On Wed, 06 Jul 2011 06:37:33 -0700, Larry Jaques
wrote:

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.

Excellent. I learned my "something new every day" early today.
Thanks. I'd wondered why they used that frequency in airplanes.

Probably good for the old-fashioned mechanical gyros too.. which had
to have motors that ran at high RPM. Of course modern strap-down nav
systems tend to use fiber-optic or ring laser gyros.

I wonder why 400Hz though, rather than 360 or something that's an
integer multiple of 60Hz.. perhaps it originated in the UK where it
would be an integer multiple of their 50Hz? I see an online claim
that WWII-era German aircraft used 500Hz.

Here's the MIL spec for aircraft power from '59:
http://www.everyspec.com/MIL-STD/MIL...D_704.1080.pdf