H21 Heli crash videos

[thecontroller]

here
(http://www.youtube.com/watch?v=NDb_UCZs7ZM)
does anyone know why these tests were conducted etc? i am presuming there was no pilot on board

[its the bish]

h21 hele crashhas anyone else noticed the flashes from inside the fuselage at approx 10 & 24 seconds? reminds me of the train versus nuclear flask "test" some years back where flashes were seen along the underframe of the locomotive immediately before impact & the power unit making a rapid exit through the locomotive roof! Perhaps there is a logical explanation for these flashes in this video,maybe connected with the undercariage failure, or was it stage managed stage effects? I bow to your greater wisdom fellow ppruners!:rolleyes:

[MightyGem]

Camera flashes perhaps??

[212man]

"reminds me of the train versus nuclear flask "test" some years back where flashes were seen along the underframe of the locomotive immediately before impact "

Jesus, reminds me of that well known TV series "I'm a conspiracy theorist, get me out of here."

MG: I agree

TC: I think you're right (no pilots on board)!

[slowrotor]

See the remote control wire from the tail?
The ground pilot probably underestimated the difficulty of flying a RC helo.
Loss of control in 10 seconds would be average, without a long training program.

[NickLappos]

The flashes are automax lights, part of the test equipment, they mark the exact location of three fuselage points at impact, because they mark the film very specifically.

Or they are the alien pilots, smiling for the camera....

Those landings are done at about 15 feet per second, based on some back of the envelope calculations I just did. The design sink speed of the Black hawk is 42 feet per second (including gear collapse) and it can hit at 12 feet per second without any damage. Therefore, these landings would probably result in no damage if done in an H-60!

This illustrates the power of the modern design requirements - the H-64 and H-58D are similar, I believe as is the S-92 and AB-139.

[B Sousa]

Couple of locations come to mind. One would be NAS China Lake, just a few miles North of Edwards AFB, or NAS Fallon Nevada.
It obvious a tethered aircraft on a hard landing, second one looks like something went wrong with the controls or maybe a Fixed Wing type thought he could fly the box. Or he could have run out of tether, thus no control. Dont think that was part of the test.

[TwinHueyMan]

"The design sink speed of the Black hawk is 42 feet per second (including gear collapse) and it can hit at 12 feet per second without any damage. Therefore, these landings would probably result in no damage if done in an H-60!"

I was about to say those videos look like Army H60 pilots doing a type transition.

[Graviman]

Just to gain perspective 42 feet/sec is about 28 mph, which is almost the speed a test car will be doing when it hits a solid crash barrier (deformable offset is 40mph). I'm guessing only part of the energy is absorbed by the gear strut pressurisation and collapse, so 20g peaks would be seen as the fuselage contacts the ground. Probably at least a foot or two of deformation between pilots seat and ground to keep crew safe. Some design!

Mart

[CS-Hover]

Hi
in the context.... Helicopter crash-landing test (http://www.youtube.com/watch?v=P4jetY7oiwE)
maybe nick and others can give some "numbers" to this... :ok:

seems a 76 somewhere in the video...

[NickLappos]

CS,
Great movie. That is a Huey first, probably at about 8 to 12 fps, since that is the speed where the skids bend to let the belly touch. The next machine is the S76 ACAP (a totally composite fuselage that was built in about 1982 for the pre-Comanche research). It was designed for 42 FPS as well, and you can see the pilot's seat (CP only for some reason) stroke fully in the last sequence. The seat is designed to start moving at about 20 G's and hold that G or less for its full 10" stroke, allowing the fuselage to be sacrificed while protecting the crew. The fuselage is designed to hold all primary cabin dimensions within about 6", and must keep out the primary masses (transmission and engines) for the 20G impact. The baseline S76, H-60 family and the S92 were designed to these fuselage requirements (as were the H-64 and the AB-139).

[Graviman]

Amazing vid, CS-Hover. I spent a while as a crash engineer in the auto industry, before i decided engin's were my thing (heli powertrains even better!). The numbers are actually suprisingly simple to work out - in metric, sorry: :uhoh:

Say machine is descending at 42 feet/sec or 12.8 m/sec, and limiting peak deceleration allowed is 20g. Using
Vel^2 = 2 x Accel x Dist (remember to convert accel to m/sec^2)
gives minimum crush distance of 0.42 m or 1.4 feet. This is the ideal case assuming everything neatly collapsed at exactly 20g - trust me it doesn't!

