Hybrid airplane motor

Take a standard piston motor and add an electrical motor/generator between the shaft and propeller.

So, with electrical storage, the stepper motor can drive extra power from short term storage, and replenish at cruising speed. The resultant piston moor can then run at fixed speed, really simplifying design. This is the optimum hybrid aircraft prop engine, great for ultra lites.

The piston motor can be geared down to low RPM, so you end up with this two piston, fixed speed, engine with electrical energy providing infinite torque variation. Store enough energy for five minutes of flight, or one take off. The rest of the energy comes from the combustion chamber.

The piston engine is now electronically controlled, constant fuel consumption, constant rotation lowers the weight all around. It is easier to mount,  a bit farther into the cowl.   The electrical system provides all the instrument power, with the five minute back up.  Engine vibrations into the chassis greatly reduced.   Add more electrical storage and include two electrical wing props, possibly VTOL capable. The craft has enough storage to get you mostly to cruising where three engine flight is possible.

The whole idea is why waste all that rotation power. Intervene at the main prop shaft and run the electric modulator as a computer controlled, dual torque flow  clutch.