Dynamics of a Rotor Controlled by Aerodynamic Servo Flaps: Theory and Comparison with Available Test Data Available to Purchase

A theory is developed to describe the dynamic behaviour, control angles to trim and stability derivatives of an aerodynamic servo‐controlled rotor. The analysis is restricted to constant chord rotor blades which are torsionally deformed by the servo flap to give changes in rotor pitch angle, as this is the form in which the system is most likely to be used. Also, the aerodynamic centre and elemental C.G. lines are assumed to coincide with the blade torsion axis. Since the stiff hinge assumption is used, the analysis is applicable to blades with offset or ‘stiff’ flapping hinges, or to cantilever rotors, which can be simulated by a rigid blade with a stiff hinge. Comparison with some N.A.C.A. test tower results shows that the theory developed gives excellent agreement with the available experimental results. In Appendix I the stability of the tip path plane is examined, using the equations derived in the report, and three regions of instability are shown to be present. A practical rotor must be designed to operate below the lowest instability region, as is the case for the N.A.C.A. test rotor. Equations for ∂a1s/∂µ and ∂a1s/∂q are developed for the low speeds near hovering in Appendix II. Other derivatives can be easily derived from the general equations of motion given in Table 1.