H21 Heli crash videos
Join Date: Jul 2003
Location: Port Townsend,WA. USA
Posts: 440
Likes: 0
Received 0 Likes
on
0 Posts
Nick said:
That is interesting. How does that work?
Does the wire get smaller and absorb the energy? or just friction?
they use the support wires drawn through dies, to absorb the energy, up to about 12 g's.
Does the wire get smaller and absorb the energy? or just friction?
Join Date: Jul 2002
Location: Somewhere, Over the Rainbow
Posts: 200
Likes: 0
Received 0 Likes
on
0 Posts
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
-Mike
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
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
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
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
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.
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.
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
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
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
Join Date: Apr 2003
Location: USA
Age: 75
Posts: 3,012
Likes: 0
Received 0 Likes
on
0 Posts
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!)
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!)
Nick......Landing to a hover doesn't count ! 
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
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" 
. 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
. 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
Join Date: Jul 2002
Location: Somewhere, Over the Rainbow
Posts: 200
Likes: 0
Received 0 Likes
on
0 Posts
Graviman:
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
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
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
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 
.
Mart
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 .Mart
Last edited by Graviman; 4th Apr 2007 at 08:32. Reason: Own flying endeavours trivial compared to most on this forum - no need to mention.
