To fit an electric trim to the rudder and elevator, how do you a)
determine the size of the actual trim tab to be effective and b) determine
the size of the servo motor?

Pierre Swanepoel

Very good question.

You have to make some assumptions based on the dynamic pressure on the tab
to calculate the torque about the tab hinge.

Get yourselves a copy of Von Doenoff "Theory of Wing Sections" and look on
page 215 and up.

You probably cannot make the hinge and tab too strong :)
If it fails you die.

Paul Lamar


The Lancair site has trim servos listed and available to buy. My Wheeler
uses a small RC Allen unit that I bought from aircraft spruce for around
$200.00, and has around one inch of travel.

Kevin Alderman


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