crashworthiness
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crashworthiness
Some recent accidents prompted recent thinking on this subject. I've always been confident of walking away from any forced landing in a Pitts with the knowledge of what people have done to them and survived. Similar view of other types with a steel tube fuselage. Need to consider objects which may hit your head or equipment stupidly installed under the seat. eg fire extinguisher installation not really meeting the g loads for the design crash case.
I suppose that newer types certified to the current FAR 23 with stronger seats and head injury criteria are good but simply doesn't impress me enough. I believe that Airtourers are good in this respect although a much earlier design.
I've always thought that it would not be good to be in an accident with a fibreglass aircraft. Especially true of fibreglass ultralights, homebuilts and LSA's. Seems to me that people don't consider this when deciding what to buy or fly. The flash new .... looks very appealing and economical on the ramp at the local aero club but I'll stick with the rag and bones machine or an Airtourer.
I suppose that newer types certified to the current FAR 23 with stronger seats and head injury criteria are good but simply doesn't impress me enough. I believe that Airtourers are good in this respect although a much earlier design.
I've always thought that it would not be good to be in an accident with a fibreglass aircraft. Especially true of fibreglass ultralights, homebuilts and LSA's. Seems to me that people don't consider this when deciding what to buy or fly. The flash new .... looks very appealing and economical on the ramp at the local aero club but I'll stick with the rag and bones machine or an Airtourer.
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Most fatalities in "otherwise survivable" accidents seem to be head injury related. Other than stall speed, I don't really see how one construction type is better or worse than another? I suppose tube construction may compess a bit more to obsorb energy, but in accidents where the airframe is substantially compressed the G forces are such that survival is pretty iffy anyway. A helmet is probably the best aid to survival but I must admit I don't wear one. Next to that (discounting a parachute) is a decent memory foam cushion to help reduce spinal injuries.
SS
SS
djpl, I agree with your sentiments, but not necessarily your perception of the facts.
Crashworthiness is a clear enough issue - that of minimising injury to aircraft occupants following an accident. Go back 50 years, and the consideration of this issue was extremely minimal, whilst nowadays it is a fundamental subject that must be considered during the design and certification of any aeroplane.
But it is an increasing issue. The latest generation of light aircraft are firstly a lot faster - and so the energy of any impact is potentially greater - something has to be done with that energy to stop it transferring itself into the occupants. Also a great many of these aircraft use advanced composite materials - post crash these materials emit all sorts of nasty stuff capable of causing both short and long term medical issues or causing death through inability to escape the wreckage.
An additional issue is that parts 23 and 25 use stupidly low loads when considering seat structures - typically about 77kg / 170lbf, so the structure may well not retain larger occupants. Some GA aircraft (mostly either UK developed microlights or US developed helicopters) are increasingly using much higher and more sensible numbers in this regard - but it is a crashworthiness issue that sooner or later is going to start causing problems.
BUT, old=good, new=bad, is almost certainly not true.
G
Crashworthiness is a clear enough issue - that of minimising injury to aircraft occupants following an accident. Go back 50 years, and the consideration of this issue was extremely minimal, whilst nowadays it is a fundamental subject that must be considered during the design and certification of any aeroplane.
But it is an increasing issue. The latest generation of light aircraft are firstly a lot faster - and so the energy of any impact is potentially greater - something has to be done with that energy to stop it transferring itself into the occupants. Also a great many of these aircraft use advanced composite materials - post crash these materials emit all sorts of nasty stuff capable of causing both short and long term medical issues or causing death through inability to escape the wreckage.
An additional issue is that parts 23 and 25 use stupidly low loads when considering seat structures - typically about 77kg / 170lbf, so the structure may well not retain larger occupants. Some GA aircraft (mostly either UK developed microlights or US developed helicopters) are increasingly using much higher and more sensible numbers in this regard - but it is a crashworthiness issue that sooner or later is going to start causing problems.
BUT, old=good, new=bad, is almost certainly not true.
G
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Cirrus, Columbia and Diamond aircraft have seats and airframes that can withstand a 26G impact, to meet FAR part 23 requirements. This is probably more than a human can withstand, but they also improve your chances by fitting seatbelts with built-in airbags (as does Cessna). Older aircraft designs will collapse on much lower impacts, and have far more hard edges to brain yourself on. The latter problem is likely to have a significant affect on the outcome of a ditching.
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Cirrus seem to have the safest design for a vertical impact: honeycomb aluminium seat squabs that progressively collapse, after the aircraft has hit the ground under the parachute. However, that only works if you haven't already squashed them by kneeling on them ...
