In this work we consider the modelling of a modular aerial robot obtained by rigidly interconnecting a certain number of ducted-fan aircraft. It is shown how different geometric configurations lead to different dynamical properties of the overall system which can be exploited to improve the achievable closed-loop performances in certain scenarios. Suitable constrained control allocation problems are formulated to show how the modular system performs in presence of possible extra payload and of force and torque disturbances that may derive from the physical interaction with the surrounding environment.