Cwonent Part Notice

ScMf.r^ A review of lighter aircraft development programs over the pas t.three decades Indicates a trend of increasing emphasis on the considera tion of static aeroe las tic effects. While early concerns addressed only the impact on air vehicle structural integrity, current design philosophy recognizes and addresses aen jelastlclty as a primary design parameter affecting structural optimiza tion, vehicle aerodynamic stability, control ef fee tiveness, and overall performance. Examples from wind tunnel tes ting, analytical s tudies, and opera tional aircraft applications are presented to Justify this emphasis, illus tra te current methodology and analysis techniques, and make a case for an integrated approach to the consideration of static aeroelastlc effects at all stages of the design process. Introduc tion Y. C. Fung, the author of one of the most prominent texts on the subject, defines aeroelasticity in terms of the "phenomena that reveal the effect of aerodynamic forces on elastic bodies" (Reference I). Another text, Reference 2, refers to aeroelastlc phenomena as "the effects, upon the aerodynamic forces, of changes In the shape of the airframe caused by these same aerodynamic forces," Both of these texts make a distinct differentia tion be tween "dynamic phenomena" and the "static aeroelastlc phenomena" which the following discussion will be limited to. More specifically, the topic here is the role of static aeroelasticity in the design of modern fighter aircraft. * Static aeroelastlc effects are manifested In the form of changes in the total load or lift on the aircraft, or In changes in the overall distribution of load or lift. These changes affect the structural integrity of the vehicle, its static stability, the effectiveness of various control surfaces, and the overall flight performance. The characteristics and magnitude of these ae roe las tic ef f ec ts are dependent on the aerodynamic she p*» of the vehicle, the structural orlenta tion, the s tructura I s tlffneas, and the particular flight condition In terms primarily of Mach number and dynamic pressure.-" v Historically, the s tudy of aeroelasticity began in the early 1920'a. However, serious considera tion of aeroelastlc effects in the design of fighter aircraft, was probably not given until the late 19^0's, when significant advances in alrcraf t performance provided capability for opera tion at high subsonic speeds and associated dynamic pressures. As indicated In Figure I, the emphasis on consideration of aeroelasticity has increased over the pas t three decades. The early 1950's efforts were characterized by minimal considera tion, limited to assessing the possible impact on the vehicle structural ir. grlty as a result of overa11 changes In the vehicle aerodynamic characteristics. Aeroelastlc effects were addressed in structural opt 1mlza tion efforts In the 1960's and serious consideration was being given to the Impac t on performance, relative to con'rol effectiveness and aerodynamic stability. The ^O's saw Increased euphaala on struc tural optimization to enhance performance with the advent of serious aeroelastlc tailoring and deslgned-ln structural flexibility. Design philosophy today recognizes aeroelasticity as a primary design parame ter with dedicated testing and analyses being considered a necessary and Integral segment of the vehicle design process.