Al,
They are called single phase "split phase" types. These fans sound like jet engines and because of the 400Hz they kind of act like a speaker too and produce a very loud tone. One was used in the avionic video monitor, you can see the wiring on page 3 and a picture of it on page 18 of this article:
http://worldphaco.com/uploads/The_19...o_monitor..pdf
Attached a diagram that might help, showing the circuit. A series resistor can be used to slow them down.