Re: Wetzone Engineering: Airships providing artificial rain for f ighting fires. (fwd)



> It reminds me of something Arthur C. Clarke, the author, encountered during
> WWII.  He was an engineer working over in Great Britain.  Allied bombers had
> a tough time landing after their missions because of the prevalent fog
> around the air fields in England.  They had the idea to build giant fires
> (natural gas jets) at the end of the runways to literally burn off the fog.
> The first bomber to cross over the end of the runway almost crashed due to
> the severe turbulence caused by the fires.  Hey, it looked good on paper.
> 
> Steve O
> 
	Yeah, that does make sense. The thing I'm wondering is, how high does 
that turbulence go? I suspect that it could be made to work, but very likely 
not with the "fly in low" idea over huge raging fires. 
	From high up, you can still drop water, and it will come down in a 
fine mist. (That's another factor. As you drop water, it accelerates to a 
terminal velocity that shears the surface tension of the droplets, making them 
smaller.) This repeats until you essentially have a fine mist. Angel Falls, 
the highest waterfall in the world is about a 3000' drop off of a Tepui 
(flat-topped mesa/mountain) in Venezuela. From what I understand, no water 
hits the ground, as it all turns into mist in midair. 

	Coming in from the windward side, you might avoid the updraft by 
dropping water that blows in to the edge of the fire, then encroach upon it in 
stages. But you'll have to avoid the in-draft, as the fire sucks in all air 
around it. I don't know how much current an airship can resist or push 
through. I suspect it's partially based on the design. 

	The ballast problem might be trickier, as Josh points out. However, 
the SkyCat 1000 (not yet built) could hold 1000 metric tons of water, or 
2,200,000 pounds. That's about 275,000 gallons. I think I saw something about 
"one quarter million gallons", so they might, in fact, be thinking about 
dropping the whole load. (I thought maybe they'd retain half to retain weight, 
but that's not really good for firefighting... "Sorry, we can't put out any 
more fire, even though we have another 125,000 gallons." That would go over 
like the proverbial lead balloon! :-)  )

	However, I think I see another way around it, maybe. The Zeppelins of 
old, and some of the more recent airship designs too, I think, were 
rigid-frame airships. Not simple balloons with one giant inflated bladder, but 
a skin around a rigid frame, with individual gas bladders inside. With a setup 
like that, and some simple (yet large) compressors, you could vary the 
buoyancy of the airship on demand, and fairly quickly. It'd be like letting 
helium out of a balloon, except they'd be storing it in compressed form to 
re-deploy as needed (when a helicopter or plane dropped a load of water.) 
	They talked about "sustained rainfall of 10,000-20,000 gallons/hr.", 
which would be between 80,000-160,000 lbs. of weight per hour. You'd need to 
be able to compress between 1333-2666 lbs/minute of lifting capacity. 

http://www.howstuffworks.com/helium.htm/printable  shows a whole lot about 
helium, including how to calculate balloon size and lifting capacity. They say 
that one cubit foot of helium can lift about 28.2 grams, or roughly one once. 
They also say that there are 448 grams in a pound, but I think it's really 
453.6, so take that for what you will. 

Anyway, 453.6/28.2=16.1 cubic feet of helium to lift one pound. So we're 
talking about a compressor that can pump out between 21446.809 and 42893.617 
cubic feet per minute from a distributed number of gas bladders throughout the 
airship. Not simple to coordinate, but certainly not impossible. At the 
high-end of 43K/min, if there were 16 bladders (reasonable to assume in 
something the size of the SkyCat 1000) it would only require 2680.8511 cubic 
feet/minute per bladder, which should be reasonable to do with one or more 
industrial compressors. 


	So it might be feasible, but there are certainly some engineering 
considerations to work out. However, if SkyCat is seriously talking with them, 
they must feel that it's a possible thing. 

	Does anyone know of any airship companies that do the compression-to-
compensate-for-ballast thing? Or have I just invented a new technique? (If so, 
I want it named after me! :-)  )


-- 
Pat
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	 Patrick G. Salsbury - http://reality.sculptors.com/~salsbury/
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