LPeacock Cooling fan motors are a classic example you want it to switch on run at a constant speed so yes Brake fan motors and Hyd pump cooling fans and also fuel pumps are good examples.
Everything in an areoplane is a comprimise the aim being since the day's of Wilbur & Orville to get the maximum power for the minimum weight and from the minimum expended energy-switching on the genny means some Avtur gets used running it.
So 400Hz is the best fit at present as it gives us 3 phase 120 degrees apart with the least amount of iron and copper as barfit1 says. It also gives us the best Power (and I dread to go here because sums aint my strong point) but you must remember for a sine wave that we deal with rms because its impossible to measure max power like we would in a dc circuit where P=IV.
3 phase= 3 sine waves 120 degrees apart ( the next bit you cant do but I remember it from collage for the simple reason I spent a lot of time trying to work out what the F was going on) If you take a sine wave and sample the power at 6 points during 1 cycle square each value add them all together and divide by 6 then take the square root of the answer you get the rms or average power.
1.414 times rms gives you Peak power so do the sums for each phase for the total power of the gen in 1 revolution and that is the best fit for todays technoligy however with the 380 we may move on and good for us but will uncle sam certify it if he didn't invent it ?-now there's a whole new topic.
sorry for the misspelling barit1 to late to go back now
