a compendium of tech stuff

Jun 10, 2012

On 12:11 PM by Lalith Varun   1 comment





A Cycloidal Rotor consists of several blades that rotate about a horizontal axis that is perpendicular to the direction of flight. Blade span is parallel to the axis of rotation and the pitch angle of each of the blades is changed periodically as the blade moves around the azimuth of the rotor.


Blades at the top and bottom produce a vertical lifting force while those at the left and right produce very little force because of their small angle of attack. When resolved into vertical and horizontal directions, the sum of horizontal components is zero, resulting in a vertical thrust. A unique and desirable characteristic of cycloidal blade system is its ability to change direction of thrust enabling any vehicle utilizing this system to take-off and land vertically, hover and to fly forward or reverse by changing the direction of thrust. For implementation on a vehicle, two cycloidal rotors would be necessary, one on each side of the fuselage.

Lateral motion and roll control is achieved through differential control of the magnitudes of the two vectors.



Yawing motion is accomplished through directional control of thrust vectors.



ADVANTAGES:
It provides the same hover capability as a conventional rotor. However unlike a conventional rotor, the blades on a cycloidal rotor operate at constant speed along the entire blade span, allowing all the elements operate at their peak efficiencies.
Cycloidal rotors operate at much lower rotational speeds than conventional rotors, and as such the acoustic signature should be significantly lower.
The greatest advantage of this design is the possibility of greater thrust to power ratios than can be achieved by a conventional rotor.

DISADVANTAGES:
The mechanism required to achieve the periodic pitch changes for each of the blades is by nature more complex than what is required for a conventional rotor.
The complex flow surrounding the rotor makes analysis of cycloidal propulsion difficult.
Weight of the rotor is another problem. The huge no. of components necessary for operation, i.e. multiple blades, bearings and linkages incur more weight penalty compared to a conventional rotor.

REFERENCES:
http://www.inderjitchopra.umd.edu/projects/proj10.html
http://drum.lib.umd.edu/bitstream/1903/3068/1/umi-umd-2875.pdf

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1 comment:

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