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There are a lot of impact absorbing gels, one example here.

Could some kind of more advanced gel be introduced into aircraft cabins, which expand rapidly on impact (like air bags) and fill the entire cabin, thus protecting the occupants from injury or death?

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    $\begingroup$ I'm calling high likelyhood of that video being faked, and there is a big difference between being lightly patted by a shovel and getting smashed into the floor by 10 g of acceleration. $\endgroup$ – ratchet freak Mar 17 '17 at 9:47
  • $\begingroup$ This post reminds me of this scene from Demolition Man (movie) $\endgroup$ – Ron Beyer Mar 17 '17 at 12:15
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    $\begingroup$ See this question; the basic answer is that human beings cannot survive the G forces in a very sudden deceleration/impact and no amount of padding will change that. The forces involved are far too high for the human body. I could also mention that there's a very high chance that video is faked, or at least misleading: you can't see what protection the person being struck really has under his clothing, so there may be much more to it than just gel. $\endgroup$ – Pondlife Mar 17 '17 at 17:59
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    $\begingroup$ That gel works by becoming hard and brittle with sudden impacts while being soft when slowly deformed. This requires some density, so a foam will never have this characteristic. Besides, the required stopping distance for airliner speeds is far too high, see Pondlife's comment. $\endgroup$ – Peter Kämpf Mar 18 '17 at 6:37
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Unfortunately, not to any great advantage.

An airliner travels at several hundred kilometres per hour; even when landing and flying at its slowest (which it does only for a very short time) it will still be travelling at a considerable speed.

At such speeds, any impact in a crash is likely to be characterised by two things (I've left aside fire, to concentrate on the matter of impact alone):

  • a very significant change in velocity (deceleration)
  • a release of a great deal of energy

The deceleration of an aircraft in flight that hits something will be tremendous. If you have 30 metres in which to decelerate from (say) 500 km/hr to 0, padding won't make any difference to the bodies being decelerated.

If the padding is resistant enough to prevent an object experiencing such a deceleration from simply continuing on its way and smashing through everything in its path, then the padding may as well be a block of concrete for all the softness it could offer.

On the other hand, if the padding not so hard as to smash the bodies that crash into it into pieces, then they will go straight through it and smash themselves to bits on the first harder thing they encounter.

In fact, at such decelerations, not only is there no middle way between too hard and too soft, any padding aiming for the middle ground would be simultaneously too hard (it would certainly cause catastrophic injuries to the bodies encountering it) and too soft (it wouldn't prevent them smashing into other objects).

Then, an impact of the kind you describe releases a huge amount of energy. The things involved in such impacts aren't so much as damaged as cease to exist. Everything stops being what it was. You might as well wish for padding to protect you when you're on the inside of an exploding bomb.

Perhaps you were referring to lesser impacts that would be survivable with some protection, which is reasonable. Indeed, an aircraft can readily survive turbulence that breaks the bones and heads of passengers not wearing seatbelts.

But in this case, the idea sadly fails as not very practical.

  • How much damage would 300 or so exploding gel pods, or airbags, do to passengers? Once again, that's a release of quite a lot of energy.
  • How much damage would they prevent, compared to say, just wearing seatbelts?
  • How much would they interfere with the subsequent evacuation?

They simply wouldn't procure any advantage, or at least, only at the cost of a much greater disadvantage.

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    $\begingroup$ "If you have 30 metres in which to decelerate from (say) 500 km/hr to 0" Thats not a remotely realistic scenario. The only kind of crash where that happens is an aircraft flying almost perpendicularly into terrain at a fairly large fraction of cruise speed. Almost all removely survivable crashes happen at take-off or landing, when the speed of the aircraft is more like 200km/h and the plane has much more space to stop than 30m, which isn't even the length of a 737. $\endgroup$ – David Richerby Mar 18 '17 at 10:52
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    $\begingroup$ At least the deceleration itself is non lethal . Going from 500km/h (139 m/s) to 0 on 30m is a mean deceleration of $\rm (0 - 139^2) / (2 \times 30) = -322 \text{m/s}^2$ or -33g. This is done on 0.26s. I believe the human body could stand these 33g eyeballs out during a quarter of second. $\endgroup$ – mins Mar 18 '17 at 12:33
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    $\begingroup$ @DavidRicherby 500km/hr was just one example speed, and one kind of crash. I discussed the case of those lower-speed, potentially survivable accidents separately $\endgroup$ – Daniele Procida Mar 18 '17 at 14:57
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    $\begingroup$ @DanieleProcida But it's a very bad example that tells us almost nothing. It's taking a crash that's very, very far from survivable and saying, "Well, this idea wouldn't help with something close to the worst possible case, so there's no point. Oh, and by the way, it wouldn't help much with more survivable accidents." Roughly two-thirds of your answer focuses on this unreasonable case. $\endgroup$ – David Richerby Mar 18 '17 at 15:03
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    $\begingroup$ @DavidRicherby it might tell you nothing, but if anything is clear to someone who reads questions here regularly, there is no end to the things that that people don't realise. People aren't born knowing these things and there is no harm in spelling them out. If there's just one person for whom it is new and useful information, good. $\endgroup$ – Daniele Procida Mar 18 '17 at 15:14

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