To understand flight controls and how to control an airplane, you need but one resource:

Stick and Rudder, by Wolfgang Lagenwiescheavailable through almost any bookseller. It's been in print since the late 40's, early 50's or so, and is very relevant for model flyers, since all airplanes fly the same way.

For your ailerons, you can use one servo with appropriate linkage, or two servos, directly operating a single aileron each. Very large models have multiple servos on the control surfaces to make sure there's enough power. Basic models, though, usually need only one servo to operate ailerons.

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