**Papers Published**

- Kholodar, Denis B. and Dowell, Earl H.,
*Behavior of airfoil with control surface freeplay for nonzero angles of attack*, AIAA Journal, vol. 37 no. 5 (1999), pp. 651 - 653 .

(last updated on 2007/04/10)**Abstract:**

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.**Keywords:**

Aerodynamics;Degrees of freedom (mechanics);Oscillations;Approximation theory;State space methods;Integration;Runge Kutta methods;Mathematical models;Equations of motion;Motion control;Velocity;