Investigation on Aeroelastic Instability of a Distributed Propulsion Tiltrotor

This paper investigates aeroelastic instability of a conceptually designed 6,500 lb class distributed propulsion quad tiltrotor. An aeromechanical representation is developed using the comprehensive rotorcraft analysis, CAMRAD II. The analytical model integrates a soft-in-plane hingeless rotor, dynamically scaled from the validated Boeing Model 222 configuration, with a flexible wing/pylon structure. The analysis employs a free wake geometry model to rigorously capture the complex aerodynamic interference effects between multiple rotors and wings. The stability analysis of the semi-span configuration identifies an air resonance instability, primarily driven by the coupling of the wing beam mode with the rotor low-frequency lag mode. A parametric study is conducted on critical design parameters for the distributed propulsion tiltrotor. The full-aircraft analysis suggests that neglecting aerodynamic interaction leads to an incorrect prediction of a stable system. The primary destabilizing mechanism is identified as the wake generated by the front wing impinging upon the rear rotor. These findings confirm that high-fidelity full-vehicle wake modeling is indispensable for securing aeroelastic stability in distributed propulsion tiltrotors.