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Tweaking AP Settings for a Lancair 235 (Read 519 times)
Jul 5th, 2018 at 6:28am

Bill Reister   Offline
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Hi all,

Have one of the most sensitive planes flying, a Lancair 235 (with an O-290 engine; short tail, short landing gear, NOT a 320/360 airframe).  Went through this years ago with a TT AP, now need to learn about getting it right with Skyview AP settings.

After trial and error over many hours in Phase 1, the following settings give me smooth flying as long as the air is smooth and without being annoyingly abrupt in corrections for turns, etc.  However, if I hit a bit of light chop the plane instantly goes into an APIO which I have to damp for a moment with my hand.  The on-screen help doesn't give a lot of explanation of exactly what each setting does nor of the range of values, etc.  Thoughts?

Torque - 100%
Sensitivity - 21
Pitch Gain - 1.5
Altitude Gain - 0.3
Pull Rate - 1.5
VSI Gain - 0.5
G Error Gain - 1.0
G Error Limit - 0.25
Climb - 500
Descent - 500


Thanks for any help!
 
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Reply #1 - Jul 5th, 2018 at 5:59pm

Dynon Avionics   Offline
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From our AP engineer:

"It may not be directly related to the stated problem, but alt gain and vsi gain should probably be the defaults. We dont' recommend changing those settings very often. If it were me I'd fix the above, and then back down on sensitivity a bit."
 

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Reply #2 - Jul 7th, 2018 at 2:12pm

Bill Reister   Offline
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Dynon Avionics wrote on Jul 5th, 2018 at 5:59pm:
From our AP engineer:

"It may not be directly related to the stated problem, but alt gain and vsi gain should probably be the defaults. We dont' recommend changing those settings very often. If it were me I'd fix the above, and then back down on sensitivity a bit."


Ok I will try that.

Have you come up with more descriptive documentation about what each of the settings does and how they relate to each other?
« Last Edit: Jul 7th, 2018 at 2:12pm by Bill Reister »  
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Reply #3 - Aug 26th, 2018 at 7:15am

Bill Reister   Offline
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Bumping this.  The recommendation from Dynon did not eliminate the problem.

I would describe the problem as this:  The AP applies too much pitch correction without "waiting" to see if a partial pitch correction fixes the vertical excursion. 

The small Lancairs are notorious for being pitch-sensitive, perhaps Dynon could add a setting which limits pitch adjustment and then "waits a little" to see what effect that had before applying more change?  Even better would be a "learning algorithm" which learns over time what pitch setting is likely to provide level flight based on power and airspeed.  That way it could actively move towards an "estimated correction pitch" instead of simply continuing to add / subtract pitch until vertical speed is excessive?
 
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Reply #4 - Aug 27th, 2018 at 6:29am

RayInGA   Offline
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RVs are also pitch and roll sensitive. I think my sensitivity is around 15.

Try dropping sensitivity to 10 and gain to 1. If that is too little pitch, increase sensitivity slowly.
 

Ray Eaker
RV-7A flying since 27 Jan 2017
Dual Skyview 1000T with all available Dynon VFR goodies
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Reply #5 - Aug 28th, 2018 at 3:34pm

mmarien   Offline
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Murray M.
Saskatoon SK CAN

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In anything but smooth air the AP pitch in my Glasair II flies by the altitude forty or fifty feet in both directions. What works for me is just what you said. I apply a little pressure on the stick when it tries to fly by the altitude. Once I have the oscillations checked it holds altitude fairly well until it's bumped into oscillating again. In smooth air it's not a problem. It just needs a little help in rough air.
 

Glasair II FT - o320 - P-Mags - EFII - MTV 3 Blade CS - VP-X - Single 10" Skyview - Stratux Dual Band - zooooom ...
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Reply #6 - Aug 29th, 2018 at 12:27am

David Brown   Offline
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Bill Reister wrote on Aug 26th, 2018 at 7:15am:
Bumping this. The recommendation from Dynon did not eliminate the problem.

I would describe the problem as this: The AP applies too much pitch correction without "waiting" to see if a partial pitch correction fixes the vertical excursion.

The small Lancairs are notorious for being pitch-sensitive, perhaps Dynon could add a setting which limits pitch adjustment and then "waits a little" to see what effect that had before applying more change? Even better would be a "learning algorithm" which learns over time what pitch setting is likely to provide level flight based on power and airspeed. That way it could actively move towards an "estimated correction pitch" instead of simply continuing to add / subtract pitch until vertical speed is excessive?



There is a very detailed Autopilot Tuning document on the website. Print it off and take it with you. Sensitivity probably needs dropping down to 10-12 and playing from there. Trim is important, and if you have auto trim get that calibrated first.
 
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