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Author Topic: Could airbags make airflight safer?  (Read 6052 times)

Herman Melville

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Could airbags make airflight safer?
« on: 05/06/2009 12:28:38 »
Could plane fuselages be fitted with vast airbags (or a great number of smaller airbags) to asborb crash impact? Or, could there be some other way to absorb impact, based on the design of planes and/or the materials used to make them?

Given this week's news, it seems that greatest efforts could and should be made to ensure that air travel is safer.


 

Offline Don_1

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Could airbags make airflight safer?
« Reply #1 on: 05/06/2009 12:36:55 »
If a plane crashes on land, I should think air bags (assuming they don't burst) would cause the plane to bounce and the pilot would lose whatever control he had over the plane. Then the plane would crash again and again. The poor passengers would be like beans in a rattle.
 

Offline JnA

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Could airbags make airflight safer?
« Reply #2 on: 05/06/2009 16:13:48 »
To be fair, statistically air travel is relatively safe.
 

Offline Karsten

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Could airbags make airflight safer?
« Reply #3 on: 05/06/2009 16:25:44 »
To be fair, statistically air travel is relatively safe.

Yes, since last Sunday, statistically speaking, about 500 people have died in automobile crashes in the USA alone.
 

Offline LeeE

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Could airbags make airflight safer?
« Reply #4 on: 05/06/2009 16:33:11 »
Airbags are effective at relatively low speeds i.e. < ~ 60 mph but jet airliners travel much faster and even when making controlled landings are still traveling at ~ 150+ mph, meaning that there is much more inertia to overcome.  In an uncontrolled crash, the speed, and therefore inertia, is likely to be much higher.  As well as this, aircraft fuselages are simply not designed to stay in one piece following a crash - making them strong enough to do so would increase their weight beyond the point where they could fly and the weight of the airbag equipment would also still have to be added.
 

lyner

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Could airbags make airflight safer?
« Reply #5 on: 05/06/2009 16:39:55 »
The time over which an air crash can last is much greater than for a simple car accident. Air bags don't stay inflated for long so they might all have deflated again by the time the bumpy landing was over. If they stayed inflated for longer then there would be certain occasions when people couldn't escape asap.
 

Herman Melville

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Could airbags make airflight safer?
« Reply #6 on: 05/06/2009 17:09:48 »
It was a stupid question. Sorry. Please ignore.
 

lyner

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Could airbags make airflight safer?
« Reply #7 on: 05/06/2009 18:35:37 »
Naah. Where would we be without 'fringe' questions?
 

lyner

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Could airbags make airflight safer?
« Reply #8 on: 05/06/2009 18:38:12 »
Actually, the deceleration is much less in an air crash. The plane seldom lands into a massive brick wall, or equivalent. If it does hit a mountain, an airbag / seat belt/ St Christopher badge is unlikely to help you.
 

Offline turnipsock

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Could airbags make airflight safer?
« Reply #9 on: 05/06/2009 21:28:22 »
I see that you can now get motorcycle leathers with airbags, that could be entetaining if the go off at the wrong time.
 

lyner

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Could airbags make airflight safer?
« Reply #10 on: 05/06/2009 23:22:11 »
Five seconds of being the Michelin Man!
 

Offline JnA

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Could airbags make airflight safer?
« Reply #11 on: 06/06/2009 01:05:40 »
It was a stupid question. Sorry. Please ignore.

no.. it wasn't a stupid question, you were thinking laterally.. this should be encouraged.

It reminded me somewhat of the Seinfeld character 'Kramer' and his idea to put oil in bladders in tankers so in the event of something catastrophic the oil would stay contained. It's a brilliant idea in theory..


 

Offline LeeE

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Could airbags make airflight safer?
« Reply #12 on: 07/06/2009 21:17:43 »
Actually, the deceleration is much less in an air crash. The plane seldom lands into a massive brick wall, or equivalent. If it does hit a mountain, an airbag / seat belt/ St Christopher badge is unlikely to help you.

I'm afraid I have to disagree with you; a descent rate > ~10 feet per second (fps) at touchdown is likely to damage the aircraft, so although the downward vector may be a lot less than the vertical vector it'll still be like hitting a brick wall.

Typical descent rates, for airliners, on approach are around 10-12 fps but then they 'flare' just before touchdown to reduce this to < 3-5 fps (and a 5 fps touchdown would be pretty hard - have a look at this youtube vid of an MD80 that failed to flare before touchdown: http://www.youtube.com/watch?v=8Pk1N6GzeOo - if you look carefully you'll see the fuselage flex, but fortunately not break up.  They were lucky to only lose the tail).

In any case, you'll only be able to keep your descent rate < ~20 fps in a controlled crash, and you'll probably lack the power or control to make a flare (otherwise you wouldn't be crashing).  In a crash resulting from uncontrolled flight though, most aircraft will eventually end up with a very high descent rate, typically several hundred mph.
 

Herman Melville

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Could airbags make airflight safer?
« Reply #13 on: 08/06/2009 09:48:38 »
I read somewhere that even in the event of complete engine failure, planes can glide for 200 miles. Is this really true?
 

Offline Yomi

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Could airbags make airflight safer?
« Reply #14 on: 08/06/2009 09:51:25 »
this can't be true just because of the huge weights of modern aeroplanes they need atleast a engine working in case of disaster to fly to a safe region to avoid a crash
 

lyner

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Could airbags make airflight safer?
« Reply #15 on: 08/06/2009 12:57:20 »
Look at this link
http://www.airliners.net/aviation-forums/general_aviation/read.main/2499076/
The opinion here is that a jet aircraft (no propellors to act as drag)  should be able to glide several tens of miles and land at about 140mph.
If you get it right, you can flare just before impact and limit your vertical speed to something comfortable. You, of course, need some power from somewhere, to drive your flight controls - you have a RAT (ram air turbine) for that, which you drop down underneath when you need it.
Witout reverse thrust, you need a long runway or a soft buffer at the end.
Talking of soft buffers . . . . .
 

