In order to create a new solar aircraft totally powered by the sun, a new method able to handle such a complex system must be developed. The project aim is to make a round-the-world flight in so as to promote the sustainable development. The aircraft power train will consist of solar cells placed on the wings, the energy storage system, the energy management electronics, the brushless DC motor and propellers. This paper presents the method to optimize the motor together with the propellers, to save the maximum of energy in the power train. Two different tooth shapes are considered, straight and standard. The conclusion is surprising, as the better results are obtained with the straight tooth shape, although the mutual flux is smaller in this case. The optimization process shows a potential to analyze simultaneously all the parameters to determine the optimum. © 2006 IEEE.