In practice, the landing gear is designed to collapse at 10g (thanks Nick), over a distance of ~0.6m. This means once fuselage contacts (denoted on film by automax flash) machine is still decending at speed worked out from
Vinit^2 - Vel^2 = 2 x Accel x Dist
which using example figures gives 6.8 m/sec. Same equation as above then means fuselage must crush 0.12 m or 0.39 feet. In practice frame crush will be a series of small collapses, each below 20g, so that 6" requirement will soon be used up.

If design is optimised machine does not bounce as all of the impact energy is absorbed in the collapse. In practice crew seating will also collapse to ensure any peaks stay below 20g. Crew gets out and walks away to post on PPRuNe about the advantages of flaring on EOL. :}

Mart

[CS-Hover]

hey, stop :D

it's not mine :O , i only found it in youtube ;)

nick:what you mean with "see the pilot's seat (CP only for some reason) stroke fully in the last sequence"

regards

[NickLappos]

Grav,
The landing gear will take about 10 G's before they give way, and they stroke about 2 feet, using air-oil and then a frangible honeycomb tube. The S92 uses a telescoped aluminum tube with a tube-cutter.
Then belly crush is programmed to take up the rest.

CS, look in the last sequence, taken inside the cabin looking forward. Note that the CP left seat strokes downward as the crash continues, and when the aircraft is stopped, the head is so far down it is almost out of sight. The seats in the H-60 and S-92 have wells below them so the seat mechanism disappears into the hole as the seat strokes downward.

[MightyGem]

To put it another way, 42'/sec is a ROD of 2520'/min. I haven't flown the Lynx for a while but you could probably do an EOL without bothering to pull collective at the bottom, and walk away. :eek:

[Graviman]

Trouble is this loading is seen on the design board/workstation as a once in an aircraft life load case, MG. Even though there would be many components that might "appear" undamaged, they would have accumulated all of their fatigue damage in one hit. Using the analogy, you would have dropped Nick's bean jar ;) (although that is more for tubine blade creep, but same principle).

Mart

[MightyGem]

Errr...I wasn't suggesting that the aircraft could be used again!!

[ShyTorque]

Importantly, 12 feet/sec = 720 feet /min!
It always gave me a warm feeling that, at the bottom of a 3 degree glideslope in a Blackhawk (+/- 500 fpm), if I ever found myself in zero/zero conditions, if necessary all I had to do was level the aircraft and let the undercarriage do it's thing. :ok:

The pilots' seats we had (I think they are standard fit) had a system that used the controlled extrusion of metal rods through dies in the seat backs to cushion the impact.

[NickLappos]

Shy, the seats are standard, just be sure nobody stores stuff in the seat wells under them. If so, the stuff will stop the seat stroke, and limit the safety enhancement, since stroke distance equates to G's of protection.

The pax seats have similar protection, they use the support wires drawn through dies, to absorb the energy, up to about 12 g's.

These are the kinds of protection that the "new" standards for LUH left out:
from the LUH rRFP (note they are low, and not even requirements):
The Light Utility Helicopter, operating as a Federal Aviation Administration (FAA) certified rotorcraft, shall provide for occupant protection in a crash through designs that protect aircraft crew and passengers. The Army requests information on industry's ability to meet the design standards for crashworthiness and crew survivability as defined by the Federal Aviation Regulations (FAR) Part 27 or Part 29, Sections 561, 562, and 785 as of December 13, 1989.

[JimEli]

can you say, "basilar skull fracture?"

[slowrotor]

Nick said: they use the support wires drawn through dies, to absorb the energy, up to about 12 g's.

That is interesting. How does that work?
Does the wire get smaller and absorb the energy? or just friction?

[NickLappos]

slow, exactly, the wire is pulled thru a die that is smaller than the wire, so it squeezes it, and this absorbs the energy.

[Alfa Hotel]

Nick,

One aspect I noticed is how far forward the upper body, of the dummy in the front, travels. Aren't the safety harness' suppose to prevent this from happening?

[TwinHueyMan]

UH-60 passenger and crew seats use the wire bit too, stiff wire that anchors halfway down a shaft on the backrest, comes up, loops around an attaching hook, then goes back down about a foot IIRC and is attached to nothing. Acts like a pulley, with the wire bending around the circular metal portion of the attach hook as it passes through during the stroke, absorbing the energy. We had a nasty crash in Afghanistan where the helicopter hit pretty hard, everyone in their seat and seatbelted lived. The pax onboard (Marines) were well off enough that they hopped out and started pulling security right after!

-Mike

[Graviman]

Amazing stuff, TwinHueyMan, this must go a long way to help trust the machine. Was the machine salvagable, or are you not able to give details?

