This paper describes the operation, design, performance, and application of high reliability, variable speed constant frequency (VSCF) aircraft electric power generating systems. A high frequency, multi-phase, brushless generator supplies power to a frequency converter which conditions the variable frequency generator output into precision 3-phase, 115/200V, 400 Hz aircraft power, using the cycloconverter principle. Systems have been built with ratings from 20 to 150 kva. For a 75 kva system, the weight to rating ratio is about 1.6 lbs/kva and rated load efficiency is 80%. Predicted MTBF for current systems is in the 2000 to 6000 hour range.