Herman Melville

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Could airbags make airflight safer?
« Reply #16 on: 08/06/2009 16:09:21 »
Look at this link
http://www.airliners.net/aviation-forums/general_aviation/read.main/2499076/
The opinion here is that a jet aircraft (no propellors to act as drag)  should be able to glide several tens of miles and land at about 140mph.
If you get it right, you can flare just before impact and limit your vertical speed to something comfortable. You, of course, need some power from somewhere, to drive your flight controls - you have a RAT (ram air turbine) for that, which you drop down underneath when you need it.
Witout reverse thrust, you need a long runway or a soft buffer at the end.
Talking of soft buffers . . . . .

Interesting, thanks. Via that link I found this:
http://www.nytimes.com/2001/09/10/world/jet-pilot-who-saved-304-finds-heroism-tainted.html

However, I think that was a bit of a fluke. More sobering info here:
http://www.planecrashinfo.com/database.htm
 

Offline LeeE

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Could airbags make airflight safer?
« Reply #17 on: 08/06/2009 20:12:01 »
Look at this link
http://www.airliners.net/aviation-forums/general_aviation/read.main/2499076/
The opinion here is that a jet aircraft (no propellors to act as drag)  should be able to glide several tens of miles and land at about 140mph.
If you get it right, you can flare just before impact and limit your vertical speed to something comfortable. You, of course, need some power from somewhere, to drive your flight controls - you have a RAT (ram air turbine) for that, which you drop down underneath when you need it.
Witout reverse thrust, you need a long runway or a soft buffer at the end.
Talking of soft buffers . . . . .

If the only problem is loss of power then you should be able to make a controlled landing, but this isn't the same as an uncontrolled crash.  In a controlled landing you should be able to flare and so keep your descent rate at touchdown within the airframe limits (if you're a very good pilot, and very lucky - low-level gusts and windshear can easily upset even the best unpowered approach)

How far an unpowered aircraft can glide depends upon its glide-ratio and its altitude.  The higher its glide-ratio, the more units it can move forward for each unit down, and the higher it is, the more downward units it has in which to move forward.

The Air-Transat Airbus A330, which managed to land in the Azores after running out of fuel over the Atlantic, glided for 65 nautical miles (120km) from an altitude of 33,000ft and it was calculated that the glide-ratio of the Gimli-Glider Boeing 767, which also managed to land after running out of fuel was 12:1.  In both cases though, their speeds at touchdown were much higher than would normally be the case - the glide speed was about 200 kts for the A330 and about 220 kts for the B767, compared with typical landing speeds of 135~145 kts for both types of aircraft (I believe the touchdown speeds for both landings were ~ 200kts).  In both cases the aircraft could not fly slower because they could not use 'flaps', which although provide more lift, allowing the aircraft to fly slower, also produce much more drag, which needs to be overcome by more power if the aircraft is not to be slowed to the point where it stalls and simply drops out of the sky.

Just for comparison, typical modern competition gliders have glide-ratios better than 50:1 and there is an open-class glider (which has a wingspan of 30.9m, greater than that of early Boeing 737 airliners) that has a glide-ratio of over 70:1.
 

lyner

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Could airbags make airflight safer?
« Reply #18 on: 08/06/2009 23:22:39 »
V interesting LeeE.
Cheers.
It always crosses my mind at least once when up at 10km and coming in to land.
 

Herman Melville

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Could airbags make airflight safer?
« Reply #19 on: 09/06/2009 09:42:28 »
In both cases the aircraft could not fly slower because they could not use 'flaps', which although provide more lift, allowing the aircraft to fly slower, also produce much more drag, which needs to be overcome by more power if the aircraft is not to be slowed to the point where it stalls and simply drops out of the sky.
How slowly would it need to be moving to drop out of the sky?
 

Offline LeeE

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Could airbags make airflight safer?
« Reply #20 on: 09/06/2009 21:15:42 »
In both cases the aircraft could not fly slower because they could not use 'flaps', which although provide more lift, allowing the aircraft to fly slower, also produce much more drag, which needs to be overcome by more power if the aircraft is not to be slowed to the point where it stalls and simply drops out of the sky.
How slowly would it need to be moving to drop out of the sky?

It depends upon how much it is carrying; a lightly loaded aircraft needs less lift so can travel slower before stalling.  Stall speeds for large airliners, with power and flaps deployed can be between ~100-150kts, depending on weights and design.  With power but no flaps the speed range is roughly between 160-190 kts (incidentally, I found that the max tyre speed for an A330 is 204kts, so the tyres are designed to cope with a no-flaps landing).

An important thing to remember is that aircraft also have a minimum control speed, which is higher than the stall speed, so once an aircraft has stalled it will be going too slow to be controlled; control can only be regained by increasing speed.  Without power, this means sacrificing altitude for speed, which isn't usually an option if you stall on approach as you're already close to the ground.

Once an aircraft has stalled it'll be unlikely to simply 'stall-ahead' and remain level; one wing is likely to drop, but with no control you can do nothing about it and at low altitudes you simply don't have enough time to both pick up speed, to regain control, and level the aircraft out before hitting the ground/water.

Have a look at http://en.wikipedia.org/wiki/Vmc#Regulatory_V-speeds for a list of the different critical airspeed types.  Note that no actual figures are given as these are specific to each aircraft design, but apart from the multi-engine specific speeds, they're common to all aircraft.
 

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Could airbags make airflight safer?
« Reply #20 on: 09/06/2009 21:15:42 »

 

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