Mythbusters Explosive Decompression Experiment

Bob Gardner wrote:
The speed of the airplane at altitude has nothing to do with it. The
pressure differential between the cabin and the great outdoors is the only
factor...airspeed does not exert any pressure on the sides of the fuselage.

Bob Gardner



Well, yes and no.

It depends on the shape of the hole and its placement relative to the
geometry of the fuselage (that is: relative to the apparent air flow).
With speed, the hole may assist adding pressure (as does a
forward-pointing pitot tube) or it may assist depressuring, due to
Bernoulli effect, (as demonstrated by a household-plumbing vent-stack in
a strong wind).

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?

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

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?


R. Hubbell


Then Mythbusters put explosive all around the window to blow it out and
deliberately cause an explosive decompression. The crash test dummy,
"Buster," was damaged but was not sucked out the window. If he had been a
real person he would have been injured but probably lived. His arm was badly
damaged enough that a human arm might have been lost. So Mythbusters patched
everything up and used a shaped charge to blow out the whole wall. The
explosive decompression ripped the entire top off the fuselage and much of
the wall out, but the seats and the crash test dummy remained in the
airplane. I would guess that if the "Buster" had been a live human he would
have been seriously injured and possibly killed.

Mythbusters then talked about how strong these airplanes really are and
closed with photos of the Hawaiian Airlines plane that suffered an explosive
decompression similar to the one that the show created with a shaped charge.
The only person killed was a flight attendant who was pulled from the plane
by the airstream, but the passengers all survived.

I thought the show was fascinating. It really demonstrated the engineering
that goes into an airliner. Besides, I like watching things blow up. It must
appeal to my inner 12 year old.

--
Christopher J. Campbell
World Famous Flight Instructor
Port Orchard, WA


If you go around beating the Bush, don't complain if you rile the animals.

On Mon, 12 Jan 2004 08:26:04 -0500 "Dennis O'Connor" wrote:

Neonates do die, fortunately not with great frequency... As a working doc I
immediately wondered about Caisson Disease from the rapid decompression,
when I read your posting... The fetus is normally well protected and
buffered by the body of the mother for trauma like that... And, the total
psi/bar drop in that form of decompression is minor compared to divers, et.
al., however the rate of change of the decompression is far more
instantaneous than for caisson workers and divers, so if it was Caisson
Disease the rate of change had to be the key..


If that were true others on board would also have suffered from "the bends".
If the mother was severly traumatized (and who wouldn't have been) then
that could easily have caused complications. Sever emotional trauma sets
off a chain reaction of chemical events in the body. They are designed
to protect but it could have been too stressful for the baby.


R. Hubbell


Denny
"David Brooks"
However, at one of the passengers soon after gave birth to a little girl
who
died a day later. There was no particular pathology. Milagro they called
her. She was my sister-in-law's niece.

"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.

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.

In article qmHMb.35613$nt4.69560@attbi_s51,
Bob Gardner wrote:
The speed of the airplane at altitude has nothing to do with it.

I don't know, have you ever used an aspriator? It uses the Bernoulli
principle to create suction by passing a jet of water by a hole. Used
to use them all the time in chemistry class. I would think the slipstream
by a hole in an airplane would be the same as being in a much lower
static pressure environment.

--
Ben Jackson

http://www.ben.com/

"Bob Gardner" wrote in message news:qmHMb.35613$nt4.69560@attbi_s51...
The speed of the airplane at altitude has nothing to do with it. The
pressure differential between the cabin and the great outdoors is the only
factor...airspeed does not exert any pressure on the sides of the fuselage.

Bob Gardner

My point was that the explosion *could* cause other damage which
*could* bring the airliner down (the Souix City Iowa crash of a United
DC-10 for example). In the case of the MB episode, they wanted to see
IF a decompression could bring down an airliner. Well, the last
explosion was large enough to cause a very rapid decompression,
however with the plane sitting on the ground that's ALL that occured.
If the aircraft was in flight you might have ruptured hydraulic lines,
fuel lines, airframe damage and the large hole in the fuselage that is
causing a lot of drag. All these factors would increase the origional
damage in a more serious emergancy.

