KFC200 not engaging.

[FloridaMan]

KFC200 will not engage. 

*Prior to this, when I would hold CWS and use the electric trim, it would disconnect the AP. This used to not happen and I would often manually hold CWS and trim the plane when needing to level off after an aggressive change in altitude or a steep turn. Before the AP failed to engage at all, CWS continued to work as expected, I just couldn’t use the electric trim without it disconnecting the AP. 
 

*Now as soon as I flip the switch it immediately disconnects with a beeeeep. 
*Moving either side of the yoke mounted split trim switch independently doesn’t move the trim, so neither side appears stuck. It appears that the left side of the split switch just needs to be moved up or down and the right section of the split switch controls the direction. Split switch appears to work correctly with neither side appearing stuck. 
*If I hold the red yoke mounted disconnect button I can engage the flight director while the button is held down. Attempting to engage the autopilot doesn’t work, but also doesn’t beeeeeeep. Pressing the red button with the FD enabled will disable the FD and all other FD connected annunciators. Red button appears to work correctly. 
 

Any thoughts? It behaves like I’m using the electric trim without pressing CWS, but CWS and the electric trim switch both appear to be working unless there’s a second channel or logic somewhere. 

[PT20J]

Sounds like a good question for @Jake@BevanAviation. Does it pass preflight TEST with at least four flashes of the TRIM annunciator? It's been a while since I flew a KFC 200 and I don't remember ever trying MET with CWS, but I understood that standard King logic was to turn off the AP whenever MET was operated, so I'm surprised that it worked with the CWS button held down.

Skip

[FloridaMan]

12 minutes ago, PT20J said:

Sounds like a good question for @Jake@BevanAviation. Does it pass preflight TEST with at least four flashes of the TRIM annunciator? It's been a while since I flew a KFC 200 and I don't remember ever trying MET with CWS, but I understood that standard King logic was to turn off the AP whenever MET was operated, so I'm surprised that it worked with the CWS button held down.

Skip

I thought the purpose of CWS was to temporarily deviate from the AP without disconnecting. I don’t think I have a trim annunciator. I just looked up an image of the panel and I’ve never seen that red “trim” illuminate, even with testing. Maybe someone intentionally hid it. 

[PT20J]

TRIM annunciator is in lower right corner of the KA 285.

[Jake@BevanAviation]

CWS is used to release the solenoids so the pilot can control the aircraft as long as the switch is held.  When released the system will sync to the current pitch attitude but the roll axis will try to follow the heading bug or course pointer if the individual mode is selected and the bug/pointer is not under the lubber line.

You can not have autotrim and MET (manual electric trim) at the same time.  If the computer is engaged and you move the left side of the spilt rocker it will disconnect the system.

Things that will keep a KFC 200 from engaging are listed below

• failure of the power supply triggering the power monitor circuit
• left side of the split rocker not returning to a neutral position
• open current path for the holding coil in the control head
• compass valid missing when selecting a lateral control mode
• failure of autopilot disconnect relay
• broken engage lever switch

The key to quickly breaking down the system is does the engage switch latch? If so do the solenoids engage? Do you get the AP on annunciation in the remote annunciator? If the switch does not latch can you hold it closed and the system try to respond to input changes?

[PT20J]

38 minutes ago, FloridaMan said:

just looked up an image of the panel and I’ve never seen that red “trim” illuminate, even with testing. Maybe someone intentionally hid it. 

All the lamps should illuminate during test. Perhaps the bulb is burned out. I never had a failure on the KFC 200, but on the KAP 150 a trim monitor failure kicks off the autopilot and illuminates the TRIM light. The autopilot monitors the trim logic carefully because trim runaway can lead to loss of control.

[FloridaMan]

23 minutes ago, Jake@BevanAviation said:

CWS is used to release the solenoids so the pilot can control the aircraft as long as the switch is held.  When released the system will sync to the current pitch attitude but the roll axis will try to follow the heading bug or course pointer if the individual mode is selected and the bug/pointer is not under the lubber line.

