Performance, Vibration, Load, and Whirl Flutter Stability Analyses of Tiltrotors with Swept-Back Blades

This study investigates the performance of tiltrotors in helicopter and airplane modes, hub vibration, blade and pitch-link loads, and whirl flutter stability using various swept-tip configurations, including different magnitudes of the sweepback angle (Λ) and different radial locations (r_s) where the sweepback angle starts for tiltrotors. The aeromechanics modeling and analyses of the tiltrotors are performed using CAMRAD II, a rotorcraft comprehensive analysis code. TRAM, a 25% scale model of the V-22 tiltrotor, is used as the baseline tiltrotor model with unswept-tip blades. A larger sweepback angle improves proprotor performance and whirl flutter stability; however, it degrades the blade and pitch-link loads and hub vibration. As the sweepback starting location moves closer to the midboard, it improves hover performance and whirl flutter stability; but, worsens the blade and pitch-link loads and hub vibratory loads. Therefore, from these two parametric studies, the optimal blade sweepback configuration for tiltrotor is determined to be Λ = 20° and r_s = 80%R when considering rotor performance, loads, vibration, and whirl flutter stability.