Dynon AP "Asks" For Nose Up Trim

[Toobuilder]

Just started flying this AP, so forgive if this is a common issue. I can trim the airplane for nice hands off level flight in smooth air, but when I engage the autopilot, the display indicates it's out of trim and needs nose up. I can trim it up until the indicator light goes out, but when I turn off the AP, the airplane is way out of trim nose high. It seems the AP doesn't know the airplane is in trim.

Is there an adjustment to tune this behavior out?

[BruceEicher]

I have this happen too. Sometimes the amount of unneeded up trim is surprising when I disconnect the AP.
I look forward to Dynon's or others answer.
Thanks for asking the question.

[MelJordan]

I assume you have the limiting bracket installed on the servo the prevents the possibility of the arm going over center. If that is correct, then it is likely the bracket has become magnetized. If the bracket or the two screws used to install it are magnetized it will cause that behavior. Most RVs don't really need the bracket as our control system limits the arm movement well within a safe range, but that is something each builder should determine. If you feel you need the bracket, see if you can get it demagnetized and that should fix the issue.

[BruceEicher]

Originally Posted by MelJordan

I assume you have the limiting bracket installed on the servo the prevents the possibility of the arm going over center. If that is correct, then it is likely the bracket has become magnetized. If the bracket or the two screws used to install it are magnetized it will cause that behavior. Most RVs don't really need the bracket as our control system limits the arm movement well within a safe range, but that is something each builder should determine. If you feel you need the bracket, see if you can get it demagnetized and that should fix the issue.

I did leave out the limiting bracket...

[Toobuilder]

I do have the limiting bracket on both roll and pitch.

[gator]

Has anyone talked to Dynon about this?

[Toobuilder]

Well, they are on the forum, so I would have expected an answer from them if nobody else had direct answers.

Also, I know of one other airplane exhibiting the same behavior - but no limiting bracket installed. Evidence suggests that the presence of the limiting bracket is not the root cause.

[Lionclaw]

I experienced the same issue. Both of my SV32 servos eventually failed, but I can't say for certain if it was related. If I remember correctly, the pitch servo eventually started reporting that it was slipping constantly, and it was exerting very little force on the control system. Torque was set to 100. Dynon replaced both of my servos with SV42 units and I experienced no further issues.

Aside from the failures, If I were to build another 9 I would go with SV42 servos from the start. The SV32 units were always slipping when it was bumpy. You can always dial down the torque on the 42s.... I think they're about 1lb heavier.

[Toobuilder]

Considering how heavy the Rocket is in pitch when solo, I do have the 42 installed there. This servo will keep the nose up, even in a hard turn. And yes, torque is set to 100%

However, this condition exists when the airplane is trimmed for hands off flight and calm air. The servo is hardly working at all, so should not be slipping.

[vlittle]

Originally Posted by Toobuilder

Considering how heavy the Rocket is in pitch when solo, I do have the 42 installed there. This servo will keep the nose up, even in a hard turn. And yes, torque is set to 100%

However, this condition exists when the airplane is trimmed for hands off flight and calm air. The servo is hardly working at all, so should not be slipping.

I changed the geometry of my elevator bellcrank to balance the pitch forces in my rocket. Worked extremely well, but it does require more stick throw.

I use an SV32 and get the trim alerts as well. It may be due to the control sensitivity of our rides at high speeds. I will try turning the gain down.