Frise-type aileron – An Aileron having the nose portion projecting ahead of the hinge line. When the trailing edge of the aileron moves up, the nose projects below the wing s lower surface and produces some parasite drag, decreasing the amount of adverse yaw.
Engineer Leslie George Frise (1897-1979) developed an aileron shape which is often used due to its ability to counteract adverse yaw. The Frise aileron is pivoted at about its 20% chord line and near its bottom surface. The leading edge of the aileron is bluntly rounded so that when the aileron is deflected up (to make its wing go down), the leading edge of the aileron dips into the airflow beneath the wing and adds significant drag to that wing. The resulting drag causes the aircraft to pivot (turn) in the desired direction.
The leading edge also gives a servo assist to the stick force – the moment of the leading edge in the airflow helps to move the trailing edge. The down-moving aileron also adds energy to the boundary layer by the airflow from the under-side of the wing that scoops air by the edge of the aileron that follows the upper surface of the aileron and creates a lifting force on the upper surface of the aileron aiding the lift of the wing. That reduces the needed deflection angle of the aileron.
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