Planes with holes in them


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Cosmoline
June 24, 2003, 03:35 PM
Does everyone realize that a pressurized jet is actually leaking air out of multiple holes? I just recently learned this. If added up, my guess is they'd be a lot bigger than a .45" hole. The pressurization system simply pumps more air in than leaves, and can compensate for all sorts of problems short of having a massive part of the hull removed.

So, would a bullet hole through the hull of a plane really cause massive decompression and/or passengers getting sucked out? And if not, why can't we start flying with CCW's?

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Mike Irwin
June 24, 2003, 03:43 PM
Yes. There are no perfectly sealed aircraft.

No, massive decompression is not something that's going to suck someone out through a .45 caliber hole in the skin of the aircraft.

Beats me.

4v50 Gary
June 24, 2003, 03:47 PM
It's not the decompression that will bring a plane down. The only known incident of a person being "blown" out of the plane was the James Bond flick.

The real threat of a wayward bullet is damage to the hydraulics. From sleek jet to plodding brick with wings.

Pilgrim
June 24, 2003, 03:47 PM
You are quite right that aircraft are quite leaky. You are also quite right that a bullet hole will not cause explosive decompression. However, a bullet hole in the right place can take out a hydraulic system or destroy an engine due to foreign object damage, i.e. a bullet going down the intake.

Several years ago a 737 over Hawaii lost a good portion of the "roof" while at altitude. Some people were lost because they weren't strapped into their seats, but that was more a result of a 400 mph windstorm blowing through the cabin than explosive decompression.

Pilgrim

Bobarino
June 24, 2003, 03:54 PM
while i'm not a commercial pilot, i am a pilot and have read oodles of books on aircraft systems and talked to lots of A&P's for the majors and the little guys and there is just simply no truth to the decompression myth. the plane is pressurized by bypass air from the turbine compressors. there is a valve (or several) called a Bleed Air Valve that lets air out of the cabin and regulates the the pressrue contained in the cabin. is is constantly opening and closing to regulate cabin pressure. cabin pressure is not regulated by squeezing more air in, rather it is regulated by letting pressurized air out. cabin pressure only gets raised about 6-8 PSI durring flight. if someone shot through the skin of the plane, or even shot several holes through the skin, the bleed air valve would close a little and thats all that would happen. planes are not airtight in the first place and they are not meant to be.

so everyone that fears the the dramatic depressurization can rest easy. i suppose if someone were to fracture a stuctural member of the plane witha bullet it could fall apart, but the stucture of a plane is beefier than one might think. a .45 will probably not do it much harm.

Bobby

Bobarino
June 24, 2003, 03:58 PM
one more point. you can shoot a plane in the hydraulic system, electrical system, or any number of other systems and the plane will still be flyable. commercial planes especially, have redundant systems. and those systems have redunant systems. and those systems have back ups. shooting a hydraulic hose will only cause a valve to close and a bypass valve to open. you would really have to let 'er rip inside a plane with an M60 and few hundred rounds to REALLY make a plane unflyable. the weakest link in the chain is the fragility of the pilot(s).

Bobby

Mike Irwin
June 24, 2003, 04:43 PM
Even multiple redundant systems can be disabled, though.

The DC-10 that crashed in Sioux City, Iowa, in 1989 is an example of that.

The tail engine compressor fan disintegrated, sliced through the main, reserve, and emergency hydraulic lines and drained the entire hydraulic system in about 2 minutes.

The incredible thing about that crash is that almost 2/3rds of the people survived. The crew was able to get the thing on the ground in a semi-controlled fashion, steering the entire aircraft using the throttle controls.

They were actually in line for a pretty good belly-flop landing, but IIRC they were hit with a wind gust from which they couldn't recover.

Apparently later simulator tests, designed to recreate the situation facing the crew, pointed at one conclusion -- it was impossible for the crew to fly the aircraft.

bogie
June 24, 2003, 04:47 PM
I've got a buddy who has a Cessena 182 (small single engine airplane).

He lost a door hinge. Didn't ask him about bowel control.

He's still around, so's the plane, and the door stays on.

MrAcheson
June 24, 2003, 04:57 PM
During the Aloha Airlines flight a stewardess was sucked/blown out when most of the ceiling tore away from the aircraft. However that was from severe structural metal fatigue, not a bullet. Likewise I believe a 747 lost some people because of the sudden fusilage rupture when a cargo door opened in flight.

Commercial planes have many redundant systems, but they are often co-located for maintenance purposes. A single bullet/fragment might be able to take out a bunch of hydraulic lines because they are all strung next to each other. Commerical aircraft are not designed to be shot at from without or within.

Also, if an engine fails critically enough, they can spit fragments and destroy important things. This isn't so important on wing mounted engines, but this is what brought down that DC10 in the 80s. I believe the tail engine compressor failed critically and severed all the hydraulic lines.

