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Aerodynamic Optimization Study of a Coaxial Rotor in Hovering Flight

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A primary design goal with a coaxial rotor is to minimize the combined sources of losses on the upper and lower rotors that have their source in aerodynamic interference. To this end, parametric studies were conducted using a free-vortex wake method to study the aerodynamic interference effects of changing interrotor spacing, blade twist rates, and blade planform on the interdependent loads produced on the upper and lower rotors, respectively. A formal, multistep optimization process was then conducted by coupling the aerodynamic method to an optimization approach based on the method of feasible directions, the goal being to expeditiously find the individual blade geometries that would give the highest levels of efficiency from the coaxial as a system. Because of the inherent aerodynamic differences between the upper and lower rotors of a coaxial, it is shown that the best performing coaxial rotors may require the use of different blade shapes on each rotor, but substantially different blade designs may also achieve similar values of aerodynamic efficiency. It is also shown that the nonconvexity of the design problem for a coaxial rotor may limit the usefulness of formal optimization methods, and extensive parametric studies may still be required in the process of design.

Document Type: Research Article


Publication date: October 1, 2012

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  • The Journal of the American Helicopter Society is the world's only scientific journal dedicated to vertical flight technology. It is a peer-reviewed technical journal published quarterly by AHS International and presents innovative papers covering the state-of-the-art in all disciplines of rotorcraft design, research and development. (Please note that AHS members receive significant discounts on articles and subscriptions.)

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