THE tiltrotor has been a solution for high-speed vertical lift, which provides a dramatic increase in range and speed, while retaining vertical lift capability of traditional edgewise rotor helicopters. Because a tiltrotor requires sufficient power to lift the aircraft vertically, it normally has ample power available for high-speed cruise. Its cruise speed and range are limited directly or indirectly by proprotor/pylon/wing stability, known as whirl flutter. The flutter boundary limits the maximum speed, but also limits range because the high wing stiffness required to eliminate flutter results in thick wing sections, which are not efficient for high-speed flight. Whirl flutter is an important design consideration for tiltrotor aircraft. A major risk mitigation step for whirl flutter is the use of modeling and simulation analyses to ensure adequate speed margin during the design process. With the advance of computer technology and rotorcraft analysis methodology, rotorcraft comprehensive analysis tools have been developed for practical rotorcraft design and engineering applications, including Rotorcraft Comprehensive Analysis System (RCAS)[1], DYMORE [2], and CAMRAD [3]. These tools have been extensively evaluated and are widely used for conventional helicopter performance and loads analysis. To use these tools for tiltrotor whirl flutter analysis, however, rigorous validation studies are needed.

A validation study of DYMORE and MBDyn for a stiff in-plane tiltrotor stability was conducted in [4, 5]. Predictions using both analyses show fair to good agreement with the experimental results. DYMORE and MBDyn were also examined for soft in-plane tiltrotor aeroelastic stability predictions [6, 7]. Fair to good agreement is seen between analytical predictions and test results. CAMRAD was validated for XV-15 stability analysis in [8]. Since then, CAMRAD was used for improving XV-15 whirl flutter stability margins [9, 10] and for large civil tiltrotor design [11–13]. Floros et al.[14], and Shen et al.[15] present the development of models of an unmanned stiff in-plane gimballed tiltrotor