Limit Cycle Oscillation Flight Test Results of a Fighter with External Stores

TLDR

The categories observed represent the broad spectrum of aeroelastic responses encountered by fighter aircraft with external stores. The study aims to present flutter analysis results, including an analytical model, store configurations, and mass properties, as realistic check cases for validating nonlinear flutter analysis methods. Oscillatory wing response data were measured on an F-16A during flutter tests of several external store configurations, and the results were combined with analytical flutter analysis details. Flight tests revealed limit cycle oscillations and high‑amplitude responses resembling classical flutter, classified into three categories, with theoretical flutter analyses accurately identifying sensitive store configurations and frequencies, a strong correlation with modal composition, but linear analysis failing to predict amplitude or onset velocity.

Abstract

Oscillatory wing response data were measured on an F-16A aircraft during flutter tests of several external store configurations. Previous testing had shown the F-16 to exhibit limit cycle oscillations (LCO) in the transonic regime, During the present tests, LCO were encountered as well as the sudden onset of high-amplitude oscillations. This sudden high-amplitude response closely resembled that of classical flutter. In all, three distinct categories of response behavior were seen during these tests: classical flutter, typical LCO, and nontypical LCO. These categories are representative of the broad spectrum of aeroelastic responses encountered by fighter aircraft with external stores. Theoretical flutter analyses are shown to adequately identify flutter- or LCO-sensitive store configurations and their instability oscillation frequencies. In addition, a strong correlation between the flight test response and the modal composition of the analytical flutter mechanism is evident. However, the linear analysis fails to provide insight into the oscillation amplitude or onset velocity, which are of primary importance for external store certification on fighter aircraft. Flutter analysis results are presented along with details of the analytical model, the store configurations, and the store mass properties for use as realistic check cases for the validation of nonlinear flutter analysis methods.