|Subject:||Re: [Paparazzi-devel] Airspeed Sensor|
|Date:||Wed, 28 Aug 2013 07:25:58 -0300|
Compressibility effects in air appear at high velocity only (near MACH 1), so for our classical models, you can consider that air is incompressible (approximation is really good below mach 0.3 : 100m/s).
Stall speed is linked to lift drop at high angle of attack, mainly due to airfoil behavior at high angle of attack. Lift is air density dependent, so yes, is linked to air pressure, and air pressure can be linked to air temperature (ex: ascending flows due to locally temperature increase enables gliders to climb). So you can just calculate the stall airspeed difference at different pressures using the air density difference at different pressures (http://www.engineeringtoolbox.com/air-temperature-pressure-density-d_771.html).
But what is important, is that Pitot tube (like the sensor you have) is not really measuring airspeed directly, but Dynamic Pressure (Total pressure minus Ambient Pressure, so it is already air density dependent). And lift is directly proportional to dynamic pressure. So stall speed given by your sensor should not depend on air density. The result is that the airspeed given by the sensor is not 100% good (because it depends on air density at the moment of the measurement) but it gives you the good dynamic pressure which is directly linked to stall speed...
I am not sure to be very efficient to explain this...
Le 28 août 2013 à 00:36, alonso acuña a écrit :
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