Altitude capture

scgarrett3037

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Apr 18, 2011
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16
I'm just starting to test out my AP in my RV12, and have the following issue/situation that I would like to get some suggestions or ideas on.  Here is the situation.....I'm flying level at 2500 msl and dial in an altitude of 2000 msl.  I now turn on the AP and the aircraft begins a CLIMB at a pretty good angle.  After the planes climbs about 300 ft I disconnect the AP.  I'm somewhat nervous letting it continue.  Your thoughts??
 

dynonsupport

Dynon Technical Support
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Mar 23, 2005
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Are you sure you calibrated the pitch servo in the right direction? If you gave it pitch down when it wanted pitch up in the calibration process, it would do this.

You should be able to test this on the ground. Engage the AP on the ground and give it a altitude bug well above you and well below you. Does it move the elevator the right way?
 

scgarrett3037

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Apr 18, 2011
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My ground test resulted in the following:  With the A/C on the ground at 500 msl, I set in 2000 ft for an altitude and engaged the AP.  The elevator moved to show a FULL climb deflection and the pitch servo reached the limit and you could hear it making a slipping sound when it reached the limit.  It wanted to keep going.  I set the AP altitude to 000 ft and engaged the AP, again the elevator went into a FULL climb movement and the servo reached the limits.  More to follow tomorrow.
 

dynonsupport

Dynon Technical Support
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If you do a servo test in the autopilot setup menu, does the stick make the indicated movements? If you can give our tech support a call at 425-402-0433 while you're at your airplane, that might help us help you figure out what's going on in real time.
 

mmarien

Murray M.
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Dec 26, 2009
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Saskatoon SK CAN
If you change the bug from 2500 to 2000 it should descend not climb. Your servos seem to be backwards. Try the calibration again. Pages 10-11 of the Installation manual

On the ground the servo will go to full pitch and then start slipping because all indications are that it's still level - right. Same as the roll. If you set the TRK bug to something, the servos will go to the limit and then start slipping as the TRK never changes when sitting on the ground.

In the air there are are two limiting factors to climbing (or descending). The first is the climb rate, set either as the default or by using the VS bug. You can select this with the ALT MODE in AP. The second is the air speed. If the air speed slows to less than what you have set as the minimum during a climb, then the AP will lessen the pitch to maintain the minimum air speed while still climbing.

When I'm at cruising altitude and getting close to the destination I just move the altitude bug to circuit level and let the AP take me there. It will never pitch below the VS settings and will lessen the pitch to keep below the maximum air speed. I have my GPS495 VNAV set the same way so it will give me a warning as to when to start the descent (VNAV). Yeah, I know, I'm lazy when it come to deciphering. :-/

You should check and set all your AP settings according to your airplanes performance starting with the calibration and then go test them in the air. You should start with some real mild settings VS=200fpm and air speeds well within the Vy and Vne and increase them as you get comfortable that the AP is maintaining those limits.
 

scgarrett3037

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Apr 18, 2011
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16
I performed a calibration setup again and the setup was successful.  I understand why the aircraft will continue to try to climb when attempting to reach an altitude above its present level.  However, I don't understand why it climbs when the assigned altitude is below the aircraft.  Calibration was successful!  Dynon support thinks it might be an internal setting regarding the G load.  The G load should be 1 on the ground and mine is set at .8.  Therefore the aircraft attempts to reach 1 G......thus the climb..??  The datalog file has been sent to Dynon for review.  We will see what the Engineering dept has to say.  
 

scgarrett3037

New Member
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Apr 18, 2011
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I was asked by Dynon to return my D180 for service (which I did). Support mentioned that the G-loadmeter needed to be adjusted. Hopefully, a more detailed explanation will be reported here for everyone to view.
 

scgarrett3037

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Apr 18, 2011
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Item returned

I received my D180 back from Dynon on 9/19/11 with no information provided on what they did to fix the issue. :'(
 

dynonsupport

Dynon Technical Support
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Mar 23, 2005
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Essentially, one of the sensors (an accelerometer, most likely, but I'm writing this remotely from the AOPA expo location without access to our troubleshooting databases, so I'm not sure) probably wasn't meeting it's specifications. This, in turn, can cause AP issues like you were experiencing.

We don't at this time provide individual detailed trouble reports beyond whether the problem was hardware, software, or not reproducible, but we're getting better at this over time. We want to provide meaningful information, but often, the details won't be meaningful to you, the end customer. Without REALLY knowing "how the sausage is made", customer X's symptoms and diagnosis will often not correlate to customer Y's very similar but not quite exact symptoms and different eventual diagnosis, so we don't want to put information out there that is too technical and is prone to being misunderstood without lengthy back-explanations (which aren't practical to produce for every failure). All that said, if you give tech support a call, they can look back through the case and give you a little more detail about what was found.
 
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