highaltitude.log.20081015

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[01:10] <Laurenceb> hello
[01:10] <Laurenceb> anyone home
[01:22] <Laurenceb> god I hate windoze
[01:22] <Laurenceb> something is intermittently using COM2
[01:22] <Laurenceb> preventing me talking to my tronics
[01:23] <Laurenceb> maybe I should just wipe my xp partition
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[08:53] <robert1971> !whois
[08:54] <robert1971> whoisrjharrison
[08:57] Nick change: robert1971 -> rjharrison
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[09:01] <rjharrison> ls
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[13:47] <jcoxon> afternoon all
[13:57] <gordonjcp> hello
[13:57] <gordonjcp> did you hear anything of the ISS passes?
[14:01] <jcoxon> wasn't listening :-(
[14:01] <jcoxon> when was it?
[14:02] <gordonjcp> well there was one at about 10:15 where Richard Garriot was on voice
[14:02] <gordonjcp> I got nothing off the next pass about an hour ago
[14:03] <gordonjcp> got a recorder set up for this next pass though
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[15:06] <edmoore_> jcoxon: yo
[15:06] Nick change: edmoore_ -> edmoore
[15:10] <gordonjcp> http://www.gjcp.net/~gordonjcp/na1ss.png
[15:12] <edmoore> ok. that's cool
[15:14] <gordonjcp> now consider that it was received with my homebrew j-pole and my elderly Trio TS7730
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[15:54] <Laurenceb> http://wiki.ukhas.org.uk/code:parafoil_tests
[15:54] <Laurenceb> ^ ats awsome
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[16:04] <naxxfish> afternoon all
[16:51] <SpeedEvil> Afternoon.
[16:52] <SpeedEvil> Is this a flight Laurenceb ?
[17:08] <Laurenceb> no
[17:08] <Laurenceb> me running about
[17:09] <SpeedEvil> Ah
[17:09] <Laurenceb> I'm very impressed with the performance
[17:11] <Laurenceb> kalman filter works a treat
[17:11] <SpeedEvil> Where are the errors? Low speed where the GPS has poor heading info?
[17:11] <SpeedEvil> There is a way to get better test traces.
[17:11] Action: SpeedEvil passes Laurenceb a CD entitled 'Chariots of Fire - the soundtrack'.
[17:12] <Laurenceb> what errors?
[17:12] <SpeedEvil> where the GPS and the gyro heading diverge
[17:12] <Laurenceb> well
[17:12] <Laurenceb> you would expect that
[17:12] <Laurenceb> gps isnt perfect
[17:12] <SpeedEvil> true
[17:12] <Laurenceb> gps+gyro is better
[17:12] <SpeedEvil> yep.
[17:12] <Laurenceb> the good thing is they dont diverge much
[17:13] <Laurenceb> its well within spec
[17:13] <SpeedEvil> So you've not made any major stupids.
[17:13] <SpeedEvil> Unless you cross the equator :)
[17:14] <SpeedEvil> http://risks.catless.org/Risks/3.44.html
[17:14] <Laurenceb> haha
[17:15] <Laurenceb> I'm going to try it without the radio
[17:15] <Laurenceb> problem is theres a rugby match on my "testing area" atm
[17:15] <SpeedEvil> You mean a drop test?
[17:15] <SpeedEvil> From what?
[17:15] <Laurenceb> no a running about test
[17:15] <SpeedEvil> Ah.
[17:15] <Laurenceb> I need a bike with a basket on the front ideally
[17:16] <Laurenceb> it'd be much more stable
[17:16] <SpeedEvil> comp.risks is worth reading.
[17:16] <Laurenceb> I dropped my usb/rs232 adaptor on my laptop and the j key is a bit dodgy now :-/
[17:16] <Laurenceb> really need a few assistants and a bike for easier testing
[17:17] <SpeedEvil> Oh yes.
[17:17] <SpeedEvil> And to show that nothing ever changes.
[17:17] <SpeedEvil> http://risks.catless.org/Risks/24.58.html#subj1.1
[17:17] <Laurenceb> lol
[17:18] <SpeedEvil> http://risks.catless.org/php/risks/search.php?query="fly+by+wire"
[17:18] <SpeedEvil> is prolly a good read.
[17:18] <SpeedEvil> Everything from blocked sensors causing crashes to sticks on airliners getting wired up left-right inverted.
[17:18] <SpeedEvil> Nearly killed people that one.
