Chasing altitude

fastfred58

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Aug 6, 2020
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21
I have a skyview system and when in level cruise it chases the chosen altitude on AP . what is the correction for this?
 

lancair360

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Oct 19, 2020
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152
Did you do the full AP tuning? It’s a separate guide for setting all the gain functions.
 

DBRV10

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Jun 15, 2008
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Brisbane, Qld. Australia
Not a lot of helpful info from you. Like aircraft type, what settings you have. Post them up so we can comment.

Are you running software at least in the V16 range? This is critical.

Also, what servos? Are you on the inner most hole without going over centre ? Most applications will be the middle hole.
 

fastfred58

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Joined
Aug 6, 2020
Messages
21
Not a lot of helpful info from you. Like aircraft type, what settings you have. Post them up so we can comment.

Are you running software at least in the V16 range? This is critical.

Also, what servos? Are you on the inner most hole without going over centre ? Most applications will be the middle hole.
It is a factory built 2010 Kitfox. I don't remember the hole setting. The servos are what ever DYnon uses.
software is current
 

porterjames

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Sep 26, 2016
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45
It depends on what you mean by the autopilot chasing altitude.
I think my autopilot is tuned about as well as can be expected, In cruise I notice a plus or minus 20 feet oscillation in relative smooth air to very light chop. Sometimes it may be plus or minus 10 feet in very smooth air. Some of this is related to the autopilot adjustment and some to up and down air column movements. I have a LSA with a 900 series Rotax (100 HP). With a fixed pitch prop I notice RPM changes with the oscillations. Obviously I also notice TAS/ground speed changes as well.
On routine local/pleasure flights I don't even pay attention to these changes, however on long leg cross country flights I use the airspeed bug to maintain an airspeed that results in a relative level flight attitude rather than chasing a specific altitude.
I tried both methods on straight line courses and found that I could average about 1.8 KTS. more when using a constant airspeed over a constant altitude. Of course this usually means accepting plus or minus changes in altitude depending on the air column movements, but these usually cancel each other out over long distances. I didn't calculate the effect on fuel burn but I assume there would be a minimal savings.
 

fastfred58

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Joined
Aug 6, 2020
Messages
21
It depends on what you mean by the autopilot chasing altitude.
I think my autopilot is tuned about as well as can be expected, In cruise I notice a plus or minus 20 feet oscillation in relative smooth air to very light chop. Sometimes it may be plus or minus 10 feet in very smooth air. Some of this is related to the autopilot adjustment and some to up and down air column movements. I have a LSA with a 900 series Rotax (100 HP). With a fixed pitch prop I notice RPM changes with the oscillations. Obviously I also notice TAS/ground speed changes as well.
On routine local/pleasure flights I don't even pay attention to these changes, however on long leg cross country flights I use the airspeed bug to maintain an airspeed that results in a relative level flight attitude rather than chasing a specific altitude.
I tried both methods on straight line courses and found that I could average about 1.8 KTS. more when using a constant airspeed over a constant altitude. Of course this usually means accepting plus or minus changes in altitude depending on the air column movements, but these usually cancel each other out over long distances. I didn't calculate the effect on fuel burn but I assume there would be a minimal savings.
Calm day , 912 uls with grond adj. prop. . It gets off the selected alt then over corrects then tries to correct and over corrects in the other direction . This repeats over and over. I will check the servo shear pins next. It seems like the auto pilot setting are always changing on mine
 

n28et

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Jul 27, 2013
Messages
25
I experienced the same issue. I discussed the issue with Dynon during Sun-N-Fun this year. They suggested I check for play in the pitch linkage by engaging the servo and then try to moving the stabilizer. Turned out that while I don’t have any play in the system, the outcome was essentially the same.

Dynon doesn’t provide installation instructions for my aircraft like they do for the RV series of planes. Unfortunately, the bulkhead I chose to mount the pitch servo to wasn’t stiff enough and flexed back and forth as the stabilizer was moved! It was no wonder the AP was chasing its tail. The fix was to beef up the bulkhead.

Good luck.
 

jcarne

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Joined
May 10, 2020
Messages
33
It is a factory built 2010 Kitfox. I don't remember the hole setting. The servos are what ever DYnon uses.
software is current
You mention your software is current so I wonder if this is yet another issue with the autopilot. Before updating my alt hold was spot on, now it does was you mention, hunts up and down like it hasn't been tuned before. I went up and tuned it again to see if I could get improvement. What's weird, look at where my gain ended up before getting good results. The real game changer though was upping the alt gain. I upped it from 0.6 slowly to 0.9 and now she holds altitude really well again. I have not tested in really juicy turbulence yet though, only light.
 

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RVDan

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Aug 8, 2012
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Frederick, MD
It seems to me that after every SW update, the AP performance changes and the AP tuning needs to be rerun.
 
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