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GRT Autopilot "wallowing" on short approach

walkman

walkman

Well Known Member
Setup: GRT HXr with 2 GRT servos
Weather: VMC with light/no winds

I have used the a/p for alt, hdg, gnav enroute and a few approaches without issue.

yesterday I flew a coupled SAP 25 @ LZU and rode it down much lower than before. The aircraft was rolling and wallowing down the last couple hundred feet, I decoupled at around 200' above TDZE.

It was swinging around enough that it might have affected me had I been in IMC.

Any tips on what to adjust to make this stop? Gains etc are all currently set at factory defaults.
 
I've seen this with my TT autopilot at low speed. My assumption is that the ailerons are causing adverse yaw, which only a pair of feet or a 3 axis autopilot will fix.
 
walkman said:
Setup: GRT HXr with 2 GRT servos
Weather: VMC with light/no winds

I have used the a/p for alt, hdg, gnav enroute and a few approaches without issue.

yesterday I flew a coupled SAP 25 @ LZU and rode it down much lower than before. The aircraft was rolling and wallowing down the last couple hundred feet, I decoupled at around 200' above TDZE.

It was swinging around enough that it might have affected me had I been in IMC.

Any tips on what to adjust to make this stop? Gains etc are all currently set at factory defaults.
Click to expand...

Sounds like you need to tweak you gains up some. Look at this post on the GRT forums. When you change one it affects others so some experimenting is in order.

http://www.grtavionics.com/forum/viewtopic.php?f=10&t=40

My unit takes me down to a hundred feet or so pretty smoothly...I usually fly my approaches at 100 kts until field is in sight, the slow and dirty up.
Close to minimum approaches I fly at 90 and then can lower partial flaps as needed. It it's that low runway length is not an issue.
 
I was getting the airplane fairly slow, below flap speed, and was getting the flaps out, trimming etc, perhaps that exacerbated the problem somewhat.

I will look at the gains this weekend.
 
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