Wind Tunnel Testing of an Instrumented Rotor at High Advance Ratio

Abstract

Compound helicopter designs utilize a slowed main rotor, which reduces RPM as flight speed increase to maintain sub-critical tip Mach numbers. These concepts are therefore expected to operate at high advance ratios (1.0 or higher). There is a need for experimental data sets in this flight regime to validate and develop predictive tools. Systematic testing in the Glenn L. Martin Wind Tunnel (University of Maryland) was conducted on an instrumented Mach-scale articulated rotor (1.7 m diameter) up to an advance ratio of 1.61. The following measurements were taken: steady and dynamic 6-component hub loads (fixedframe), shaft torque (rotating frame), root flapping angles, pitch link loads, blade torsion and flap bending moments at 5 spanwise stations, and 16 chordwise blade pressures at 30% radius spanwise location. The selected results detailed in this paper revealed insights into high advance ratio, reverse flow phenomenon such as reverse chord dynamic stall and the resulting impact on loads. The combination of rotor advance ratios beyond 1.0, large collective pitch sweeps, and blade surface pressure measurements makes this data set unique.