  Freeplay is a significant source of nonlinearity in aeroelastic systems and
is strictly regulated by airworthiness authorities. It splits the phase plane
of such systems into three piecewise linear subdomains. Depending on the
location of the freeplay, limit cycle oscillations can result that span either
two or three of these subdomains. The purpose of this work is to demonstrate
the existence of two-domain cycles both theoretically and experimentally. A
simple aeroelastic system with pitch, plunge and control deflection degrees of
freedom is investigated in the presence of freeplay in pitch. It is shown that
two-domain and three-domain cycles can result from a grazing bifurcation and
propagate in the decreasing airspeed direction. Close to the bifurcation, the
two limit cycle branches interact with each other and aperiodic oscillations
ensue. Equivalent linearization is used to derive the conditions of existence
of each type of limit cycle and to predict their amplitudes and frequencies.
Comparisons with measurements from wind tunnel experiments demonstrate that the
theory describes these phenomena with accuracy.
