Possible causes of auto-trim failure in one direction...

[Tommy]

Hi guys. I have finally got the chance to bring my J (Factory KFC 200) to have the A/P issue looked at. The avionics guys pulled the pitch servo and sure enough there are issues with it (transistors replaced, armature replaced etc). 

 

Now it seems like it's working again - I have't tested it yet - except the whole system only auto-trims in one direction (not sure which direction)! 

 

Now before my A&P asked to pulled more bits and pieces out for repair - as they dont's seem so sure where the problem is - I am all ears for any suggestions! 

 

Thanks, 

 

[LANCECASPER]

I just went through this - its the switch made by Bendix King on the yoke thats going bad. There are three microswitches inside.

 

http://mooneyspace.com/topic/14138-cleaning-the-yoke-trim-switch/

[orionflt]

Does the normal trim work in both directions? are they testing it on the ground? if so, it may only be auto trimming in one direction because of the pitch of the aircraft. auto trim will adjust the trim tab to maintain level flight if you are sitting nose up it will trim to lower the nose no matter where you position your flight controls. 

 

Brian

[Marauder]

Hi guys. I have finally got the chance to bring my J (Factory KFC 200) to have the A/P issue looked at. The avionics guys pulled the pitch servo and sure enough there are issues with it (transistors replaced, armature replaced etc). 

 

Now it seems like it's working again - I have't tested it yet - except the whole system only auto-trims in one direction (not sure which direction)! 

 

Now before my A&P asked to pulled more bits and pieces out for repair - as they dont's seem so sure where the problem is - I am all ears for any suggestions! 

 

Thanks, 

 

 

Tommy -- you have to be the most unluckiest J owner I have ever heard of. It seems you've had issues with almost ever system in your plane. 

[PTK]

Tommy, if it's this BK yoke trim switch you need, (aka split trim switch), I have one. PM me if interested.

[John Pleisse]

It is still likely the pitch servo or computer. But you may want to consider the trim servo (obviously). If it is OK, you need to check the chain driven trim servo tension. Many times there can be tension issues and binding that send avionics tech's to all other trouble shooting options, when something so simple can create many problems, especially with the King 140 series...they are great, when they work.

[Marauder]

Tommy, if it's this BK yoke trim switch you need, (aka split trim switch), I have one. PM me if interested.

image.jpg

 

 

Think of it as a jewel in that fine Swiss watch. Sorry Peter, that was a low hanging fruit... Couldn't resist myself.

[ryoder]

Why are we talking about boy bands?

[Tommy]

Ok went for a flight today

The ALt hold is working perfectly if the aircraft is trimmed reasonably well.

But if my J is really out of trim on decent the Trim flashes and AP disengages. Presumably the auto trim failed.

The manual eletric trim I working fine both direction...

I guess I can live without auto trim but it is a nice feature to have

[orionflt]

ok, that sounds like there is an issue in the circuit that senses the pitch of the aircraft in relationship to the trim. on some auto pilot systems you also have a visual indicator of trim position vs where the trim needs to be set to reduce the correction needed for the autopilot maintain level flight. this can be used to manually trim the autopilot to keep it from disconnecting. that is assuming it is not giving you false readings because it would be the same circuit that feeds the autopilot.

Brian

[carusoam]

Tommy,

There are some parts for a BK A/P being listed by Scott in Kansas...

See if there is anything that matches your needs...

Best regards,

-a-

[Marauder]

Ok went for a flight today

The ALt hold is working perfectly if the aircraft is trimmed reasonably well.

But if my J is really out of trim on decent the Trim flashes and AP disengages. Presumably the auto trim failed.

The manual eletric trim I working fine both direction...

I guess I can live without auto trim but it is a nice feature to have

Must be a conspiracy. I had the same issue over the weekend. I fixed mine by reseting the breaker. As Brian (orionflt) pointed out, it is giving you the trim indication, just not complying with it.

[Tommy]

At what stage of the flight you reset the breaker? 

[Marauder]

At what stage of the flight you reset the breaker?

You can reset a breaker anytime. In my case, I was flying on a downwind when I noticed my trim indications were showing up on the autopilot controller but it wasn't relieving the back pressure needed from the approach flap extension. I was seeing the trim switch command a trim movement but the trim wheel wasn't moving. I pulled the trim breaker and reset it. The trim motor has been working since.

I was told these Klixon breakers need to be "exercised" periodically to make sure they work correctly. I was told to pull and reset them periodically - which I do about once a month.

I also noticed an interesting thing while doing that. The breakers over the years that I eventually had to replace were easier to pull than other breakers with similar ratings. In other words, when a 10 amp breaker is easier to pull than a 2 amp, I knew something was up.