autopilot behavior on glide slope

[Solana]

I had done the Dynon inflight autopilot tuning guide, and all seemed well except it was not properly tracking glide slope. Once it was very twitchy, other times it would stray above and then below glide slope until it went full deflection. I then found out that the settings which the inflight tuning guide tells you not to mess with are critical for the glide slope behavior. I found a post which showed settings that worked for some other RV-10s, and adjusted altitude gain, pull rate, VSI gain, and G error gain. Now I get great behavior on the glide slope!

What I want to learn to make a more informed adjustment of these settings is to what each of them controls. Can anyone answer that for altitude gain, pull rate, VSI gain, G error gain, and G error limit?

 

[Solana]

Let me add that this is the info from a July 2012 posting on the Dynon forum from Dynon tech support:
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Here are some settings that have been known to work well for a couple of customers. Your mileage may vary:

Torque 90
Sens 20
Aspd min 83
Airsp max 190
Vspd 500
Pitch gain 30
Alt gain 18
Vsi gain 25
Pull rate 18
G err gain 16
G err limit 17
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The link is:
http://dynonavionics.com/cgi-bin/yab...num=1341676234

The way I used these setting recommendations was to keep the settings I had established following the in flight Dynon procedures, and then increase the other 4 settings to the numbers in this list. Like I said, it worked. I follow the glide slope with little deviation, and things like lowering the flaps do not throw me off the glide slope.

Rick Solana
RV-10

 

[Solana]

I have not yet heard from Dynon Tech support, but I did find an old post of theirs regarding the use of the autopilot settings. Maybe I am answering my own question. Here it is:

If the airplane is flying smoothly and holding an altitude, the thing to do is to increase ALT GAIN slowly until the correct altitude is held. After that you may need to increase VSI gain if it overshoots the target alt after a climb or descent.
Increasing ALT GAIN will also cause the AP to hold the desired vertical speed until nearer to the target altitude, and not round out so soon.
Here are the complete tuning instructions for your convenience:



TORQUE:
Adjust until servo does not slip during normal AP flight, and be comfortably overridden by the pilot.



SENSITIVITY:
ADJUST TORQUE FIRST
Increase gradually until airplane "twitches" when on altitude, then reduce by one
or two. If servo slips, increase torque.



PITCH GAIN:
ADJUST SENSITIVITY FIRST
After sensitivity is set, increase gradually if airplane does not settle on altitude.



Altitude Gain:
ADJUST SENSITIVITY FIRST
Increase gradually if airplane levels off too soon.
Reduce gradually if airplane overshoots altitudes after climbs or descents.



Pull Rate:
ADJUST SENSITIVITY FIRST
Controls the rate the AP will pull when changing vertical speed.



VSI GAIN:
ADJUST SENSITIVTY FIRST
ADJUST ALTITUDE GAIN FIRST
Increase gradually if overshooting climbs, decrease if rounding out too early.



G_error_gain:
ADJUST SENSITIVITY FIRST
Increase if bumps are not smoothed enough; Decrease if ride is too harsh.



G_err_limit:
ADJUST SENSITIVITY FIRST
Controls the max G the autopilot will push or pull to correct a bump (up to the G limiter).

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Mike Huff
Dynon Technical Support