[17:19] <Laurenceb> hmm theres one bug I still dont understand
[17:19] <Laurenceb> when I first turned it on it kept losing the gps
[17:19] <Laurenceb> the uC was timing out waiting for packets about 10s after it got a 3D lock
[17:20] <SpeedEvil> GPSs can be flaky IME on boot
[17:20] <Laurenceb> so I hard rebooted it, and it appeared to work
[17:20] <SpeedEvil> Many tend to have best performance only some while after lock.
[17:20] <Laurenceb> then I started off down the field and it went again
[17:20] <Laurenceb> intreagingly as I went under a load of trees
[17:21] <Laurenceb> it was fine after a couple of minutes of runtime
[17:22] <Laurenceb> at the time I just thought it was losing lock, but according to the datasheet the 0x6D packet it timed out waiting for it guarenteed at 1Hz
[17:22] <Laurenceb> this isnt good :-(
[17:24] <Laurenceb> I dont quite get what could have gone wrong... the evidence doesnt point to a dodgy datacable, as it stabilised after a few minutes
[17:25] <SpeedEvil> Power completely off, and power on for a few dozen cycles, and do some logging
[17:25] <SpeedEvil> Maybe.
[17:25] <Laurenceb> and the timeout was caused by waiting for an ISR to set a flag
[17:25] <SpeedEvil> Also some time on a shaker-table / tie to a cat.
[17:25] <Laurenceb> he
[17:25] <Laurenceb> I may hard reset the gps
[17:26] <Laurenceb> i.e. disconnect the SRAM backup battery
[17:26] <Laurenceb> I've had modules screw up before when left on or turned on/off a lot inside
[17:27] <Laurenceb> the good news is it had 9 sats !
[17:29] <SpeedEvil> :)
[17:32] <SpeedEvil> Also seartching the above site for 'gps' is werothwhile.
[17:50] <Laurenceb> any idea how I can print a float in c without the sign infront?
[17:50] <Laurenceb> ie. print -2.3 as 2.3 ?
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[17:53] <SpeedEvil> dunno
[17:54] <Laurenceb> I'm going to pretend the gps issue doesnt exist and work on some cosmetics to the downlnk code :P
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[18:23] <naxxfish> hmm, this may be a FAQ but what's the cheapest yet not utterly useless GPS module people tend to use?
[18:24] <naxxfish> i've had a look at the wiki but some personal input would be nice :)
[18:24] <SpeedEvil> Are you going to be going to high altitude?
[18:24] <naxxfish> we're designing for up to 60,000ft at the moment
[18:24] <Laurenceb> I'm using the lassen iq atm
[18:24] <SpeedEvil> Lassen IQ is popular.
[18:24] <Laurenceb> its seemingly very impressive
[18:24] <Laurenceb> performance, but I might have a bug with mine...
[18:25] <Laurenceb> need to do some more testing
[18:25] <naxxfish> since this payload may not actually fly, i want to keep costs down
[18:25] <naxxfish> we have an 80 quid budget for our part of the payload, which includes all the sensors and navigation kit
[18:26] <Laurenceb> http://www.dpieshop.com/trimble-lassen-iq-12-channel-gps-module-p-237.html
[18:26] <Laurenceb> where are you based?
[18:26] <naxxfish> cheers
[18:26] <naxxfish> canterbury
[18:26] <Laurenceb> ah
[18:27] <Laurenceb> guildford
[18:27] <naxxfish> cool
[18:27] <Laurenceb> theres a few people in cambridge
[18:27] <naxxfish> so I gathered
[18:27] <naxxfish> this payload is for a 2nd year project at uni
[18:27] <naxxfish> (i'm doing computer systems engineering)
[18:27] <Laurenceb> groovy
[18:28] <naxxfish> the original breif was "build a weather station" but we thought it wasn't fraught with enough disasters XD
[18:28] <Laurenceb> haha
[18:29] <SpeedEvil> DGPS requires hardware of certain sorts.
[18:29] <SpeedEvil> oops
[18:29] <Laurenceb> naxxfish: some tests I just did http://wiki.ukhas.org.uk/code:parafoil_tests
[18:29] <naxxfish> pitching it to the supervisor was interesting ... "We want to do the weather station project" "Ah, i see, quite interesting" "... but we want to put it in the stratosphere" "!!!"
[18:29] <Laurenceb> with the iq
[18:29] <naxxfish> cheers
[18:31] <naxxfish> i'm thinking of building an inertial navigation system of sorts
[18:31] <SpeedEvil> You can't really.
[18:32] <SpeedEvil> You can't get better than GPS.
