In-Flight Wing Deformation Characteristics During Limit Cycle Oscillations

Oscillatory wing response data were measured on an F-16C aircraft during limit-cycle-oscillation (LCO) testing of an external store configuration. The configuration tested exhibited typical LCO response in the transonic flight regime. Deformation characteristics were measured at 11 locations on the wing and missile launchers during various LCO events. These measurements allowed viewing of the aeroclastic mode of instability for various flight conditions. Details of a linear flutter analysis model are presented, and the predicted eigenmode from the linear flutter analysis is compared to the in-flight measured mode. The measured LCO modes are also compared for level flight vs elevated load factor flight and subcritical LCO vs critical LCO conditions. At the onset of LCO, the mode shape bears a strong resemblance to the flutter mode predicted by linear flutter analysis. Further, the wing deformation characteristics during LCO vary significantly with respect to Mach number and load factor. The nonsynchronous motion of the LCO diminishes and becomes more synchronous as the Mach number increases beyond 0.90. This contradicts the trends predicted by linear flutter analyses and suggests that a change in the oscillation bounding mechanism occurs over the flight region examined. [PUBLICATION ABSTRACT]