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Dynon Autopilot Sudden Pitch Down

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I have the dual 10 inch Dynon Skyviews and integrated 2-axis autopilot.  During some 30kt xwind turbulence at 9500 feet today I saw this.

 

Trim Nose Down, then Slip Trim Nose Up.

 

When I hit the nose down trim twice, the plane suddenly pitched down hard.  I disengaged the autopilot and flew out of the turbulence.  Then a little later hit some 27kts xwind at 8,000 and the scenario repeated.

 

 

Any guesses?

 

 

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Although I didn't follow it this far, and my system is a little different, as I said earlier I had something similar happier in high DA and -6 on the flaps in a 500 fpm climb.

I took it out of AP changed to 0 flaps and climb was not an issue.

I suspect the same situation could apply to turbulence caused climb.

The video (obviously not a CT) looks like some overcompensation is going on at points. The plane took some time to catch up with the trim change and the pilot was still putting in trim.

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What's the question?

 

The question is why did the AP throw the plane into a hard pitch down when it asked for a pitch down trim adjustment during these odd set of messages being displayed.  The manual says the servos can get overloaded and cause these message to appear intermittently...but when I pushed the pitch toggle for a nose down adjustment, the AP seemed to overcompensate and throw the plane into max pitch down all at once.

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The question is why did the AP throw the plane into a hard pitch down when it asked for a pitch down trim adjustment during these odd set of messages being displayed...

 

When messing with an LSA AP make sure you are current on upset recovery.

 

Guesses:

  • Disconnect while out of trim
  • Vertical "gain" setting is too aggressive
  • Servo stopped slipping due to applying nose down trim 
  • You entered sudden lift
  • Trim detection setting issue
  • Altimeter setting change

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It's odd that it had a large pitch excursion when you engaged the "level" mode.  If it was reasonably trimmed while you were hand flying there should not be much change setting that mode.  What type airplane and servo size?

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When messing with an LSA AP make sure you are current on upset recovery.

 

Guesses:

  • Disconnect while out of trim
  • Vertical "gain" setting is too aggressive
  • Servo stopped slipping due to applying nose down trim 
  • You entered sudden lift
  • Trim detection setting issue
  • Altimeter setting change

 

 

It happened twice, 20 minutes apart in the same way.  I have used the AP a lot, but have never seen the slipping message before, and have never seen the hard nose down pitch from the AP before...

 

The only thing common was the big xwind in both scenarios.  I am gonna ask Lone Mountain about it, if it's a 'feature' fine, I will deal with that, if it's broken, then I want it fixed.

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It's odd that it had a large pitch excursion when you engaged the "level" mode.  If it was reasonably trimmed while you were hand flying there should not be much change setting that mode.  What type airplane and servo size?

 

It wasn't in level mode, it was in AP-HSI mode for VFR flight.  Its a CTLSi with Dynon Skyiews and integrated AP.

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It happened twice, 20 minutes apart in the same way.  I have used the AP a lot, but have never seen the slipping message before, and have never seen the hard nose down pitch from the AP before...

 

The only thing common was the big xwind in both scenarios.  I am gonna ask Lone Mountain about it, if it's a 'feature' fine, I will deal with that, if it's broken, then I want it fixed.

 

Maybe you were experiencing the limit of turbulence in which your AP works well?  The limit is lower in a light sport.

 

The crosswind has no effect at altitude except on the difference between your heading and track.  Use your wind arrow and data to visualize the wind relative to the terrain.  When you are in the lee of terrain is where the turbulence is.

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9gph

2270rpm

220kts

 

CTLSi? 

 

Quote:

I have the dual 10 inch Dynon Skyviews and integrated 2-axis autopilot.  During some 30kt xwind turbulence at 9500 feet today I saw this.

 

 

What's goin' on, man?

 

Didn't see no 9000 feet neither!

 

Quiddit - you jus messin wid us!

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I have the dual 10 inch Dynon Skyviews and integrated 2-axis autopilot.  During some 30kt xwind turbulence at 9500 feet today I saw this.

 

Trim Nose Down, then Slip Trim Nose Up.

 

When I hit the nose down trim twice, the plane suddenly pitched down hard.  I disengaged the autopilot and flew out of the turbulence.  Then a little later hit some 27kts xwind at 8,000 and the scenario repeated.

 

 

Any guesses?

 

Uhhhhh, what.