[18:32] <Laurenceb> why?
[18:32] <naxxfish> based on some research I was doing with ground vehicles a year or two ago
[18:32] <SpeedEvil> You need GPS and INS
[18:32] <Laurenceb> yeah
[18:32] <SpeedEvil> combined.
[18:32] <SpeedEvil> Otherwise it drifts unreasonably.
[18:32] <naxxfish> yes, that's what i was doing
[18:32] <Laurenceb> why bother?
[18:32] <Laurenceb> if its just a weather station
[18:32] <naxxfish> well, if i understand correctly, you could better measure gusts and such with the additional sensing
[18:33] <Laurenceb> hmm ok
[18:33] <SpeedEvil> To an extent, yes.
[18:33] <SpeedEvil> 3 axis accelerometer, magnetometer should about do you.
[18:33] <naxxfish> gps on it's own I can see how you might get overall wind speed
[18:33] <naxxfish> yep, that's exactly what I have planned
[18:34] <naxxfish> I'm using a similar rig on a model board
[18:34] <naxxfish> er
[18:34] <naxxfish> model boat
[18:34] <Laurenceb> similar rig?
[18:34] <naxxfish> accelerometer/magnetometer/gps
[18:34] <Laurenceb> nice
[18:34] <Laurenceb> how are you filtering it?
[18:34] <naxxfish> since it's quite important the boat knows what way it's facing :p
[18:35] <naxxfish> i'm thinking of using some kind of weighitng system for data points
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[18:35] <Laurenceb> so you havent got any working code?
[18:35] <naxxfish> i've got some code that works, but not with any filtering
[18:36] <Laurenceb> you probably want a 4 state kalman filter
[18:36] <Laurenceb> x,y,v_x,v_y
[18:36] <Laurenceb> for a boat that is
[18:36] <naxxfish> that sounds sensible
[18:37] <naxxfish> i'll research that :p thanks
[18:37] <Laurenceb> can you assume its travelling forwards?
[18:37] <naxxfish> not really - currents and such
[18:37] <Laurenceb> hmm ok
[18:37] <Laurenceb> not so simple then
[18:37] <naxxfish> indeed
[18:38] <Laurenceb> maybe current x and y in there as well then
[18:38] <Laurenceb> so 6 state
[18:38] <Laurenceb> but youd need an extra sensor
[18:38] <Laurenceb> maybe some sort of speed sensor
[18:39] <Laurenceb> a differential pressure sensor would do it
[18:39] <naxxfish> how would that work?
[18:40] <naxxfish> oh, like a flow meter type affair?
[18:40] <Laurenceb> pitot tube
[18:40] <naxxfish> ahh okay
[18:41] <Laurenceb> so compass + pitot gives ~ your velocity relative to the water
[18:42] <Laurenceb> gps gives absolute velocity and position
[18:42] <Laurenceb> I guess accel would help but I dont think its needed
[18:42] <Laurenceb> guess that would make an 8 state filter
[18:43] <naxxfish> ah, accel would allow you to get the pitch/yaw
[18:43] <Laurenceb> current x,y position x,y velocity x,y accel x,y
[18:43] <Laurenceb> its a boat? 2D ?
[18:43] <naxxfish> sorry, not yaw, roll
[18:44] <Laurenceb> oh
[18:44] <Laurenceb> thats getting fancy
[18:44] <Laurenceb> what are you running this on?
[18:44] <naxxfish> it's sort of required so you don't decide to turn a really tight corner when your rolled over 45 degrees in that direction
[18:44] <naxxfish> probably a gumstix
[18:45] <Laurenceb> well I guess so if its a really high performance boat
[18:45] <naxxfish> aquisiton would come from a atmega168 or similar
[18:45] <Laurenceb> I'd just ignore the roll and make the boat stable
[18:45] <naxxfish> hmm - this is also possible
[18:45] <Laurenceb> yeh mega168 :D
[18:46] <jcoxon> evening all
[18:46] <Laurenceb> hi jcoxon
[18:46] <naxxfish> alo :)
[18:46] <Laurenceb> naxxfish: are you familiar with kalman filtering?
