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Why use a trim tab at all? Consider a Mac servo controlled, spring-biased, aileron trim system. Such systems are utilized in Bonanzas, Cozys, the Cirrus SR20 and others.
My implementation uses a small servo, mounted at the aft center of the main spar web, that moves a pivot arm through a 3" arc. Attached cables pass thru the phenolic stick mounting pads to two independent springs per side for redundancy. Each spring is separately attached to the large area washer securing the backside of the rod ends that connect the aileron control rods to the stick. The bolt securing each rod end is changed to use a cotter pinned castle nut instead of a lock nut. The springs are under tension and they add a small amount to the stick force required to displace the ailerons. However, anyone that has rolled a Lancair into a steep turn knows that plenty of stick force is required to initiate such a turn. The system is easily overpowered if trimmed to the maximum in one direction and a full aileron deflection is required in the opposite direction. Trim is actuated thru a rocker switch (left side down, left wing down, etc.) with the servo indicator seldom out of the green "servo-centered" indication. This trim system works, meeting my requirements of KISS, no undue additional balance weight and no unsightly tab on the aileron.
Scott Krueger
N92EX
PS: Spring biased aileron trim also dampens the effect of winds on the control surfaces when you airplane is parked outside.
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