>From: Spike Jones <spike66@ibm.net>
>Reply-To: extropians@extropy.com
>To: extropians@extropy.com
>Subject: Re: JetPacks vs. AirCars
>Date: Sat, 21 Aug 1999 17:01:39 -0700
>
> > > hal@finney.org writes: ...But jetpacks only last 30 seconds. ...
> >
> > Robert J. Bradbury wrote: I'm not sure that I buy this. As I recall,
>the
> > fuel in a JetPack was fairly low energy (perhaps ammonia based???)...
>
>I did some calculations on air cars after reading Engines of Creation
>several years ago. Suppose nanotech gives us materials that have
>enormous strength. What then could be done?
>
>As it turns out, the sci-fi version of aircars with four horizontal
>rotors is pretty hopeless even assuming superstrong and light
>materials. It takes enormous amounts of energy to spin small
>diameter rotors fast enough to create even moderate lift, even if
>one is given freedom from normal strength of materials
>considerations.
>
>In fact, we already have air cars in a sense: helicopters. Of course
>these are inconvenient, since their rotor diameter is so large,
>but it helps illustrate the fact that as rotor diameter decreases,
>it takes relatively more energy to maintain hover. The human
>powered helicopter has an enormous rotor.
>
>The amount of wind and noise involved in lifting an aircar is
>considerable. Our example in nature would be tornadoes,
>which sometimes lift cars. Of course a highly directed
>rotor would be far more efficient than a tornado, however
>one is still likely to wreck ones neighbor's flower bed on
>takeoff, and their cat may *never* be seen again. {8^D
>
>There is a version of fighter jet now in the engineering development
>stage which achieves vertical takeoff and landing via a horizontal
>rotor in each wing. kewwwalllll. {8^D I seriously doubt we
>ordinary proles will have anything like that until nanotech
>changes everything. spike
>
I recall that in the Vietnam years, the US army had some kind of little
flying platform, circular with the rotor on the bottom... Don't know any
other details, but I did see pictures.