The starting point of any design is usually either the customer user requirements or the competition rules. For the IMechE UAS Challenge, the starting point of design is always the rules, which are released in October in the year before the competition fly-off in June. This design process is somewhat iterative in nature, with the designer/ engineer cycling backwards and forwards around the design circle, even completing multiple circuits before honing in on an optimum design selection. Given the initial premise that the designers are working on the design of a fully electric multi-rotor, the main user requirements will consist of the big five: Endurance, Speed, Payload Capability, MTOM and Cost. Clearly, there are an almost infinite number of possible selections available to the designer/engineer. When calculating the propeller efficiency using the Thrust coefficient, Power coefficient and Advance Ratio equations, care should be taken to resolve the forward velocity term to coincide with the tilt angle of the rotor disk.