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  #11  
Old 11-26-2019, 03:06 PM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by RickSolana View Post
Fuel imbalance seems like a good guess. Have you tried starting a flight on the other tank and seeing if it trims in the other direction?
The auto trim is to keep the plane in the trim position. Steve indicated that when he turn off the A/P, the plane is not trimmed and he has to manually trim it back.

Steve,
Do you know if it always trims it in one direction?
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  #12  
Old 11-26-2019, 04:02 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Bavafa View Post
Steve,
Do you know if it always trims it in one direction?
Do this test: Deliberately trim it off to the stick-right side, then engage the autopilot. If the autopilot trims it further right, the wires are crossed.
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  #13  
Old 04-13-2020, 05:05 PM
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sglynn sglynn is offline
 
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Default Trimming left

Quote:
Originally Posted by BobTurner View Post
Do this test: Deliberately trim it off to the stick-right side, then engage the autopilot. If the autopilot trims it further right, the wires are crossed.
Bob, I tried your suggestion of trimming right today. Results are, when I trimmed right, the AutoTrim brought it back to center and kept going to trim left. It trimmed left about 50% of the way. When AP turned off, RV was out of trim. Trimmed was straight up. Tanks equally full. Calm day.

So I tried the opposite. I manually trimmed all the way left hoping to see AutoTrim bring it back to the right a little. It did not. It stayed full left.

Weird. I'm thinking of doing the trim calibration again. Any other ideas?

When I fly manually I barely notice the need to trim left or right much. Pretty stable. So if I can't get the autotrim left to work better I'll just turn auto aileron trim off.
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  #14  
Old 04-13-2020, 10:33 PM
climberrn climberrn is offline
 
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My AP has put the trim in a left descending attitude most of the time. Talked to Dynon about it and they didn?t have any suggestions. They even sent me a replacement AP head. No changes. For a while I turned the auto trim off in settings. Recently turned it back on to try and get it figured out.

Kinda gave up on the auto trim. Looking forward to hearing what you find out!

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  #15  
Old 04-14-2020, 06:18 AM
Scott Hersha Scott Hersha is offline
 
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You haven?t mentioned where the slip/skid ball is during all this. When auto trim goes all the way out is the ball centered? If not, what happens to auto trim when you center the ball? Do you have a rudder trim tab or wedge? If everything else checks out maybe you could try burning the left wing down enough to see if it auto trims back to the right.
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  #16  
Old 04-14-2020, 07:18 AM
PilotjohnS PilotjohnS is offline
 
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Default Sensor

It sounds like the AP sensor is not level with the wings, or the rudder trim is off.
I would make sure the wings are even with the horizon in ap mode, and when flying by hand in trim.
Then recheck level of ap head or whatever sensor it uses.
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  #17  
Old 04-14-2020, 08:04 AM
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vlittle vlittle is offline
 
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I see the same behavior with the autotrim system I designed. It predates the Dynon system, but it uses the Dynon serial streams to integrate and compute trim corrections.

The algorithm integrates the servo corrections over a specific interval, makes a trim adjustment, then repeats the process. The long term objective is that the integral will be zero.

With roll, fuel imbalance, an off-center ball, or a cross-wind in track-hold mode will cause the trim system to neutralize off-center. The job of the roll trim is NOT to level the wings, but to trim out the external influences that affect the track or heading.

A simple experiment: go fly and manually neutralize your roll trim to wings level. Now watch your heading and ground track. In any typical situation, these will change while you are in perfect trim. The autopilot, when engaged, corrects to maintain heading or track using the trim system.

I once flew 200 miles on my autopilot with a broken shear screw in my roll servo. My roll trim system flew the aircraft fine, making minor course corrections along the way. It was only a 90 degree course change where I noticed something wrong. There was not enough trim authority to make that dramatic turn.

So just stop worrying and trust the technology. Nothing can go rong.

V
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  #18  
Old 04-14-2020, 11:00 AM
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sglynn sglynn is offline
 
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Default Trimming left

Quote:
Originally Posted by vlittle View Post
I see the same behavior with the autotrim system I designed. It predates the Dynon system, but it uses the Dynon serial streams to integrate and compute trim corrections.

The algorithm integrates the servo corrections over a specific interval, makes a trim adjustment, then repeats the process. The long term objective is that the integral will be zero.

With roll, fuel imbalance, an off-center ball, or a cross-wind in track-hold mode will cause the trim system to neutralize off-center. The job of the roll trim is NOT to level the wings, but to trim out the external influences that affect the track or heading.

A simple experiment: go fly and manually neutralize your roll trim to wings level. Now watch your heading and ground track. In any typical situation, these will change while you are in perfect trim. The autopilot, when engaged, corrects to maintain heading or track using the trim system.

I once flew 200 miles on my autopilot with a broken shear screw in my roll servo. My roll trim system flew the aircraft fine, making minor course corrections along the way. It was only a 90 degree course change where I noticed something wrong. There was not enough trim authority to make that dramatic turn.

So just stop worrying and trust the technology. Nothing can go rong.

V
Vern
Thanks for your interests in this topic. Per questions: I do check the ball and its centered. Plus I test trim going in one direction then 180 degrees in the other direction. It always trims to the left. Seems like if it were working correctly it would trim to the right sometimes. Plus I forgot to mention when AP does auto trim to the left it appears RV is flying tilted to the right as if heavy right wing. Manually bringing trim back to neutral levels the plane. I do not have any trim tab on rudder. I'll re-calibrate per installation manual, test again, and tell you if re calibration changed anything. Note aileron trim works great manually and pitch trim works great too.
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  #19  
Old 04-14-2020, 01:40 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by vlittle View Post

So just stop worrying and trust the technology. Nothing can go rong.

V
?Rong? ? Is this a subtle joke that went over heads? If not there?s a message!

OP: Is your control system ?smooth?? Any chance the autopilot is hanging up with a bit of right aileron, and your trim system is trying ti fix it?
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  #20  
Old 04-14-2020, 03:56 PM
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sglynn sglynn is offline
 
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Default auto-trimming left

UPDATE: I re-calibrated thru HDX. I was reminded that I'm also using Advanced ACM (VP-X type power supply), but that shouldn't matter. I think the recalibration might have reset "centered" slightly different. Just went for a flight test. There was some improvement.
1. Starting with trim centered - it stayed center and auto-trim didn't go far left as before. It did go a little left, but only slightly and plane seemed trimmed.
2. Set trim to far right - Auto-trim brought it back to center. Good. It use to over correct to far left. But this was only a 5 minutes test.
3. Set trim far left - Auto-trim did not bring it right back to center. In fact, I never see the annunciator say it is trimming right. Auto-trim never moves right. Just left.

Ideas on why it doesn't trim right are appreciated.
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