Measuring airspeed

[cgroves]

Hi Guys:
I am working on a technique for experimentally deriving the min sink and max L/D trims for my gliders. I can accurately measure the sink rate using a logging altimeter but am trying to find a way to measure the airspeed in order to find the max L/D. The eagletree units look nice but are too large to fit in the nose spaces of my gliders. I need something the size of a RAM2 or ZLog which measures airspeed or a way of measuring the airspeed from the ground (by myself unless people want to help out right at sunrise). Looking for ideas here so throw out anything you can think of.

[Sev Fontaine]

Well... depending on budjet... you could buy a PX139 pressure transducer (116$) and make your own pitot static tube setup (less than 10$). This is relatively small (1 x 1 x 1 inch). The pressure transducer needs to be supplied a 5 v source (from BEC would be ok... only 20 mA) and will give a 0 to 4 volt output depending on pressure. You'd also need to log voltage from the transducer which can be converted to dynamic pressure using the supplied calibration curve.
Other information you'd have to know to convert the dynamic pressure to airspeed are: altitude (which you say are already logging) to find the static pressure/density, air temperature (which can be measured on the ground using any thermometer) and finally the atmospheric pressure (from environment canada website, a barometer, or the ottawa airport weather station)
If you decide to go this route let me know and i'll support you by setting up an excel spreadsheet to convert dynamic pressure to airspeed.
The PX 139 Transducer can be purchased online from Omega.ca