My idea is for a co-axial light helicopter/UAV powered by two V-twin engines driving gears attacthed to co-axial shafts and also driving a swiveling tail rotor either through gears and shafts or an electric motor.
The advantage to this system would be relatively inexpensive and abundant engines and parts and easy to learn controls. Also,even if one engine were to fail,the tail rotor could be swiveled in either direction to compensate for the torque of whichever engine remained. When both engines are operating,tail rotor could be used for forward thrust and pitch changes.
Control of vertical up or down would be a matter of increasing or decreasing both engines power. Increasing or decreasing power on one engine would provide direction.
Future versions could possibly lock one blade from each rotor parallel to fusealage and one blade perpendicular to fuselage to allow airplane like flight using engines to drive tail rotor in thrust position for more efficient flight.