highaltitude.log.20090723

[00:00] <RocketBoy> I bleive burst pressure is the pressure of the surrounding atmosphere not balloon pressure
[00:03] <RocketBoy> I assumed release pressure was 101kPa
[00:03] <SpeedEvil> yeah
[00:03] <SpeedEvil> I wasa about to say that
[00:04] <SpeedEvil> As it matches wolfram's idea of the pressure to 10% or so
[00:06] <RocketBoy> got to go - cu guys
[00:06] <SpeedEvil> wave
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[11:39] Nick change: ShellEvil -> speedevil
[11:45] Action: Laurenceb thought of a cool way to despin rockets
[11:45] <Laurenceb> spool out long reels of thin line radially
[11:47] <speedevil> yeah
[11:47] <speedevil> unless you manage to tangle it :)
[11:48] <Laurenceb> to despin the first stage for re-entery, you can spool out the nose cone
[11:48] <speedevil> why do you need to
[11:48] <Laurenceb> after it seperates to release the second stage
[11:48] <Laurenceb> the gyroscopic precession stops it re-entering properly
[11:49] <Laurenceb> it goes in sideways
[11:49] <speedevil> ah
[11:51] <Laurenceb> just have a two part nose cone with about 5m of line wound around the top of the launch tube
[11:52] <Laurenceb> should result in a rotation rate of just a few rpm
[11:52] <Laurenceb> not sure what a sensible splashdown speed is
[11:53] <Laurenceb> with no chute it will be at about ~50m/s
[12:01] <Laurenceb> a little 20cm chute gets it to <10m/s
[12:02] <Laurenceb> gtg, cya
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[15:32] <rjharrison> SpeedEvil a closer vice of transition to float http://www.robertharrison.org/listen/time.png
[15:32] <rjharrison> view
[15:35] <SpeedEvil> That's really a quite sharp transistion - it's mostly over 2Km?
[15:42] <rjharrison> yep
[15:42] <rjharrison> http://www.robertharrison.org/listen/transition.png
[15:42] <rjharrison> This will say here for a while should the others be interested
[15:56] <rjharrison> http://www.robertharrison.org/listen/transition.png
[15:57] <rjharrison> A slight improvement
[15:57] <rjharrison> one can see a wiggle on the altitude when in float
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[16:13] <rjharrison> SpeedEvil and finally http://www.robertharrison.org/listen/transition2.png
[16:19] tenyen_ (n=tenyen@asdfasdf.ethz.ch) got lost in the net-split.
[16:24] <SpeedEvil> Okaay
[16:24] <SpeedEvil> http://www.mauve.plus.com/balloon.gif
[16:25] <SpeedEvil> seconds since midnight on the bottom, altitude on left in red, rise-rate in meters per second on right and in green
[16:26] <SpeedEvil> rise rate is smoothed somewhat - but it's not unreprasentative of the raw data
[16:27] <SpeedEvil> So it actually slows down over most of an hour
[16:28] <SpeedEvil> but going from 1m/s to 0m/s is about 10 mins.
[16:36] <rjharrison> SpeedEvil that's cool
[16:36] <SpeedEvil> xephem says that night happend at that altitude some time earlier
[16:37] <SpeedEvil> as in a couple of hours before it slowed
[16:41] <SpeedEvil> If the cause of the slowdown was helium leaking out - then it surely wouldn't have stopped 'slowing down' at zero.
[16:42] <SpeedEvil> I think it's got to be internal pressure. The descent rate of 6cm/s or so after the stall looks plausible for helium loss.
[16:42] <SpeedEvil> barring icing of the orifice.
[17:03] <rjharrison> Ouch I don't like the idea of orifice icing
[17:04] <SpeedEvil> It's a big problem for air stewerdesses aparantly at high altitude :)
[17:04] <rjharrison> REducton in pressure ... reduction in volume ... incrase in density ... therefor nutrally boyant
[17:04] <rjharrison> SpeedEvil
[17:05] <rjharrison> neutrally
[17:05] <SpeedEvil> reductionin pressure - reductioninvolume?
[17:06] <rjharrison> ahhh
[17:06] <rjharrison> Lower vol > pressure :)
[17:07] <rjharrison> Lower vol should give > pressure :)
[17:07] <SpeedEvil> My hypothesis is - the balloon is constraining the helium from expanding as it would like. This reduces the volume of the balloon and hence the free lift.
[17:07] <SpeedEvil> As free lift goes to 0 - it stops ascending
[17:08] <rjharrison> How about big temp drop cools helium and inc density
[17:08] <rjharrison> and voila
[17:08] <SpeedEvil> With enough helium in it - you get past the region that this is possible - and the balloon continues to ascend til it bursts
[17:08] <SpeedEvil> the surrounding air is at about the same temp
[17:08] <SpeedEvil> so the effects cancel
[17:09] <SpeedEvil> to a degree anyway
[17:09] <rjharrison> humm
[17:10] <SpeedEvil> Anyway - the only logical way to solve this is to build a 27Km tall tower, so we can experiment easily.
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[17:11] <rjharrison> hi edmoore
[17:11] <edmoore> hi
[17:11] <edmoore> got email
[17:11] <edmoore> ty
[17:11] <rjharrison> bit more focused
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[17:14] <rjharrison> SpeedEvil that's a good idea (tower)
[17:14] <rjharrison> We would also have the tallest structure in the world
[17:15] <SpeedEvil> And somewhere for laurenceb to launch from.
[17:15] <rjharrison> drop from
[17:15] <SpeedEvil> Also - a lift to the top, with a rack of spacesuits that are 10 quid to hire on the ground, and get more expensive as you go up :)
[17:21] <rjharrison> lol
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[17:46] <rjharrison> Off home
[17:46] <rjharrison> loaters
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[19:19] <rjharrison> edmoore SENSORS ORDERED
[19:20] <rjharrison> opps
[19:20] <edmoore> OK!
[19:20] <rjharrison> olo
[19:20] <edmoore> good news
[19:20] <rjharrison> Humm I give up I can't type
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[19:28] <SpeedEvil> :)
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[19:39] <edmoore> Hi RocketBoy
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[21:04] <RocketBoy> hi edmoore - did you see the results of my experinenting with blowing up party balloons?
[21:05] <edmoore> Let me have a look back ion history - i left client on last night but wasn't really at the computer
[21:05] <SpeedEvil> nothing really complex.
[21:05] <SpeedEvil> just that they drop in pressure, then rise again
[21:06] <SpeedEvil> edmoore: also - a closer view of the transistion to float
[21:06] <SpeedEvil> http://www.mauve.plus.com/balloon.gif
[21:09] <edmoore> Interesting data rocketboy
[21:10] <edmoore> I wonder if that correlates with plastic/elastic stress/strain curve
[21:10] <RocketBoy> I cant see why met balloons would be significantly different in profile
[21:10] <SpeedEvil> Earlier in my pontificating, I'd been assuming that it'd just carry on expanding like a soap bubble.
[21:11] <SpeedEvil> was this a latex, or a silicone balloon?
[21:12] <RocketBoy> latex as far as I know - I'll just go an smell one
[21:12] <rjharrison> RocketBoy do you have the links to your pressure experiment
[21:13] <SpeedEvil> Not that I can think of a good reason for them to differ much
[21:14] <RocketBoy> smells the same as met balloons - mmmmmmmmm lovely
[21:14] <edmoore> back in a bit
[21:15] <RocketBoy> rjharrision - just in the logs for yesterday at 23:28
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[00:00] --- Fri Jul 24 2009