Targeting Pod Effects on Weapons Release from F-18C Hornet; Trident Scholar Project rept. no. 366

摘要

In recent years, the capability of computational fluid dynamics (CFD) to predict the trajectories of stores has greatly expanded. In this study, a CFD code developed at NASA has been used to explain an unexpected flight test result in order to assess the accuracy of CFD as applied to store separation. In December of 1998 during routine bombing practice at Fallon, NV, an F-18C released a Mark 82 JDAM bomb which impacted the Targeting Forward-Looking Infrared Pod (TFLIR) on the aircraft fuselage. This trajectory was entirely unexpected as that flight condition had previously been cleared as safe for store release. It had been assumed that the addition of the TFLIR would not cause a significant change to the aircraft's flowfield; an assumption which proved inaccurate. This study was designed to investigate whether CFD analysis could predict and explain the results of the aforementioned flight, and to determine the efficacy of CFD to predict and explain the effects of three different targeting pods of different geometries all carried by the F-18C Hornet. The three pods examined in this study were the TFLIR, the ATFLIR, and the Litening pod. The TFLIR and ATFLIR are geometrically quite similar while the Litening pod is both longer and wider. Surprisingly, flight tests showed that the ATFLIR and TFLIR pods had significantly different effects on the aerodynamic loads created on the bomb. Initial speculation centered on the physical differences between the forward ends of the pods, but this research revealed that the most important aspect was the shape and placement of the rear end of the pods. The initial investigation analyzed the aerodynamic effects of each pod on a bomb located adjacent to the pod on the inboard pylon beneath the wing.