 Balloons,
blimps, dirigibles, airships and the like get their lift because the
gas or hot air in their envelopes is less dense than the surrounding
air and therefore rises. The more rarified the gas, the greater
the lift. The logical extension of this is that if the gas bag
is filled with literally nothing, then the lift should be enormous.
Should be, but isn't. The problem is fairly
obvious if you happen to have a toy balloon handy. Blow air into
it and it inflates, but suck air out of it and it squashes flat and
sinks because of the pressure of the air around it squashes it flat.
It's easy to make a balloon with a vacuum inside it, but if it
flattens it won't get any lighter because the volume decreases and
therefore there's no displacement.
In 1670, a Jesuit, Francis Lana, suggested in
his book Prodromo dell'Arte Maestra that the way to
overcome this was to forget the old latex balloons and use airtight
copper spheres about eight yards in diameter. Trouble is, any
metal strong enough to maintain a vacuum is going to be dashed heavy
and certain to sink like a lead... well, you get the idea.
 During
the 1930, this squashy balloon problem was countered with a couple of
ideas that tried to replace metal spheres with machinery. In the
1933 "vacuum dirigible" above, the copper globes were replaced with a
fuselage filled with a pair of helical fans that were supposed to
reduce air pressure to the point of near vacuum and hence produce
lift. Meanwhile, the "suction lift" flying machine on the right
tried to achieve the same thing using a bank of bladeless turbines
similar to those invented by
Tesla.
It was all very clever, but unfortunately
eliminating the weight of the metal spheres doesn't help if you just
lumber it back on again tenfold with a lot of machinery and a
pressure-proof hull.
Makes a nice wind machine, though. |
