At 12:11 PM 12/13/2005, Pat Barthelow wrote:
>Folks:
>I had a friend in 6th grade lose an eye with a simple rubber band and
>paperclip that rebounded back into his eye when he shot it...Please wear
>Goggles....
>
>Also, a while back I came across the mother of all antenna launchers... This
>should have been featured in the show, "Home Improvement", with "Tim The
>Tool Man Taylor..."
There was an episode of H.I. that had a pneumatic toilet paper roll
launcher. J.D.Streett was the effects supervisor on the show, and built
it, pretty much as you describe. http://www.jdsfx.com/
>The PVC pipe, compressed air, pneumatic system is fairly cheap, easily
>homebrewed, and sends tennis balls with antenna attached, as high as 160 ft.
> Test shots send un tethered tennis balls 600 ft high...
>[600 ft is hard to believe, in my opinion, but would be VERY impressive, at
>field day, if true]
600 ft is a bit hard to believe, especially with a fuzzy standard tennis
ball (they are fairly draggy and not very heavy). If you didn't have to
contend with air drag, that's a muzzle velocity of about 200 ft/sec to get
to 600 ft, and 200ft/sec is very practical with a tennis ball and compresed
air.
at 200ft/sec muzzle velocity, you get to about 200ft in about 3 seconds.
Then you start to fall, but you quickly approach terminal velocity of
around 54 mi/hr (78 ft/sec), so you actuall hit the ground at about 7 seconds.
Doubling the muzzle velocity to 400 ft sec only gets you to about 300 ft in
3.3 seconds, and you're already a good fraction of the way to sonic speed
(mach 0.4), so the drag is already increasing dramatically. Even going to
1000 ft/sec muzzle velocity and totally ignoring sonic effects, you're only
up to about 460 ft.
The problem is the light weight of the ball. Weight it up, so its around a
pound, and you've got no problem making it to 600 ft.
However, you're unlikely to need to launch an antenna to 600ft, so the
tennis ball cannon is actually a pretty good way to go.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|