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Old Nov 06, 2012, 09:50 AM
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Originally Posted by Joel K. Scholz View Post
Gary about 2 1/2 of mac.Bmatthews , you were correct that itt needs substantial reflex and elevator to maintain level flight. How were you able to predict this?
You have a cambered airfoil that has a negative pitching moment (nose down). The CG must be ahead of the neutral point for stability, which makes a negative pitching moment.

The only way you have of balancing these negative moments is to provide positive pitching moments with the ailerons and elevator. They have very short moment arms to the CG, so they will have to make a reasonably large downward force behind the CG. The only way they can do that is to have quite a bit of upwards deflection.

A better airfoil designed for use in a plank with reflex to start with would have a zero or slightly positive pitching moment. This would provide better performance and the trim force required: less drag, more lift, less power required.

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