[18:46] <naxxfish> not yet i'm not :p
[18:46] <Laurenceb> http://wiki.ukhas.org.uk/code:parafoil_main
[18:47] <naxxfish> i've put it on my "to research" list
[18:47] <Laurenceb> ^ thats my implimentation
[18:47] <naxxfish> cool
[18:47] <Laurenceb> on mega168
[18:47] <naxxfish> sweet
[18:48] <Laurenceb> http://wiki.ukhas.org.uk/code:kalman_filter <-- thats the bit you'd be interested in
[18:49] <naxxfish> funky
[18:49] Action: naxxfish bookmarks them all
[18:49] <Laurenceb> its two state but you could just swap matrix.c for a matrix library and it'd do any size state vector
[18:51] <naxxfish> hmm
[18:51] <naxxfish> ah - here's another question i wanted to ask: barometric pressure sensors
[18:51] <Laurenceb> I havent used them sorry
[18:51] <naxxfish> ah, never mind
[18:52] <Laurenceb> but I might be able to help :P
[18:52] <naxxfish> well, the one we've got that's in budget is only rated for "indoor use"
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[18:52] <naxxfish> now, quite what that is supposed to mean i don't know
[18:52] <gordonjcp> means you're not meant to get it wet, maybe
[18:52] <Laurenceb> probable not moisture tolerant
[18:52] <naxxfish> that's what i'm assuming at the moment
[18:53] <naxxfish> would i be right in thinking that i could just make sure it doesn't get too cold (don't want things getting too cold anyway) that it'd be fine?
[18:54] <naxxfish> as i said, this is a prototype which may not even fly - and if it did we wouldn't expect everything to work perfectly
[18:55] <naxxfish> just other sensors we've found have been rather pricey and would be our entire budget
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[19:19] <Laurenceb> hi edmoore
[19:19] <edmoore> yo
[19:20] <edmoore> abou to disappear to remove the 4kg of product put into my hair today after haircut
[19:20] <Laurenceb> haha
[19:20] <Laurenceb> yes they use some horrible stuff
[19:21] <jcoxon> evening edmoore
[19:23] <Laurenceb> brb
[19:23] <edmoore> yo jcoxon
[19:24] <jcoxon> all set?
[19:24] <edmoore> pretty much
[19:25] <edmoore> annoyingly I have to be away tomorrow afternoon
[19:25] <edmoore> when most of the stuff will be done
[19:25] <jcoxon> okay cool
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[19:25] <jcoxon> and all is cool for rharrison to launch?
[19:26] <edmoore> yep, I think so
[19:26] <edmoore> should all work out well
[19:27] <jcoxon> cool cool
[19:29] <Laurenceb> edmoore: you launching as well?
[19:30] <edmoore> yes
[19:30] <edmoore> nova 9
[19:30] <Laurenceb> cool
[19:30] <Laurenceb> any nice features?
[19:30] <edmoore> alt record attemp
[19:30] <Laurenceb> ah
[19:30] <edmoore> and to get good footage for channel 5 who are filmingnit
[19:30] <edmoore> right, oign to jump in the bath
[19:30] <edmoore> bbl
[19:30] <edmoore> going*
[19:30] <Laurenceb> nice
[19:30] <Laurenceb> cya
[19:36] <Laurenceb> hi RocketBoy
[19:42] <edmoore> back
[19:43] <Laurenceb> that was v fast
[19:43] <Laurenceb> did you clean behind your ears?
[19:46] <Laurenceb> :P
[19:46] <edmoore> absolutely
[19:47] <Laurenceb> ed: you might be interested in http://wiki.ukhas.org.uk/code:parafoil_tests
[19:47] <Laurenceb> I was just about to do some more tests with the radio disabled so its 1Hz data but it started raining
[19:47] <Laurenceb> £$%£$
[19:48] <edmoore> cheers lb
[19:48] <Laurenceb> I'm extremely impressed
[19:48] <Laurenceb> with the accuracy
[19:48] <RocketBoy> hi Laurenceb
[19:48] <SpeedEvil> What sort of accuracy are you seeing do you think?
[19:49] <Laurenceb> <1 meter
[19:49] <Laurenceb> I'd got a 9 sat lock XD
[19:51] <Laurenceb> the annoying thing with it being 0.2 hz is its missing the movements in the rate output
[19:51] <Laurenceb> the rate is basically just noise from me clutching it in one hand and my laptop in the other
[19:51] <SpeedEvil> You're computing internally at 1Hz?
[19:51] <Laurenceb> no 50Hz
[19:52] <SpeedEvil> I mean from the GPS
[19:52] <Laurenceb> yeah the gps comes in at 1Hz
[19:52] <Laurenceb> kalman is updated at 50
[19:52] <Laurenceb> the code can send a packet out at 1Hz if it gets a DTR from the radio
[19:53] <Laurenceb> but radio requies 4.5 seconds to send a packet
[19:53] <Laurenceb> hence the 0.2Hz
[19:53] <Laurenceb> simple solution is: unplug the radio
[19:53] <SpeedEvil> ah
[19:53] <SpeedEvil> can't you just wind up baud rate?
