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Carlos- I've been thinking about the full tanks in airplanes thing a bit more and I have a few remarks to add to what I said last night (while under the influence of, perhaps, one NyQuil too many - I've got a rotten cold right now). BTW -The question about the cargo bay being pressurized or not usually buggs me about as much as the one that we've all heard from non-divers "How long can you stay underwater with those OXYGEN tanks on your back?". (We all know, the O2 tank is more properly carried as a stage bottle...) First (before somebody jumps on me about it) I should have said that the cargo bays on all JET AIRLINERS are pressurized. A lot of light & medium twins (and maybe some turboprops as well) have unpressurized cargo compartments in the wing nacelles (behind the engines) and in the nose. Second thing is that a jet airliner is NOT airtight, as most people seem to think. They leak all over the place where control cables, hydraulic lines, wire bundles and the like exit the pressure hull to go out into the nose, wings and tail. That's OK - there's just no point in trying to make those places 100% airtight. Bleed air from the first stage engine compressors (of which there is plenty) is ducted through the A/C pacs (to get heated, cooled or whatever) and then into the cabin. By pumping it in faster than it runs out, they maintain cabin (and cargo bay) pressurization. Automatic outflow valves blow off excess pressure to maintain the cabin altitude selected by the guys in the pointy end, usually equivalent to about 8000 ft while at cruise altitude. OK- now to the point. A typical jetliner that you might fly into an island (diving) destination is about 150 - 175 ft long (727, DC-9, etc). Lets say that the pressurized portion of that length is about 125 ft. I seem to remember the fuselage diameter of a 727 (also 737 & 757) being about 12 ft. The volume of that tube (Pi x R squared x Length) would be roughly 14,000 cubic feet. The volume of air in , say, an '80 is roughly half of one percent of that. Not enough to cause the plane to blow up, even if it was all let out at once! I'm not even sure if your ears would pop. But, as we both know, the noise and commotion in the cargo bay (right under everybody's feet) could be pretty awesome! Like I said last night - I don't think the airplane would be damaged structurally, but much lesser things HAVE caused crashes - remember the EAL L1011 that plowed into the Everglades because of the distraction created by one lousey burned out lightbulb in the cockpit? I don't blame the airlines one bit for being chicken-shit about full tanks! PS- For anybody who has never heard one go off, when the safety blew on that tank in the filling trough, we were all CERTAIN that a tank had exploded. It's that loud! Oh well, I guess I've beaten this to death. Good Diving; Ray At 02:38 PM 4/19/96 -0300, you wrote: >Ray, > >Thank you for your detailed explanation. I knew there had to be a reason, but >I couldn't figure it out by myself. > >Come to think of it, I too was in a dive shop once when a burst disk blew. And >yes, the room cleared quite quickly. > >My tanks are filled, and I'd go diving if a storm hadn't blown my plans higher >than your ejection seat. > >Cheers, > >Carlos 8^) > > >>OK, Stupid- >> >>Here's the deal. The cargo bay on EVERY pressurized aircraft IS pressurized! >>Think about it - what shape do those long, skinny baloons take on when >>inflated. It's a round tube, right? Why? 'Cause if you wanted that round >>tube to have one flat side, you'd have to make that one side a LOT stronger >>(and heavier) than the rest of the baloon. What shape is an airliner? Right >>- a long tube. Wanna guess why? How strong and heavy would the (flat) floor >>structure have to be to withstand the loads of pressurization? A LOT! >> >>I'm a mechanical engineer (and pilot)who spent 4 years working at Boeing (on >>757, 737-300, 727 and -just a little -767). The airlines and aircraft >>manufacturers will spend a fortune to get every ounce out of an airframe >>design. Just think about how much it costs in fuel to haul even 1 extra lb >>of weight around over the lifetime of an airliner (as opposed to the profit >>generated by 1 more lb of payload). >> >>As to the thing about one extra bar of pressurization in the tanks - I >>agree, except for one thing...I remember being in my favorite dive shop one >>Friday night (many years ago..) when the safety blew on somebody's tank that >>was being filled. A crowded dive shop emptied instantly (as did the filling >>trough). You never heard such a noise in your life! I think if that happened >>to and airplane that I was flying on, I would instantly turn seat 16A (or >>whatever) into an ejection seat - powered by a stream of shit!. And I think >>I would have a hundred or so people ejecting ahead of me.The aircraft, >>however, probably would not be damaged...the airlines are just poor sports >>who consider this sort of thing unacceptable - THAT'S WHY THE MAKE YOU EMPTY >>YOUR TANKS!
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