Mythbusters Explosive Decompression Experiment

On Mon, 12 Jan 2004 23:37:03 -0800 "C J Campbell" wrote:


"R.Hubbell" wrote in message
...
| On Sun, 11 Jan 2004 21:13:28 -0800 "C J Campbell"
wrote:
|
| Now, that was cool!
|
| Mythbusters pressurized an old DC-9 and fired a bullet through the wall
to
| see if it would cause an explosive decompression. It didn't. Then they
fired
| a bullet through the window to see if the window would shatter and cause
an
| explosive decompression. The bullet only made a small hole in the window
| because the windows are made of shatter-proof plastic. No explosive
| decompression.
|
| I don't watch much TV but I admit I would have liked to have seen this.
|
| Can you provide more detail on how they setup the test?

They took a derelict DC-9 at an aircraft graveyard and plugged up the holes.
They had real trouble with the cockpit because the windows had been removed.
They tried to replace the windows with plywood cemented in with foam, but
the plywood proved to not be strong enough to allow pressurization of the
aircraft. It kept blowing out, sometimes spectacularly.

The pistol was mounted on a stand in the cabin and fired by remote control
using a servor cannibalized from a vending machine, of all things. The
handgun was a 9 mm automatic; it looked like a Glock.

The aircraft was pressurized using one of those giant ground starter units
designed for 747s, a huffer. They dumped huge sacks full of packing peanuts,
scattering them around the cabin to so that the airflow inside the cabin
would be visible. The bullet holes disturbed the airflow so little that even
the packing peanuts stayed where they were.

|
| What was the cabin pressure? What was the pressure external to the
| DC-9? Did they have a huge pressure chamber?

They calculated the pressure differential at 35,000 feet to be 8 lbs psi, so
they pressurized the interior to 8 lbs psi. As mentioned, they had trouble
doing this. The plywood in the cockpit could only stand about 6 lbs psi. At
one point the plywood blew out and ejected a cushion from the pilot seat
more than 125 yards. They finally ended up reinforcing it enough to
withstand the 8 lbs psi differential. I guess the lesson there is that if
you ever lose a cockpit window you can forget about restoring cabin pressure
by plugging it up with plywood.

|
| What about the temperature differentials? There's also a pressure
| differential from the flow of air over the fuselage. Correct?
| How did they simulate that?

The 8 lbs psi differential comes pretty close to the pressure differential
for an aircraft pressurized to 6,500 feet flying at 35,000 feet. After all,
the total weight of the entire atmosphere is only 15 lbs psi. If anything,
they erred on the side of increased pressure differential. A pound of air
psi is a pound of air psi, no matter what the source.

One thing I found interesting which they did not talk about was watching the
skin of the airplane inflate and become taught as the airplane was
pressurized.



That brings up another question (don't have to answer, just food for thought)
How many pressurization cycles did the DC-9 experience over its lifespan?




Once they managed to induce an explosive decompression using the shaped
charge, the damage was incredible. The whole top of the fuselage was ripped
off and big chunks of the wall where the explosion was were missing. It
looked like those photos of the Hawaiian Airlines incident, only much worse.
I think it might have been possible to continue to fly the aircraft, but it
would have been very difficult, depending on how much damage the debris did
to wings, tail, engines and control surfaces.

Of course, to do that kind of damage a terrorist would have to somehow get a
shaped charge the size of a basketball onto the airplane, place it properly
up against the wall of the fuselage, and detonate it, all without being
noticed. In any event, a bullet will not do that kind of damage, unless the
bullet is some kind of anti-tank artillery round. It was obvious that any
handgun bullet is too small by several orders of magnitude to do any
significant damage. You could have pressurized that plane for space flight
and the result would have been the same. Well, no it wouldn't. That much
pressure would have started popping windows or something long before they
would have had a chance to fire their gun or set off their explosives. But a
bullet hole would not have made a measurable difference even then.




They did a reasonable job of recreating the environment but we all know
how hostile things are at 35,000 and 600 mph and -35 degrees, where air is
less dense.


So the question is would any of us be willing to head up to 35,000, crank her
up to mach .76 and get out the Glock and let loose a few rounds??

Also suppose the bullet hits some wiring or hydraulics or fuel line, etc.


Not me.


R. Hubbell