VALIDATION AND UNDERSTANDING OF UH-60A VIBRATORY LOADS IN STEADY LEVEL FLIGHT

This paper presents prediction and validation of basic performance, airloads and blade loads of a UH-60A Black Hawk helicopter in steady level flight. The focus is on high-speed flight. Consistency of lift prediction in high-speed flight is examined by step-wise modeling refinements. None of the modeling refinements can accurately predict the phase of blade lift. Harmonic analysis of flight test lift and comparison with prediction reveal that the phase prediction problem is a manifestation of inaccurate vibratory lift prediction, particularly 3/rev and 4/rev lift. Blade lift at high speed is shown to be dominated by elastic torsion. Section pitching moments are over-predicted inboard and under-predicted outboard. The physics of vibratory loading is also examined from the perspective of rotor structural response. Predicted flap and lag bending moments and pitch link loads are compared with flight test data. Oscillatory and vibratory load patterns that are common to rotors of all configurations are used to assess the validity of the present analysis.