highaltitude.log.20070119

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[04:25] <Professor> evenin
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[19:18] <mc-> laurenceb, how's your helium valve?
[19:20] <laurenceb> well it works fine, I've tested it on 3v
[19:21] <laurenceb> I've done some rough fluid dynamics and it looks like it will work up to about 24km
[19:21] <laurenceb> above that the air is too thin for it to vent fast enough
[19:22] <mc-> just wondering, if there's a simpler way
[19:22] <mc-> ie a flap that opens based on the pressure difference?
[19:23] <laurenceb> pressure difference decreases with altitude
[19:23] <laurenceb> With a servo I can program it to stabalise at the target altitude
[19:24] <mc-> but as the balloon grows, it will increase the internal pressure?
[19:24] <mc-> due to the elasticity of the fabric.
[19:24] <laurenceb> no the pressure remains a certain percentage above atmospheric
[19:25] <laurenceb> the surface area of the balloon increases and the thickness of the rubber decreases
[19:25] <laurenceb> overall effect is pressure decreases
[19:25] <mc-> so you need a large area valve to let the helium out?
[19:26] <laurenceb> yes thats why my valve will do basically usless above approx 24km
[19:26] <laurenceb> its just a 15mm polypipe one from wikes
[19:27] <mc-> how about a membrane with holes in it, as the balloon grows the holes expand?
[19:27] <laurenceb> you need it to be software controllable I think
[19:28] <laurenceb> I'm thinking of a large diameter flap type valve servo operated
[19:28] <mc-> I did some experiments with butter and a resistor. WHen the resistor got hot, the butter melted, and let out the gas.
[19:28] <laurenceb> the balloon its onto 40mm pipe so thats a lot of diameter to use compared with 15
[19:29] <laurenceb> I want to close the valve
[19:29] <laurenceb> melting things wont do that
[19:30] <laurenceb> its very easy, you could build a polypipe thing is 1/2 an hour for £10
[19:31] <laurenceb> bolt a servo onto the valve and fit 40mm pipe on one end and 15mm on the other
[19:31] <laurenceb> so yuo can also use it to inflate the balloon
[19:31] <mc-> I meant to add, it required 2 balloons, 1 balloon was vented at altitude.
[19:31] <laurenceb> Ic
[19:32] <laurenceb> sorry can't stay 4 long , work & stuff
[19:32] <mc-> cya
[19:32] <laurenceb> jcoxon, if you read this email me about whats happening with the launch :)
[19:33] <laurenceb> ok cya all
[19:33] <laurenceb> oh mc- do you know?
[19:34] <mc-> it
[19:34] <mc-> is scrubbed this w/e
[19:34] <laurenceb> ok :(
[19:34] <laurenceb> cya
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[21:30] <DarkFlib> http://stratocat.com.ar/indexe.html <-- received that in my email today
[21:31] <DarkFlib> 40 million cubic feet with ascent rate of 1000feet/minute
[21:32] <DarkFlib> so assuming that the ascent was constant (unlikely) it hit its 'critical zone' at 60,000feet
[21:33] <DarkFlib> and took another 4 hours after that to hit 123,000feet
[21:39] <DarkFlib> 1840kg payload mass...
[21:39] <DarkFlib> 1kW photovoltaic panels for power
[21:39] <DarkFlib> gondola is stabilised to prevent rotation away from the sun...
[21:40] <DarkFlib> total cost $31.9M (mostly payload)
[21:41] <DarkFlib> not much info on the balloon itself..
[21:41] <DarkFlib> but pretty cool for a 31day flight
[21:45] <DarkFlib> ahhh... used helium...
[21:45] <DarkFlib> thought it would have... but not advertised on any of the sites...
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[23:41] <laurenceb> I've put up a valve page :-)
[23:45] <laurenceb> you can see some pictures, it's under ideas on the wiki
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[00:00] --- Sat Jan 20 2007