Numerical Evaluation of Gust Loads on Tiltrotor

In aircraft design, the loads induced by atmospheric gust encounters are often critical for airframe structural sizing. Consequently, it is extremely important to develop methods that can predict these loads accurately. Current certification regulations include precise requirements concerning the determination of atmospheric loads. In particular, they require that such loads are calculated considering the aircraft dynamic response - including the effects of elastic deformations - to discrete gusts and continuous turbulence. In comparison to classical fixed-wing turboprops, tiltrotors often require a higher modeling complexity, because the unsteady forces generated by the rotors cannot be neglected. The paper presents a numerical tool, denominated MASST, specifically developed to build models that join a detailed FE model of the aircraft, made of different type of elements (e.g. beams, plates, solids, etc.), with a model for steady and unsteady aerodynamic forces, as well as with accurate models of rotors, servo-actuators and the Flight Control System. MASST, combined with the NASTRAN Monitor Points, can provide a high accuracy evaluation of the dynamic loads in any given section of the airframe. The methodology presented is applied and validated on the AW609 airframe dynamic FE model. In particular, different modeling options are compared to identify what is the best approach for the identification of gust loads for this peculiar aircraft configuration.