[19:54] <Laurenceb> I wrote a shell script to shove the packets into gnuplot
[19:54] <SpeedEvil> ah
[19:54] <Laurenceb> yeah, but I'd have to rewrite the flight code a lot
[19:54] <Laurenceb> and then it wouldnt be a proper test
[19:55] <SpeedEvil> oh - right
[19:57] <Laurenceb> so... can anyone find the test location on google maps... ?
[19:58] <SpeedEvil> @n,e IIRC
[19:58] <SpeedEvil> @n,w IIRC
[20:00] <Laurenceb> eh
[20:01] <SpeedEvil> you enter @56,-5 on google-maps and it goes to 56N,-5W
[20:01] <SpeedEvil> you enter @56,-5 on google-maps and it goes to 56N,5E
[20:01] <Laurenceb> ah
[20:14] <Laurenceb> edmoore: the lassen iq, do you use packet 0x^D ?
[20:15] <Laurenceb> *0x6D
[20:16] <Laurenceb> its supposed to be transmitted at 1Hz
[20:16] <Laurenceb> I'm using it to detect new gps fixes
[20:17] <Laurenceb> but for about 1 minute after lock it was sporadically stopping
[20:17] <Laurenceb> i.e. there would be a gap of 2 to 3 seconds with no 0x6D packet
[20:18] <Laurenceb> how do you go about detecting a new gps position?
[20:25] <SpeedEvil> If it's not giving the packets you expect, debugging that'd be a good plan. Log it all to the laptop, and try interrupting the GPS signal, and doing 'stuff' to it to get it to behave badly?
[20:25] <SpeedEvil> All three of the GPSs (in NMEA mode) that I've used for OSM have had occasional oddities.
[20:25] <Laurenceb> yeah
[20:25] <Laurenceb> need it to stop raining first
[20:26] <SpeedEvil> From positions marked valid at 0,0, to fliers hundreds of kilometers off, to times when they just sulk inexplicably for a bit.
[20:26] <SpeedEvil> http://geotate.com/en/products looks interesting.
[20:26] <SpeedEvil> (thoguh not directly relevant)
[20:26] <SpeedEvil> basically software radio GPS.
[20:27] <SpeedEvil> But instead of doing anything clever, it just logs 128K to a snapshot.
[20:27] <Laurenceb> yeah
[20:27] <Laurenceb> thats something I'm working on
[20:28] <SpeedEvil> ?
[20:28] <SpeedEvil> Asked about price and availabilty, but nothing as yet.
[20:29] <Laurenceb> http://www.amazon.com/s?ie=UTF8&search-type=ss&index=books&field-author=Kai%20Borre&page=1
[20:29] <Laurenceb> ^ I'm working through that book
[20:30] <SpeedEvil> http://www.shapeways.com/blog/archives/111-New-Material-with-a-66.6%25-introductory-discount.html
[20:41] <Laurenceb> I've had recievers start acting dodgy after their ram gets corrupted
[20:41] <Laurenceb> removing the backup battery solves that one
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[20:55] Nick change: rharrison -> rjharrison
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[20:56] <rjharrison> registered my nick
[20:56] <rjharrison> evening all
[20:57] <rjharrison> Weather still looking good for saturday
[21:02] <rjharrison> Is everyone working hard on their projects?
[21:06] Action: SpeedEvil isn't. :(
[21:06] Action: SpeedEvil is doing stuff like fencing and getting up on ladders that are _way_ too tall.
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[21:10] <Laurenceb> I'm finishing off the mni rogallo airframe
[21:10] <Laurenceb> need to watch some of my test videos to get the trim correct
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[21:13] <rjharrison> Well at least you are all busy
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[21:25] <jcoxon> evening rjharrison
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[21:35] <rjharrison> How are you doing jcoxon
[21:35] <rjharrison> It's going to be an early morning launch on saturday
[21:35] <rjharrison> Spoke with ed
[21:36] <SpeedEvil> how early?
[21:36] <rjharrison> 8am launch 6:30am meet at churchill
[21:38] <rjharrison> jcoxon r u going to be arround? If not camb. then tracking fron london?
[21:39] <jcoxon> still debating that
[21:39] <jcoxon> i'll be tracking
[21:39] <jcoxon> just depends where
[21:39] <rjharrison> fnoble did you manage to get the LED to turn off when shooting video?
