First, i'm quite ignorant on aerospace engineering, so I hope I don't make too many incorrect assumptions.
If you don't know what an Autogyro/Gyroplane is, here is the Wikipedia article of it.
- The concept:
Basically, the idea would be to have two (or less/more) rotors on opposite sides of the aircraft, however, the shaft of the rotors would be connected to smaller propellers that would be exposed to the jet of air from the aircraft's engine.
The idea would be to take advantage of this jet of air generated by the engines to partially increase the speed of rotation of the rotors, since in the case of a Gyrocopter/Autogyro, they need the aircraft to move in a direction to be able to glide (of course, there are types of Autogyros that are connected to the engine).
I don't think that would be enough to make the aircraft take off vertically, but maybe it could produce more lift for heavier aircraft.
And to be honest, I think this rotor would spin so fast that you would have to add an electromagnetic brake, and well, if you have an electromagnetic brake, you have an electromagnetic motor. What could also change the speed of the rotors to more or less revolutions. I know if the goal is vertical takeoff, then hook the rotors to the engine right away with a transmission or something. But in my (ignorant) view, this would increase complexity, weight and maintenance costs.
And for the little I know, I can imagine that it wouldn't be that efficient since the thrust would be spent to spin the rotors, but I don't know if this waste would be small or big, or even if it would be enough to make it rotate fast enough to generate any significant lifting power.
- Why the question:
I ask this because one of the few VTOL planes that almost reached the civilian market was the "Fairey Rotodyne".
According to what was said about this aircraft, the rotors (which worked as in an Autogyro/Gyrocopter after the vertical take-off) were able to eliminate 40% of the aircraft's total weight during flight; making it an interesting option.
However, the way this hybrid plane took off vertically was pumping fuel to the tip of the propellers (turning it into a Tip-jet), which added to the complexity of the aircraft.
And that was just one of the reasons that it didn't attract many customers: when turning the tips of the propellers into rockets, an absurd noise was generated (and if that noise could be louder than the two engines in the wings, it was certainly something that could not be ignored).