A cyclorotor, cycloidal rotor, cycloidal propeller or cyclogiro, is a fluid propulsion device that converts shaft power into the acceleration of a fluid using a rotating axis perpendicular to the direction of fluid motion. It uses several blades with a spanwise axis parallel to the axis of rotation and perpendicular to the direction of fluid motion. These blades are cyclically pitched twice per revolution to produce force (thrust or lift) in any direction normal to the axis of rotation. Cyclorotors are used for propulsion, lift, and control on air and water vehicles. An aircraft using cyclorotors as the primary source of lift, propulsion, and control is known as a cyclogyro or cyclocopter. A unique aspect is that it can change the magnitude and direction of thrust without the need of tilting any aircraft structures. The patented application, used on ships with particular actuation mechanisms both mechanical or hydraulic, is named after German company Voith Turbo.
Operating principle
Cyclorotors produce thrust by combined action of a rotation of a fixed point of the blades around a centre and the oscillation of the blades that changes their angle-of-attack over time. The joint action of the advancement produced by the orbital motion and pitch angle variation generates a higher thrust at low speed than any other propeller. In hover, the blades are actuated to a positive pitch (outward from the centre of the rotor) on the upper half of their revolution and a negative pitch (inward towards the axis of rotation) over the lower half inducing a net upward aerodynamic force and opposite fluid downwash. By varying the phase of this pitch motion the force can be shifted to any perpendicular angle or even downward. Before blade stall, increasing the amplitude of the pitching kinematics will magnify thrust.
History
The origin of the rotocycloid propeller are Russian and relates to the aeronautic domain. Sverchkov's "Samoljot" (St. Petersburg, 1909) or "wheel orthopter" was the first vehicle expressly thought to have used this type of propulsion. Its scheme came near to cyclogiro, but it's difficult to classify it precisely. It had three flat surfaces and a rudder; the rear edge of one of surfaces could be bent, replacing the action of an elevator. Lift and thrust had to be created by paddle wheels consisting of 12 blades, established in pairs under a 120° angle. The blades of a concave shape were changing an angle of incidence by the means of eccentrics and springs. In a bottom of the craft 10 hp engine was arranged. Transmission was ensured by a belt. Empty weight was about 200 kg. "Samoljot" was constructed by the military engineer E.P. Sverchkov with the grants of the Main Engineering Agency in St. Petersburg in 1909, was demonstrated at the Newest Inventions Exhibition and won a medal. Otherwise, it could not pass the preliminary tests without flying.
In 1914, Russian inventor and scientist A.N. Lodygin addressed the Russian government with the project of the cyclogiro-like aircraft, his scheme was similar to Sverchkov's "Samoljot". The project was not carried out.
In 1933, experiments in Germany by Adolf Rohrbach resulted in a paddle-wheel wing arrangement. Oscillating winglets went from positive to negative angles of attack during each revolution to create lift, and their eccentric mounting would, in theory, produce nearly any combination of horizontal and vertical forces. The DVL evaluated Rohrbach's design, but the foreign aviation journals of the time cast doubt on the soundness of the design which meant that funding for the project could not be raised, even with a latter proposal as a Luftwaffe transport aircraft. There appears to be no evidence that this design was ever built, let alone flown. Based on Rohrbach's paddle-wheel research, however, Platt in the US designed by 1933 his own independent Cyclogyro. His paddle-wheel wing arrangement was awarded a US patent (which was only one of many similar patents on file), and underwent extensive wind-tunnel testing at MIT in 1927. Despite this, there is no evidence Platt's aircraft was ever built.