Wind tunnel investigation of a supersonic tailless airplane at low subsonic speed

Abstract

An investigation was made in the Cal Tech-Merrill low speed wind tunnel at Pasadena City College to determine the lift and moment characteristics of a sweptback wing and a comparable delta wing, both with a 65° sweptback leading edge and a double wedge symmetrical airfoil section. Both wings were tested with and without a fuselage. Leading edge flaps and slats, trailing edge plain flaps, split flaps, Fowler type flaps, and fillets were tried to determine their effects on these characteristics. The complete airplane was designed with the idea that it should be a tailless airplane. The results showed unfavorable longitudinal static stability characteristics which could be improved but which could never be completely overcome at the stall when the wings were tested with the fuselage. A horizontal tail surface was necessary for longitudinal static stability at the stall but proved ineffective at the lower angles of attack. The maximum lift coefficients for both wings of about 1.3 were higher than for a two dimensional double wedge airfoil section of approximately 0.8. The angles of attack at which these were reached were about twice as high as for the two dimensional section. Tuft surveys showed the formation of two strong vortices from the leading edge of both wings first appearing at an angle of attack of approximately 10°. These vortices separated from the upper surface of the wing before reaching the trailing edge. Comparison of results for the two wings indicated that the discontinuity of the trailing edge at the root of the sweptback wing was detrimental to the maximum lift. There was an optimum deflection of the trailing edge split flap as a high lift device. On the delta wing alone the plain flaps were very effective in increasing the maximum lift while the split flaps were ineffective. Ailerons on the sweptback wing wore effective at all angles of attack through the stall.