On Wed, 6 Jul 2011 03:00:05 +0000 (UTC), David Lesher
wrote:

GeoLane at PTD dot NET GeoLane at PTD dot NET writes:


Why do they use 400 Hz for anything?

400 Hz reduces the iron needed in magnetics such as generators,
motors and transformers. Weight is a big big factor in aircraft.
Also makes it easier to get the speed required for gyro instruments.