Unified Modeling of the TiltRotor Aeroelastic Stability Testbed for Proprotor Whirl Flutter

Abstract

The present paper studies whirl flutter stability of the TiltRotor Aeroelastic Stability Testbed (TRAST) using the comprehensive analysis code Rotorcraft Comprehensive Analysis System (RCAS). The TRAST wing and pylon are systematically developed in RCAS as beams based on a NASTRAN model starting with a spar and more sophisticated models are incrementally built up by adding components one at a time. Natural frequencies are compared with those of the NASTRAN model at each step. The elastic wing–pylon beam model is then combined with an elastic gimbaled rotor model, and whirl flutter analysis is carried out. Comparisons are made between uniform inflow and dynamic inflow for aeroelastic stability. Increased flutter speed with dynamic inflow is observed against uniform inflow. Wing and pylon aerodynamics are also added to the model, and their effects on aeroelastic stability are examined. A few key design parameters [pitch spring stiffness, rotor rotational speed, and pitch–flap coupling ()] are varied, and their effects on whirl flutter speed are examined. In particular for TRAST, the pitch spring stiffness and pitch–flap coupling have an important influence on whirl flutter speed.