109 stem from the rather obvious fact that the former operates in air rather than water. In a standard atmosphere (1 atm at 20 C), water is about 800 times denser than air, which means the CycloRotor operates at much higher rotational speeds. CycloRotors can be used as either main propulsion or auxiliary propulsion devices. If they are used as the main propulsion, their thrust-to-weight ratio is vital as they will have to lift the vehicle vertically into the air – not a feat that a marine propeller ever has to perform. They will provide lift, forward thrust and full vehicle motion control. No wings or control surfaces are needed. Steinke explains: “They allow vehicle designs that are very compact and very manoeuvrable. Thus, they are the best fit for cargo drones, and even more so for ‘flying cars’ carrying people and flying autonomously.” As an auxiliary propulsion system, CycloRotors can provide stability, precise steering and enhanced manoeuvrability, particularly in load-lifting applications such as flying cranes, he adds. Steinke reports that CycloTech has had enquiries from companies in many countries, including Japan, the USA and the UK, for CycloRotors for use in main and auxiliary propulsion roles. While the basic principle is well established, the company holds US, European and Chinese patents covering novel details of the CycloRotor’s control mechanism and a vehicle/rotor combination. Bumblebee 2.0 is the second flying prototype and the successor to Bumblebee 1.0, which was used for indoor flight tests in 2021. The updated machine has reduced weight and an improved flight control system, and it is being used for open air flight tests. “We will continue to expand the flight envelope incrementally until we reach the limits of the current capabilities of the demonstrator,” says Klemens Hofreither, chief engineer, aircraft. “We want to demonstrate the unique manoeuvre capabilities of a CycloRotorequipped aircraft by showing the decoupling of the flight path and vehicle attitude at low speeds followed by a forward-flight campaign.” Cyclogyro propulsion system Hofreither explains how the system works: “A cyclogyro rotor contains a number of parallel blades rotating around a central axis. Each blade is mechanically connected to a central hub by a connecting rod. By moving the hub eccentrically from the axis of rotation of the rotor, the angle of attack of each blade changes periodically during a revolution. This accelerates the air through the rotor and generates thrust. “The individual pitch angle of the blades is controlled by a pitch mechanism. The magnitude and direction of the cyclogyro rotor thrust can be directly controlled by the eccentric positioning of this hub. “This provides a uniquely simple and fast way to control the thrust vector of the propulsion unit and change the position of the aircraft without tilting any of the aircraft structures – a capability that no other propulsion system offers.” The exact details of the pitch-change system’s mechanics are closely guarded, but patent drawings illustrate the principle. A general arrangement drawing depicts a circular hub with a connecting rod pivoting on its perimeter and connecting to a second pivot on the blade, which is secured by a third pivot ahead of the second to the outer rim of the CycloRotor assembly, which is concentric with CycloTech Bumblebee 2.0 | UVD The magnitude and direction of the cyclogyro rotor thrust can be directly controlled by the eccentric positioning of this hub Uncrewed Systems Technology | April/May 2024 Inspiration for the CycloRotor came from the Voith Schneider Propeller (VSP), such as the example fitted to this seagoing and harbour-capable tractor tug (Image courtesy of Voith Group)
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