Fly320s
June 24, 2003, 05:22 PM
A couple of corrections, if I may...

there is a valve (or several) called a Bleed Air Valve that lets air out of the cabin and regulates the the pressrue contained in the cabin.
The Bleed Air Valve regultes the bleed air from the engine to the air conditioning/pressurization system. The outflow valve is what lets the conditioned air leave the cabin. Actually, the outflow valve is more like a door. The one's I've seen are about 6 x 6 inches. Most aircraft have two or more of them.

The hydraulic lines in DC10's were rerouted in the tail area. Now, all three lines don't pass through the same area next to each other so a similar incident won't happen again. I know, there are no absolutes but the odds are decreased.
Likewise I believe a 747 lost some people because of the sudden fusilage rupture when a cargo door opened in flight.
Yep, I think that was United, but I'm not sure. When the cargo door let go it took part of the passenger flooring with it along with some passengers. There were people sitting in seats directly next to the opening who remained there during the entire descent and landing.

Art Eatman
June 24, 2003, 07:45 PM
And if you lose the rudder controls on a single-engine Cessna, you can still turn the airplane by banking and opening the appropriate door. Left door for left turn, etc...

:), Art

amprecon
June 24, 2003, 09:00 PM
I am an A&P and Private Pilot working on instrument rating and inspection authorization. As previously stated, a single round from a handgun, if it did manage to breach the hull would not have any significant effect on the ability to fly the aircraft. Unless it damaged a vital component or non-vital component that by domino effect, affected a vital component.
The pressurization systems of aircraft in the large category, 12,500lbs and more, will not even notice a half-inch hole. Paper and light items like clothing might be sucked into the hole which would stop your leak, but that's it, maybe besides the hissing noise that might be heard. The air pumped in is necessary to produce the pressure, but it's the amount let out by the outflow valves, which in turn is controlled by the pressure regulator managed by the flight crew, which controls the amount of pressure in the cabin, hence the amount of oxygen.
Since a Cessna 182 doesn't normally have a pressurization system, it can be flown with both doors off and it won't affect the flight characteristics of the aircraft, just a little more breezy. Those types of aircraft normally fly below 10,000ft agl anyway where pressurization isn't necessary because of sufficient percentage of oxygen at that flight level.
Hope this helps.

TangoRomeo
June 24, 2003, 09:27 PM
rotflmao!!!!!!

Sorry Art. But I suddenly got this vivid picture in my mind's eye of an instructor trying to teach your technique to a new student.

Instructor- "OK, that looks pretty good; maybe just a little less aileron and a little more left door."

Student (with look of terror)- "OK sir, give me a second while I make sure my seatbelt is tight.:what: :D

WT
June 24, 2003, 10:05 PM
There was a DC-10 that crashed near Paris after the cargo door blew out. All aboard were killed.

In 1972 a second DC-10 (American Airlines) also lost its cargo hatch but managed to land safely at Detroit Airport.

BenW
June 24, 2003, 11:11 PM
The DC-10 that crashed in Sioux City, Iowa, in 1989 is an example of that.
I went to a talk by CAPT Hayes of that flight last month. Apparently the reason they lost all hydraulics is because the secondary and tertiary systems were routed right next to the primary, so all three systems were toasted in the same hit.

That flight was a great example of dealing with the "impossible." Seeing the after-crash images, it was amazing that people, especially the cockpit crew, survived.

M2 Carbine
June 25, 2003, 12:58 AM
This would be a big bullet hole.
It's a hole about the size of a 50 cent piece in the turbine engine compressor of the Bell 407 I was flying.
It just kept on running for about a half hour until I got to the base.

http://www.imagestation.com/picture/sraid67/p98b26bc40eca0d356aa6b83f3102b8b0/fbd7f07e.jpg

Autolite
June 25, 2003, 01:42 AM
Fly320s gave a pretty good description of how cabin pressurization is acheived. Many aircraft use engine bleed air directly for cabin pressurization but I think the larger airliners use the engine bleed air to drive a separate turbine/compressor unit meant just for cabin pressurization. Like Fly320s says, outflow valves are generally about the size of a large grapefruit however the emergency depressurization (dump valve) in a C130 is about the size of a garbage can lid. So the concept of a hole created by a single pistol round causing a massive depressurization is pretty much "blown out the window" ... :)

UnknownSailor
June 25, 2003, 01:43 AM
M2 Carbine

:what:

That is all.

Mike Irwin
June 25, 2003, 01:46 AM
Ben,

Yep, the designers never factored in a possible catastrophic rupture in the compressor fan.

M2 Carbine
June 25, 2003, 02:10 AM
Well UnknownSailor let's see.

I had a piston engine in a Bell G47 swallow a valve.
The clutch in a G47 fail about 175 foot on climb out. The engine went wide open. The tachometer needle ran out of numbers and was starting around the guage again.