 

This isn't your video. This was posted to youtube on may 17th. Your hobbs meter 1550, and you have a tach, which is not shown on rotax configured displays.

 

Second, the RPM is wrong. Unless it is horribly misconfigured, you won't be using 2270 RPM while flying anywhere close to 190+ mph IAS level flight. You would basically be in a dive.

 

Your PSI would be redlined too, and 8.9 gph would mean you have a leaking fuel line.

 

There's a dozen more inconsistencies, including the fact that you won't have side by side displays in a CT.

 

Check what video you linked. If you are pulling a stunt, shame on you.

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Maybe you were experiencing the limit of turbulence in which your AP works well?  The limit is lower in a light sport.

 

The crosswind has no effect at altitude except on the difference between your heading and track.  Use your wind arrow and data to visualize the wind relative to the terrain.  When you are in the lee of terrain is where the turbulence is.

 

That's my current guess.  That the AP was behaving as configured and the xwind component was upsetting the servos to their max torque.  And the message are an anomolie of that.  When I tried to pitch down as the message indicated, the sudden break and hard nose down pitch I am guessing had something to do with the AP releasing.  If this is how it operates normally, it is a surprise to me....

 

The wind arrows are rough estimations of wind direction and speed.  That's one reason I know the xwind was high, over 30kts.  The xwind is important, because I think the AP was affected by a glancing wind direction and thats the reason for the slip message.  If it was a headwind, I am not sure it would have done it this way.

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Uhhhhh, what.

 

This isn't your video. This was posted to youtube on may 17th. Your hobbs meter 1550, and you have a tach, which is not shown on rotax configured displays.

 

Second, the RPM is wrong. Unless it is horribly misconfigured, you won't be using 2270 RPM while flying anywhere close to 190+ mph IAS.

 

Your PSI would be redlined too, and 8.9 gph would mean you have a leaking fuel line.

 

There's a dozen more inconsistencies, including the fact that you won't have side by side displays in a CT.

 

Check what video you linked. If you are pulling a stunt, shame on you.

 

Didn't say it was my plane or vid.  I give it as an example of the AP messages displayed.  I didn't take a vid of my panel doing this.  The messages are key, not the other info on this guys panel.

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Your plane flies in the relative wind, the crosswind does not increase torque required by the servos.  There is no glancing crosswind only the relative wind which is on your nose. The crosswind causes you to crab it is not the source of  any AP issue.  Turbulence is another matter.

 

What does the manual say the slip message indicates?  It is probably about servo slips which would theoretically be the result of being out of trim.

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Didn't say it was my plane or vid.  I give it as an example of the AP messages displayed.  I didn't take a vid of my panel doing this.  The messages are key, not the other info on this guys panel.

 

It's important that we know that. I was looking for other telltale signs of failure in the system.

 

You should do a recording of your own. Linking other people's vids is really not helpful when troubleshooting anything.

 

You posted once saying it was someone else.  Two minutes later you posted again, but removed the statement it was someone else.  What the hell?

 

Looks like he doubleposted. See: http://ctflier.com/index.php?/topic/2931-dynon-autopilot-sudden-pitch-down/#entry37137

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After disengaging the autopilot, did you have to re-trim your CT for level hands off or was it trimmed rather neutral once the A/P disengaged?  I had a big pitch down once on a CTLSi I was flying on autopilot, only to realize I had accidentally been pushing the nose down trim switch with my hand while I was futzing with something.  Had the slip and trim up warning, disengaged the A/P and had to re-trim, that's when I realized what I had done.

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CTLSi 413L had autopilot trim problems and still does.  When new, and with the autopilot engaged, it would give you a trim up message even though the airplane was in trim.    If you trimmed up then it would be out of trim when you disengaged the autopilot.

 

Flight Design said the autopilot servo mount was probably magnetized.  The autopilot servo mount  was removed and degaussed and reinstalled.  It worked fine for about 60 hours and then started acting up again.

The plane is in for further analysis and repair.

 

Don't know if this is associated with your problems but thought I would throw it out for info.

 

Flight Design had said they were going to get new mounts that were not magnetized.  No work on that yet.

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Charlie Tango is right that a crosswind component should not have anything to do with anything regarding servos.

 

Might be on of those "Stick and Rudder moments" that shows an underlying misunderstanding.

 

Rather than duplicate effort, please see the thread he just started for better explanation.

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