This paper outlines some of the effects of fan angular momentum on ducted fan UAVs. All aircraft will be affected by their propeller’s angular momentum, however, ducted fan vehicles are particularly susceptible due to the relative sizes of the fan and the airframe. During maneuvers, the angular momentum of the fan causes a gyroscopic torque that must be countered by the UAV’s control surfaces. If not accounted for during design, the gyroscopic torque can result in a reduction of the vehicle’s maneuverability. In this paper, the equations of motion for a ducted fan vehicle are provided to visualize the gyroscopic torque. It is also important to understand how the gyroscopic torque scales with fan radius. Through this knowledge, a constraint equation is formulated that ensures that the UAVs control surfaces can counteract the gyroscopic moments acting on the vehicle. It is also shown that, to ensure the control surfaces are adequate, the control surface effectiveness must scale with the square of the fan’s radius if equivalent body angular rates are required. In some cases, however, it may be more beneficial to the vehicle to design a contra-rotating fan system. It is shown how this system eliminates the gyroscopic torque that is present in a conventional single fan UAV. However, contra-rotating fan systems have unique dynamic properties, and modal analysis is used to compare the dynamics of both configurations.