KFC-150 problem

[M016576]

I'm having a problem with my KFC-150 autopilot- hoping someone might have an easy fix.

The autopilot passes it's self-test, engages on the ground and in the air, holds altitude just fine, but when I engage the heading, NAV or APP functions, the autopilot overshoots the track and won't hold it steady. I'm talking like 30 degrees AOB for a 5 degree heading correction. The computer just came back from AP central, so it's supposedly working correctly. I'm thinking a servo issue or a connection between the aspen and the KFC computer? I pulled the computer and sprayed the computer with contact cleaner- no luck there.

On the ground, when I try to get it to follow the heading bug, it works fine (puts in corrections and takes them out correctly), it's just airborne, where it seems like the autopilot doesn't recognize that the commanded heading is approaching, so it isn't taking the correction out.

Anyone know off hand where the roll servo is located on a KFC installation so I can check that, too? Thanks!

[Danb]

I had a similar issue in my J model which turned out to be the servo, try setting the heading bug on the ground and hold the yoke and see if there are appropriate forces against.l

[Piloto]

The roll servo is located in the left wing, in front of the aileron control rod. Like Danb said, on the ground check for a substantial force on the yoke when the A/P is engaged. Clean the servo connector contacts that is next to the servo.

 

José

[M016576]

Thanks guys- I'll give that a try tomorrow

[schule]

I had a similar problem in pitch and it was a bad servo. Autopilots Central sent it out for rebuild vs. $16K for a new one from King. Good luck.

[M016576]

Follow-up and close out on this:

I first took Jose's advice- but my roll servo was in the right wing, not the left. It looks like the bell crank can support the roll servo in either wing. I found that you can actually see the rigging just by shining a flashlight into where the aileron pushrod enters the wing... For those that may find this thread.

Anyways... Cleaning the contacts didn't work.

I got the pinout diagram from KFC-150 installation manual and found that there is a pin for "roll attitude" that goes from the gyro source to the autopilot.

I took the aircraft to Chief and Terry ran a continuity check on that pin... Sure enough, nothing. He pulled the computer and took the connector off- the roll attitude wire was broken off at the pin! Luckily, he had a few king connectors laying around- so he recrimped on a new connector and voila- everything is now working perfectly!

Total time to fix- 45 minutes.

Easy day!

[carusoam]

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