AC electrical buses are common in airplanes from light piston twins all the way up to the largest airliners. I usually see both a 115v and 36v AC bus with a 400 Hz output frequency. How do most airplanes regulate the output frequency coming from the AC generator?

  • $\begingroup$ Sometimes they don't have AC generators, but use inverters to convert from DC to AC. $\endgroup$
    – Lnafziger
    Commented Feb 12, 2016 at 1:25
  • $\begingroup$ This is probably not a good conversation to start here in the comments, but don't generators and alternators product AC current? $\endgroup$
    – ryan1618
    Commented Feb 12, 2016 at 1:26
  • $\begingroup$ Actually, there are AC and DC generators (it's a generic term), but an alternator is a specific kind of generator which produces AC electricity. $\endgroup$
    – Lnafziger
    Commented Feb 12, 2016 at 1:32
  • $\begingroup$ Doesn't necessarily have to be moved, but wouldn't this make more sense at EE.SE, since this is essentially asking "How do you regulate the output frequency of AC generators?" I'm pretty sure it's done the same way in aircraft as it is anywhere there's an AC generator that needs to output a fairly stable frequency (i.e. every one of them). $\endgroup$
    – FreeMan
    Commented Feb 12, 2016 at 14:22
  • $\begingroup$ @FreeMan So far as I understand normally that's done via a governer on the prime mover. $\endgroup$ Commented Feb 12, 2016 at 14:57

1 Answer 1


It's done using mechanical device called constant speed drive. Works almost the same as CVT transmission in a cars. The more complex thing is phase adjustment as airplane usually has multiple engines and generators. But that is not done as different generators always power different buses!

  • $\begingroup$ And in the A380 the mechanical drive is eliminated entirely I think. $\endgroup$ Commented Feb 12, 2016 at 8:10

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