231 Trim Power Wiring

[PeteMc]

Talking to my avionics guy about an AP trim disconnect issue I've been having (1980 K).  He's questioning how the Trim power is run to the panel rocker switch that he hasn't seen before, but I don't remember it ever being rewired since I've owned the plane.  Right now he says the lines go from the breaker to a buss and then to the Trim rocker switch in the panel. 

Any other K owners know how their power is run?  He's going to rerun the line from the breaker directly to the switch.  But just a curiosity why it was done this way.

 

 

 

Edited September 20, 2022 by PeteMc

[N201MKTurbo]

What autopilot do you have? More important than what plane you have.

[Aerodon]

I looked at my Mooney wiring diagrams - nothing on the trim power (as expected because it is often part of the autopilot).  Then I looked at a KFC diagram, it has a 'FCS' bus  (flight control system) that feeds the autopilot, trim and compass system, each with its own circuit breaker.  The FCS bus is powered via the main bus, with a relay and a 1A CB.  In this way, the entire A/P can be disconnected by pulling the 1A breaker, or the trim can be disabled by pulling the Trim breaker.

It's really important that you understand your system, and not mess with the design.

The answer you are looking for lies in the wiring diagrams for the autopilot installed in your plane.  Don't let anyone make changes without this information in hand.

 

Aerodon

 

[PeteMc]

37 minutes ago, N201MKTurbo said:

More important than what plane you have.

 

 Okay...     Per the message heading and per the body of my question...   A 1980 231 K.

 

(Sorry, it's late and I couldn't resist.... )

[PeteMc]

6 minutes ago, Aerodon said:

Then I looked at a KFC diagram, it has a 'FCS' bus  (flight control system) that feeds the autopilot, trim and compass system, each with its own circuit breaker.

Thanks!   I'll pass that on and have him dust off some of his old manuals!! 

[PT20J]

Assuming you have a B-K KFC…

[LANCECASPER]

10 hours ago, PeteMc said:

 

 Okay...     Per the message heading and per the body of my question...   A 1980 231 K.

 

(Sorry, it's late and I couldn't resist.... )

If it's a 1980 231 and you have a King Autopilot and it was installed by Mooney it's a KFC200.

But Mooney also offered the Century 21, 31 and 41 autopilots in that year.

Which one do you have?

[PeteMc]

Yes, indeed a KAP/KFC200 original installation (w/ Aspen Pro Max now in place of the FD/DG).  And the info from @Aerodon and @PT20J seems to be on the mark.

I've been searching for the wiring diagram online and so far no luck.  If anyone has one for the 200, or even better the full installation manual, they can point me to online I'd appreciate it.   (I kept a copy of the one for the 150 PT20J posted.)

And as a curiosity...  Did Mooney change up the wiring for the power when they installed a Century vs a King AP? 

 

[PT20J]

What may be confusing your avionics tech is that he may not realize that the TRIM switch is a circuit breaker switch. Trim installations with yoke-mounted switches need a circuit breaker to protect the yoke switch wiring from shorts and the CB needs to be able to be manually pulled in case a switch defect causes a trim runaway. Most installations use a pull-type breaker, but Mooney used a circuit breaker switch.

Skip

[PeteMc]

17 minutes ago, PT20J said:

What may be confusing your avionics tech is that he may not realize that the TRIM switch is a circuit breaker switch.

No, I think it gets all that.  He does a lot of work on PC-12s up to Amazon's 737/67s.  So guessing it's just a memory reboot to get back to "Mooney" mode and how they did things. 

 

EDIT:   Just fixed above "737" vs my rebellious fingers 777.

 

Edited September 21, 2022 by PeteMc

[Aerodon]

Power distribution from KFC200 manual

[PeteMc]

30 minutes ago, Aerodon said:

Power distribution from KFC200 manual

Thanks!