of that movie.
I have yet to lose my bet.
Alt3

[Gomer Pylot]

More likely, several good and decent helicopter models were harmed in the movie. Models don't cost nearly as much as real helicopters, and to the average movie-goer look identical. Scale is everything.

[Lonewolf_50]

If I remember the story correctly, Vic Morrow was hit by a real Huey during the filming of "Twilight Zone" movie and it killed him.

:(

Not sure if that is a "crash" and I don't think it was an autorotation, but that's a Class A mishap however you slice it.

[tucumseh]

The "fact" that military helicopters autorotate and "glide" to a graceful landing upon double engine failure at any altitude was one of MoD's key defences in the Chinook Mull of Kintyre case. It was the reason given why they ignored their own regulations regarding certification of Safety Critical Software for FADEC.

[Ian Corrigible]

Another 'hard landing,' experienced by a USMC CH-46E participating in the Cobra Gold exercise in Thailand. Seven injured but thankfully no fatalities.

http://i.imgur.com/I5hWpOw.jpg (http://www.marinecorpstimes.com/news/2013/02/marine-several-hurt-helo-hard-landing-thailand-022013)

I/C

[Um... lifting...]

S-92 video of certification autos. These guys had the advantages of:
*A hard-surfaced runway
*Test pilots
*Pre-briefing and controlled entry
*Nobody shooting at them
*A perfectly sound machine
and probably others

And it still isn't all that pretty when you get right down to it.

Autorotation of a heavy helicopter is no day at the beach.

4JqmoWAhv5g

[Dennis Kenyon]

Just a short note ref Hollywood and featured helicopters ... in 2001 I flew one of the MD500s (littlebirds) for a short while while making Scott Free's production of Black Hawk Down.

It probably isn't generally known that the number one story ship pilot on that shoot in Morocco was the super American film pilot Bob Zee. (can't pronounce his full name!) While holding a 175 feet hover above Bob's MD500 below with the camera ship filming above us both, a group of local kids brought in a large catapult made up from a strip of car inner tube. They managed to launch a piece of rock at Bob's 500 while I held station above.

The rock removed Bob's T/R assembly but being the pilot he is. Bob stuffed the heli down towards the sand and pulled off a 100% non damaging landing ... if probably a tad on the 'hard' side. With the kids rounded up I landed alongside, where an engineer borrowed my T/R so Bob could fly out and back to the film base at Sale. Then with the T/R switch repeated for me, both machines were recovered safely back to base.

More on request. Dennis Kenyon.

[ericferret]

In 1975 I flew down to Illesheim near Frankfurt in a British army Gazelle. While waiting for the drivers to do whatever it is that drivers do I was offered a front seat ride in a Huey Cobra going on airtest. I made small talk with the pilot and asked about the autorotation characteristics. Ok he said here we go we've just been shot down.
At that point I spoted the difference between American and British army pilots.
British pilots had practice engine failures, Americans got shot down.

Remember Vietnam had only just finished and the Americans had real combat time. My deepest respect and thanks for the best flying day I ever had.

Mind you the German army pilot who took us for a ride in a CH53 at Soest and was clearly a frustrated Messerschmitt pilot gave it a good good run for the money and that also sticks out as a memorable day.

[JohnDixson]

Um-lifting:

It was done at max gross.

[212man]

thanks John, I usually refer to that video when briefing (S92) autorotations in the simulator(s) - all of which replicate the behaviour shown quite well.

[SASless]

An account I once heard sums it up.

The fellow was flying a Huey B Model Gunship in Vietnam. He got into a losing exchange with a couple of .51 Caliber Machine Guns....took several hits that resulted in the loss of hydraulics, tail rotor control and the engine. He by necessity entered autorotation and headed for the ground aiming for a rice paddy adjacent to some houses.

He said everything was going fine despite hitting some tree tops, a power line and power pole, going through the roof and end of a house, a brick wall and it was not until he hit a rice paddy dike did he lose control.

Sometimes....it just isn't doing an EOL to a cow pasture.

[Lonewolf_50]

FWIW:
Blackhawks autorotate just fine, but there's a recommended entry altitude, and airspeed, that if you aren't within easy reach of makes the entry a bit tough, and all ensuing is a catch up game.

The original question was mostly a display of gross ignorance, given that from a high hover, you can't enter an auto, and you are in a not so nice zone of the HV diagram, particularly if you have a high gross weight.

Military helicopters do autorotate. They have to , it's in the spec.

That's the answer to the question originally posed.

[Ian Corrigible]

21 POB, six hospitalized. Report here (http://www.stripes.com/news/pacific/21-injured-when-us-helo-makes-hard-landing-in-south-korea-1.216781).

http://a57.foxnews.com/global.fncstatic.com/static/managed/assets/660/371/USChopperKorea1.JPG (http://www.foxnews.com/world/2013/04/16/no-injuries-reported-after-us-military-helicopter-reportedly-crashes-near-north/)

I/C

[minigundiplomat]

If military helicopter operations were easy - it would have been civilianised by now.

There is a crapload of difference between fully laden, hot n high, 100' above hostile territory, on NVD, whilst dodging rounds, then flying 2 VIP's to Gloucester race course.

[Lonewolf_50]

Ian, I'd say he hit pretty hard. :E

[Jack Carson]

In the case of a CH-53E hard landing you would have to figure in what effect 2000 gals. of JP4 would have on the post hard landing situation.

