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Crashable Aircraft

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Terminal velocity is so called because it is usually fatal. It also happens to be the velocity reached by a falling body in air, at which air resistance balances gravity.

For an unladen human in a face-to-earth position, terminal velocity is about 120mph. For any randomly-shaped lump of stuff with a lower density than a human, terminal velocity will be less.

Formula 1 cars are cunningly designed in such a way that crashes at speeds exceeding 100mph are often survivable. Even regular cars, with crumple- zones and airbags, often permit survival of 80mph+ collisions. And, in both these cases, the structure that has to absorb the impact is quite small - there is maybe a metre and half of energy-absorbing structure between you and the thing you've just driven into.

So.

Rather than attaching parachutes, escape pods or automatic rosary beads to large passenger aircraft, why not just make a regular crash survivable?

First, we want to replace all the seats in the plane with lightweight, easily-breakable replacements that won't hurt anyone.

In the event of an impending crash, and after advising passengers to don oxygen masks, simply flood the entire cabin and cargo hold (quite quickly) with fast-curing (and preferably non-flammable) medium-density polyurethane foam. As long as there are a few metres of this foam between the passenger and the fuselage (in the direction of impact), the foam would absorb impacts at up to a couple of hundred mph, saving the lives of the majority of the passengers.

Of course, extracting the passengers would be tricky, especially if they have hair, but hey. And, if it all goes very wrong, the bodies are at least protected from looting, fire, bears etc.

MaxwellBuchanan, Jul 27 2014

better than expanding foam, utility fog! http://en.wikipedia.org/wiki/Utility_fog
[mitxela, Jul 27 2014]

Piper PA-28 http://en.wikipedia.org/wiki/Pa-28
Neat [8th of 7, Jul 28 2014]

Supermarine Spitfire http://www.telegrap...kes-to-the-air.html
[pocmloc, Jul 29 2014]

...and this too: http://www.supermarineaircraft.com/
[hippo, Jul 29 2014]

[link]






       //medium-density polyurethane foam//.   

       Have you used fast-curing urethane foam? I have, and I have the burn scars to prove it. Presumably you're going to equip all passengers with asbestos-and-aerogel insulating clothing as well?
Custardguts, Jul 27 2014
  

       //I have the burn scars to prove it//   

       So, you lived, then?
MaxwellBuchanan, Jul 27 2014
  

       I like this idea but I'm not sure the premise is correct. An airliner in an uncontrolled dive will have a terminal velocity significantly higher than that of a skydiver or even an F1 car at full tilt. Impact energy goes with the square of velocity so the comparison with automotive crumple zones may be misleading.
EnochLives, Jul 27 2014
  

       Well, it depends. Think of all the ways a plane can crash.   

       (1) Falling short of a runway, overshooting, or power failure on take-off: vertical speed is probably very slow. Horizontal speed is substantial (typically 100-200mph), but unless there's a mountain in the way that speed will be bled off over a few seconds as the aircraft grinds, cartwheels and breaks up.   

       (2) Failure of power or control at altitude. Plane will usually settle into a glide. Similar to (1), but with possibly higher forward speed at time of ground contact.   

       (3) Bomb or missile. Aircraft breaks up. If substantial chunks of fuselage remain intact, their freefall speed will be on the order of 100-200mph vertically.   

       (4) Dead stall (as in that Air France one). Vertical speed probably less than 20mph, horizontal speed less than 150mph.   

       (5) Failure to see a mountain. Vertical speed negligible, but horizontal speed alarming.   

       (6) Wingover (wingtip into ground) and cartwheel. Speeds on the order of 100-200mph.   

       I would contend that all but (5) would be somewhat survivable if you were encased in foam and more than a few metres away from the aircraft skin in the direction of travel.   

       I don't know of any cases where an airliner has entered an uncontrolled dive, though I expect there are a few.   

       Main point: in most crashes, the mass-mean deceleration is less than 20G (actually less than 10G), meaning that the centre of mass of the aircraft (or wreckage) is less than 20G. People die because the aircraft structure is not built to withstand anything like 10G, hence, either:   

       (a) the structure of the aircraft collapses around them, crushing them or   

       (b) they freefall through the aircraft structure until they hit the terrain (or, rather, the parts of the aircraft in contact with the terrain), experiencing much higher G's.
MaxwellBuchanan, Jul 27 2014
  

       //automatic rosary beads // Where is this idea? I must bun it.
Voice, Jul 27 2014
  

       What about the weight of the passengers behind you? You just became their crumple zone.
DIYMatt, Jul 27 2014
  

       Huge airbags on the outside, provide cushioning and reduce (virtually) the overall density of the plane and so it's descent speed...   

       Done cunningly, no need to have an inflation system, just let them be filled from the air rushing past....   

       Admittedly triggering them by mistake during flight would not be good thing.   

       PS just realised I must have gone on a Malaysian Airline plane, as we went Japan->UK with a layover in Kuala Lumpur...aghh
not_morrison_rm, Jul 27 2014
  

       Radio control aircraft have similar trade-offs. Bottom line is you can build an aircraft to fly well or you can build it to crash well. The "fly well" radio-control aircraft are light-weight and cheap but are totally destroyed/pulverized by a high- speed crash. The smaller number of "crash well" aircraft use durable, shock-absorbing materials such as corrugated plastic. These tend to be heavy, expensive, and worse-performing.   

