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Elevator Servo/Trim

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Aug 27, 2006
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Randy asked for my opinion about the pros and cons of elevator trim with or without servo.
My elevators have a tab on both sides, one is a servo tab (right side) and the other is servo & trim (left side). Their "span" is one rib bay each. I think many of the later Skybolts have trim tabs with spans of 2 rib bays.
I don't know how the "Mac" servo/trim system is designed, but mine has a cable that runs to a small lever mounted to the seat structure on the left side to control the trim. The cable is connected to lever and torque tube mechanism mounted in the horizontal stabilizer. Friction at the lever-end holds the selected trim setting.
The elevators are also mass balanced, but I don't know how much weight is in the "ears".
The advantage of this system as I see it is simply lighter stick forces for aerobatics.
The disadvantages may be the added complexity in construction and maintenance, and flutter potential. I've never had a hint of flutter in mine, but depending on design, your results may vary.
If you plan on doing a fair amount of akro, my advice would be to add the servos, but again, I don't know anything about the "Mac" system.
Here is a photo that shows the servo/trim tabs on my Skybolt.

Edited by: Eric

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