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How to ground test trim servo?

Tommy

By Tommy
in General Mooney Talk

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Marauder Grand Master

Marauder

Posted
Posted

Depends on system. For the STEC without autotrim (manual electric trim), you set HDG/ALT or VS mode and pull or push the yoke. After about 3 seconds, the trim up or down light should come on to indicate you need to trim. The indication should reflect the correct direction of trim required based on whether you were pushing or pulling the yoke. Using the trim switch, check to see the trim servo is moving the wheel in the correct direction and the light goes out.

With autotrim, same process but the autotrim servo should kick in by itself and attempt to relieve the out of trim condition by trimming the plane in the correct direction.

PTK Grand Master

PTK

Posted
Posted

Tommy, press CWS to synch the existing pitch and then engage the AP.  Same thing you would do on climb-out for example. The FD should command wings level and existing aircraft pitch. Then go through the motions of trim up and trim down with the vertical trim control. The trim wheel should move in the corresponding direction within a couple seconds. Resynch with CWS in each direction.

 

In the air the FD will command wings level and existing pitch and will autotrim to maintain that pitch.

 

Also, to be clear specifically for trim servo, with engine running because gyro needs to be erect, CWS to engage FD and then engage autopilot. Now push and pull on the yoke. Doing so activates sensors causing trim to run in appropriate direction. CWS first to engage FD.

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Piloto Grand Master

Piloto

Posted
Posted

I have a Century 31 A/P. On pre take off check I set the trim with the UP/DN switch on the yoke. That checks the trim servo. The same for the King A/Ps. I rarely use the trim wheel.

 

José

Tommy Mentor

Tommy

Posted
  • Author
Posted

My manual electric trim (on the yoke) seems to be functioning fine.

 

But I don't think I have pitch control / alt hold ability with my KFC 200 A/P (I am going to do a thorough test on Saturday)

 

Does it follow then that the problem is with the computer module not the trim servo motor???

PTK Grand Master

PTK

Posted
Posted

My manual electric trim (on the yoke) seems to be functioning fine.

 

But I don't think I have pitch control / alt hold ability with my KFC 200 A/P (I am going to do a thorough test on Saturday)

 

Does it follow then that the problem is with the computer module not the trim servo motor???

No. Can't draw conclusions just going by manual electric trim split switch. You really need to flight test and see what FD is doing. See #4 above!

carusoam Grand Master

carusoam

Posted
Posted

Lesser APs (KAP150) have alt hold and CWS...

It would be somewhat unique to get a KFC 200 and not get the third dimension control.

A KAP 100 would do that job...

Write yourself a test protocol of all the things you want to test during the flight. Every button on the AP and every button on the yoke. It's a todo list with the import things you want to test....in the order you want to test them.

Just remember, you are a Mooney pilot. Keep the clean side up, remember to look for other pilots. No heads down in the cockpit while reading manuals and trying different things...

Best regards,

-a-

Tommy Mentor

Tommy

Posted
  • Author
Posted

Do I need to hold onto the control wheel in order to trigger off auto trim when performing AP preflight test?

carusoam Grand Master

carusoam

Posted
Posted

The AP document indicates five or so tests it does at start-up. The beeps at the end of the cycle indicate which tests were successful.

The document outlines the test, the drawings show the four servos. One of them is pitch. One of them is trim.

Beyond that...AP Central?

Does that help?

Best regards,

-a-

carusoam Grand Master

carusoam

Posted
Posted

That is from my KAP 150.

The BK website has the same information for the KFC 200.

Unfortunately, I am only really familiar with my system.

I am more familiar with my system, because you gave me this good idea... To review how many servos I have and how they are tested.

I would expect that you can go to BK's site. Download the KFC 200 document and compare to what you have (part number by part number if needed) fortunately the instruments on the panel have their model number easily visible. Your POH is also full of the bits and pieces, weights and locations for W&B reasons.

The KFC is vey similar to the KAP, but adds the FD (flight director) capability. I would expect that the warm up test cycle should operate in a similar fashion.

Let's see if you get the same five? beeps on your system that are on the KAP's system.

Can you access this site?

https://www.bendixking.com/Downloads/Documents

Select the KFC 200 system that best matches yours. There are five versions of pilot guides based on the various boxes that make up the system...

If you get all the beeps, you get a success tone at the end (stretching my memory at this point). If you don't get all the beeps, which one is missing?

An interesting way to make the system fail....turn off the trim circuit breaker. (Or fail to turn it on, hmmmm?). The system has the trim on it's own circuit breaker in the event of run-away trim condition, it can be disabled. I found this to be challenging because, I would turn off all the circuit breakers prior to engine start, not turn the trim CB back on, and then try to start the AP...

See how that can be an issue?

Does that seem to help?

Keep in mind, I am only a private Pilot. No CFI. I am openly sharing what I know. It may not be safe to use for you or your airplane...

Best regards,

-a-

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