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Member Since: September 2, 2007

Country: United States

  • Pete, Fellow glider pilot here (mostly theoretical at this point though... work y'know), also named Pete, based out of California... I've had a pet project for longer than I can remember to design and build such an instrument, my challenge has been the ever improving state of sensors and compute power ... it changes before I get a chance to implement something that I'm happy with... so I'm permanently planning... anyhow.. from my long research the following stream of consciousness is issued...

    Vario... there is a fair amount of info out there about using the BMP085 as an vario sensor (its just been end-of-lifed and replaced with the BMP180 (i think) by the way), but folks these days seem to be looking at the less 'noisy' and faster sample rate MS5611 (from Measurement Specialties), these as smaller (yes thats possible) , slightly higher resolution and can supply up to 100 readings second for that rolling average to bring the noise floor down even further. They are a little hard to source in the US (Sparkfun please look into supplying these .. pretty please) but its possible to buy them in Europe and have then delivered, they are more expensive but they appear to be worth the bump in price, I fried my first one trying to solder it so be careful. Regarding using accelerometers... most folks don't need them for 'simple' variometers, its only when you are getting into complex very well compensated varios that accelerometers are needed. They can be used to compensate for (amongst other things) sideways gusts that may influence the pressure readings, as well as differentiate real air mass induced climbs from climbs due to 'stick' lift`. This also brings up the need to have an airspeed sensor (i.e sense 'pitot' pressure in addition to 'static' pressure), summing these properly will give you a 'total energy' vario (i.e Potential energy from height + kinetic energy from speed), properly used can be used to cancel any stick lift (i.e. pull up with stick, reduces Kinetic energy, but increases Potential energy), differences in Total Energy should tell you if you are actually climbing or sinking. You can go beyond this and model the neutral airmass sink rate of the glider against its polar and you can get a 'netto' variometer that tells you slightly different info... is the airmass I'm in rising or sinking, you can further correct this info in circling turns with an accelerometer and even a compass (or GPS) for bank angle and turning G loads...its quite a complicated subject when you start to get into it...

    Most of the hobby open source varios (or the simple Hang glider units that you can hang around your neck) go for just pressure differentials based on static pressure changes using most often a BMP085(or similar) but more recently a variant of the MS5611 is getting favoured (yes I'm English) , check the the Meas Spec sweb site out, there are low res and hi res ones, be careful to get the right one -BA03 if memory serves.

    You can do a lot and get lots or useful info from the combination of Pitot (airspeed) measurements, Vario climb rates and GPS info... such as estimated wind direction (simple vector math of airspeed, compass heading and gps ground track), instantaneous glide angle or range to a defined altitude including info on glider polar curve, airspeed, wind speed, ground track ... hell you could even download the free DEM worldwide elevation data and build a terrain model that allows you to know when you will hit the mountain on your present track based on the above and a GPS posiiton and some extrapolation... the possibilities are endless. Its a fascinating project that you will never be finished... if you are anything like me.

    Logging... phew... there is a standard logging format that is used by most commercial electronic glider instruments the .IGC format (its an open standard), available and well defined from the various web sites such as http://www.fai.org/gnss-recording-devices/igc-approved-flight-recorders or http://carrier.csi.cam.ac.uk/forsterlewis/soaring/igc_file_format/ . This is designed to allow for height and position (plus a motor sensor, noise or vibration) logging suitable for various levels for badge claims... simple badges, competition and world or national records. The standard builds in some sort of encryption and 'anti-tamper' stuff, thats probably a bunch of hassle, but if you can get an .IGC interpreter working you can do some wonderful 'after the fact' rendering of your flights on many web based tools that are out there that use resources like Google maps or Google Earth.. check this out... http://www.doarama.com/activities/1408 not me just a local pilot.

    Good luck.. I'm very interested in your progress with this...


  • I just found a couple of companies that manufacturer the elasomer strips, SparkFun may want to try to contact them and see if they can get a supply in...

  • I just found a couple of companies that manufacturer the elasomer strips, SparkFun may want to try to contact them and see if they can get a supply in...

  • I got them right after I posted, and they are excellent, small, fast accurate and low power...nice product.

  • Been waiting for my backkordered sensors to get back in stock... I know.. impatience is not a virtue... but I wanna play :-)
    Looks they are in stock but my order is still backordered ... odd... wassup with that ?

  • Thats exactly the piece of software I've been yearning for... I have four or more systems at home (Linux/Mac/Windows) I lose count sometimes, multiple more at work (Linux and Solaris) and the iPhone... now if only DropBox worked on Solaris too...that would be my nirvana.

No public wish lists :(