Here's a little more clarification.
The "jet" is powered by a small pusher prop on a brushless motor mounted on rubber bushings... pretty quiet.
The speaker will be housed within the fuselage but instead of holes to allow sound to pass I was thinking of a taut plastic film over the speaker housing. May even amplify a bit like an acoustic guitar.
As far as the characteristic sound of a real turbine that would be ideal but to sample that and utilize would require a loop... not feasible. So, make a jet sound when you play with your kids. Bet it sounds like static noise that trails off as you run out of breath. The key is the doppler effect as the plane goes by.
So what I am after is noise, small, and simple. Hope this clarifies things a bit. I've been reading about zener diodes, rf noise, etc, but the learning curve is steep.
Thanks,
FMD