In this paper we present a modular control architecture for unmanned aerial vehicles. Given a stabilizing control law, we aim to improve the performances of the vehicle by means of an internal model regulator. To simplify the design procedure, which especially in the nonlinear case might be fairly complicated, we show how it is possible to compose the separate control modules (stabilization and internal model) in an easy and reliable structure. The proposed technique will be tested on the loitering benchmark: in other words, the UAV is required to follow a target and perform a dynamic trajectory around it.