physics of an aeroplane crash

Originally posted by humy
Arr but you have to compare the danger of giving the passengers parachutes while the plane is spinning out of control towards the ground with the danger of not giving the passengers parachutes while the plane is spinning out of control towards the ground -both options are extremely dangerous, yes, but the question is which of the two options is generally ...[text shortened]... killed as a result, only to find he then lands the plane perfectly safely. That would be tragic.

If an airliner gets into a tail spin, or anything similar, it will start to disintegrate in the air, the structure simply cannot withstand that kind of treatment. Parachutes under those circumstances would be irrelevant. The plane would fall apart in the sky before anyone had a chance to put them on.

If the plane has control problems, but is flying straight and level and assuming the engines and wings aren't going to pose a hazard to the passengers there is also the minor inconvenience of the lack of air pressure at 10,000 feet. As well as the difficulty of getting out of something that is moving that fast.

Also, consider the Air France flight where the co-pilot managed to stall the plane (a bad enough stall is non-recoverable in an airliner). Even then it's doubtful the passengers would have survived parachuting into the sea.

The odds are more like a million to one against compared with a million to one against. Parachuting from airliners is only an option in action movies. If there were any safety advantage to parachutes the airlines would provide them.

Originally posted by googlefudge
Maybe something made out of graphene might be strong/light enough...

But I doubt the extra reinforcing of the aircraft would be worthwhile.

The size of the parachute[s] needed to support a 50~60 ton jet-liner
for a survivable landing [one where you escape with minor bone fractures]
is pretty large, and the odds of such a system actually working ...[text shortened]... he said airliner to plunge uncontrollably
out of the sky.... let's just say they are not good.

Hmm...

Escape pods?

Tractor beams?

Inertial dampeners?

Heisenberg compensators?

This is the Science Forum. Surely any problem can be solved!

Originally posted by DeepThought
If an airliner gets into a tail spin, or anything similar, it will start to disintegrate in the air, the structure simply cannot withstand that kind of treatment. Parachutes under those circumstances would be irrelevant. The plane would fall apart in the sky before anyone had a chance to put them on.

If the plane has control problems, but is flying ...[text shortened]... ction movies. If there were any safety advantage to parachutes the airlines would provide them.

I shouldn't have said tailspin in my earlier post. I almost didn't, but then hit submit. I think most jumbo jets, when they go down, tend to go down in a straight line. Some poindexter here probably has the stats at his (or her) fingertips.

Originally posted by Soothfast
I shouldn't have said tailspin in my earlier post. I almost didn't, but then hit submit. I think most jumbo jets, when they go down, tend to go down in a straight line. Some poindexter here probably has the stats at his (or her) fingertips.

I think Duchess's was the first post mentioning a spin, probably as a rhetorical flourish. But the concept seemed to have taken root and was being left unchallenged. There's airliners that have disintegrated in flight, most famously the de Havilland Comet before they worked out that square windows were a bad idea.

I've no idea what the statistics are for how they come down, it depends on what goes wrong. If there's a sudden depressurisation then complete airframe failure is a possibility. With something like a shootdown that can happen, but isn't inevitable - Korean Airlines flight 007, which strayed into Soviet airspace in 1983 and was shot down, remained intact until impact. I've an idea it depends on if the damage is at the front or the back of the plane, there was a flight where the entire forward section of the plane fell off due to a tear developing (I don't know the flight number, this is from a documentary I saw 20 odd years ago) leaving the nose cone plummeting towards the sea and the rest of the plane in a steep climb, which then stalled and went down. In Air France flight 447, the one I mentioned in my previous post, the plane will have been in one piece until it hit the Atlantic ocean.

It's not all doom and gloom, there have been incidents where the pilots have lost all flight control and managed to bring the plane down using differential thrust and saved some or all of the people on board.

http://en.wikipedia.org/wiki/Flight_with_disabled_controls

Originally posted by robbie carrobie
why does everything get pulverised when an aeroplane crashes? Is it a transference of energy when the aeroplane meets something more dense than itself, like a mountain or a tall building? Can anyone explain it in really clear and simple terms? Also why can aircraft flight not be made more safe as in providing parachutes for passengers or protective airbags that go off on impact?

A plane is heavy and moving quickly, so it has a lot of kinetic energy. Upon impact, the plane comes to a halt, and the kinetic energy has to go somewhere. The density of the impact material is not important in this picture unless the impact site has such a low density that the airplane can come to a halt gradually.

