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Dynon HDX - AP Panel Off-Line

Piper J3

Well Known Member
I’m helping a friend with RV-12, dual Dynon HDX, with remote Knob and AP Panel.

Everything was good for 200TT and the last flight had HDX warning that AP Panel Off-Line.. and, sure enough, it was. The stabilator trim is not functioning either with the manually operated trim switch. We are told that stab trim goes through the AP Panel, so if the AP Panel takes a dump, you lose stabilator trim. Makes for some fun flying…

I would think the trim would fail "safe" and keep functioning, but apparently not.

The reason for posting this thread is to just give a head’s up on the potential for trim being inoperable at inopportune moments...
 
Jim-

It is my understanding that the trim motor should work regardless of the status of the AP panel ... assuming there are not any wiring glitches or stuck switches.

The text below is from the Dynon SkyView instillation manual (version 15) section 18, which covers the AP panel instillation ... (should also apply to the HDX I should think):

Trim Motor Control Safety Features
• Pilot trim controls override Copilot trim controls.
• If SkyView Network connection or SkyView power is lost, the trim motor functions will continue to function as long as avionics power is available at Pin 9. When SkyView is not powered on (not communicating with the SV-AP-PANEL) the speed scheduling features (QUICKEST TRIM SPEED / SLOWEST TRIM SPEED) are not available. In this failsafe mode, the trim motors will run at their full speed when trim buttons are pushed.
• If a trim control button is detected as pushed when power is first applied to Pin 9, trim control will not activate until the button is first released.
• If a trim control button is pushed for more than five seconds (or longer, such as a stuck button), trim control on that axis will be temporarily inactivated until the button is first released.
• Motor outputs are protected against short circuits.


Looks like checking the power on pin 9 would be a good place to start.
 
Last edited:
Jim,
Coincidentally, while flying last week in my (recently sold) 2016 RV12 (with dual SkyView Touch and the AP Panel) I received a caution: AP Panel offline. At the same time I lost trim control. Fortunately I was in cruise flight, and able to land without problem.

Dynon support asked if the autopilot still worked when controlled from the Touch screen.. it did. They confirmed loss of trim was expected if the AP Panel failed, and requested I return the AP Panel for repair. In the meanwhile I installed a borrowed AP Panel and everything (AP and trim) worked fine, consistent with my AP Panel being the culprit.

John,
I looked at the installation manual you referenced. My interpretation is that if the SkyView panel fails, or connection between SkyView and the AP Panel is lost, trim will still work. However, it is not clear to me that trim should still work if the AP Panel itself fails. It would be nice if it did!

I'll post what Dynon concludes after they are done inspecting my AP Panel.
 
I can confirm that if the AP panel fails (there is a common failure for dynon) the trims will not work. I had the same issue and dynon fixed it for free, but I was on the ground for three weeks waiting on shipping/repair/shipping.
 
One AP Panel failure with loss of trim in an RV-12 is bad, but two identical failures in RV-12’s, both with loss of trim, is really not good.

Luckily the RV-12 can be man-handled with a stuck trim. I wonder what other folks do that experience this failure in a high-powered flying machine?

I can’t believe Dynon would have the trim servo controlled by a part that is not designed to fail “safe”.
 
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