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Flaperons
 
Author: Clay Ramskill

FLAPERONS

One neat way to get some flaps on your plane is by the use of flaperons - a term implying use of ailerons as flaps. If you have a computer radio, or go to the trouble of a mechanical mixer, the rest is easy - after all, the ailerons would be there, anyway.

There are, however, some intrinsic problems associated with the use of flaperons; not insurmountable problems, but they must be addressed. The worst of the problems fall into two areas: 1) Adverse yaw while the 'flaps' are down, and 2) Pitch trim changes when lowering the 'flaps'. We'll address these separately.

ADVERSE YAW. With 'flaps' down, use of ailerons to bank the plane will produce a yaw, or turning action AWAY from the intended direction of turn. This is called adverse yaw, and makes turning with any sort of precision very difficult. With both ailerons down, any aileron deflection will cause more drag on the rising wing - the one on the outside of the intended turn. Note fig. 1; to roll to the right, the right flaperon is raised, decreasing drag on the right wing - and drag on the left wing is increased as that flaperon is dropped further. This imbalance of drag on the wings will try to yaw, or turn, the plane to the left, opposite our intended right turn.

Adverse yaw effects are worsened by a long wing (high aspect ratio), or by shorter tails and smaller fin/rudder areas.

Counteracting adverse yaw effects is easier said than done manually. All you have to do is feed in large amounts of rudder in the direction you wish to turn! A much better bet for most of us is to use mixing on the radio - what you need is to have aileron-to-rudder mix when the flaperons are down.

PITCH TRIM. As with any flaps, there will likely be a pitch trim change as flaperons are lowered.

The trim change can vary from negligible to violent, either up or down, depending on the plane. As a general rule, planes with long tails and large stabilizers, and high-aspect ratio wings, will tend to pitch up with flaps down. But aircraft with smaller stabs and shorter tails, and low aspect ratio wings, may very well pitch down.

Lowering flaps on a Seniorita, Telemaster, or most trainers, then, will cause the plane to pitch up. On a Hots, CAP, or many acrobatic craft, the pitch action may well be downward. And some 'in-between' planes will have very little reaction. These pitch trim effects are also dependent on your flying speed when lowering flaps/flaperons, and the power setting at the time.

Counteracting pitch trim effects could be done by manually resetting trim each time you lower or raise the flaperons, but this is NOT recommended. Again, the best solution is mixing - either mechanical, or through your radio. Unfortunately, very few radios other than computer types offer the required flap-to-elevator mix.

A few more notes:

1) Be sure to allow for the higher aileron deflections in the down direction. Ailerons must be configured to handle normal aileron deflection, PLUS any flap deflection.

2) Don't even THINK about using barndoor or outer panel ailerons as flaperons. Use only strip ailerons. This is because lowering flaperons effectively raises the angle of incidence. You do not want the outer part of your wing to have higher incidence or angle of attack than the inner portions - that leads to tip stalls, big time!

By all means, if you can cope with the yaw and trim considerations, go for it - flaperons can add a new dimension to your flying enjoyment!

 


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