Differences in the aerodynamic performance data obtained at different test facilities were observed for the Wortmann FX-63-l37 airfoil. Earlier investigations found that the size of the hysteresis loop was affected by the tunnel environment and that single strut mounting of a three dimensional wing model interfered negligibly with the wing. Theoretical and experimental evaluations of a half wing model mounted with an end plate gap were done. Vortex panel method was used in the theoretical evaluation. The results from this indicated an effect of reduced aspect ratio with increase in end plate gap size. Tests were conducted in the VPI Stability Tunnel at low Reynolds numbers for different gap sizes including sealed gap. Results from the experiments showed that even very small gaps produce substantial changes in zero lift angle of attack (αu) and the change in αu, was reduced as Reynolds number increased. Sealed gap test results did not show such a behavior. Flow visualization of the flow through the gap showed a significant flow through the gap even at very low Reynolds number and small gap size. / Master of Science