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Old 03-22-2021, 07:53 AM
KazooRV-9A KazooRV-9A is offline
Join Date: Feb 2016
Location: Kalamazoo, Michigan
Posts: 131
Default Aileron trim installation power source?

I'm installing an electric aileron trim servo, should it be powered from a servo master switch, or can it be powered directly from a +12v source?
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Old 03-22-2021, 08:01 AM
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rv8ch rv8ch is offline
Join Date: Feb 2005
Location: LSGY
Posts: 3,737

I used a switch to deal with the dreaded runaway trim problem. I doubt I will be able to react to a real runaway in time to make any difference, but I ran out of things to put on my switches. You could even double it up with your autopilot servos power switch.
Mickey Coggins
"Hello, world!"
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Old 03-22-2021, 08:26 AM
fixnflyguy fixnflyguy is offline
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,373
Default What I did

I have electric aileron, elevator and flaps, each one controlled through the MAC stick grip switches, but their power source is individual breakers. I wanted capability to disable each one individually.
Bill E.
8A7 / Advance NC
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Old 03-22-2021, 08:31 AM
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Carl Froehlich Carl Froehlich is online now
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,941

Aileron and Elevator trim on one pull breaker. Flaps on another. Autopilot servos on another pull breaker.

I use the auto trim feature on the SkyView autopilot to provide trim switching functions for the stick top hat switch. It also provides a three second lockout of trim motion (a mitigation for run away trim). This works both when autopilot is on and off.

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Old 03-23-2021, 07:48 AM
KazooRV-9A KazooRV-9A is offline
Join Date: Feb 2016
Location: Kalamazoo, Michigan
Posts: 131

In talking with a couple of other RV owner/builders in the area, neither of them have any "quick" remediation for runaway trim servos. It's clear that it's standard practice to be able to quickly disconnect all autopilot servos, but not necessarily the trim servos. I understand that there's a flight test to control the plane with a stuck trim, it's not something that's easy, but it can be flown.

I have an Aerotronics panel that was ordered by the previous builder, and it does not include a trim servo master switch, and also has an EXP Bus that uses solid state current limiters, meaning no physical CB to pull, even it you did catch and realize that a trim servo was "running away".

Is it actually more common to wire the trim servos, without a master switch?
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Old 03-23-2021, 09:04 AM
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Robertc Robertc is offline
Join Date: Jul 2015
Location: Omaha, NE
Posts: 69

TCW makes this for exactly what you’re trying to do. YMMV Bob.
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Old 03-23-2021, 09:58 AM
KazooRV-9A KazooRV-9A is offline
Join Date: Feb 2016
Location: Kalamazoo, Michigan
Posts: 131

Wonderful looking device.... But, one more failure point in the system, lots of wires to install, expensive, another manufacturer to rely on.

If a runaway failure of a trim servo can be mitigated with brute force, and that's been the Van's philosophy with the design, why would I add another component into the system?
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