[airevaclover]

Hi I am Brandon I am 10 and I have study about planes and helicopters. The reason why they need an tail rotor it to keep it steady during flight if they do not have a tail rotor they would simply keep turning till they crash and possible explode in fire. If you have any comments or questions email me at [email protected] thank you

[DirtDiver]

The Tail Rotor :
The tail rotor is very important. If you spin a rotor using an engine, the rotor will rotate, but the engine and the helicopter will try to rotate in the opposite direction.

This is called
TORQUE REACTION.

The tail rotor is used like a small propeller, to pull against torque reaction and hold the helicopter straight.

http://www.helis.com/howflies/anim05.gif
http://www.helis.com/howflies/anim04.gif

Source: Principles of rotary flight (http://www.helis.com/howflies/prflight.php)

[SASless]

Mini....just how does one "dodge" Rounds? I know the Brits do that by quaffing back a half dozen Pints bought by others then looking at their Breitling and muttering something to the effect they "must be off" and "Cheerio!".

[Lonewolf_50]

Jack, I don't think CH-53E's typically fly with JP-4. JP-5 and JP-8 are the preferred fuels. FWIW. ;) (Better BTU per pound, higher flashpoint, etc)

[Jack Carson]

LW50, I was thinking more in terms what affect 2000 gallons of fuel would have on the potential survivability of a crash. As a reference, the Marines had a CH-53D with 650 gal external aux tanks crash in a ditch in South Korea back in the 1980s. For the most part the impact was survivable but the post impact fire resulted in severe thermal injuries and multiple fatalities to crew and passengers.

[Wirbelsturm]

How about using the aircraft as a tool to achieve an aim. Utilising the full flight envelope (and occasionally beyond the flight envelope in combat situations) upto and including max weights in hostile environments both in terms of weather and situation.

Most civilian operators place strict 'wear and tear' usage limits on their machines that the military do not.

p.s. We used to practice auto rotation to a running landing in the S61 all the time!

[ralphmalph]

Wirbelsturm,

Negative.

Limits are not to be exceeded.

Unless you have ****** up! If you have not planned correctly, for speed, time, location.....then you need to exceed limitations.

If you plan.....And the whole world breaks loose....different

[Jack Carson]

Ralphmalph is correct. Limitations are just that, limitations and are not to be exceeded. Military aircraft component overhaul times and lives are computed based on an aircraft usage spectrum that is negotiated between the military customer and the manufacturer. This is one area that tends to get complex when the actual usage spectrum differs from the one originally negotiated or changes throughout the life of the vehicle. As an example, the negotiated usage spectrum may call for one autorotative descent every 4 flight hours when in actuality an aircraft assigned to a training outfit may do many times that in the course of its life. This example was sighted as the cause for the premature failure of main gear box free wheeling units in aircraft used for training.

[Wirbelsturm]

ralphmalph,

I don't believe any pilot 'plans' to exceed any limitations neither did I intimate such. The likelihood of transgressing a limit is always going to be greater when operating at a reduced margin toward that limit.

For example I broke the MRGB twin engine torque limit during a SAR pickup in the lake district many years ago. The weather was extreme with high winds and a pickup from 20m below a ridge line which was 90 degrees to the wind leading to extreme turbulence above the pickup site. Despite thorough planning and using smoke to show the demarcation line a sudden squall placed the aircraft below the turbulent boundary layer and the torque required to recover the rate of descent prior to impacting the hill was higher, transiently, than the twin engine torque limit.

No amount of planning could have predicted the situation.

The upshot was to return the aircraft to base, SOAP analysis of the MRGB and dropping of the mag plugs for inspection.

The danger occurs when crews accidentally transgress limits but then don't report them. Then other crews operating the aircraft after the event reap the repercussions, not the original crew.

[topendtorque]

I don't believe any pilot 'plans' to exceed any limitations

with respect, clearly you are on another planet from those who do, the evidence of which is often spread across the planet at random. True no pilot worth the title should or generally would, but there's the others - see? They lurk in the shadows, the wheat fields and the open mesa.

you'll see stories about them here, there and elsewhere.

[minigundiplomat]

Mini....just how does one "dodge" Rounds? I know the Brits do that by quaffing back a half dozen Pints bought by others then looking at their Breitling and muttering something to the effect they "must be off" and "Cheerio!".

SAS,

1. Not having a foreign policy developed by a recovering alcoholic, who couldn't point to America on a map [of America].
2. Listening to the J2 brief.
3. Not flying at 80 Kts and 300 feet, using the same ACP's day in day out.
4. 3D manouvering instead of 2D thinking.

[ralphmalph]

Mini,

I now work as a civvy with a lot of Americans.......points 2-4 are lost on them...fact!

A real shame.

[Lonewolf_50]

ralph & minigun: two zero value posts. Please pat yourselves on the back. (And whomever wound you up ... was that SASless? )

Jack: good point on life limits and the wear and tear training aircraft experience. However, when we compare where this discussion has gone since the stupid question that started it (see the title) I wonder why the mods don't just shut it down.

The initial dumb question has been answered.
Military aircraft have to autorotate, and military pilots both practice autorotation, and train for autorotation.
Likewise with civil helicopters and pilots.

Maybe this thread needs to be closed.