I have noticed in both real flight and sim modes that a high throttle setting will result in the plane going into a shallow dive that the autopilot does not compensate for in terms of straight and level flight. At first I thought this only happened if you left the throttle stick at its highest setting after going into auto model. However, I was experimenting with speed control (in real mode) while the plane was flying in auto mode. I intentionally set a slightly higher cruise speed (using air speed sensor control) than the plane could achieve since I wanted to see the plane's maximum speed in miles per hour, and then back off the meters per second max cruise speed and find where they matched. As soon as I sent that high cruise speed setting, the plane entered this shallow dive.
I don't believe this is simply a trim issue. First, I have the plane trimmed for level flight at high throttle. Second, even if trim is out slightly, I would expect the autopilot to compensate.
I have not changed or experimented with the throttle to pitch or pitch to throttle PIDs. Could the default settings be the cause of this behavior? Should I be looking at other control parameters?
Have you tried increasing Nav Pitch Altitude PI and decreasing Nav Pitch Airspeed PI. The defaults are the same so they are probably canceling each other out so you don’t have any altitude control. I am not really an expert but that would be the first thing that I would try. Maybe increase altitude PI by 20% and decrease Airspeed PI by 20% and see how that flies.
If you do that be sure and let us know what happens.
Hi Bret. I never got around to testing the PI changes noted above. However, I noticed in the last firmware update that this behavior no longer exists in sim mode. I have not tried it yet with a real flight. I know it's easy to suspect a software bug, but I do believe that there was a flaw. If I recall correctly, others noted this same behavior.