Posted on 12/14/2001 1:32:12 PM PST by spycatcher
"...the chute bag".... This is a canvas bag which you jump into and ride down the chute.
...It is sewn, as in the diagram, so that the air pressure from falling inflates the sack causing it to seal the sides of the chute
You are not serious that you think a canvas bag is going to create a seal in the chute that will slow a body's decent as it approaches terminal velocity.
I'll say it again: hamburger.
I am absolutely serious, because I understand the physics involved.
The bag doesn't have to make a "seal", it only has to balloon out to fill a significant cross-section of the tube. At that point, the air resistance becomes huge, because unlike a body falling in open sky, the air being displaced by the falling body has nowhere to go except to try to squeeze past the remaining spaces between the bag and the tube walls.
To run some numbers, in an 18x24 inch tube, to fall 3 stories you have to displace 90 cubic feet of air. Even if the drop bag expanded to fit so loosely in the shaft that there was an inch of clearance all the way around it (between the bag and the tube walls), there would only be 0.58 square feet of area for the displaced air to squeeze by, while you and the bag itself would have a cross section of 2.44 square feet. This means that if your falling velocity were X, the air whistling past you in the one-inch space between you and the tube walls would have to be blowing upwards past you in a confined space at 4.2x.
If you were falling at a mild pace of 20mph, you'd be forcing air to blow up past you at a hurricane-velocity speed of 84mph. Rather than accelerating to fall faster, most likely the air resistance against the fluttering edges of the bag would SLOW YOU DOWN to a slower pace.
To do a kitchen-table experiment demonstrating the same effect, get a paper towel tube, or a poster mailing tube. Seal one end (to simulate the sealed "drop room"), then find a rubber ball that's not much smaller than the inner diameter of the tube. Even if it fits relatively loosely into the tube (as long as it's not a *lot* smaller), you'll find that when you drop it into the open end of the tube, it descends very slowly into the tube, buoyed by the resistance of the air in the tube as it tries to force its way up past the falling ball.
You speak of "terminal velocity", without seeming to understand that terminal velocity is not some physical constant, it's situationally dependent upon the mass of the falling object, and the air resistance it encounters. And the air resistance of an object falling down an air-filled tube that is roughly the same diameter as the falling object is *huge*, because the air below it can't simply "move aside", it has to "squeeze up past" the falling body, thus the terminal velocity in that situation is surprisingly low.
Big Bucks for thousands of those. I'm thinking of a parachute that doesn't catch as much air as the regular type. Jumpers would fall at a faster rate but would fall almost straight down. Less chance to be pushed by winds or crash into adjoining buildings.
Some kind of inflatable landing pad could be deployed a the base of the building by rescue workers.
In addition, smaller chutes would be cheaper and easier to pack.
BASE jumping would work for me!
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