New WTC design evacuation plan (in memory of those who jumped)

I didn't miss that part, I read it very clearly:

"...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.

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 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.

copycat...with the computing power available today, you could make GPS-steered parachutes where the jumper just rides it down to a soft landing in a predesignated drop zone.

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.

""all 32,000 at or below ground level and 200 yards away in less than 3 minutes."" It just isn't possible. The logistics alone are plain silly. Did you ever see the start of a marathon? They don't have to fall anywhere and they aren't battered and beaten at the start but they still tens of thousands of people can't get 600 feet in seconds. And aren't these office workers we're talking about here? Not exactly have reputed as being all in their early twenties and ten pounds underweight, do they? If you go back to the free fall part of it you're really losing it. Understand that every body is not going to be spaced exactly three seconds apart and if the 'air pressure' is going to slow them signifcantly, which it must if they are to survive, then the largest persons are going to be slowed much more than any smaller person. One average sized person followed by two thin ones will immediately have the two thinner persons compacted against the normal sized one creating an even larger mass which, by these calculations, this mass will be slowed even more causing even more bodies to compact against it creating an even larger mass restricting the air flow even more .....

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.