The single rotor design has dominated modern helicopter design until today since 1941 when Sikorsky successfully obtained the world's first order to mass-produce his single rotor system helicopters for the US Government.

However in about the same time, in late 1940's, Peter James Papadakos (1914-1992) of Gyrodyne Company started the design, development, testing, and production of coaxial helicopters, and from the 1950's to the early 1970's, Gyrodyne sold thousands of coaxial helicopters to the military as UAVs and for anti-submarine warfare operations

Figure 13 A Papadakos Coaxial Helicopter

Kamov Design Bureau of Russia has concentrated their efforts on coaxial helicopters and developed the only coaxial attack helicopters, such as KA-50, KA-52, to rival the US Apache and Comanche.

Figure 14 Russian Kamov KA-50 Attack Helicopter

The Gyrodyne coaxial design varied in size and complexity and ranged from small single seat helicopter to radio controlled models QH-50 series of coaxial UAV helicopters.

Figure 15 QH-50A Anti-submarines UAV