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Airliner Decompression Question

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posted on Sep, 8 2005 @ 05:54 PM
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We've all seen movies where an airliner has a structural failure of some sort - bombs, whatever - and sudden decompression occurs.

The part that amazes me is the long period of time that air is escaping from the fuselage.
With a hole big enough to allow a person to fall out or be sucked out, it seems the internal fuselage pressure would stabilize with the external atmospheric pressure at that altitude in just a second or two.

I can envision a venturi like effect from 500 mph + winds flowing by the hole in the fuselage, but there would have to be a commensurately large open area to allow make-up air into the fuselage.
The real danger would be in getting too close to the opening.

Any airliner personnel on here that could comment?




posted on Sep, 8 2005 @ 06:35 PM
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I'm working on pilot but I know a few things about decompression and such.

A couple of things act on the air inside the aircraft.

Bernoulli's Principle (I believe) is that more speed =less pressure. Also the (high) concentration of air within the plane will go out into the (low) concentration of air outside the plane, which is the actual decompression. However the actua high speed of movement of the plane simulates even less pressure outside the plane. Also air will be forced into the plane by irregularities on the structure, which makes heavy turbulence behind the rupture in the structure of the aircraft, so anyone right behind the rupture in the plane will basically feel a wall of air hitting them. Only the actual decompression will end, but the turbulence caused by the MOVEMENT of the plane is continual, and since air is rushing in air is displaced and blah blah blah meaning that the entire plane will be really really turbulent no matter where the hole is.

I would ask a real physicist about this.



posted on Sep, 8 2005 @ 07:49 PM
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Originally posted by Desert Dawg
I can envision a venturi like effect from 500 mph + winds flowing by the hole in the fuselage, but there would have to be a commensurately large open area to allow make-up air into the fuselage.



I thought that the pressurized air would be forced out of the fuselage and stop when the pressure equalizes, i never heard of make up air



posted on Sep, 8 2005 @ 08:39 PM
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The pressure would be gone almost instantly, there is no real suction as evidence by that aloha air flight that lost the entire top to the plane, just 1 unsecured flight attendant fell out.



posted on Sep, 9 2005 @ 12:37 AM
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ya, thats in movies. If the top rips off it will get real windy, imagine sticking your head out of the car when driving 70. now times that by 5 ; )



posted on Sep, 9 2005 @ 09:10 AM
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I thought that the pressurized air would be forced out of the fuselage and stop when the pressure equalizes, i never heard of make up air



I should have explained it further.
If air is still flowing out of the aircraft due to a low pressure area at the hole in the fuselage it has to come from somewhere.
Since commercial airliners are well sealed, there would have to be an opening somewhat commensurate with the size of the hole in the fuselage.

One small, but interesting bit along these lines is the small frame-less hinged window cut into the side window of most of the low wing Piper single engine airplanes.
It opens easily at flight speeds of 100 mph or so.
Sticking your fingers out of the small opening - about 4 x 6", the 6" being on the horizontal - you can feel the boundary layer, laminar airflow, whatever you want to call it passing by.
Further out your fingers go, the stronger the airflow - obvious, I know, but it is indicative of airflow at high speeds.

Anyway, the little hinged window - that seats into a routed out opening and fits flush due to it's 45 or so degree outer edges and the matching angled opening in the side window - does have a latch, but airflow keeps it shut with no problems.
There is a slight resistance when it's cracked open and that's due to the high pressure area on the inside of the fuselage trying to keep the window closed.

There is no turbulence near the window and instead of admitting vent air as it would appear, what's happening is the opening is pulling in "make-up" air from the not completely sealed fuselage area and exhausting it through the vent window.
All of which shows a low pressure area outside the aircraft and a high pressure area within although the pressure differentials are quite low.


Interestingly, somewhat the opposite happens with my 32 Ford roadster.
No fenders, hot rod engine etc.

When the top is on, a low pressure area is created within the cockpit area and air will bleed in through the gaps in the doors.
The air is hot due to the hood side panels are louvered and the hot engine compartment air is exhausted into the airflow along the car's body and when it hits the low pressure area at the front and rear door gaps it get's sucked into the interior.
The temperature differentials between ambient and hot engine air are usually around 15-20 degrees F., and on very hot days it may run as high as 30 degrees F. different.

Granted, completely backward from the aircraft scenario, but interesting nevertheless.
The difference is probably due to the large side window openings and small ingress areas at the door gaps as well as the large speed differential between a roadster running 70 mph and an airliner traveling 500 mph +.

As a small side note, the definition of a true roadster is, folding windshield, soft top and no roll-up windows.



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