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Tiger Moth adherents will tell you that as you only crash at 30mph, and all the energy is absorbed in snapping the wires, there's not a lot left to do you unnecessary damage.
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A lot of the modern work on crashworthiness goes back to Dr John Stapp's experiments in the early post-war years. He subjected himself to decellerations of 45 g in a rocket sled slowing from over 500mph and wind blasts of over 500 mph with only minor injury.
A curious effect of his research was that the observation that the military crews were involved in mode survivable accidents travelling to and from the base in their cars than they were in operational flying.
He then went on to pioneer much of the work in automotive crashworthiness.
I suspect crashworthiness may enter into peoples decision making when buying aircraft at some time in the future, in the same way that it has for cars. At present, there is very little information in the public domain to use as a basis for assessment, and who's going to pay for an aircraft equivalent of EuroNCAP?
A curious effect of his research was that the observation that the military crews were involved in mode survivable accidents travelling to and from the base in their cars than they were in operational flying.
He then went on to pioneer much of the work in automotive crashworthiness.
I suspect crashworthiness may enter into peoples decision making when buying aircraft at some time in the future, in the same way that it has for cars. At present, there is very little information in the public domain to use as a basis for assessment, and who's going to pay for an aircraft equivalent of EuroNCAP?
Hi all - been lurking on and off PPrune for a couple of years, finally taking my first PPL steps (3 hours in the book!). Nice to see a subject that I can comment on without feeling like a complete idiot!
EuroNCAP is a bit of a con actually - cars are made to get the best result at exactly the specified parameters (I've even heard of one that is stronger on the LHS only because the EuroNCAP only crashes LHD cars).
The thing to bear in mind is that cars are designed to give good results at 30 mph and the injuries go up exponentially (with the energy profile). Basically don't expect to have a good outcome at any speed over 60mph that involves a sudden stop. In aviation terms that would be the ground I guess...
Having said that, there is no reason that the interiors of aircraft shouldn't be designed to meet the car requirements - that is a peak decelaration of 80g over no more than 3 m/s (for a 6.8 kg mass travelling at 25 kph) in the head impact zone. The directives are there and all cars currently on sale in Europe meet this. Add in a four point harness (at least) and helmet, survivability goes up considerably for lower speed impacts. Higher speed decelerations will still cause brain injury though.
Best advice is not to crash really - if you really have to, try to scrub off as much velocity as possible before hitting hard things, and when you do, hit head on as the brain doesn't like sideways loads (tears it apart along the middle).
Not a pleasant subject, but very interesting all the same!
JC
EuroNCAP is a bit of a con actually - cars are made to get the best result at exactly the specified parameters (I've even heard of one that is stronger on the LHS only because the EuroNCAP only crashes LHD cars).
The thing to bear in mind is that cars are designed to give good results at 30 mph and the injuries go up exponentially (with the energy profile). Basically don't expect to have a good outcome at any speed over 60mph that involves a sudden stop. In aviation terms that would be the ground I guess...
Having said that, there is no reason that the interiors of aircraft shouldn't be designed to meet the car requirements - that is a peak decelaration of 80g over no more than 3 m/s (for a 6.8 kg mass travelling at 25 kph) in the head impact zone. The directives are there and all cars currently on sale in Europe meet this. Add in a four point harness (at least) and helmet, survivability goes up considerably for lower speed impacts. Higher speed decelerations will still cause brain injury though.
Best advice is not to crash really - if you really have to, try to scrub off as much velocity as possible before hitting hard things, and when you do, hit head on as the brain doesn't like sideways loads (tears it apart along the middle).
Not a pleasant subject, but very interesting all the same!
JC
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In my capacity as a volunteer firefighter, I was called to a plane crash at our local airport. It was my buddy, in a C150M which I knew very well, who had affected a very unsuitable arrival angle relative to earth. I figured from the marks in the ground, that he stopped in about eight inches.
The inverted aircraft was remarkably intact in the cabin area - a strong testamonial to excellent Cessna design. We had no real trouble getting him out, as he was not trapped in at all.
The coroner, who knows such things, told me that based upon the examination, my buddy had experienced a 200G deceleration, which was not survivable for any duration.
But the airframe was not hugely collapsed, there was no head strike, and no entrapment. The propeller flange was a third peeled off the crankshaft though...
It is my opinion that the Cessna 150M displayed excellent crashworthiness. Even the seatbelt ripping would have provided its own amount of deceleration.
