Autopilot porpoising-KFC225

[Mark89114]

My Mooney Ovation with KI-256 and KFC225 autopilot has an issue where it hunts up and down a couple of degrees.  It is really annoying.  All other functions work, VS, ALT capture, etc.  It was varying up about 4 degrees and down not as much, barely perceptible altitude change about 20 feet.  I took it to a highly respected autopilot shop, recommended from here and was not impressed with results.  They did some work on a pitch trim servo, tested the ADI, tested and blew out static system.  They seemed highly confident in each fix, in order I listed but they finally tightened up a spring in the elevator control system and told me it was fixed.  I don't believe it is.  I fly the plane for long legs, hours at a time and the problem still exists, I think tightening the spring just dampened out the oscillations. 

More details:

• The trim doesn't seem to be running during porpoising
• Same porpoising when left in PIT mode only, not ALT
• I think it is also porpoising in VS mode but hard to tell

I spent $3600 on them testing and replacing parts when the "final solution" was tightening a spring.  I do have a call into their expert, but he hasn't called back yet.  Is this level of fluctuation just the way it is?  I find that hard to believe.  I am just trying to educate myself so when I get a return call I can question intelligently.

Any feedback appreciated     

[Marcopolo]

Mark,

 

  I had a very slight but noticeable oscillation with KI-256/KFC200 AP engaged in cruise in my K model last year.   The King AP "king" (my opinion) Bob Bramble (913- 680-4169) cleaned and adjusted the clutch on the pitch servo and all has been perfect since.  In cruise flight it would start the oscillation after a minute or so, I could put very slight pressure forward or aft on the yoke and it would cease the oscillation, but as soon as I removed the pressure it would start again.

  Bob specializes in BK HSI's AI's, FD's, DG's and VG's, but if you ask nice he may still do the servo adjustment/repair if necessary.  I would suspect that most shops may be able to make the same adjustment, no rocket science involved.

 

Hope this helps, good luck,

Ron

 

 

 

[Zwaustin]

Plus one for Bob .... I sent my KI256 out with the KFC200 AP computer part KC295 and the KC292 controller and came back good as New. Worked great up to the point I sold plane for upgrade. 

[kmyfm20s]

I have the Stec 55x in my Eagle and it oscillated as well. I had it looked at a while back and the pitch servo cable had very little tension. Tightening it had helped but a lot but it still oscillates a little. When the plane is loaded light it seems to be worse than when loaded heavy with the weight in the back. I always attributed this to the long bodies being nose heavy. The same thing happens when I hand fly it.

[flyboy0681]

Another plus for Bob, but unfortunately, his days are numbered as a King repair station.

[thinwing]

Was the porpoising occurring about once a second?Did the shop replace the tach sensor on the pitch servo?

[Mark89114]

Maybe a little slower than once per second, it wasn't very fast.  But yes they did test the tach sensor and it was "spiking the voltage" and it was replaced.  Didn't change anything.  I did talk to the tech yesterday and the only thing left is the actual computer which they are unable to test.  There is an accelerometer which he is guessing could be generating a noisy signal.  Airplane is going in for annual next week,  going to have a real hard look at all controls related to pitch before I go on to next step which is bench checking the computer.  They didn't have a spare to swap out so didn't get that test option.

Edited June 16, 2017 by Mark89114

[63-C-]

The King KFC225 is an attitude based autopilot.  I would recommend taking another look at the attitude indicator as this is the main signal the autopilot computer is looking at during pitch mode operation.  The computer and adi in that system does require a setup / calibration and also requires a special jig from King.   Sending them for repair together is usually needed unless you have the 225 test set.  

[flyboy0681]

Just now, 63-C- said:

The King KFC225 is an attitude based autopilot.  I would recommend taking another look at the attitude indicator as this is the main signal the autopilot computer is looking at during pitch mode operation.  The computer and adi in that system does require a setup / calibration and also requires a special jig from King.   Sending them for repair together is usually needed unless you have the 225 test set.  

Better hurry, all of the King repair stations are going to be history in exactly four days.

[peevee]

32 minutes ago, flyboy0681 said:

Better hurry, all of the King repair stations are going to be history in exactly four days.

That got pushed out a couple months 

[mike_elliott]

On ‎6‎/‎14‎/‎2017 at 0:31 PM, kmyfm20s said:

I have the Stec 55x in my Eagle and it oscillated as well. I had it looked at a while back and the pitch servo cable had very little tension. Tightening it had helped but a lot but it still oscillates a little. When the plane is loaded light it seems to be worse than when loaded heavy with the weight in the back. I always attributed this to the long bodies being nose heavy. The same thing happens when I hand fly it.

Have your shop run the servo motor a minute in both directions. Stiction on the armature is the culprit on STEC's. This fix was from a field engineer at STEC a number of years ago when I had this issue. I made up a 9 pin sub d connector harness and would run both servos every annual, no issues after this.

 

[LANCECASPER]

On 6/14/2017 at 8:57 AM, Mark89114 said:

My Mooney Ovation with KI-256 and KFC225 autopilot has an issue where it hunts up and down a couple of degrees.  It is really annoying.  All other functions work, VS, ALT capture, etc.  It was varying up about 4 degrees and down not as much, barely perceptible altitude change about 20 feet.  I took it to a highly respected autopilot shop, recommended from here and was not impressed with results.  They did some work on a pitch trim servo, tested the ADI, tested and blew out static system.  They seemed highly confident in each fix, in order I listed but they finally tightened up a spring in the elevator control system and told me it was fixed.  I don't believe it is.  I fly the plane for long legs, hours at a time and the problem still exists, I think tightening the spring just dampened out the oscillations. 

More details:

• The trim doesn't seem to be running during porpoising
• Same porpoising when left in PIT mode only, not ALT
• I think it is also porpoising in VS mode but hard to tell

I spent $3600 on them testing and replacing parts when the "final solution" was tightening a spring.  I do have a call into their expert, but he hasn't called back yet.  Is this level of fluctuation just the way it is?  I find that hard to believe.  I am just trying to educate myself so when I get a return call I can question intelligently.

Any feedback appreciated     

I used to have a KFC225 in an Ovation. I live near San Antonio and the only time it would porpoise is if I was flying directly over SeaWorld . .  just kidding.

 

What part of the U. S. do you live in? This may help in getting you a good recommendation on a shop that doesn't just throw parts at it. Central Texas Avionics in Georgetown TX helped with a trim switch issue on the KFC225 but seemed to know King Autopilots inside and out. I would be very confident taking my airplane back there for an autopilot issue. They were very fair also.

[Piloto]

Try cleaning the connector contact pins at the tray and at the attitude indicator. Lubricate the yoke shafts with silicon lubricant. Try orienting the passenger side nozzle toward the avionics rack. It helps a lot with cooling.

José

[freff]

anyone have recommendations for king autopilot repair near Georgia?   I have a similar oscillation on my KAP100 / KI256, but roll rather than pitch.