Help me diagnose my KFC200 issue...

[Geoff]

Hi all,

 

Looking for some help...

 

Before flight I performed ground checks per pilot manual on AP and all servos were functioning properly.

 

Scenario is that in flight the AP in NAV or HDG mode tracks well then drifts off continually for a full 360 degree turn with increasing bank all the way around. The command bar shows level flight initially then slowly follows wings into turn. Wings continue to roll into ever steeper turn command bar lagging behind. Command bar does not command return to original NAV or HDG. Interestingly, the compass slave indication deviates from centered to full deflection opposite direction of turn when more than 90 degrees off NAV or HDG and then comes back to center as turn comes 360 degrees back to original heading.

 

Aircraft is well rigged and flies straight and level when trimmed.

 

Any ideas?

[Bob - S50]

Don't know anything about the specifics of the system, but sounds like reverse sensing to me.

 

Any recent maintenance on the system or any of its components?  If so, could a couple of wires gotten reversed so it thinks it is left of course when it is really right of course and vice versa?

 

Does the annunciator show "BC" for back course?

 

Curious to hear what you finally find.

 

Bob

[Geoff]

No recent maintenance on system and BC is not illuminated in the annunciator.  Annunciator is fully functional and tested on ground pre-flight.

[DAVIDWH]

And I repeat:

 

Autopilots central, Tulsa

 

Barry or Randy......918-836-6418 

 

These guys see it every day.

 

Best,

 

DH

[jlunseth]

I have not had this problem with my 200, but I have seen it in a couple of autopilots in some training Cessna's a few years ago.  From the fact that the command bar is lagging, I would say that the AP is disconnecting, and I would suggest that the next time it happens - if you don't get it fixed first - that you check the annunciator panel to make sure the AP is still on (the "AP" should be lit).  It should be easy to tell if it disconnects, the "AP" symbol goes to a flashing red light.  But the annunciator panel is normally mounted out of the scan of the pilot and you don't always see the light when it happens.  I have had my annunciator panel moved over to the pilot's side for exactly this reason.  If you have the set up where the AP buttons are down near your knee in the center console, it is possible to accidentallly disconnect the AP with your knee. 

 

The plane may be well rigged, but any aircraft will degenerate into a graveyard spiral if left completely uncontrolled.  The usual cause is just a little bit of a crosswind that lifts one wing every so slowly, once the bank and spiral start they will accelerate.  And that is one of the things that leads me to think that you are experiencing an AP disconnect - the aircraft is drifting into a graveyard spiral because it is not being controlled.

[Geoff]

I think you could be onto something with the crosswind thought being the cause of the initial deviation.

 

My suspicion is the AP just stops receiving an input from either the HSI or the ADI.  Not sure which signal is lost but it just seems to 'drift' into a spiraling turn.

 

I actually have video of the event but it is too large to post to the site and the AP annunciator shows all normal during the entire event.  Very strange.

[Piloto]

It does not look like an autopilot problem to me. The fact that the slave indicator is not centered tells me that the heading output of the HDG gyro to the AP and slave indicator is disconnected somewhere. Check the heading gyro connections in the tail cone and the slave indicator. The HDG gyro is the round black can on the avionics shelf. If the HSI is pointing in the right direction your HDG gyro is good. Disconnect the related connectors and spray contact cleaner and reconnect. 

 

José

[Geoff]

Just talked to Randy at Autopilots Central.  His suggestion is that I have two problems at once.

 

1) The computer KC 295 has a intermittently failing resistor that is likely to be the source of the drifting.  Further the fact that the command bar does not command a return to the correct heading supports this conclusion.

 

2) The remote DG KG102A may be struggling to keep up with DG procession in steep turns resulting in the deflection of the slave indicator.

 

What do you guys think if I take these one at a time and ship him my KC 295 for bench testing and take Jose's suggestion on the DG and see if this resolves at least part of my issue.  If not then proceed to have the KG102A looked at.

[carqwik]

Do whatever AP Central suggests...btdt and they were spot-on as to what was causing problems (cold solder) in my KFC-150.

 

The fact that it always works initially and then starts to fail is suggestive...of what I don't know but maybe heat build up causing a failure?  My Stormscope won't heading stabilize when it's hot outside (think AZ summer) so it fails its initialization....but get it up into cool air and it works just fine.

[Bill Dunn]

We use AP central. They are very knowledgable! If you live anywhere near us we actually have the full test set for the KFC 200.

I would have to agree though, it sounds gyro related to me. We can also test that on the bench.

[PTK]

Geoff, I have found Randy at Autopilot Central and Larry at Sarasota Avionics to be extremely knowledgeable. If you haven't done so already do speak with Larry as well. It's always good to get more than one opinion.

[Geoff]

Anyone know what the going rate is to OH a KG102A gyro?

[PTK]

Anyone know what the going rate is to OH a KG102A gyro?

 

Bob Bramble, Aerolab Aviation Services is the specialist. Honest and very reasonable.

 

http://www.aerolabaviation.com/AEROLAB%20AVIATION%20CONTACT%20US.html

[Piloto]

Anyone know what the going rate is to OH a KG102A gyro?

$1295 at www.centuryinstruments.net  

 

Good quick turn around service.

 

José

[fantom]

$1295 at www.centuryinstruments.net

Good quick turn around service.

José

Have you tried Triumph, just off KFXE? Price is a little less, no shipping, no sales tax, and excellent service in my experience.