I do worry that the aircraft which use very rigid composite cabin structures, would have to be much more inventive to provide safe deceleration for the occupants inside the cabin, and is there room?
Seatbelt airbags? I've ridden in Cessna's test seat, and had the airbag blown at me. I suppose it's okay, but I am not keen on the requirement for a formal maintenance activity (and expense), when a seat is removed and reinstalled in the aircraft, and the bi-annual recertification, which is quite costly.
I put my trust in a well adjusted four point Hooker Harness!
Cheers, Pilot DAR
The inverted aircraft was remarkably intact in the cabin area - a strong testamonial to excellent Cessna design. We had no real trouble getting him out, as he was not trapped in at all.
The coroner, who knows such things, told me that based upon the examination, my buddy had experienced a 200G deceleration, which was not survivable for any duration.
But the airframe was not hugely collapsed, there was no head strike, and no entrapment. The propeller flange was a third peeled off the crankshaft though...
It is my opinion that the Cessna 150M displayed excellent crashworthiness. Even the seatbelt ripping would have provided its own amount of deceleration.
I do worry that the aircraft which use very rigid composite cabin structures, would have to be much more inventive to provide safe deceleration for the occupants inside the cabin, and is there room?
Seatbelt airbags? I've ridden in Cessna's test seat, and had the airbag blown at me. I suppose it's okay, but I am not keen on the requirement for a formal maintenance activity (and expense), when a seat is removed and reinstalled in the aircraft, and the bi-annual recertification, which is quite costly.
I put my trust in a well adjusted four point Hooker Harness!
Cheers, Pilot DAR
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I saw a program about an Indy car driver, who was testing the car and had all sorts of accellerometers attached to the car. He crashed and sustained 130G and walked away. Obviously it was very short duration but the big thing was the car protected him.
In the same way the Diamonds I like to fly have the 26G cockpits and seats. This is nice to know, and nice to know that in a forced landing which doesn't go horribly wrong it is unlikely that the engine will end up on your lap (unlike the Cessna 172 for example which has nothing to protect you). In reality so long as you don't nose dive into the ground, if you make a forced landing and stop in ~10m, the G forces shouldn't peak at more than about 20G (if my maths is correct).....
As someone used to tell me when flying over the LA sprawl.....if the engine fails, aim for the loft window. At least the wings will absorb some of the impact and you may walk away..........
In the same way the Diamonds I like to fly have the 26G cockpits and seats. This is nice to know, and nice to know that in a forced landing which doesn't go horribly wrong it is unlikely that the engine will end up on your lap (unlike the Cessna 172 for example which has nothing to protect you). In reality so long as you don't nose dive into the ground, if you make a forced landing and stop in ~10m, the G forces shouldn't peak at more than about 20G (if my maths is correct).....
As someone used to tell me when flying over the LA sprawl.....if the engine fails, aim for the loft window. At least the wings will absorb some of the impact and you may walk away..........
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Didn't help Cory Liddle, when he flew his SR20 into an apartment window in New York. The engine continued into the room, but the rest of the aeroplane bounced back out and plummeted. I'm not sure that composite wings are as good at absorbing energy as aluminium ones.
The general rule is more g is survivable over a shorter time span (that's milliseconds or parts thereof) - it's all down to where the energy goes!
Until there is legislation, the manufacturers will not improve the crash performance of GA aircraft, and there won't be legislation because not enough people are killed or seriously injured in GA (compared to the roads for instance). The development costs of making a 60 knot + ground impact at a high angle survivable in most cases (and without leaving the occupants in a vegitative state) would be huge as well. Then there's the weight penalty to think about..
What about if the cabin was made into a survival cell (ie rigid in itself but effectively seperate to the airframe)? It could then break away in an impact... They do it on those mad jet powered power boats used in the States.
JC
Until there is legislation, the manufacturers will not improve the crash performance of GA aircraft, and there won't be legislation because not enough people are killed or seriously injured in GA (compared to the roads for instance). The development costs of making a 60 knot + ground impact at a high angle survivable in most cases (and without leaving the occupants in a vegitative state) would be huge as well. Then there's the weight penalty to think about..
What about if the cabin was made into a survival cell (ie rigid in itself but effectively seperate to the airframe)? It could then break away in an impact... They do it on those mad jet powered power boats used in the States.
JC
Last edited by Dak Mechanic; 12th Jan 2007 at 08:33. Reason: clarity!