Actually, touching on discussion with MG, i am curious what say an S-70 is designed to withstand and fly away from. I would imagine so many "hard landings" will be factored into the fatigue life (Miner's law for fatigue calcs). In theory as long as component doesn't yield, it still has some service life. In practice even with some damage a component may not actually start to crack (as long as damage does not cause stress concentration).

Mart

[NickLappos]

Alfa,
The belt behavior is a lesson learned, because the inertia reel doesn't stop that bend forward. The most severe injury is cyclic striking the face, and in futire incarnations, airbags on the inst panel will be used (Comanche had them). Nonetheless, the crew survival after horendous accidents is amazing. One Sea Hawk accident had the aircraft fly into the ground at very high sink rate, come apart and then slide into a stand of trees. The crew walked away from the wreckage, and the only recognizable pieces in the wreckage were the fuel cells, which were substantially unharmed, but no longer housed in the surrounding structure.

Again, these levels of protection were selected by studying 3800 lost Hueys, and chosing to pretect the crew in the 95th %ile event.

[SASless]

Some aircraft have seltbelts that attach to the seat which is free to slide for adjustment fore and aft by means of rails with detents for the latching mechanism.

The Army added armor to the seat and pilots added weight to the seat load by the wearing of body armor and other equipment.

Alas, when the aircraft crashed with any significant forward momentum....the seat with a tightly secured human crash dummy launched itself against or through the forward end of the aircraft.

Several Chinook pilots found themselves outside the aircraft in a hostile environment with very serious injuries.

Attaching the belts to the floor of the aircraft then added a problem of using the pilot's innards as a cushion for a runaway armored seat.

:uhoh:

[Graviman]

Nasty way to learn about development issues, Sasless.

Nick, before airbags were fitted to cars in Europe, steering column crush cans gave a suprising improvement to injury level. The UK data interpretation expert is a guy by the name of Prof Murray Mackay, who i think recently retired from Birmingham Uni - very helpful chap. Collapsible cyclics with rubber tips might offer a good retrofit for machines already in service.

Out of interest, what range of g factors would be expected for service landings?

Mart

[NickLappos]

Mart,
There are break-away cyclics, as you suggest. The funny thing about airbags is that the Army insisted in installing them in the Comanche, even though it had a side stick that was no head hazard at all!

The typical landing in service is usually less than 1.2 g, and a really rough one might be 1.5 (on a bet I once flew a traffic pattern to a landing and stayed below 1.1g on the g meter!)

[SASless]

Nick......Landing to a hover doesn't count ! :=

[Graviman]

Never been keen on airbags for cars either, Nick, especially the large airbags standard in US - they are fitted for folks who excercise the "right not to wear a seatbelt" :ugh: . Would rather column pulled away than have an explosive device going off in my face, at a time when i am trying to think fast...

Just to clarify that's 1.2 to 1.5g total (or 1.1g for the more skilled pilot), so i don't need to add 1g static. A rotor a fraction of the MAUM, designed for -0.5g, would thus easilly handle this. I am curious because ground vehicle designers usually consider 1g +2g/-1g, since driver limits speed by feeling of reduced g.

Mart

[NickLappos]

Yes, Grav, the g metter will read 1.5g if you make a horrible landing, thus the airframe "feels" an increase of 50% on the landing loads.

[TwinHueyMan]

Graviman:

http://www.armyaircrews.com/images/footage/081204_uh60.jpg

Don't have any of the shots from our guys on my computer. The story is the marines wanted to be impressed, the pilot did some neg Gs, the chalks floated up (unsecured in the cabin) into the cockpit and jammed the collective down, near flat pitch. Had a very significant decent rate in when they hit the ground. It was level at considerable speed, rolled out a bit then hit an earthen wall head on and flipped. The only fatality was the crew chief that did not have his seatbelt on, just a tether. Everyone else, belted into their seats, pretty much walked away.

Also, some L model Blackhawks have the Cockpit Airbags, a buddy had one go off in flight once which dispelled any doubts us A model guys had about their existance!

-Mike

[Graviman]

That is incredible, TwinHueyMan! A real statement on survivability in that machine - great pity about crew chief, though. It is amazing how stuff floats about in a reduced g environment, fun but a worry for control jamming.

The real problem with airbags, for cars in particular, is that all the testing is done with the dummy in the nominal driving position. In real accidents folks don't always sit how they're meant to. Some of Murray Mackays talks had cases where folks had injured themselves by having arm across steering wheel when airbag went off, and there have been other out of position fatalities :( . For my $0.02 an airbag is a last resort, with perhaps cartridge driven collapse of cyclic preffered - as long as trigger mech is reliable in high vibration environment :ouch: .

Mart