Just an idea kicking around my head right now. Too many projects ahead of it. But I've been thinking an extended shaft with a edf rotor to provide the whine, with a standard prop for the pull. I'm not sure how long that extended shaft might have to be but I'm pretty sure it would be custom made on my lathe. Would probably need a short shroud around the rotor and provide an exhaust outlet that might look scale. I figure the shroud would be just enough to protect the rotor. I dont know how loud or what pitch the whine would be at slower prop speeds. Maybe also program in a slow start ramp up on the motor to simulate a turbine spool up. With my DX18 I could sequence each engine start up.

Edwin