       So, you could build an airliner to withstand crashes (e.g. include a very strong "shell" around the passengers plus "cushioning" such as a whole- aircraft air-bag and set of parachutes) but tickets would cost roughly 2x to 4x what they do now.   

       Would you pay twice as much to reduce your risk of dying on a given plane flight from 1 in ~20 million to, say, 1 in ~200 million?
sninctown, Jul 27 2014
  

       //Would you pay twice as much to reduce your risk of dying on a given plane flight from 1 in ~20 million to, say, 1 in ~200 million?// A lot of people would...
Voice, Jul 27 2014
  

       // A lot of people would...//   

       ..And that's why lotteries and casinos make so much money.
Custardguts, Jul 27 2014
  

       I would have thought that surviving the impact is only part one of surviving the crash. The next big survival obstacle is the 100+ tonnes of burning kerosene. What if sufficient foam was injected into the cabin such that it completely filled the void and generated a hydrostatic pressure that was sufficient to pop the structure apart prior to impact? i.e. the wings, fuel tanks, tail, engines etc. are shed, sort of like a moulting insect, leaving a ballistic lozenge of foam-encapsulated passengers.
EnochLives, Jul 28 2014
  

       Jettisoning of mass would help a lot. If a pilot had an "oh dear it seems to be going horribly wrong" button which jettisoned fuel, non-functioning engines, the contents of the cargo hold, the toilets, overhead bins, the cart with the Johnnie Walker and cartons of Silk Cut, all the in-flight magazines and the packets of headphones... the plane would be a lot lighter. Much lower terminal velocity and stall speed. Crash would be a lot more survivable.
bs0u0155, Jul 28 2014
  

       Deaths from falling bottles of Johnnie Walker however, would increase above the presently low baseline.
bs0u0155, Jul 28 2014
  

       // button which jettisoned fuel, non-functioning engines, the contents of the cargo hold, the toilets, overhead bins, the cart with the Johnnie Walker and cartons of Silk Cut, all the in-flight magazines and the packets of headphones... the plane would be a lot lighter.//   

       Fuel, yes. Engines, maybe - would seriously affect the W&B, and without power to the control surfaces that is a Bad Thing. As to the rest, why not just jettison everything aft of First Class ?   

       // Deaths from falling bottles of Johnnie Walker however, would increase above the presently low baseline //   

       Would that be from cranial injuries, or cirrhosis of the liver ?
8th of 7, Jul 28 2014
  

       //why not just jettison everything aft of First Class//   

       Actually, you're more likely to die in 1st class. The place to be is over the wings. Nice strong structure there.
bs0u0155, Jul 28 2014
  

       //Would that be from cranial injuries, or cirrhosis of the liver//   

       A little of both... actually. Working in alcohol research, you'd be amazed at precisely how little alcohol does to the liver. Directly at least.
bs0u0155, Jul 28 2014
  

       // The place to be is over the wings. Nice strong structure there. //   

       Indeed. The Supermarine Spitfire and the PA-28 <link> are both particularly well proportioned in that area.   

       The C-130, being a high wing, is rather less attractive, but has sufficient other features to endear it to the canny air traveller. However in the Cessna 172 it's something of a deficiency...
8th of 7, Jul 28 2014
  

       so there's a sound argument for the widespread adoption of the Supermarine Spitfire as personal transport from a safety point of view?
bs0u0155, Jul 28 2014
  

       Got it in one. You get a nice safe seat over the wing, outstanding agility, considerable immunity from heat-seeking MANPADS, ecelllent rate of climb and high top speed, grass strip capability, optional hardpoints for stores, and 20mm cannon.   

       On the downside, they are somewhat maintainance heavy, the cockpit is rather cramped, and wherever you land you're in constant danger from other pilots who want to quietly murder you (nothing personal, mind) and take your aeroplane.
8th of 7, Jul 28 2014
  

       //...nice safe seat over the wing, outstanding agility, ... e[x]celllent rate of climb and high top speed, grass strip capability, optional hardpoints for stores...//   

       I was in the process of posting an idea inspired by this but I found it is baked. <link>
pocmloc, Jul 29 2014
  

       [pocmloc] I was about to add a link to the idea you briefly posted, but I'll add it here instead (see link).
hippo, Jul 29 2014
  

       If, presumably, the plane is travelling forwards, the place to be is in the aft, near the tail cone, behind that several meters of foam and human flesh matrix.
RayfordSteele, Jul 29 2014
  

       //the place to be is in the aft//   

       Depends on the crash. First class passengers do have a higher death rate, but there are probably a few compounding factors. 1. They're probably older 2. The complementary gin provides a baseline motivation to stay in the aircraft. Conversely, the economy experience has people trying to leave perfectly serviceable aircraft.
bs0u0155, Jul 30 2014
  

       Actually its the strength benefit of the tail section that makes the difference.
RayfordSteele, Jul 30 2014
  
      
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