Sunday, February 26, 2012

DFC90 Update

So after flying the DFC90 a bit more, I have noticed a couple of pretty significant glitches.  The first one is that I keep getting an intermittent “Servo Limit” warning on the PFD.  It seems that when this happens, the AP seems to get stupid.  Typically it is when I try to fly the plane on the heading mode and then the aircraft will either fail to turn, turn slowly, or turn very aggressively and then blow through the heading bug setting.  This has also happened a few times in NAV mode as well.

The next issue is the uncoupled envelope protection.  I have stalled the aircraft, I have dived the aircraft and I have over banked the aircraft.  Only twice have I been able to get any warning.  One time was an overbank and the second time was while flying with the Flight Director and as I reached short final I got an “Underspeed” warning.
The last issue is the Flight Director itself.  It doesn’t work!  I have tried to hand fly three different ILS approaches and the Flight Director is so far off that I am not even legal if I tried to follow it.  Very disappointed!

I called Avidyne and Gardner Avionics and the answer they are giving me is that it’s the servos on the airplane, not the autopilot.
I posted this issue on COPA and Dave from Nexair told me to not swap anything out until someone that knew how to check the rigging flew the aircraft.  Then he said he was coming to Montgomery, so I fly up on Saturday and met him.  He has installed a bunch of these autopilots in Cirrus and knows the workings of them very well.  We took the aircraft for a test flight and he determined three things.  Servos are fine, Autopilot is bad and the rigging on the aircraft was WAY out of spec!  One of the tests he performed was the setting of the servo.  He would hold the trim all the way to the right, but keep the plane straight and level.  Then let go.  It is supposed to take 4-6 seconds to reach a standard rate turn.  My aircraft peeled off like a P-51 in three seconds to the right.  Next we did it to the left.  To the left my aircraft banked like it was on a Sunday stroll in about eight seconds.  You could also see it on the ground when he put in full deflection left and right that they weren’t even close to being set up the same.  Once we landed he called the VP of Avidyne and got them understanding the issue, so now all I have to do is get my avionics shop to call Avidyne and call Dave and get it fixed.  Fingers crossed!

3 comments:

  1. It's nice that you have access to a specialist. I suppose it's like relying on your GP when you need, say, a dermatologist. Someone who knows your airplane and the equipment in question in detail seems warranted.

    You do seem to have been very systematic in trying each of the features of the autopilot so that you have a detailed description of what is not working properly. All helpful for diagnosing, I'd guess.

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    1. I was extremely lucky that Dave just happened to be coming down from MA and offered to help. That is the power of COPA and why owners should become members of organizations like COPA. I'm not so sure my avionics shop is all that happy about it, because basically it is in their court to fix and I think they wanted to pass the buck. We'll see, I'm still waiting on a call back.

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  2. Nice job, Mike. The videos and diagrams really help me understand your problems with the new AP. Should be helpful for other Cirrus pilots with similar problems. . . .

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