So, if the MB'ers were ONLY trying to prove they could cause a rapid
decompression then the speed of the airliner in flight is not a
factor. However if the goal was to see if a rapid decompression could
cause an airliner to crash, then you have a lot more factors to
consider than the initial incident.

I really like MB as a show however it's chewing gum for the mind. I
feel their attempts at trying to prove or disaprive a myth is far from
the final word. I'm sure everyone in the scientific community likes to
tune in each week and laugh at their methods.

"Bob Gardner" writes:

The speed of the airplane at altitude has nothing to do with it. The
pressure differential between the cabin and the great outdoors is the only
factor...airspeed does not exert any pressure on the sides of the fuselage.

So...it doesn't matter where one places the static port?

--kyler

"Kyler Laird" wrote in message
...
| "Bob Gardner" writes:
|
| The speed of the airplane at altitude has nothing to do with it. The
| pressure differential between the cabin and the great outdoors is the
only
| factor...airspeed does not exert any pressure on the sides of the
fuselage.
|
| So...it doesn't matter where one places the static port?

I have seen static ports located just about everywhere on fuselages. It
probably does not matter much as long as it is on the side of the fuselage.
If there really was a big pressure difference due to the slipstream on the
fuselage then most static ports would be located toward the aft end, because
the biggest low pressure area would be towards the front, just like a wing.
It appears that the biggest factor in locating the static port is
convenience of plumbing the static lines.

A couple of notes/questions...

Given that it is fairly rare for someone to only fire a single shot under
these circumstances, shouldn't the effect of the typical three shots have
been considered? While a single shot to the window only created a single
hole, would it not be possible for three shots into that same window to
compromise the window structure resulting in the entire window failing and
coming out of the aircraft?

I'm not an engineer so please forgive me if this next is in the "duuuhh"
category. Assuming a breach the size of a window in an aircraft in flight,
would not some type of "siphon" (or whatever) effect occur from the movement
of air across the fuselage, which would further remove air/people/etc from
inside the fuselage?

Those were just a couple of things I thought of while watching the
demonstration...



"Nomen Nescio" ] wrote in message
...
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From: "R.Hubbell"

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?


R. Hubbell

I wouldn't think that the airflow would make a significant difference. But
the temp. difference?
You hit on an area that I was wondering about myself. It was done at
ambient(maybe 60 -
80 deg.F). The properties of materials certainly can change at -60 deg F.


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(Ben Jackson) wrote in message news:DYQMb.41817$5V2.62520@attbi_s53...
In article qmHMb.35613$nt4.69560@attbi_s51,
Bob Gardner wrote:
The speed of the airplane at altitude has nothing to do with it.

I don't know, have you ever used an aspriator? It uses the Bernoulli
principle to create suction by passing a jet of water by a hole. Used
to use them all the time in chemistry class. I would think the slipstream
by a hole in an airplane would be the same as being in a much lower
static pressure environment.

I don't think that would make a great deal of difference, assuming the
hole isn't forward facing as Icebound points out.

The moving air over the hole would certainly create a pressure
differential between the inside of the tube and the outside air, as
you say, but I would expect the additional increase in pressure
differential created as a result to be negligible compared with the
huge delta caused by a pressurised cabin.

There must be math for calculating the pressure drop across a hole
(it's just a venturi isn't it?) in a surface in a moving stream of air
at a given velocity. The size of the hole is definitely a factor;
smaller the better if I remember correctly, and no real effect above a
certain size.

What may be more relevant to causing general chaos in the cabin is the
high-velocity air entering the cabin through the hole once the
pressure is equalized.

Regards,

Tim Kemp