Impact of Current Density and Cooling on the Weight Balance of Electrical Propulsion Drives for Aviation

Through applying an exemplary design study, the dependencies between current density,
temperatures, and weight in an electrical drive system for a small range aircraft with conventional
electrical fan or propeller drives are evaluated. This study applies a combined numerical (Finite
Element Method FEM) and analytical approach to the machine design, calculation of temperatures,
and cooling system design (cooler, pumps, piping). A design scenario was defined using start and
climb flight in a warm tropical surrounding as the worst load case. The design has to move between
two fixed temperature limits: The maximum allowable temperature in the machine insulation and
the ambient temperature. The implemented method facilitates a comparatively fast-medium depth
design of the drive system. The derived results show, in fact, a minimum of weight at a certain
current density, which is one of the key interests for the designers of the electrical machine. The main
influences on this minimum are the temperature drops in the machine, the heat transfer to the cooling
fluid, the heat transfer to the cooler wall, and the remaining heat rejection to the ambient. Method
and results are transferable to other types of airplanes with di erent ratings.