Control-surface buzz

Abstract

The term buzz, as used here, refers to a class of control-surface oscillations sometimes encountered during flight at transonic or low supersonic speeds. Essentially these are self-excited oscillations in, a single degree of freedom--namely rotation of the flap about its hinge. It is shown that buzz can be associated with several r6gimes of flow and it is likely that the mechanism of excitation is different for each type. At least one form of instability can be related to negative aerodynamic damping predicted theoretically and does not depend on boundary-layer effects. Other forms of buzz depend on the occurrence of shock-induced separation ahead of the flap hinge, or on the presence of shock waves at the surface of the flap itself. The parameters that determine buzz characteristics are discussed, together with the available information relevant to the prevention of buzz in practice.