This paper explores application of an L1 adaptive control architecture to a light, high-aspect ratio, swept wing aircraft configuration that is inherently flexible and exhibits strong rigid body/flexible mode coupling. Specifically, we present L1 adaptive controller developed for a semi-span wind tunnel model capable of motion. The wind tunnel mount allows the semi-span model to translate vertically and pitch at the wing root resulting in better simulation of an aircraft's rigid body motion. These additional degrees-of-freedom (DOF) require that an altitude-hold/stability- augmentation system be used to maintain model position vertically on the mount in addition to the gust load alleviation (GLA)/flutter suppression controller. The control objective is to design a pitch control with altitude hold while providing gust load alleviation and suppressing body freedom flutter. The controller is an output feedback nominal controller augmented by an L 1 adaptive loop. The paper presents controller development and simulated performance responses.