Performance and Loads of a Model Coaxial Rotor Part II: Prediction Validations with Measurements

The predictions of an upgraded UMARC comprehensive analysis are compared to experimental coaxial rotor results. The experiments cover a range of collective pitch angles (θ°) from 2° to 10°, advance ratios (μ) from 0:2 to 0:5, and lift offset from 0% to 20%. The experimental rotor system is a hingeless rotor with a first flap frequency of approximately 1:6=rev and was tested in the Glenn L. Martin Wind Tunnel at the University of Maryland first as an isolated rotor and then as a counter-rotating coaxial rotor system. The analysis is validated against measured isolated rotor performance and coaxial rotor performance and loads. The isolated rotor performance and controls are predicted well with advance ratio, although thrust tends to be under-predicted. With increasing lift offset, thrust increases while power remains the same, improving rotor performance. Coaxial correlation is shown for rotor-to-rotor tip clearance, pitch link loads, and selective vibratory hub loads. The impact of rotor-to-rotor phase is examined. Matching rotor side force is a challenge in this simulation.