Optimum Performance Determination of Single-Stage and Dual-Stage (Contra-Rotating) Rim Driven Fans for Electric Aircraft

Electrical Rim Driven Fan (RDF) technology is a novel application to aircraft propulsion, and there are many factors that play a part in determining its optimal achievable performance, for example, the electrical, magnetic and thermal properties of the rim driven motor architectures; the mechanical strength, mass and friction properties of the materials used; the aerodynamics of the fans and the efficiency of the motor drive and control circuitries. Each of these factors could easily warrant their own lengthy and in-depth analyses. The aims of this paper are to provide a starting point from which to get a feel for the rough-order-magnitude of an RDFs performance and to elucidate a conventional calculative methodology suitable for a quick and easy reality-check before undertaking more accurate numerical analysis techniques. Initially, the properties of an existing aerospace fan design, namely that of the IAE V2500-A5 turbo-fan engine, is used to validate this approach and then the same methodology is used to estimate a first-guess performance prediction for a range of single-stage RDFs of varying sizes from 100mm to 500mm diameter, operating over a range of speeds from zero to 25 kRPM. Finally, a comparison between a single-stage and a dual-stage (contra-rotating) 200mm diameter RDF for a UAV application is conducted. The performance limits of the RDFs considered in this analysis have been established to ensure that the fan blades are always operating within the subsonic flow regime.