Aeroelastic response, loads, and stability of a composite rotor in forward flight

The aeroelastic response, blade and hub loads, and shaft-fixed aeroelastic stability are investigated for a helicopter with elastically tailored composite rotor blades. A new finite element-based structural analysis including nonclassical effects such as transverse shear, torsion related warping, and in-plane elasticity is integrated with the University of Maryland Advanced Rotorcraft Code (UMARC). The structural dynamics analysis is correlated against both experimental data and detailed finite element results. Correlation of rotating natural frequencies of coupled composite box-beams is generally within 5-10%. The analysis is applied to a soft-in-plane hingeless rotor helicopter in free flight propulsive trim. Changes in blade loads are relatively small; however, aeroelastic stability can be significantly improved by the use of elastic pitch-lag coupling. For example, lag mode damping can be increased 300% over a range of thrust conditions and forward speeds. The influence of attached flow unsteady aerodynamics on the blade response and vibratory hub loads is also investigated. The magnitude and phase of the flap response is substantially altered by the unsteady aerodynamic effects. Vibratory hub loads increase up to 30% due to unsteady aerodynamic effects.