AP auto trim aileron

[sglynn55]

What is autopilot doing when it auto trims aileron? I’m flying HDX and Dynon AP. My RV7A flies hands off trimmed fine. When I use auto pilot in Nav mode like when shouting an approach or following an airway the AP autotrims the aileron. When I disengage the AP the Airplane is not in trim. I have to bring aileron trim back to center for Airplane to be trimmed. So I figured AP is using aileron trim to compensate for cross wind. Is that right? Or something else? Or might I need a rudder trim that I’m not aware of yet? It does usually trim to left. I’d expect to see it trim both directions but I don’t. Could be I’m flying in same area with same cross wind. I’ll do more testing on that. Pitch auto trim works great.

UPDATE: Just flew again. It does auto trim to left in HDG mode. And it is in trim after turning off AP. I'm beginning to think I need to slight tighten my right spring/wire.

 

[vlittle]

My proprietary autotrim system does exactly the same thing. As far as the autopilot knows when holding a course, a cross-wind looks like a roll trim error so the integral of the servo corrections is used to adjust the trim. A heading hold would not produce this, but won't take you where you want to go.

 

[Raymo]

It is simply trimming to unload the AP servo. Could be due to a cross wind or unbalanced springs.

 

[sglynn55]

It is simply trimming to unload the AP servo. Could be due to a cross wind or unbalanced springs.

Thanks I think I will tighten the "RIGHT" spring a little since stick is being trimmed to the left. Sound correct?

 

[Raymo]

Yes, sounds correct, assuming it is unbalanced now.

 

[MARVILLE]

My proprietary autotrim system does exactly the same thing. As far as the autopilot knows when holding a course, a cross-wind looks like a roll trim error so the integral of the servo corrections is used to adjust the trim. A heading hold would not produce this, but won't take you where you want to go.

I have the exact same issue on my brand new HDX auto pilot and the left roll trim seems to fight with the track mode only when following a flight plan. there are no issues with the hdg mode on either autopilot mode Expert or Simplified.
I am happy to see I'm not alone with this situation but worried on how to correct this issue on my new Virus...

 

[DBRV10]

I have never experienced this over 1700 hours of Classic/SV/HDX.

Interesting.....

 

[rwthompson67]

I've been flying my new RV-14 with dual HDX and 3-axis autopilot for about a year now and the autopilot always wants to trim full left aileron once engaged. The airplane flies straight and level hands off with no rolling tendency when aileron trim is neutral. As soon as I engage the AP in NAV, or HDG, or TRACK, it starts adding left aileron trim. One would assume it's countering a right rolling tendency, but like I said, the airplane flies straight with ZERO rolling tendency when trimmed neutral aileron. As soon as the AP is disengaged, the airplane does exactly as one would expect with full left aileron trim...it rapidly rolls left and has to be re-trimmed to neutral aileron. I'm attaching a picture indicating a typical aileron mis-trim directed by the Dynon AP and Skyview system.

 

[sglynn55]

I had exact same problem. Dynon replaced the AP Control panel and that fixed it. Contact them directly. But here is a test you can try and you don't even need to be flying.
Turn everything on, while just sitting on the ground.
Turn on autopilot. It will just hold current heading, altitude. No biggy. And the stick will get stiff, or just that the AP servos are now active and engaged.
Push, with your hand, slightly on the stick in all four directions and watch for the annunciation message to appear.
When you put forward pressure on the stick, wait, it will trim up.
When you put left pressure on the stick, wait, it will trim right.
And so on. This is a good way to see if the AP auto trim, will indeed trim to the right.
But also I think my springs on the aileron trim system are not balanced and next annual I will tighten one of them a bit.

Contact your Dynon salesman. He may want to replace the control panel. (The little one with knobs for the autopilot).

 

[rwthompson67]

I had exact same problem. Dynon replaced the AP Control panel and that fixed it. Contact them directly. But here is a test you can try and you don't even need to be flying.
Turn everything on, while just sitting on the ground.
Turn on autopilot. It will just hold current heading, altitude. No biggy. And the stick will get stiff, or just that the AP servos are now active and engaged.
Push, with your hand, slightly on the stick in all four directions and watch for the annunciation message to appear.
When you put forward pressure on the stick, wait, it will trim up.
When you put left pressure on the stick, wait, it will trim right.
And so on. This is a good way to see if the AP auto trim, will indeed trim to the right.
But also I think my springs on the aileron trim system are not balanced and next annual I will tighten one of them a bit.

Contact your Dynon salesman. He may want to replace the control panel. (The little one with knobs for the autopilot).

Awesome info, thanks. I'm gonna head out to the hangar and give that a try.

 

[AZflyer21]

I have the same issue, this is a new RV14A build and still burning off Phase 1. I decided to deactivate the autotrim in Dynon, now the plane flys straight, one less thing to worry about now.

 

[DBRV10]

Your auto trim should work perfectly. When I disconnect the plane flies straight and level. As it should.

If it doesn't you have something wrong.

 

[rwthompson67]

Your auto trim should work perfectly. When I disconnect the plane flies straight and level. As it should.

If it doesn't you have something wrong.

I agree. Email sent to Dynon support and waiting for a reply.

 

[Mike]

We are having the same issue in our RV6. Autopilot with a roll mode and auto trim slowly trims full right. Disconnect autopilot and the aircraft rolls right. Contacted support and they asked for diagnostic data which I provided from both screens. Awaiting response. Pitch auto trim appears to work normally.

 

[jwilbur]

I have same problem in my RV10 but to the left. AP flies the airplane beautifully but after 20 or 30 minutes it'll be full left trim. Turn AP off and i have to retrim to center.

 

[jwilbur]

Another data point. The AP flew my RV10 for 20 minutes the other day. Trim ended up full left as it always does. I let the AP then fly a practice ILS which it flew beautifully. At the decision height I hit the up arrow for a go around and smoothly put in full power (with the appropriate amount of right rudder). The airplane started to climb out. But while climbing, the stick went a little nuts. It went right for maybe half a second and snapped back left. Then immediately did it again and again and again. I disabled the AP and flew the missed approach by hand. I'm guessing the full left trim had something to do with it. Once at altitude and I centered the trim, I put the AP back on and had no issues except that it drove the trim full left again.

This was not an isolated case. I tried exactly the same thing today and got exactly the same result.

I'd really like to get this figured out. At this point I won't let the AP fly a missed approach. I now think this AP trim anomaly may be a safety issue.