Aren't DC brushless motors just normal 3 phase ac motors driven by half a variable speed drive?
Yes, usually. They have a very high power to weight ratio. IMHO a 250HP brushless motor would weigh ~ 50kg. It would draw of the order of 2000 amps at say 100 volts; this is relatively trivial in terms of the DC-AC inverter.
The higher the voltage is used, the more efficient the electronic inverter can be, but they are very efficient anyway - well into the 90s % region.
There really is absolutely NO issue with the motor. If not off the shelf (due to the thick shaft with a prop flange on the end
) it would nevertheless be trivial. The inverter would be trivial too; this is off the shelf technology made by many firms e.g.
this.
The battery, and charging it practically (where from???), would be the fun bit
But the charging process is again straightforward and established technology for LIPO or whatever.
In the RC model world, the funny thing is that the "poor" flyers use fuel. Electric stuff is better in every way but it is "less authentic" and most cannot afford to buy enough of the £100 batteries to last them the day out
My son has had a few of these and smashed them up in the obligatory crashes. One of bis brushless motors had to be dug out from about 6" deep in the soil, but iw was fine after some cleaning up. It soon gets very expensive and now he flies mostly with the nitro engines. But the other day he blew a hole in a piston so that was his savings gone for a bit
The thing I find more puzzling in aviation is why the hell do
autopilot servos use brush motors. What you are supposed to do - and this applies to a TB20 as to a TBM850 or a King Air - is to fly until the motor (i.e. the autopilot) fails because there is nothing left of the brushes or the commutator (the two seem to have a similar life). There is no precautionary maintenance, the brushes are not replaceable, and the "motor repair" is a whole new or overhauled servo at at least $2000. This application is crying out for either brushless or microstepped stepper motors but there seems to be a total lack of imagination in the industry which keeps turning out the same old garbage. I wonder if the new Garmin autopilot uses brushless motors...