The objective of the paper is to demonstrate the validity of e utter predictions obtained using eigenvector orientations (EVO) for realistic wings used in aircraft preliminary design. Comparisons of e utter predictions between the V-g method and the EVO method are presented for an intermediate complexity wing used in optimization studies. The results presented show that the EVO method can predict the onset of e utter for aircraft wings with reasonable accuracy and can be used in design optimization studies of aerospace vehicles/components. I. Introduction T HEdesign of modern e ight vehicles requires multidisciplinary designoptimization (MDO),theintegrationofstructures,aerodynamics,controlandpropulsiondisciplines,toachieveanoptimum design based on certain performance criteria and constraints. In the design of e ight vehicles, e utter is a critical parameter that must be considered in the early stage of the design cycle. Also, with aging aircraft,certainrestrictionsneedtobeimposedinordertoavoide utterinstabilityduring thee ightregimeoftheaircraft.Alargenumber of parameter changes must be investigated in the e utter design of military as well as commercial aircraft as a result of the complexity of modern composite/metallic structures. Accurate and efe cient methods of e utter prediction for aerospace vehicle components are needed for use in aeroelastic design optimization studies. There are several aeroelastic design optimization codes being used for aircraft and spacecraft structures, such as the Automated Structural Optimization System (ASTROS) 1 and MSCNASTRAN. 2 In aeroelastic design optimization the predominant dynamic e utter instability needs to be investigated for most e ight vehicles. Several methods are being used to predict the onset of e utter instability in aeroelastic design optimization. Most of these methods arebasedoncomplexeigenvalues (p-kmethod, K-method, orKE method). 2 Recently,Afolabietal. 3 developed amethodbased on eigenvector orientations (EVO) to predict the onset of e utter instability. In their work the method of EVO was used for limited examples of panel e utter. To gain a better understanding of the EVO method of e utter prediction, further investigations need to be carried out on realistic aircraft structures. This understanding will help to devise a prediction methodology that may be implemented in MDO codes for the preliminary design of e ight vehicles. The objectiveofthispaperisto further validate the EVOmethod 3 of e utter prediction for realistic examples used in aircraft preliminary design. Abriefreviewofthe EVOmethod for e utterprediction isdescribed inthe nextsection.Anexampleofanintermediatecomplexity wing used in design optimization studies is considered, and e utter prediction results are compared to the commonly used V-g method.