Originally posted by FabianFnas
Doesn't the same happen to cars? When a car with a speed of an aeroplane hits a cliff, it just smashes out of any recognition. The only difference is that the velocity is much less.

Protective airbags in a aeroplane? Well, do you have airbags in the backseat of a car? In an aeroplane every seat is a backseat, with the possible exception of the pilots.

yes i believe it is the same, but i was wondering why, i'll read on before i comment further, nice to here from you Fabian. I fear you may be washed upon the shore of Gothenberg after an absence of some years when a shadowy figure in a black approaches you while you are working out your variations and say,

Vem är du? and he says : Jag är döden😵

The post that was quoted here has been removed

you would not need to give training if they were ejector seats, simply strap the passenger in and if the aeroplane was in difficulty the entire fuselage could by jettisoned and the passengers and cabin crew ejected safely.

Originally posted by Soothfast
Hey, how about a big parachute that opens up for the whole aircraft itself? Kind of like drag race parachutes. Almost like this...

http://en.wikipedia.org/wiki/Drogue_parachute

...but the difference would be that the parachute would be deployed in the air when all hope of regaining control of the aircraft is lost, rather than to facilitate a "nice" landing.

yes with the idea of slowing it down on impact. This would be fine if you had somewhere relatively flat but as googlefudge intimated aeroplanes are made of relatively soft material.

Originally posted by KazetNagorra
A plane is heavy and moving quickly, so it has a lot of kinetic energy. Upon impact, the plane comes to a halt, and the kinetic energy has to go somewhere. The density of the impact material is not important in this picture unless the impact site has such a low density that the airplane can come to a halt gradually.

Thank you, so where does this energy go, does it get absorbed into the mountain, or does it simply dissipate on impact?

Originally posted by robbie carrobie
you would not need to give training if they were ejector seats, simply strap the passenger in and if the aeroplane was in difficulty the entire fuselage could by jettisoned and the passengers and cabin crew ejected safely.

So the pilot presses a button, and the wings with their dangerous fuel tanks and engines drop of, then the fuselage breaks into passenger size sections (or larger) each with its own parachute.
Would look good in a movie, but not practical in real life.
One of the biggest problems with the whole parachute idea is that by the time the decision is made that parachuting is the only option, the aircraft is already too low for parachuting to be a viable option.
Most serious plane crashes involve:
- Mid air explosions / collisions (parachutes useless).
- Nose dives (parachutes useless).
- Unexpected collision with a mountain (parachutes useless).
- Incapacitation of the crew (parachutes practically useless).

Generally, if the crew still has enough control of the aircraft to allow passengers to put on parachutes, then there is still a good chance that a landing is the best option.

Originally posted by twhitehead
So the pilot presses a button, and the wings with their dangerous fuel tanks and engines drop of, then the fuselage breaks into passenger size sections (or larger) each with its own parachute.
Would look good in a movie, but not practical in real life.
One of the biggest problems with the whole parachute idea is that by the time the decision is made tha ...[text shortened]... ngers to put on parachutes, then there is still a good chance that a landing is the best option.

no just the top of the fuselage you silly man! who said anything about the wings falling off?

Originally posted by robbie carrobie
yes i believe it is the same, but i was wondering why, i'll read on before i comment further, nice to here from you Fabian. I fear you may be washed upon the shore of Gothenberg after an absence of some years when a shadowy figure in a black approaches you while you are working out your variations and say,

Vem är du? and he says : Jag är döden😵

I'm still alive and kicking. I've not met the chessplayer you mentioned, not yet. 🙂
I go in cycles. Some times I debate a lot, other times I seem to be gone to the other side.
Thank you, my friend, for caring!

The post that was quoted here has been removed

OK, not literally "spinning" out of control then; just merely loosing altitude in a SOS kind of emergency. "spinning" was totally the wrong word.

Originally posted by FabianFnas
I'm still alive and kicking. I've not met the chessplayer you mentioned, not yet. 🙂
I go in cycles. Some times I debate a lot, other times I seem to be gone to the other side.
Thank you, my friend, for caring!

Great power moves in cycles - native american saying 😀

Originally posted by robbie carrobie
who said anything about the wings falling off?

I did. It was my idea you silly man.