You can not have autotrim and MET (manual electric trim) at the same time.  If the computer is engaged and you move the left side of the spilt rocker it will disconnect the system.

Things that will keep a KFC 200 from engaging are listed below

• failure of the power supply triggering the power monitor circuit
• left side of the split rocker not returning to a neutral position
• open current path for the holding coil in the control head
• compass valid missing when selecting a lateral control mode
• failure of autopilot disconnect relay
• broken engage lever switch

The key to quickly breaking down the system is does the engage switch latch? If so do the solenoids engage? Do you get the AP on annunciation in the remote annunciator? If the switch does not latch can you hold it closed and the system try to respond to input changes?

I can say with 100% certainty, because my altitude hold behaves like a 737Max sometimes with increasing magnitude of oscillation leaving a turn or sometimes straight and level, and on one occasion leaving a booty call in Iowa, like an Asian lady in traffic, that the CWS allows the pitch trim to operate without killing the AP. 

[PT20J]

I think there is something wonky there. The KFC 200 in my 1978 J was solid in altitude hold. There should be no need for MET to work with CWS because when you release the CWS button the pitch servo will engage and hold pitch (or altitude, depending on the vertical mode) and the autotrim will retrim the elevator. Besides it would be really awkward to manipulate the trim switches and the CWS at the same time.

How about it @Jake@BevanAviation: can you use MET with the CWS button held down without disconnecting the autopilot? And, if that's not normal, what might cause it to operate that way?

Skip

[Jake@BevanAviation]

So for science I hooked up a KC295 and trim servo to my bench tester and if you hold CWS and use MET it will run the trim servo and not disconnect. I even went and tried in in a 58P that is in the hangar. Personally I have never tried this in flight cause I know that you cant have both at the same time (auto trim and MET).  In a normal operation without CWS being used you will get the system to disconnect 100%  when using MET with the AP on.

[carusoam]

Great details Jake! @Jake@BevanAviation

Thanks for sharing this stuff!  

 

I think I see a FloridaMan reporting his attitude or trim servo showing wear issues?

As in… it holds altitude mostly… but occasionally begins to oscillate altitude with increasing magnitude…

 

What causes that? Is that a worn clutch, possibly something that can be cleaned?   
 

An attempt at cleaning something to improve its functionality would be great!

Unfortunately, I can’t remember which servos have clutches, and which servo is responsible for holding altitude… 

 

Best regards,

-a-

[Jake@BevanAviation]

@carusoam Alt hold is accomplished by multiple components working together as a system.  Pitch servo, trim servo, Flight computer and attitude gyro.  If one component has issues the system will struggle at maintaining alt hold.  For example if the slip clutch for the trim servo is weak it will struggle to trim the aircraft in flight, it might work fine on the ground but with the added load in flight it will slip early and not properly adjust the trim.  

Slip clutches do wear, they are composed of spring washers, friction plates and carbon disks. With use the carbon disk will glaze the surface of the friction plate and slippage can occur.  Most commonly when there is a excessive use of spray lubricant and it works its way into the assembly it will contaminate the disk and it will slip.  Depending on the servo series 100 vs 200 the slip clutch assembly will be part of the servo (100) or part of the servo mount (200).

Other things like high servo start-up voltage, broken trim springs,  and faulty micro switch in the pitch servo will cause problems as well.  If the OP knows they have a issue with auto trim I would start with doing a good ground test of the auto trim system.  Depending on the outcome of the test that should lead them in the direction of the problem.  One thing that has got me in the past with Mooney is if the trim servo is struggling to trim on the ground it will be worse in flight, things like added resistance to the trim system can cause oscillations in flight.

Also, if there is a issue with the attitude gyro like stiff bearings causing slow rotor speed it will cause issues as well.  Sometimes you can induce a vibration to the gyro in flight and if it starts to oscillate the AI might need to be looked at .  Something to always look for on a mechanical AI is when the gyro starts to spin up is does the attitude card shake out or is it slow to erect?  If it is slow to erect that is a sign the bearings are getting stiff.

