This is a in depth, borderline software developer type question:
Flying version .15 PX4 with QGC on a Opterra plane, Im sending the DO_CHANGE_SPEED via mavlink command but it is not changing the speed in an auto mission - it stays the same. I have a HERE4 GPS and calibrated pitot tube for measuring the airspeed, TAS and ground speed to verify. Ive even tested by timing the plane as it flys that same 200ft mission and comparing the times. We do have a parameter FW_THR_TRIM set to .5, but we also have FW_AIRSP_TRIM, MIN, and MAX set to different but appropriate values.
The questions is, what other commands or parameters will override or preclude the vehicle from obeying the DO_CHANGE_SPEED command in auto mode?
I would expect that to work. Can you share a log where you try this?
Or have you tried reproducing it in SITL?
Yes I can share logs during a flight, Tomorrow Ill post a snippet that has this in there.
Here is the link to the logs uploaded to PX4 flight review.
You can see that the speed changed up wind/down wind. So we used physical markers (the runway end and the threshold marking) to measure how long it took to travel 200ft while going the same direction but commanding different speeds. This is why the waypoints show the plane doing the same route several times, we tested at different speed settings while trying to keep all other variables the same. in the end we didnt see a difference. I think it was using the throttle setting instead of the cruise speed but im not certain.
Also, forgot to mention, we are working with the manufacturer to figure out why the airspeed sensor is throwing errors, but thats a different issue.
Previously I said it was run in QGC, but we also ran it in a custom GCS and got the same results - no change in speed. This is the log from running the custom GCS. That may be an issue too, but not certain, everything else seems to work exactly the same as QGC.
We are planning to do another test soon, is there anything we should test out?
Is this what you mean?
Airspeed setpoint is higher but the airspeed is not… 
Maybe @ryanjAA has more insight.
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Thats exactly what I mean. Im not great at interpreting these, so any insight is valuable to me.
