Simplified unsteady aerodynamic and inertial force models were developed for a cycloidal propeller system operating at small forward speeds. These models were used to support the development of a VTOL concept demonstrator vehicle. The nature of the blade motion showed that interactions between the blades could be neglected to first order. The downwash through the rotor could not be neglected because of the induced angle of attack caused by the downwash. The total force was compared with wind tunnel data produced by Wheatley in the 30's and a ground test system developed for this project. It was found that the estimates produced by the model agreed with the total force and power to within 10% for the Wheatley data. Agreement between the model and the current tests was within 5% for the total force and power. The inertial loads were used to design the blade structure, the support structure, and the blade motion system. It was found that the inertial loads were much larger than the aerodynamic loads. The aerodynamic effect of forward motion or wind moving toward the propeller was defined. It was modeled as a constant velocity induced flow through the propeller that induced an angle of attack of the blades. It was found that the cycloidal propeller was very susceptible to wind gusts, but that the resultant force from the wind gust could be easily damped out. The same forward motion model was used to simulate downwash. By modeling the downwash as a constant velocity flow through the propeller, the lift and thrust of the propeller was linked to the induced flow velocity. The effect of the induced flow velocity was then linked back to its effect on the lift and thrust produced by the propeller.