Tweaking AP Settings for a Lancair 235

breister

I love flying!
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Apr 6, 2018
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20
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!
 

Dynon

Dynon Staff
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Woodinville, WA
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."
 

breister

I love flying!
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Apr 6, 2018
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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."

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?
 

breister

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Apr 6, 2018
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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?
 

Raymo

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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.
 

mmarien

Murray M.
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Dec 26, 2009
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Saskatoon SK CAN
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.
 

DBRV10

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Jun 15, 2008
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Location
Brisbane, Qld. Australia
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.
 

breister

I love flying!
Joined
Apr 6, 2018
Messages
20
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.

Hehe my "autotrim" is that whenever I feel it is out of trim I move the trim lever...  I do actually react to the trim annunciations on the Skyview, so it is "sort of" automatic.  I've noticed that slight up trim seems to work better than neutral, down trim makes it worse.

I will follow your advice once I either have a working heater or the weather warms up.  Thanks!
 
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