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Aileron deflection causes a rotation around the longitudinal axis by:
  • A
    causing sideslip, which generates a rolling moment.
  • B
    aileron secondary effect.
  • C
    changing the wing drag and the two wings therefore produce different lift values resulting in a moment about the longitudinal axis.
  • D
    changing the wing camber and the two wings therefore produce different lift values resulting in a moment about the longitudinal axis.

Refer to figure.

In an aircraft, spoilers can be installed to intentionally reduce lift for a specific wing by partially disrupting the airflow over the airfoil.
They can extend symmetrically or asymmetrically.
If spoilers on both sides are used, its primary purpose is to reduce the speed at which the aircraft is travelling.
Spoilers can also be used in a turn to assist the ailerons.
In this case, the spoiler mounted on the down-going wing will come up, reducing lift for that wing even more and therefore assisting the ailerons.
The spoiler on the up-moving wing will remain stowed.

For example, if the aircraft wants to enter a right turn, it will have to bank to the right.
The right wing will have to come down and the left wing will have to rise.
The aileron on the left will come down, producing more lift on the left wing by changing the wing camber and the aileron on the right will come up.

The spoiler mounted on the upper side of the right wing will also come up, reducing lift of the right wing even more.
This way the aircraft reaches its desired bank angle easier at low speeds.

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