Aeromechanics of a Coaxial Ultralight Rotorcraft During Turn, Climb, and Descent Flight

Abstract

This work presents the aeromechanics analysis and evaluation of an ultralight counter-rotating coaxial rotorcraft using a combined numerical and experimental approach with a focus on turn, climb, and descent flight conditions. The helicopter features a 2-by-2 bladed coaxial rotor system with teeter hinges, 6.5 m in diameter and uniform airfoil sections of the linearly twisted blades. Hover and forward-flight test data are shown with varying turn rates or climb and descent velocities. The predictive capabilities of a CAMRAD II numerical model are used to extend and support the flight test data and evaluate possible flight-envelope limitations in terms of ceiling limits and maximum climb rates. The paper focuses on rotor performance, thrust, horizontal-stabilizer loads, and blade-tip clearance, with special attention on the effects from interactional rotor aerodynamics. Results in terms of rotor performance, rotor thrust, horizontal-stabilizer loads, and rotorcraft aerodynamic angles of attack resulted in satisfactory correlation between the numerical model and the measurements. Rotor–rotor interactional effects contributed to the approaching rotor-blade tips, especially during low-speed descent flights. During turn flight, required rotor power increases with greater bank angles. Maximum axial climb rate of the ultralight coaxial helicopter was at , the hover ceiling at 2180 m, and the service ceiling at 4450 m. Ceiling limitations depended on the operating conditions and reduced with greater temperature and rotorcraft weight.