Subsonic Flutter Characteristics of a Variable Sweep Wing and Horizontal Tail Combination

Walter J. Mykytow · Thomas Edwin Noll · Lawrence J. Huttsell · Michael H. Shirk

Jan. 1970 · Air Force Flight Dynamics Laboratory, Air Force Systems Command, United States Air Force

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The project concerns a subsonic investigation of a new type of flutter phenomenon, not previously critical from a design standpoint, involving elastic modes of the wing, fuselage, and stabilizer combination and also involving aerodynamic interference between the wing and horizontal tail. The effort, consisting of design of a flutter model, vibration and subsonic wind tunnel tests, and flutter analyses, was conducted to determine important controlling flutter parameters, to evaluate the accuracy of analyses for predicting the phenomenon, to establish flutter trends and to define flutter prevention design criteria which could be used in the early design stage to avoid the problem. Some of the important features that were determined are increasing wing sweep can lead to lower flutter speeds; wing bending to fuselage torsion frequency ratios were defined which provide the mechanical coupling essential to produce the phenomenon and minimum flutter speeds as a function of wing sweep angle; vertical separation or dihedral angle can be very influential and beneficial and is more important than longitudinal separation, the effects of which were found to be small to moderate; the effects of compressibility have been shown to be detrimental and decrease the flutter speed, and conclusive proof that the interference aerodynamics between the wind and tail, and particularly, the downwash shed from the wing, is an important and detrimental feature to the phenomenon. (Author).