2.1. Magnet type
Due to the small size of the alternator, high power/low volume magnets were required. Rare-earth
NdFeB magnets may be cheaper than SmCo magnets but their maximum temperature of operation was
considered too low for use in an alternator close to high temperature equipment. Therefore, SmCo
magnets were chosen because of their ability to operate at higher temperatures.
2.2. Windage loss
Formulas predicting windage losses of rotating masses are invariably theoretical functions
approximated to practical results. Assuming turbulent flow, (1) gives one such formula for predicting
windage losses Wdisc for a disc alternator rotating in the compressor duct [7].