Behavior of airfoil with control surface freeplay for nonzero angles of attack
The behavior of a three-degree-of-freedom typical airfoil is studied by numerical time integration using a standard state-space approximation, focusing on the effects of the mean or steady angle of attack. A variety of behavior is observed and the main tendency displayed by the system as the angle of attack increases is the transition from the predominance of limit cycle oscillations to a static deflection. The magnitude of the flap motion is of the order of the freeplay gap δ. For a typical airfoil, δ is 1 degree or less. Similarly, the pitch motion is of the order of the δ, and the plunge motion is of the order of the δ times airfold chord. Hence, the motions involved are sufficiently small that classical linear aerodynamic theory is still valid.
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