It's a long time since I've flown small aircraft, but regarding the use of rudder in full scale in flight it's only required to be used in light aircraft to counter P (propeller) effect, i.e., the effect on the rudder of the twisting airflow generated by the prop. The wash from a propeller is much wider than the diameter of the propeller. Opposite rudder can be used to sideslip in flight to increase the descent rate.

There is also propeller torque effect; the twisting against the rotation of the prop by the fuselage. That's why helicopters have a tail rotor, to prevent the fuselage turning instead of the main rotor. Some WWII fighter aircraft had torque effect so great that the down side tyre was only good for a few take offs and then was changed with the opposite.

Many light twins have contra rotating props, i.e., one clockwise and one counter clockwise, so P effect is not an issue. If they don't, then it will still have an effect from one or the other engine, but not both.

The only other time it is used in flight is to keep the aircraft straight when landing in a X wind; up aileron (down wing) to wind which will cause the aircraft to turn into wind if not kept straight by opposite rudder. The other technique used in X wind landings is the 'kick straight method' which is not nearly as precise as the 'crabbing' method.

Flying a jet, the only occasions on which rudder is used are X wind landings and engine out operations, except for single engine jets when it's only used for X wind landings. There is no P effect with jets.

This is all a very simplistic discussion. If you get into aerodynamics, and I mean heavy aerodynamics, then I'm not sure too many people understand it completely, regardless of their qualifications.


There is no secondary effect of ailerons as there is with rudder. Ailerons turn the aircraft. Rudder yaws the aircraft, but in so doing, one wing travels faster than the other, generates more lift, and the aircraft turns as a result, but generally not as effectively as with ailerons. The rudder is also effective down to very low speeds, and that's why it's used in stall turns.