In the Bell 206's I had several engine and tail rotor bearing failures. A jet engine bearing screams when it's failing.

A 206 engine sucked in a plate nut that ate up the compressor.

Several hydralic control failures. (I took off after hydralic failure one time. Not one of the smarter things I've ever done)

Numerous engine and transmission chip lights and other failures.

Every time, the bird ran long enough to make a more or less normal landing.

M2 Carbine
June 25, 2003, 08:26 AM
Art Eatman--"And if you lose the rudder controls on a single-engine Cessna, you can still turn the airplane by banking and opening the appropriate door. Left door for left turn, etc..."

, Art

Art you don't turn an airplane using the rudder.
To turn, you bank the airplane using the ailerons and adding a little up elevator.
The steeper the bank, the more up elevator.

The rudder is used to correct for the adverse yaw when using the ailerons.

As right aileron is applied the nose of the airplane will yaw to the left. Left aileron, right yaw.

Using rudder alone or too much rudder will cause the aircraft to skid.

dleong
June 25, 2003, 09:20 AM
One of the members of our local flying club is an engineer with a major airline based here in the midwest. He mentioned that it was not uncommon for their mechanics to find .22-sized bullet holes on the undersides of their aircraft.

DL

Nightfall
June 25, 2003, 09:26 AM
Welcome to THR, TangoRomeo. :)

Double Naught Spy
June 25, 2003, 09:31 AM
Just a couple of points: Yes, planes leak. They are designed that way. There is no attempt to actually have them air tight and those like airliners are designed with holes. If you ever watch programs about the weather and see the NOAA planes that fly through hurricanes, you will see the guys dropping sensors to measure conditions outside the plane such as barometric pressure. The crewman opens the lid to a tub, inserts the instrument, and it drops from the bottom of the plane. When the guy opens the tube, it is a direct link out. If the cabin was highly pressurized, the crewman would not be able to open the tube as he would be opening against the pressure. Well, aircraft are pressurised to no more than sea level and often not pressurised that much. Atmospheric pressure at sea level is 14.7 lbs per square inch. That is less than half of what most of us have in our car tires.

Another very significant point has already been touched on. That is, a breach of the airplane skin does not mean drastic events will necessarily befall the occupants inside. If airplanes were so fragile that a small hole, as from a handgun, would cause an explosive decompression, then planes would be crashing a lot more than they do. While not really common, holes occasionally to get in the skin from such things as hail.

Fly320s
June 25, 2003, 04:04 PM
To turn, you bank the airplane using the ailerons and adding a little up elevator.
Close, but no banana. Elevator is only required if you wish to maintain your altitude during the turn. I won't get into horizontal component of lift versus vertical component of lift since this is a gun forum.

It all boils down to this: one or two or a few more holes from small arms will not bring down an airline. The pressurization system will compensate for the new rate of 'leakage.'

Leatherneck
June 25, 2003, 04:10 PM
M2carbine:
Who does your maintenance, and have you considered firing them? :eek:

TC
TFL Survivor

Art Eatman
June 25, 2003, 05:11 PM
I din' wanna complicate my "open the door" deal with a full-blown explanation of how to make a turn...:)

I only have 300 hours in a 172, but I figured out how to keep the little ball centered. :D

FWIW, looking at the old log book, I soloed at eight hours...

:), Art

UnknownSailor
June 25, 2003, 07:45 PM
What Leatherneck said. :)

Interesting Bell 47 note: I drove by one a couple of weeks ago that had been re-engined with a turbine. It was fitted out for crop dusting. I did a double take when I heard that high pitched turbine whine coming from something that should sound like a steriod fed VW.

Art Eatman
June 25, 2003, 08:58 PM
UnknownSailor, did you ever hear the story of a Garrett test bed deal? They hung some sort of 400+ hp turbine onto a 182. Had oxygen. Went up to some 30,000 feet. Were spotted by some commercial transport pilot. I'm told part of the conversation from the airliner included, "One of us is really wrong!"

:), Art

M2 Carbine
June 25, 2003, 11:44 PM
fly320s quote
"Close, but no banana. Elevator is only required if you wish to maintain your altitude during the turn. I won't get into horizontal component of lift versus vertical component of lift since this is a gun forum."

Of course, this isn't the place for aviation ground school.

Leatherneck
It's not as bad as it sounds:)
I'm talking about 43 years of flying helicopters and airplanes.
In 23,000 flying hours I only had one complete engine failure.
I'm one lucky SOB.:D


Art,
It's fun "freezing" a control and seeing if you can get the airplane down.
You ought to see the ride to the ground with the helicopter pedals/tailrotor "frozen" in different positions:uhoh: (check ride requirement)
Good luck in your flying.

Sorry Cosmoline for getting so far off your subject.

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