NACA-RM-A51B21

Abstract

INTRODUCTION <br>Theoretical and experimental studies show that an airplane with a low-aspect-ratio triangular wing would have desirable characteristics for flight at moderate supersonic speeds. At low speeds, however, the triangular wing has several undesirable characteristics which if not overcome will limit its use. These undesirable characteristics include low lift-drag ratios and high angles of attack at maximum lift coefficients. Thus an airplane utilizing a triangular wing would have high sinking and landing speeds and abnormally high landing attitudes. <br>The foregoing considerations have neglected the problem of trim. Because of the characteristics of a triangular wing, trim can be obtained means such as a conventional horizontal tail. The tailless design, however, further aggravates the low-speed problems associated with the use of a triangular wing. This is indicated by the data of reference 1 which show that the negative flap deflections required to trim the airplane increase both the drag and angle of attack at any given lift coefficient. In contrast, reference 1 also shows that, at a given life coefficient. In contrast, reference 1 also shows that, at a given lift coefficient, a reduction in both drag and angle of attack can be obtained by use of positive flap deflections. Use of the trailing-edge flaps as a lift producing device, however, would necessitate the use of a trimming device such as an all-movable horizontal tail. <br>In order to provide information on the low-speed characteristics of a triangular-wing airplane with a horizontal tail, an investigation was made in the Ames 40-by 80-foot wind tunnel. The model used in the investigation consisted of a thin, low-aspect-ratio, triangular wing with partial-span, slotted, trailing-edge flaps; a high-fineness-ratio fuselage; a thin vertical tail of triangular plan form; and a thin, unswept horizontal tail. The plan form of the horizontal tail was made identical, and the airfoil section similar, to that of the wing the characteristics of which throughout the subsonic Mach number range, are reported in reference 2. The choice of plan form was dictated by the following considerations: An all movable horizontal tail was chosen form a consideration of stability and control. The use of a triangular, all-movable tail was eliminated because of geometry (i.e, large, all-movable tail was eliminated because of geomstry (e.e., large root chord), while the use of an all-movable, swept tail was eliminated as a result of a consideration of control moments. Hence, the unswept tail with a supersonic-type airfoil section was chosen. The horizontal tail was located at each of three vertical positions with respect to the wing-chord plane at a fixed longitudinal position of the tail. Reported herein are the longitudinal stability and control characteristics of the various model configurations.