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RV-10 Trutrak autopilot

kevin O

Well Known Member
Have seen my autopilot go to max airspeed fault for no apparent reason. Happened three times in last 20 hrs. Will reset by cycling power. Has anybody experienced this?
 
RV-10 W/RV-10 Auto Pilot

Kevin, I have a RV-10 AP in my RV-10 and I had the same problem. Go to the pitch set up menu, press and hold Alt for two seconds. Scroll to the Max Airspeed page, fourth option, and check your setting. I had to increase mine to 170kts to avoid Max Airspeed warnings. Hope this helps. Dave.
 
There is also a max airspeed on the EFIS for the AP. So depending on which mode you were using, one of the max airspeeds could be affected. The one on the EFIS AP settings are in affect if the AP is being driven by the EFIS. The one on the AP itself is if it is being controlled using the knob on the AP itself.
 
I have seen this

I have had this same problem several times before I figured out what was causing it. I also have an SL-30 to a Bob Archer wingtip antenna. After some trial and error and some time with my avionics guys at work I determined that the SWVR was above 3.0 and the reflected power was causing the AP to fail. I adjusted the positioning of the antenna in the wing and got below 2, but I am scrapping the wingtip antenna in this years condition inspection and installing a traditional antenna.

Eric
 
Can you give me a little more info on how antenna is causing the autopilot interference. What is swvR and the significance of 2 vs 3. It is not being caused by incorrect settings. Thanks
 
SWR = standing wave ratio, or sometimes SWVR = standing wave voltage ratio, to differentiate between measuring power or voltage. Ideally your antenna should 'look like' 50 ohms; all the signal travels down the coax and into the antenna and the SWR = 1. If the antenna does not have a 50 ohm impedance, some energy is reflected back up the coax and into the transmitter, and the SWR will be greater than one. The higher the SWR, the worse the mismatch. Some transmitters do not like this, and may react by radiating spurious RF. If this gets into the autopilot electronics things may go wrong. That's the theory. It would only show up as the autopilot misbehaving during or after transmitting - you should see a correlation.
 
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