Rotor Drag

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Total rotor drag is the summation of all the drag forces acting on the airfoil at each blade position. Each blade position contributes to the total drag according to the speed and angle of the airfoil at that position. As the rotor blades turn, rapid changes occur on the airfoils depending on position, rotor speed, and aircraft speed. A change in the angle of attack of the rotor disc can effect a rapid and substantial change in total rotor drag.

Rotor drag can be divided into components of induced drag and profile drag. The induced drag is a product of lift, while the profile drag is a function of rotor r.p.m. Because induced drag is a result of the rotor providing lift, profile drag can be considered the drag of the rotor when it is not producing lift. To visualize profile drag, consider the drag that must be overcome to prerotate the rotor system to flight r.p.m. while the blades are producing no lift. This can be achieved with a rotor system having a symmetrical airfoil and a pitch change capability by setting the blades to a 0° angle of attack. A rotor system with an asymmetrical airfoil and a built in pitch angle, which includes most amateur-built teeter-head rotor systems, cannot be prerotated without having to overcome the induced drag created as well.