Re: JetPacks vs. AirCars
Sun, 22 Aug 1999 20:07:19 EDT

In a message dated 99-08-22 18:30:00 EDT, (Philip Witham) wrote:

> As for noise, nothing would be noisier than a rocket pack, with it's
> supersonic exhaust jet. This is what makes rockets so much fun to test!
> more noise the better! Earth-shaking, chest-pounding, ear-damaging NOISE!
> Yes! 8-0 ...Er, uh, must calm down... Ahem. Most of the noise from a
> helicopter is from the tail-rotor and the engine. If you generate the lift
> from a large area rotor (low "disc loading", as in a lightweight
> the noise due to making lift is quite low. This is because of the low
> velocity in the rotor downwash.

I can attest to this. I saw the old Bell jet pack demonstrated when I was about 9 years old or so. I remember REALLY looking forward to the event and then being a little put off by 1) that incredible noise, 2) the very short duration of the flight and 3) the two trucks worth of support equipment it required. Clearly this gizmo was gonna take some more work before I fly to school with my very own jet pack . . .

Years later, I saw a Harrier demostrate some amazing precision vertical flight manouvers at an air show. No question this was very cool, indeed, but once again, the noise was overwhelming, though. Made the old Mahavishnu Orchestra sound like baroque chamber music.

> And, yes, Spike, I think a nanotech Aircar can have a low rotor disc
> like a helicopter, even a non-nanotech aircar. By the way, a ducted fan
> the Moller designs use has an effective area of the inlet area of the duct,
> if it's done just right, not just the fan area. Not that I like the Moller
> designs. I want 200,000 rotors about 7mm in diameter, spinning at >10,000
> rotations per second (two blades each), to get the fundamental rotor noise
> frequency above human hearing range. This works out to be the area of a
> Cadillac or standard parking space, and a disc loading like a helicopter.
> One of these days I'll write up an aircar paper for this group - I've been
> running simulations of automated air-traffic control - self piloting
aircars -
> fun stuff.

You might want to check out J. Storrs Hall's paper on nanotech aircars. He comes to basically the same conclusions regarding size, efficiency and low noise, by using LOTS of VERY small rotors.

     Greg Burch     <>----<>
     Attorney  :::  Vice President, Extropy Institute  :::  Wilderness Guide   -or-
                         "Civilization is protest against nature; 
                  progress requires us to take control of evolution."
                                      -- Thomas Huxley