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sglynn
11-13-2019, 01:26 AM
I?m flying Dynon HDX and autopilot. Everything works. After 30 minutes or so enroute I notice my aileron trim has moved over to the left by the AP auto trim function. Why? What is it telling me? I feel the stick and can?t really feel the need to have trimmed left. Plus I think it is flying right wing slightly higher. Might the springs on the servo not be balanced exactly equal? Or might I have a heavy wing do to fuel unbalance? I move the trim back to center and I think the right wing lowered a little. The trim stays there for awhile. I haven?t noticed when it auto trims left again. If you?ve seen this before what do you think is causing aileron auto trim to move? With AP off my RV-7A is pretty hands off stable. So I thought it was trimmed out but ?.. AP auto trim is moving stick left I wonder why?

leok
11-13-2019, 03:32 AM
If you turn the Autopilot off is the aircraft in trim?

sglynn
11-13-2019, 11:02 AM
If you turn the Autopilot off is the aircraft in trim?

Great obvious question that I will have to check out on next cross country. It doesn't do it on short lunch runs. I'll be back.

Raymo
11-13-2019, 11:48 AM
Likely compensating for a cross wind. I almost never touch my roll trim but find I need to after the AP has adjusted it during XC.

Bob Martin
11-14-2019, 07:39 AM
Most likely uncordinated flight. Ball not centered.
I have 2 axis TT auto pilot and no auto-trim....but when when in track or nav mode, if I push on the rudder the ap will roll the wings to compensate.
Very much like altitude hold will raise or lower the nose with updrafts and downdrafts.
So most likey your foot is resting on the rudder pedal and the ap is compensating.
Just a guess.

sglynn
11-23-2019, 12:03 AM
Okay, here are more observations and conclusion on what's going on with Autopilot auto trim aileron. I've been testing it.

1. After the autopilot auto trims the aileron to one side or the other when I turn the AP off my RV is not trimmed. I have to bring it back to near center to be trimmed.

2. The AP auto trim moves the aileron when in NAV mode tracking a specific desired track. It doesn't do it in HEADING mode just following the heading bug.

So I think the AP uses the auto trim on aileron to help with cross wind when tracking a desired track. This seems especially true tracking inbound on approaches. The fastest way I've found to see the AP use auto trim on aileron is to shoot an approach. The AP is very fast at figuring out the heading with a few degrees offset to compensate for cross wind when tracking inbound on a specific track. And the aileron trim moves then to help keep the needle center.

That's what I think. I don't think it has anything to do with trimming the airplane for hands off flight, nor anything about a centered ball. I think it is for assisting with the crab to track a desired track. So I'm no longer concerned I may have something goofed up like wheel pants, or VS.

thanks

BobTurner
11-23-2019, 01:12 AM
This is not right. Any chance the aileron trim wires are hooked up backwards?

MCA
11-23-2019, 11:25 AM
What does Dynon support say? I'm curious and saw this in a friend's RV as well.

sglynn
11-23-2019, 05:04 PM
Correction to this. It does auto trim in HDG mode also. I flew again today and tested this aileron auto trim. After disengaging AP today when it had auto-trimmed to left, I think it was in trim. I'm starting to think my right spring just needs to be slightly tighter.

How did you others get the springs adjusted to the same tension on both sides of the stick for the electric aileron trim?

thanks



Okay, here are more observations and conclusion on what's going on with Autopilot auto trim aileron. I've been testing it.

1. After the autopilot auto trims the aileron to one side or the other when I turn the AP off my RV is not trimmed. I have to bring it back to near center to be trimmed.

2. The AP auto trim moves the aileron when in NAV mode tracking a specific desired track. It doesn't do it in HEADING mode just following the heading bug.

So I think the AP uses the auto trim on aileron to help with cross wind when tracking a desired track. This seems especially true tracking inbound on approaches. The fastest way I've found to see the AP use auto trim on aileron is to shoot an approach. The AP is very fast at figuring out the heading with a few degrees offset to compensate for cross wind when tracking inbound on a specific track. And the aileron trim moves then to help keep the needle center.

That's what I think. I don't think it has anything to do with trimming the airplane for hands off flight, nor anything about a centered ball. I think it is for assisting with the crab to track a desired track. So I'm no longer concerned I may have something goofed up like wheel pants, or VS.

thanks

RickSolana
11-26-2019, 03:54 PM
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?

Bavafa
11-26-2019, 04:06 PM
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?

BobTurner
11-26-2019, 05:02 PM
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.

sglynn
04-13-2020, 06:05 PM
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.

climberrn
04-13-2020, 11:33 PM
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!

Skyview Touch.

Scott Hersha
04-14-2020, 07:18 AM
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.

PilotjohnS
04-14-2020, 08:18 AM
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.

vlittle
04-14-2020, 09:04 AM
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

sglynn
04-14-2020, 12:00 PM
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.

BobTurner
04-14-2020, 02:40 PM
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?

sglynn
04-14-2020, 04:56 PM
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.

