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Wind tunnel and flight tests of the T-45A aircraft have identified a transonic region of reduced longitudinal stability. Wind tunnel results established the phenomenon as a flow interaction between the wing-body and the horizontal tail; however, insufficient data existed to determine the mechanism causing the reduced stability. Computational Fluid Dynamics (CFD) analysis of the T-45A in the transonic region identified the source of the reduced stability to be an increase in downwash on the horizontal tail caused by mid-span vorticity shed from the wing.

A computational analysis of the external flowfield about a fighter configuration was conducted to evaluate an Euler solver and to investigate a hybrid combination of an Euler solver and a panel method. The analysis demonstrated the usefulness of Computational Fluid Dynamics (CFD) as a configuration design tool. The configuration selected for the study involved complex flowfields for which substantial wind tunnel test data were available. The Euler code provided good estimates for the incremental effects of aileron deflections using both wing-alone and wing-fuselage modeling. In general, the addition of the fuselage to the wing-alone model improves estimates of the effects of leading edge and trailing edge flap deflections. Using a hybrid combination of Euler code results with incremental effects of the tails from a subsonic panel method provides good estimates of trimmed drag changes for small flap/aileron deflections.