Date: 06 Oct 97 02:14:23 From: Ken Rose <email@example.com> Organization: Netcom On-Line Services References: 1 2 3 4
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michael piersdorff wrote: > > Robert J. Montgomery wrote: > > Gerard Foley wrote: > > > There was usually a little bump upward in cabin pressure when > > > the doors were closed. > > > > Kind of a related question. I almost remember hearing, from some > > flight crew friend of mine, that most airlines actually decrease > > pressure prior to take-off. This way, they have to accelerate less > > mass during the takeoff process. Is this ever true? I've felt pressure > > changes in planes on the tarmac prior to takeoff (ear pop), but > > this may be caused by Gerry's pressure bump. > > 1. The total mass of air inside a 747 cannot amount to more than a few > kilograms - probably less than that of the airpump it would take to > remove it. On the contrary, the mass of air inside a 747 is substantial. If the fuselage is a cylinder 20 feet in diameter and 200 feet long (very rough, but in the ballpark), then it has a volume of (20/2)**2 * 3.14 * 200 = 62800 cubic feet. A cubic foot of air weighs roughly 1 ounce, so 62800cf of air weighs 3925 pounds, or about 1785kg. I think you probably could pump a lot of it out with a pump that weighs a lot less than that, but your other reasons for not doing it still apply.