What is an Aileron? Of the three directions of motion, the ailerons control the roll or bank of an airplane. These flap-like devices are located on the trailing edge of the wings. Some planes have the ailerons extending only half the distance of the wing whereas other planes designed for different purposes have ailerons extending the entire span of the wings. Roll Ailerons flap up and down to either make the plane roll to the left or to the right. If you wanted to make the plane roll to the right, then you would have to turn the control wheel to the right causing the left aileron to go down, and the right aileron to go up. When this happens, the right wing of the plane drops and causes the plane to turn to the right. The turn and bank indicator let pilots know what the current degree of roll is. Aerodynamics The ailerons cause the plane to roll because of the way they deflect the air. When an aileron is down, the airflow hits the leading edge of the wing and continues towards the trailing edge. Since air tends to stick to surfaces, in this case the deflected aileron. As the airflow travels over the aileron, it is accelerated downwards because of the relative position of the aileron. Due to Newton's Third Law of Motion, the force that the aileron imparts on the airflow by deflecting it down, causes a reaction where the airflow imparts a force pushing the aileron up. Conversely, if the aileron was deflected upwards, then the reactive force would push the aileron down. Torque A similar flap-like device--the elevator operates much like the ailerons, except the elevators are located on the tail assembly. It is important to note the different effects that each has on the general direction of the plane.The reason lies in the concept of torque. Torque is defined to be the distance from the center of mass times the force. The center of mass, somewhere near the crossing of the wingspan and the fuselage can be considered as a stationary rotation point. If the wingspan were the x-axis and the fuselage were the y-axis, we can draw an imaginary axis perpendicular to both these axes and label it the z-axis. Then the force acting on the ailerons would cause the plane to rotate along the x-z plane. Although the elevators and ailerons shift in the same fashion, their distances from the center of mass are on different axes, and therefore the torque acts along different geometrical planes.