Raymo
04-15-2020, 08:23 AM
Suggest pulling the floors and setting spring tension per the installation instructions. They should have slight tension when full left or right and fwd and the stick should self-center when moved left or right.

rswalden
04-15-2020, 09:11 AM
I?m flying Dynon HDX and autopilot. Everything works. After 30 minutes or so enroute I notice my aileron trim has moved over to the left by the AP auto trim function. Why? What is it telling me? I feel the stick and can?t really feel the need to have trimmed left. Plus I think it is flying right wing slightly higher. Might the springs on the servo not be balanced exactly equal? Or might I have a heavy wing do to fuel unbalance? I move the trim back to center and I think the right wing lowered a little. The trim stays there for awhile. I haven?t noticed when it auto trims left again. If you?ve seen this before what do you think is causing aileron auto trim to move? With AP off my RV-7A is pretty hands off stable. So I thought it was trimmed out but ?.. AP auto trim is moving stick left I wonder why?

Hi Steve,
I know it's a hassle, but as long as you are still in Phase 1 with nothing else better to do :) I recommend disconnecting your aileron servo springs and seeing if you have a heavy wing. Fix that, and also ensure your ball is centered... install a rudder trim tab if necessary. Once your airplane if flying true (aerodynamically), hook up the servo springs again and recalibrate your trim indicator. That might even achieve a knot or two improvement in cruise speed. I did this on an RV-12 with a heavy wing and it fixed the problem.
You have a side-by-side RV which is prone to roll force changes with passenger loads as well. Expect things to change again when you fly your first passenger. One trick to prevent your servo from doing all the work is to manage your fuel by burning more fuel out of one tank than the other.
Just my two cents worth.... Congrats on your project completion!

airguy
04-15-2020, 11:02 AM
Hi Steve,
I know it's a hassle, but as long as you are still in Phase 1 with nothing else better to do :) I recommend disconnecting your aileron servo springs and seeing if you have a heavy wing. Fix that, and also ensure your ball is centered... install a rudder trim tab if necessary. Once your airplane if flying true (aerodynamically), hook up the servo springs again and recalibrate your trim indicator. That might even achieve a knot or two improvement in cruise speed. I did this on an RV-12 with a heavy wing and it fixed the problem.
You have a side-by-side RV which is prone to roll force changes with passenger loads as well. Expect things to change again when you fly your first passenger. One trick to prevent your servo from doing all the work is to manage your fuel by burning more fuel out of one tank than the other.
Just my two cents worth.... Congrats on your project completion!

5 gallons lower on the left tank when solo will just about exactly compensate for the difference. Whenever I top the tanks I always start my fuel burn on the left side if solo.

sglynn
04-24-2020, 08:24 PM
So here is update on my auto-trim challenge. Dynon heard and proposed swapping out my autopilot (AP) head so I did. The next flight test showed two things. Auto trim to the left still happened but not past center so when AP was disengaged RV was in trim. This is good result. But test showed the auto-trim to right never came on. Dynon suggested the following tests to see if Servo may need to be replaced. Servos detect back pressure and will trim to relieve pressure.

With autopilot on tracking a heading and holding an altitude I used my hand to put pressure on the stick.
1. With forward pressure auto-trim trimmed up
2. With back pressure on stick auto-trim trimmed down
3. With right pressure on stick auto-trim trimmed left
4. With left pressure on stick auto-trim trimmed right

So indeed my servo was okay feeling pressure. When simulated with my hand the auto-trimmed functioned as designed. So I think the reason why I don’t see trim roll right under flight conditions is because my springs are not exactly matched in tension. I will tighten the right spring a bit.

Thanks you to Don at Dynon for working this issue and his good ideas on how to test the functioning.

Walt
04-25-2020, 07:34 AM
My experience:
Autotrim with trim tab works good, autotrim with spring bias trim does not.
AP will handle normal aileron operation without trim if you just manage fuel.

(I installed the trim on my 7 when I build it but removed the springs for phase one, decided I didn't need it and removed the system, that was 16 yrs ago)

azflyer21
04-25-2020, 09:20 AM
I have dual HDX with the ACM and AP control module, I experience the same thing only it trims to the right. Then I get the annunciation to Trim Left, when I do the plane feel coordinated, then it eventually starts the trim to the right. I will try the re-calibration to see if it helps, if there's really no solution I'll turn off the autotrim.

vlittle
04-25-2020, 09:39 AM
Here is a somehing to look at:

Please post a photo of your autopilot roll servo linkage. If it is not rigged so that it provides symmetrical forces L & R, Dynon's autotrim algorithm may be trying to trim out the asymmetry in forces.

Here is a photo from my Rocket torque tube, and the geometry. I realize many installations are different than this.

http://www.vx-aviation.com/sprocket/photos/controls/pitch_roll/roll_servo_attach.jpg


Not shown is the arm of the servo motor also makes a 90 degree angle to the pushrod at neutral. It's all about keeping all the angles at 90 degrees when neutral. You may have to lengthen or shorten pushrods to achieve this.

V