Aging Aircraft

Unsteady forces caused by Vortex bursting in the vicinity of an aircraft structure evoke structural responses called buffeting which can inflict severe damage on an aircraft structural. Modal identification tests performed on the complete F-15 aircraft at Dobins Air Force Base have also shown that certain modes of dynamic response characteristics occur which are not necessarily restricted to the motion of only vertical tail. in several critical modes, the wing and the horizontal tail are involved. This has the effect of introducing quadratic non linearities and amplifying or creating high amplitude vibrations which together with vortex induced motion at high angle of attack cause buffet. Tail vibrations and tail buffet are common problems which twin tailed aircraft such as this F-15 and F-18 experience. A significant reduction of the buffet problem is sought by the application of smart structures. At critical frequency regions characteristic of buffet, Smart Structures alter the response of the material in such a way that buffeting is reduced. Several types of actuators and actuator installations will be examined and their applicability for buffet alleviation will be identified. Some simple experiments on a model will be performed, and the feasibility of reducing vibrations at a selected band of frequencies will be demonstrated.