This paper describes some interesting transitional behavior in the limit cycle response of a typical section airfoil with a loosely connected flap subject to a fluid flow. The freeplay non-linearity associated with the flap connection has considerable practical importance since wear and maintenance problems inevitably accompany moving mechanical parts. Piecewise linear systems have been studied within the non-linear dynamics community for some time. However, application to a relatively complicated, fluid-structure interaction problem such as this shows the ubiquity of a number of characteristically non-linear features. Special attention is focused on almost-or quasi-periodic behavior, and the correpsonding stability transitions. Brief reference is made to some prior experimental work which suggests the extent to which these responses can be realized in wind tunnel testing © 1998 Elsevier Science Ltd. All rights reserved.