In 1911 B.N.Yuriev (then student) completed development of theoretical concept of the helicopter with single main rotor. This concept included collective and cyclic pitch, anti-torque tail propeller. Layout of his helicopter is now became a classical scheme - so common that it seems that 'it always was that way'.
As it was common in Russia, domestic project of a student failed to get an official support, and inventor was left on his own. As a result, planned 70hp Gnome engine was replaced by 30hp Anzani, rotor blades were fixed (necessary materials were too expensive). Goals were limited by study of trust and reaction of rotors.
'Prototype' was ready on Spring 1912, and got a Golden Medal on the Second International Aircraft Show (Moscow) as a 'remarkable theoretical project'. Front section was of wooden construction, uncovered rear fuselage - bamboo.
Tests were carried out during Fall 1912. First conclusion was that Anzani engine is unsuitable - produced too much vibration, did not run smooth enough and failed to provide low rpm's. Soon the main rotor mast (made from soft steel tube) was broken, putting tests to the end.
Yuriev and his fellow students started to develop a unified 'engine-rotor' group to be used in single- and multi-rotor helicopters, including engine of their own design. But outbreak of the WWI stopped the project completely - its participants were drafted.
Technical data for Yuriev helicopter
Engine: 1 x Anzani rated at 30hp, main rotor diameter: 8.0m, length: 6.0m, empty weight: 250kg