V-22 EMPENNAGE BUFFET DYNAMICS

This paper presents the development of the V-22 empennage buffet design loads for both VTOL and airplane mode flight regimes during the Preliminary Design (PD), Full-Scale Development (FSD), and Engineering and Manufacturing Development (EMD) programs. Empennage buffet was considered to be a design driver from the beginning of the V-22 program. A plan consisting of scaled XV-15 wind tunnel and flight test data and V-22 wind tunnel data was implemented to define the buffet environment during PD. During initial development, the primary forcing function for empennage buffet was thought to be wingtip and rotor-induced vortices. The data are discussed in terms of overall oscillatory loads, spectral analysis, and scaling of wind tunnel results. A description of the power spectral density (PSD) analyses used in the design process is presented along with correlation with wind tunnel measured loads. Subsequent airplane mode flight and wind tunnel testing identified the wing root and over wing fairing as sources of high energy vortices which also excited the empennage. The impact of designing for these higher loads on the stiffness requirements of the EMD empennage for natural frequency placement is discussed. Due to the significant impact on the empennage dynamics, an analytical and wind tunnel program to understand and define aerodynamic design changes to reduce these higher loads was undertaken. The results of simplified and rigorous PSD analyses techniques using the wind tunnel measured pressures are presented.