Flight Measurements of the Effects of Simulated Leading-Edge Erosion on Helicopter Blade Stall, Torsional Loads and Performance

The leading edges of the main rotor blades of a Wessex helicopter were artificially roughened to simulate light to moderate erosion of unprotected light alloy blades. Pitch link loads were measured in forward flight for various spanwise extents of leading-edge roughness, and the values of forward speed at which a pre-set limit of oscillatory pitch link load was reached were determined. This limit was set so as to avoid excessive fatigue damage to the modified control linkage. With a representative length of roughness, the speed at which the limit load occurred was reduced by 24 kn. This marked reduction was associated with premature blade stall, detected by trailing edge pressure measurements, and subsequent stall flutter together with an increased power requirement.