Jozef Lipkowski, a Polish engineer and inventor working in France and Russia, designed a huge helicopter-type flying machine in Russia at the end of 1904. According to descriptions in the contemporary press, the proposed aircraft featured two vertical co-axial shafts of steel tubes, to which two gigantic contra-rotating 'screws' (rotors) were attached. Each 'screw'consisted of two half-circular 'wings' (blades) which were supported by a long steel tube and comprised a wooden 'felloe' and steel 'spokes' covered with doped silk. A nacelle, accommodating the aviators and two engines, one for vertical and the other for horizontal flight, was mounted beneath. A rudder and a propulsive airscrew on a horizontal shaft were attached to the nacelle and provided means of control.
Early in 1905 the Pitulovskie Establishments in Petersburg constructed one complete rotor for the proposed aircraft for tests which were aimed at determining whether a vertical ascent would be possible. Ground trials with the gigantic rotor device, driven by an electric motor, yielded remarkably interesting results, confirming in full the designers calculations. An official report, dated 16 March, 1905, and signed by Prof N. L. Shtchukin, who was appointed to witness and supervise the experiment, stated that Lipkowski's rotor, consisting of two 'half-wings' with an overall diameter of 16m and a combined gross area of 200 sq m, which were powered by a 35hp (electric) motor, lifted 778kg at 40rpm, this indicating a lift/power ratio of 22.22kg/hp (or more than twice as good as the then best achievements).
For these initial tests the half-circular blades were set at a very efficient angle of incidence of 3.5°. Later Lipkowski made further trials with the blades set at various angles from 5° to 8°. Allowing for unforeseen contingencies and the possible loss of rotor efficiency in a complete machine, the designer accepted a lift/power ratio of 12.5kg/hp as the basis for his final calculations. Estimated weights of various elements of his giant helicopter included: two rotors 2000kg; nacelle, steering and transmission systems 1000kg; crew and fuel 1000kg; two engines 4500kg; the estimated gross weight of the machine being 8500kg. Lipkowski proposed using a 700hp engine for vertical movement and a 150hp engine for horizontal flight. In later years he went to France to see whether he could obtain the required engines, but impressed with Wrights' and Bleriot’s flights, he came to the conclusion that the future of flying belonged to fixed-wing aircraft and abandoned work on his pioneering project.
Jerzy B. Cynk "Polish Aircraft 1893-1939", 1971