VAF Forums - Dynon AP "Asks" For Nose Up Trim

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- - Dynon AP "Asks" For Nose Up Trim (https://vansairforce.net/community/showthread.php?t=113567)

Bruce,
The code was only supposed to change the trim detection, so I don't have an obvious reason that it would change the actual performance of the autopilot at all. I have our AP expert looking into it.

Thanks for the feedback on trim performance. We're getting good feedback on that so it looks like positive change.

Bruce, that would be an undocumented design feature.

I am getting the trim indications that are annoying, but until the code is stable I will put up with the flags not the ride. ;) Thanks for Beta testing! Having done some before it can be fun!

Quote:

Originally Posted by BruceEicher (Post 893125)

I flew a two hour round trip yesterday using the new AP program. Testing the results I found the pitch in perfect trim each time I disengaged the AP.

But it seems now that the altitude struggles to hold steady. I was cruising high in smooth air but several times a small bump would cause the pitch to hunt, up and down about 5 cycles 50 feet or so before settling. Also when I dialed in an altitude change either up or down it would overshoot the 500FPM then overshoot the new altitude starting the hunt again. Before this new program the pitch was rock steady.

Do you recommend any setting changes, or other thoughts?

Hi Bruce,

Thanks for trying the trim fix out. Were you getting any pitch SLIP indications when it was misbehaving?

Other things being equal, my recommendation would be to run the airspeed hold portions of the autopilot tuning guide (here: http://www.dynonavionics.com/downloa...uide-Rev_B.pdf) I'd also double check for any slop between the elevator and the servo.

We'd like to get a copy of the dynon diagnostic log for that flight, if that's possible. You can get in touch with us at support@dynonavionics.com; please put it to my attention.

Thanks,
Lawrence Doan
Autopilot Guy

Quote:

Originally Posted by dynonsupport (Post 893534)

Hi Lawrence,

No servo slip.
I will download the log tonight, check for linkage slop and take a peek at the tuning guide PDF.
We fly to Montana this holiday weekend so I will gather more data I'm sure.
Thank you.

Dynon as always stepped up and took care of the issue. Lawrence read my flight data and saw servo or linkage slop. The servo was the problem, mailed it in and repaired, back in a week, No charge. Now the altitude is rock steady, and the trim is accurate.

Thanks Dynon!

FYI, before the new public beta trim program, we believe the out of trim condition kept a load on the servo, thus taking out the lash/slop. The new program lets the system relax in-trim. So it might uncover further linkage or servo slop in other's...YMMV....

So far I would recommend the new trim program...

Apologies - AP newbie question

My AP has been working perfectly in Simplified Mode since new. It held altitude, climbed and descended to target altitudes perfectly and controlled, it did everything I hoped for.

I updated to 10.2 and now it won?t do any of the above, won?t hold altitude it fly?s like a porpoise, and descends erratically ie it wont descend at a constant rate. In Roll the AP is ok, Pitch is next to useless.

To fix this new problem, Dynon has suggested I refer to the Autopilot In-Flight Tuning Guide, see extract below.

In particular, if the autopilot cannot keep up with the flight director pitch command bar, PITCH SENSITIVITY should be increased. At some point the AP will track the command bars, but follow behind them.

My question is where or what are the "Command Bars" ?

You need to change the main efis display to "flight director" presentation. Then you will see two inverted 'V' s replacing the dot and bars of the conventional display. The Vs represent the wings, the vertex is the nose. One of the Vs will move with the airplane, just like the AI; the other V is the "command bar", and shows where the box thinks the plane should be. When hand flying you nest the Vs together. The autopilot should do the same.

Here is a photo of what I'm seeing. Im guessing Ive got the V's nested ?

Derek,

Yes, those are the 'airplane' and command bars nested together.

As you turn up PITCH SENSITIVITY (and later PITCH GAIN if you need it) be sure to turn it the minimum necessary to achieve the performance you're after. As you get close to the right setting, the improvement becomes softer as you increase gains, and it's possible to over do it.

Feel free to get in touch with us at support@dynonavionics.com.

Lawrence Doan
Autopilot Guy

Dynon Support,

I was about to buy a couple of SV32 servos and use my D100 as an Autopilot. I was concerned that you are not committed to porting these fixes to the D100 series. Can you confirm Dynon's plan here?

Also, based upon this thread, will the SV32's be adequate for pitch and roll on the RV-6?

Thanks,

Larry