Dear all,
I use to fly a Skywalker X8 for AUTO mission with with an onboard Pixhawk and the last artduplane firmware, and I'm still struggling about the best way to have a reliable airspeed. On the one hand, I flew once without using any airspeed sensor, and the plane stalled because of a wrong over-estimated the airspeed. On the other hand, after having installed, calibrated and flew once successfully with the pitot tube coming with the pixhawk, I nearly got a second crash since the airspeed sensor was far underestimated. In the latter case, I guess that the tube was obstructed, maybe by snow (the area was snow-covered). So far, I used to blow into the tube (not directly) to have a rapid ground-check that the airspeed is working, but I'm now wondering whether this is good idea or not since this can obstruct the tube with water, which in turn might freeze in flight at low temperature. Does anyone have a good way to check the reliability of the pitot tube on the ground? Any general tips for improving the reliability of the airspeed sensor is welcome.
Best,
Replies
Maarten
yes, as Graham says, it's always a matter of which way an error points, an too-low IAS is usually not dangerous (like mentioned before) compared to too high - also , consequences depend on whatever stall-protecion is enabled.
We hope EKF will be able to detect and handle that soon :)
With the digital airspeed sensor you should see the IAS fluctuate slightly between 3-8km/h on the ground in still air (it settles down and is pretty accurate once in the air). If higher you can do a preflight calibration with the tube covered. Doing multiple loiters with airspeed calibration on also increases the accuracy.
As Andre K said if blocked the autopilot will try to fly the plane faster, but note it will also nose down to achieve that which can be a problem as in our case the ground got in the way before it could level out. Pitot tube was blocked with water after flying into unseen rain some 5km away.
I see indeed an small increase of airspeed when I pu my finger on the pitot tube, is this because the air is a little compressed as my skin goes a little into the tube ??
What is IAS ?
Best regards Maarten
yes, you may say it proves a bit better that there is no leaks, as it can "hold" pressure for the time you press.
- where a bad tube/hose would just register a reduced pressure by blowing, not revealing a problem.
IAS = indicated air speed
Just press your finger to the tube, that should give a small increase.
Also, the most important item on preflight checklist is to see that the IAS is not too high, - then verify throttle, GS and AS for sanity once levelling off after takeoff.
You do not need to be concerned about AS being stuck at too low position, that would only make the plane do slower manoeuvres and fly at full throttle (EKF would not treat it as a stall). If airframe can handle max throttle at level flight, you'll be able to take over and land manually anyway.