[FloridaMan]

2 hours ago, Jake@BevanAviation said:

@carusoam Alt hold is accomplished by multiple components working together as a system.  Pitch servo, trim servo, Flight computer and attitude gyro.  If one component has issues the system will struggle at maintaining alt hold.  For example if the slip clutch for the trim servo is weak it will struggle to trim the aircraft in flight, it might work fine on the ground but with the added load in flight it will slip early and not properly adjust the trim.  

Slip clutches do wear, they are composed of spring washers, friction plates and carbon disks. With use the carbon disk will glaze the surface of the friction plate and slippage can occur.  Most commonly when there is a excessive use of spray lubricant and it works its way into the assembly it will contaminate the disk and it will slip.  Depending on the servo series 100 vs 200 the slip clutch assembly will be part of the servo (100) or part of the servo mount (200).

Other things like high servo start-up voltage, broken trim springs,  and faulty micro switch in the pitch servo will cause problems as well.  If the OP knows they have a issue with auto trim I would start with doing a good ground test of the auto trim system.  Depending on the outcome of the test that should lead them in the direction of the problem.  One thing that has got me in the past with Mooney is if the trim servo is struggling to trim on the ground it will be worse in flight, things like added resistance to the trim system can cause oscillations in flight.

Also, if there is a issue with the attitude gyro like stiff bearings causing slow rotor speed it will cause issues as well.  Sometimes you can induce a vibration to the gyro in flight and if it starts to oscillate the AI might need to be looked at .  Something to always look for on a mechanical AI is when the gyro starts to spin up is does the attitude card shake out or is it slow to erect?  If it is slow to erect that is a sign the bearings are getting stiff.

The flight director appears correct and the pitch seems to overshoot when it gets into that oscillation. I sortof assumed it was something the plane may have always had since the rocket conversion, like the increase in weight and forward CG needed a PID/hysteresis tuning on the autopilot pitch control. 
 

Turning off electric trim kills the AP, but previously I could turn it back on and it would try to hold altitude without using the trim. I did this once at FL240 in cold weather because it would dart around in pitch, presumably from ice in the static lines. I turned around and descended to under 4000ft to get under the IMC because I feared too much workload if I encountered icing or moderate turbulence. 
 

CWS is on the right side of my yoke, so CWS and MET simultaneously isn’t difficult. 
 

Any chance you know off the top of your head what bulbs that annunciator takes? 

Edited October 1, 2021 by FloridaMan

[Jake@BevanAviation]

@FloridaMan  Bulbs are 14 or 28V.  King part numbers are 037-00032-0008 (14V) 037-00032-0010 (28V).

[PT20J]

Here's a thought: My 1978 M20J had some KFC 200 altitude hold weirdness similar to what you are describing when I purchased it. I took the board out of the computer that has the pressure transducer on it and found water in the transducer. I shook it vigorously until no more water came out and let it sit in the warm house for a few days and it worked flawlessly after that.

Skip

[FloridaMan]

Just went out to test some more. Here’s a video, with sound. 
 

 

[FloridaMan]

Also, with the avionics master on, I can hear a slight click, like a relay as I release the AP switch. I don’t hear it with the avionics master off, so I believe something is making a logical decision to disengage the autopilot (e.g. I believe the switch is probably okay as well). 

[PT20J]

If you want to try remote troubleshooting, I believe @Bob Weber  specializes in that. Bobweber@webairconsulting.com, (616) 822-1999.

Skip

[carusoam]

Great details Jake!

Thanks for sharing them…

Best regards,

-a-

[FloridaMan]

Additional detail. I think the switch isn’t engaging to the full activated position. I’m not  sure if there an interlock that blocks it, but I thought it was worth mentioning. 

[FloridaMan]

The copper piece in the switch in the controller had become dislodged. Easy fix. Removal of controller was 2x 5/64 hex screws.