[luke_s]

When they say "Jettisoned", it makes it sound like one of the flight computers decided to drop the panels. Wouldn't it more be the case that the panels are deliberately designed to be blown off? I have a hard time believing that any control system could react in time in case of an engine explosion...

[stephengillie]

The panels may have been designed to jettison once they reached a certain pressure differential, or they may be jettisonned by computer.

How quickly do engines explode? Is it faster than 2 cars colliding? Computers deploy air bags quickly because electricity travels faster along wires in your car chassis than the car travels into something else.

Visualize a bumper with sensors - as the bumper is deformed by a collision, a sensor shifts an electron in the copper wire, and the electron next to it shifts. There's a cascade of shifting electrons along the wire, and it races backwards through the car's body, chased by the destruction of the car as it collides with another object. The cascade of electrons hits the air bag computer, which begins another cascade of electrons to the air bag. The wave of destruction has covered most of the distance to your windshield by now. The air bag deploys as molecules of air rush from their high-pressure canister to fill it. As the bag hits its most pressurized point, your car is coming to a stop as its kinetic energy is combined with energy from the other object.

[schiffern]

Beautiful. A small correction – most airbags use pyrotechnic inflators, not compressed air.

Sidenote about airbags: they have to be folded to fit inside their module, so as it inflates it's also unfolding. In order to make sure it unfolds properly they coat it in a lubricant that can't evaporate – either talcum powder or cornstarch depending on the vehicle.

I learned this only after I scrambled out of the car my sister put in a ditch thinking it was on fire. The best part? It was a diesel car.

Who knows, maybe the engineers consider it a feature because after an accident it sure gets people out of the car quick!

[Swizec]

Most beautiful explanation of anything involving physics I have ever read.

[confluence]

Good god - you need to write books - or make movies :D.

Wonderful explanation.

[Pyrodogg]

I would venture to guess they're built to work both ways. If the computer has sufficient time and information to make the decision it releases the panels. Ex. Engine failed, shut it down, blow panel as precaution to drop pressure in that engine compartment.

They're also most likely built as the designated point of failure, like a safety valve on a boiler. If the pressure builds too high they are blown out by the pressure. Ex. engine goes critical and explodes before computer can react, the panels fail before other structural components do.

[schiffern]

They said "ejected", not "jettisoned". You can be 'ejected' from a vehicle if you're not wearing your seatbelt, so the word doesn't require active response.