Im having a problem with an digital Matek ASPD-DLVR airspeed sensor and VTOL plane. During transition phase (from Qloiter to FBWB) GPS ground speed was able to reach 24 m/s but airspeed max was around 13 m/s. Winds were about 3-4 m/s max. Minimum airspeed required in order to complete transition on this airframe (VTBird) is about 17m/s. Airspeed sensor was covered during calibration - and cover was removed before arming the plane. Im not sure how to debug this further - is there anyone with previous experience to shed a light what could be the problem here?
I have done the automatic airspeed calibration for 20 minutes doing circles and it will not budge from its current value of 3.90764.
Using this information from the documents section HERE I hand calculated what airspeed ratio value would give me a near perfect airspeed reading, which came out to be 5.35168 which is WAY higher than in the past. So now I am past the high end of 4.0 for this species of airspeed sensor.
So what I am thinking now is a bad location for the airspeed tube. If that is true for me then it will be true for your problem too!
I use a 15x10 APC prop for my VTBird instead of the supplied 15x8 which might also be contributing to this problem.
Here is what my prop to airspeed sensor locations look like:
You can see that the static ports are about an inch forward of the props but that does not mean that the ports are unaffected by prop wash. I can’t model the prop wash so I don’t know for sure but maybe what is going on here is that the pitot tube needs to be much further forward for both of us.
Meanwhile I did a airspeed calibration flight that set ARSPD_RATIO to 4.0 - which I thought would mean that airspeed data cannot be trusted (ie out of normal range of 1.5-3.0 as per docs).
My prime suspect at the moment is possibly wrong ARSPD_PSI_RANGE value (which was set to 1.0 PSI). Matek ARSP-DVLR airspeed sensor spec says “pressure range 2500Pa” - which translates to 0.36 PSI actually.
I will do new calibration flight with new psi range parameter and we will see how it goes. Pitot tube position and prop wash is probably also an issue - just not sure how big one. I can see large airspeed fluctuations during hovering.