[21:39] <rjharrison> Nice will you be able to upload coords occasionally to the tracker?
[21:40] <jcoxon> oh i'll do it completely if i can
[21:40] <rjharrison> fnoble LCD !LED
[21:41] <rjharrison> Wife has just got back from London so I'm going to have a chat with her will be back laters for those of you who are still arround
[21:41] <jcoxon> np
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[22:38] <jcoxon> ooo looking at the http://www.cambridgeauv.co.uk/
[22:42] <SpeedEvil> Now, convince them they need to have their payload able to take mach 2 impacts on sea after dropping from 30Km.
[22:43] <jcoxon> haha
[22:49] <Laurenceb> http://video.google.com/videoplay?docid=4858664474879256299&q=source:012909491234162429853&hl=en
[22:50] <Laurenceb> ^ what do you guys think the pitch is in stable flight?
[22:50] <Laurenceb> measured wrt the central spar
[22:51] <Laurenceb> I'm trying to get the trim right....
[22:56] <SpeedEvil> Can't tell from that really.
[22:57] <SpeedEvil> Guy on the ground, and a rope'd make that easy to try lots.
[22:57] <Laurenceb> need one of those backgrounds with the black and yellow squares
[22:58] <SpeedEvil> Would green and yellow work?
[22:58] <Laurenceb> its pretty much horizontal
[22:58] <SpeedEvil> weedkiller is cheap on ebay.
[22:58] <Laurenceb> haha
[22:59] <SpeedEvil> 'regulations on professional weedkillers' Naah. We have ebay.
[22:59] <SpeedEvil> 1l=3300m^2 = 18 quid.
[22:59] <Laurenceb> that test was pretty much perfectly trimmed
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[23:06] <Laurenceb> interesting that all the AOA is provided by the poor glide ratio
[23:07] <SpeedEvil> There is the simple and stupid way - which I don't see a way around.
[23:07] <SpeedEvil> Try fiddling with it at 5 degree increments.
[23:08] <Laurenceb> yeah
[23:09] <Laurenceb> I'm just duck taping the enclosure onto the wing frame to see what the c of g is like
[23:12] <SpeedEvil> what is forward v?
[23:17] <Laurenceb> its very trim dependant
[23:17] <SpeedEvil> what do you want?
[23:17] <Laurenceb> at least 10m/s
[23:17] <SpeedEvil> Max forward v, best l/d, ...
[23:18] <Laurenceb> it has a higher wing loading than that prototype
[23:19] <Laurenceb> and thats doing over 6
[23:20] <Laurenceb> when I put in the numbers for relative wing loading I get about 10m/s for this design
[23:21] <Laurenceb> I've designed it using test data :P
[23:22] <SpeedEvil> http://www.theonion.com/content/news/bush_calls_for_panic?utm_source=onion_rss_daily genius.
[23:23] <Laurenceb> annoyingly I lost the design for that prototype
[23:24] <Laurenceb> what fraction of the way along the central spar would you say the vertical comes down at ?
[23:25] <SpeedEvil> Dunno.
[23:25] <Laurenceb> ohh actually delving in my hdd there are construction photos
[23:28] <SpeedEvil> :)
[23:33] <Laurenceb> hmm looks like my C of G is in about the right place - just a few % further towards the front than halfway
[23:34] <Laurenceb> its about 53% of the way along the central spar in the video
[23:35] <Laurenceb> (from the back)
[23:36] <Laurenceb> and with the wings duck taped on this one is balancing at 52% :D
[23:37] <Laurenceb> however when the wing covering is on that will bring the c of g back
[23:41] <SpeedEvil> what's the covering?
[23:50] <Laurenceb> probably polythene dust sheet
[23:51] <Laurenceb> ripstop nylon works, but its heavier
[23:51] <SpeedEvil> Rips'd be bad.
[23:51] <Laurenceb> you have to cut polythene very accurately, but its not too hard
[23:52] <Laurenceb> polythene doesnt tend to rip - I was flying one with polythene wings in a marshy field for ages and only ever got pinprick holes
[23:52] <SpeedEvil> I'm unsure how it'd behave at -40
[23:52] <Laurenceb> its ok down to -90
[23:53] <Laurenceb> hency zero pressure balloons
[23:53] <SpeedEvil> If it can crinkle in a way that it can get a crease then that can be bad.
[23:55] <Laurenceb> it cant here :P
[00:00] --- Thu Oct 16 2008