Subject: Re: Dirigible floor lamp musings

From: [email-masked] (Nick Pine)
Date: 3 Oct 1995 07:31:30 -0400

Robert Searfoss  <[email-masked]> wrote:

>This could be an interesting project, also an interesting hazard to
>aircraft.  Might be hard for a turbine to swallow.  could tangle or
>break a prop.  Go thru a windshield...etc.  Hang on to it.!!!!  bye.

I live near the end of the runway of a small airport. It's illegal to build
anything taller than 65' where I live, ie a 20:1 glide slope, but sometimes
at night when the twin turboprops land right over my house, full-throttle,
full-flaps, I think about barrage balloons, tethered at 64'. Aluminized mylar,
perhaps, like those gift balloons that say "Surprise!" :-)

Nick

---

From: [email-masked] (Nick Pine)
Date: 2 Oct 1995 07:00:57 -0400

If the balloon weighs 1 pound per 400 ft^2 (What do dry cleaner bags weigh?),
with an R-value of 0.6 ft^2-F/Btu, and the inside air temperature is 175 F
(will that melt the bag?), and the room air is 68 F, how big must it be to
support itself?

Sea level air at 175 F weighs 0.0625 lbs/ft^3, so 68 F air should weigh
about 0.0752 lb/ft^3, ignoring humidity. The lifting force should be
at least 0.0752 - 0.0625 = 0.0127 lbs/ft^3. 

An r' radius sphere would be self-supporting when 

4 pi r^2/400 = 4/3 pi r^3 x 0.0127 ==> r = 3/(400 x 0.0127) = 1'.

Keeping the air hot requires 

(175F-68F) x 4 pi 1^2 ft^2/R0.6 = 2241 Btu/hour or 657 watts.

Too much, except for a sometime toy...

Where can I buy some very fine tungsten wire?

Nick