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Unformatted text preview: Coning Angle in Forward Flight Because the blades of a helicopter rotor are hinged near the root with a flap hinge, the blades are free to flap up or down. The lift forces will tend to flap the blades up, while the centrifugal forces will tend to push the blades down. A static equilibrium is achieved in hover, where the blades come to rest at an equilibrium “coning” angle, called β . In forward flight, the airloads tend to vary in a sinusoidal form, and a static equilibrium is not feasible. Rather, the blades undergo a limit cycle oscillation of the form: ( 29 ( 29 ( 29 ( 29 ( 29 ( 29 ( 29 ( 29 ( 29 ... 2 cos 2 sin cos sin ... 2 cos 2 sin cos sin 2 2 1 1 2 2 1 1 + + + + + = + Ω + Ω + Ω + Ω + = ψ β ψ β ψ β ψ β β β β β β β β c s c s c s c s t t t t t In this section, we will extend the derivation for the coning angle previously limited to blades in hover, to blades in forward flight. For simplicity, we will assume that the hinge point is at the origin, r=0. β dL dCentrifugal Force r Consider a small strip of the blade of width dr, at a distance r from the hinge point as shown in the picture above. This strip is subjected to lift force dL, the centrifugal force dCF, and an inretial force that resists the blade motion. It is also subjected to a drag force dD, perpendicular to the plane of the paper. This drag blade motion....
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- Spring '10
- Force, ρc, clockwise moment, forward flight, total clockwise moment