An experimental Investigation of the H-5 Variable Stiffness Blade Program. Part 2. Blade Beam Bending-Moment Envelopes

摘要

A helicopter research program was conducted with the objective of determining the bending stresses and motions experienced, in flight, by articulated rotor blades;and, thereby, to explore possible causes of a number of unexplained rotor blade fatigues failures. Measurements made with a family of blades, similar in all respects except flapwise bending stiffness, disclosed, under certain flight conditions, a hitherto unsuspected phenomenon of large amplitude resonant bending in the higher modes. It was found that in the critical conditions, the contribution of higher mode bending to the total bending moment may be as great as the sum of the steady, first, and second harmonic terms results, the necessity of, and proposed procedures for, investigating higher mode bending effects in both the design and flight evaluation phases of blade development programs are discussed.