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My bright idea ... University of Bath PhD student Robert Worthing thinks cycloidal rotor systems could deliver significant performance and energy gains in helicopter designs.

The development of cycloidal rotor systems holds a lot of promise. Theoretically, they could deliver advantages over conventional helicopter rotor designs, with improved efficiency, increased agility and greater gust tolerance, resulting in performance gains and energy savings.

A cycloidal rotor is a rotating wing device, capable of producing both rotorcraft lift and propulsion via the rotation of a number of blades about an axis that is parallel to the blade span. For standard configurations, the blades are rotating about a horizontal axis 90[degrees] to the normal flight direction. Lift and thrust forces are generated by the cyclic variation of the pitch angle of each blade via a blade pitch mechanism, usually an eccentric.

By use of the eccentric, the cyclic variation of the blade pitch can be changed in both amplitude and phase angle. This allows for thrust vectoring anywhere within the 360[degrees] of rotor rotation. Adjustment of the blade pitching allows the cycloidal rotor to be flown in any direction, making it suitable for vertical take-off and landing, forward flight and hover operation.

Since its initial development in the 1920s by Professor Frederick Kurt Kirsten of the University of Washington, the cycloidal rotor concept had largely been abandoned after further studies, owing to the complexity of the aerodynamic analysis required and the existence of insurmountable structural problems. The high blade transverse loading and overall rotor mass were typical examples. Within the past decade the cycloidal rotor concept has started to see something of a renaissance, with the increased interest in unmanned flight. Although nearly 100 years old, the physics of the concept is still not fully understood and research is in its initial stages.

Advances in experimental and computational aerodynamics, along with improved material technologies, have removed many of the early barriers to development of the concept, enabling major progress on cycloidal rotors to be made. But the modelling and analysis of the cycloidal is still a challenging task because the aerodynamics of the design are inherently unsteady, owing to the pitching of the blades, with strong interactions between the wakes of neighbouring blades. Many of the structural developments have been made possible with the advent of composites, for both the blades and supporting structure.

The unique ability to change the direction of the thrust almost instantly in any direction allows for increased aircraft agility, manoeuvrability and improved gust tolerance which will be advantageous in many operations in unmanned aerial systems. The concept promises considerable advantages over helicopter configurations, including improved aerodynamic efficiencies over a greater operational envelope, in both larger manned or unmanned craft. Improved aerodynamic efficiencies can either offer energy savings in the form of lower fuel consumption or increased aircraft operational range.

With research ongoing into the cycloidal rotor, it should be possible to optimise the rotor for the operating regime similar to a helicopter, depending on whether the craft needs to be optimised for forward flight or hovering. The majority of the research and development work has sought to optimise the rotor performance only, with further research into the development of suitable airframes.

The cycloidal rotor has the potential to be developed into an unmanned aerial vehicle that can combine the high-speed characteristics of a conventional fixed-wing craft with the hovering capability of the helicopter. Following this, development into a manned craft may then be possible.
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Title Annotation:Engineering extras: Innovation: Ideas: Careers: Gadgets: Books: Internet
Author:Worthing, Robert
Publication:Professional Engineering Magazine
Date:Oct 1, 2015
Words:553
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