In 1907 military engineer K.A.Antonov applied for, and in 1912 obtained a patent for his "Helicoplane". Aircraft was built and tested in St.Petersburg (1910).

It was a helicopter of coaxial scheme with additional propeller for horizontal movement. All rotors were driven by single 35hp engine. Aircraft had a collective pitch control of main rotors. It was supposed that 0° pitch will be used for parachuting or gliding.

Despite all systems worked as expected, "Helicoplane" failed to takeoff.

Russian Aviation Museum