Any GRT AP Tuning experts out there?

I really liked my Dynon AP and miss it since upgrading to GRT gear. I have really struggled to get this dialed into to where I think it should be. I had finally gotten the unit to hold an altitude, heading and a GPS course pretty well in smooth air and acceptable in turbulence. Today was relatively rough below 3000 and thought I would test the AP on a coupled LPV approach (VFR conditions). The GS wasn't bad, though it wandered around more than it should have, creating extreme pitch ups and speed reductions due to the lower approach speeds. This I think I can tune out with higher gains. The localizer on the other hand felt like it was being controlled by a drunken sailor. I was watching the stick endlessly going back and forth a good 4-6" while the needle was centered. I felt sea sick by DA. I tried higher and lower gains, but nothing near acceptable.

I am looking for some guidance on how all the gains interact. I was using 141% on both the Servo Gains and 80-120% on most of the general gains, based upon tuning. For the localizer, I don't know how all of these interact. I suspect all of following could be impacting the localizer tracking:

Roll Gain
XT (cross track) gain
Localizer Gain

With so many varialbes, I don't really know how to go about testing. As I mentioned the settings that I had for the Servo Gain, Roll Gain and XT Gain allowed me to track a GPS signal enroute realatively well. However, they fail miserably on the the Localizer with a localzer gain of 100. Increasing that gain made it much more twitchy (imagine the drunken sailor on amphetamines-yanking the stick faster with shorter movements). Lowering it smoothed it out some, but it was not able to keep the needle centered.

I will call GRT on Monday, but wondering if others have gone through this and have any guidance or suggestions to offer.

Thanks,

Larry

Doesn't seem to address the pitch issues, but have you upgraded to the latest software? Apparently there were some issues with loose roll coupling that were addressed.

http://grtavionics.com/apmag_tech_advisory.html

Chris

YellowJacket RV9 said:

Doesn't seem to address the pitch issues, but have you upgraded to the latest software? Apparently there were some issues with loose roll coupling that were addressed.

http://grtavionics.com/apmag_tech_advisory.html

Chris

Click to expand...

I have the latest software, but I don't think this AP fix has been released yet. It is not mentioned in the release notes and there is no indication on the website that the fix is in place. With that said, GRT is not the best in the documentation area.

The differences with the localizer must be setting related, as the AP does well enough in other flight regimes. I have been hoping this new code will tighten it up some. However, the localizer performance is MUCH worse than tracking a GPS course.

I did re-read a post on the GRT forum that indicated that the XT and LOC gains are added together. I will do some tuning with those two tomorrow. It should be calmer air tomorrow, so it should be easier to tune, but will then have to go back and re-tune when there is some chop.

Larry