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Old Sep 11, 2011, 02:46 PM
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Using it in NON 3rd party mode, i.e. ET mode

Originally Posted by nakki5 View Post
Hello turnale,

based on your code example (thanks for sharing!!) I was able to get out 16-bit value for pressure from my new airspeed sensor V3. My sensor is working in normal mode (no third party) and it gives about 1570 value 5. I tested it by blowing to high pressure side and I got about 13800 value max, which corresponds 7-segment reading 530km/h.
I am pretty sure that the values are differential pressures measured in Pa (Pascal). A speed of 530 km/h corresponds to around 13800 Pa, than you can calculate the incompressible speed by using Bernoulli's equation: v = sqrt(2*pdiff/rho), where pdiff is the reading (I assume that the initial value of 1570 in your case is an offset and needs to be subtracted) and rho the air density (1.225 kg/m^3 for standard atmosphere at ground level). The result is m/s, to get km/h just multiply by 3.6

In this example it will give 508 km/h, which is a little bit different from the 530 above, but they may have some different assumptions about the air density. To implemented compressibility correction, the equation looks like v = sqrt(2*pdiff/(rho*(1+0.25*Ma^2))) where Ma is the Mach number Ma = v/a (a speed of sound). Of cause, this requires an iterative solution.

Hope that helps

Edit: Compressibility correction is only necessary if you fly with more than around 350 km/h ...
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Last edited by EQ1; Sep 11, 2011 at 02:54 PM.
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