A validation of the Joint Army/Navy Rotorcraft Analysis and Design software by comparison with H-34 and UH-60A flight test

Abstract

A detailed comparison of the output from the NPS developed Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) computer code with H-34 and UH-60A flight test data was made in an effort to determine the validity of the code's predictions. Airload distribution across the rotor disk, power required at various airspeeds ranging from hover to cruise, and thrust moment were used as measures of performance. Although a quantitative comparison of airload distribution is difficult to obtain, qualitatively, the predictions are good. JANRAD's power required estimations are correct to within two percent for altitudes below six thousand feet but accuracy suffers at higher altitudes, particularly above ten thousand feet. A correlation between the variation in kinematic viscosity from sea level to ten thousand feet and the accuracy of the power predictions is demonstrated. in the case of the UH-60A, the equivalent flat plate area of the helicopter is shown to be a function of airspeed, significantly impacting the accuracy of the power required prediction. Center of gravity offset from the main rotor's axis of rotation and unsteady inflow effects influence the accuracy of thrust moment predictions.