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Elevator trim

K

Kaos2800

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Patron
I’m troubleshooting an elevator trim issue and looking for some insight.

The trim works normally in the down direction, but up trim is intermittent. I’ve located the relays and can hear them click for both up and down commands. I also checked the relay connections and everything appears tight.

My next step is to inspect the wiring and connections at the trim servo in the elevator. If those check out, I’m considering replacing the servo and started looking at the Van’s parts listings.

On the Van’s store, both the RV-8A and RV-14 appear to use a Ray Allen T3-12A servo, but the pricing is dramatically different:

RV-8A trim servo – $658
store.vansaircraft.com

Electronic Trim Components 1.2"

Small, Light, Powerful
store.vansaircraft.com store.vansaircraft.com

RV-14 trim servo – $295
store.vansaircraft.com

RV-14/14A T3-12A Trim Servo Actuator Only

Powerful, Small and Light
store.vansaircraft.com store.vansaircraft.com

The RV-14 listing says “servo only,” which may explain some of the price difference, but I’m wondering whether Ray Allen makes different versions of the T3-12A with different mounting configurations or other differences.

Has anyone replaced an RV-8A trim servo and can confirm whether these are actually the same unit?

I’ll call Van’s as well, but I thought I’d check here first.

Thanks in advance,

-David
 
There's only one T3-12A. And despite it being marketed as "an exact replacement" for the MAC -8A on various sites (Spruce), I recall having to make some adjustments from the plans when I built the last -7 -- DWG 4 showed the MAC 8A, but my electric trim kit used the T3-12A...
 
Disconnect and use a couple of alligator clips connect direclty to the servo using a 9-12vdc battery. This will:
- Identify relay problems.
- Identify if you have a binding issue.

Carl
 
I have seen numerous times when the relay clicks but voltage does not get to the servo. Relays are WAY cheaper than the servos, so if I were throwing parts at it, I’d replace those first - Ray Allen used to have crappy relays, but they improved them. Do what Carl suggested - check for voltage getting to the servo before you order anything.
 
Ironflight said:
I have seen numerous times when the relay clicks but voltage does not get to the servo. Relays are WAY cheaper than the servos, so if I were throwing parts at it, I’d replace those first - Ray Allen used to have crappy relays, but they improved them. Do what Carl suggested - check for voltage getting to the servo before you order anything.
Click to expand...
Ok, i’ll also check at the relay too.
 
The 'old' 'version 1' of the ray allen trim relay failed often, they now have version 2 which is much more reliable.
 
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