Aeroelastic and structural analysis of ducted composite rotors in edgewise flight

An aeroelastic model of a ducted composite rotor is developed. The analysis is to determine structural loads of the ducted rotor in edgewise flight. Rotor blade cross section sizing studies are performed using a composite rotor blade model based on Vlasov Theory. The composite blade cross sections are designed subject to strength, stiffness and frequency constraints. The ducted rotor is evaluated at different g levels (load factors) to investigate the feasibility of ducted rotors in edgewise flight without conventional cyclic pitch controls. Parametric studies of blade stiffness are also conducted to explore the dynamic characteristics of the rigid (propeller-type) rotor in edgewise flight. The study indicates that ducted rotor without conventional cyclic pitch controls poses significant challenges for composite blade structures to meet U.S. Army military specifications. The large static flap bending, and the high 1/rev blade flap motions due to lack of cyclic controls result in high blade flapping moments at the roots, which dominate the blade structural design and may cause blade fatigue problems.