Experimental Investigation of Annular Wing Aerodynamics

A low-speed wind-tunnel investigation was conducted to explore the behavior of annular (ring) wings. Effects of aspect ratio as well as gap were investigated. Ring wings using a low Reynolds number Eppler section and a NACA 0012 profile were manufactured and tested. Measurements were recorded using a six-component sting balance. Experimental and theoretical trend comparisons were effected using a vortex-lattice code. The experimental results indicate wing efficiency factors well above 1 are achievable. The effect of gap was to increase the wing lift-curve slope as well as efficiency. The large increases in aerodynamic efficiency were generally mitigated by the significant minimum drag coefficient. Pitching moment characteristics were unfavorable and were dominated by dissimilar stall behavior between the upper and lower wing sections.

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