Amethod which translate a hingeless rotor into a virtual offset flapping rotor and its application in the design criteria of stability and control are presented. The hingeless rotor is assumed to be infinitely stiff in torsional and chordwise bending, and has a flapwise flexibility with nonuniform mass and stiffness distributions. The virtual offset of the flapping hinge and the spring restraint about it are defined with the mass exciting coefficients and the rotating natural frequency, rather than with the Southwell coefficient and non-rotating natural frequency which are presented by YOUNG
2) and WARD
3). Therefore not only natural flapping term, but also mass excited flapping term of hingeless rotor coincide with those of the virtual offset flapping rotor, and the translating errors of aerodynamic exciting coefficients are decreased fairly in comparison with those of the straight blades of YOUNG, WARD and BRAMWELL
4).
For the stability and control design of hingeless rot r, the allowable range of blade stiffness factor, virtual offset, Losk number and deltathree angle are presented. These design parameters of hingeless rotor are specified to diminish the variation of control retardation angle with advance ratio and to decrease the gyroscopic cross coupling moment from the standpoint of flying qualities.
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