NACA-RM-L51I06

Abstract

INTRODUCTION <br>Wings of triangular plan form appear, in many respects, to be structurally and aerodynamically suitable for high-speed airplanes; however, adequate longitudinal control is difficult to obtain for these airplanes with manually operated controls. For example, constant-chord flap controls have good effectiveness at low speeds, but inherently have undesirably high hinge moments (reference 1 and 2), and half-delta tip controls, which permit a wide choice of hinge location for aerodynamic balance, have low control effectiveness at low speeds (reference 3). In another case, a canard was found to be virtually ineffective as a fixed trimming device at high lift coefficients in a low-speed investigation of a canard triangular-wing arrangement (reference 4). In a low-speed investigation of a 45&#176; triangular-wing model conducted in Great Britain1 by Lock, Pass, and Meikler, some promise has been indicated for all-movable tails located behind the center of gravity although some instability was encountered near the stall. An all-movable tail, in addition to providing longitudinal control, should overcome some of the other difficulties encountered with semitailless airplanes. The horizontal tail would provide additional damping in pitch, which is low for triangular wings (reference5), and perhaps eliminate the possibility of tumbling (a continuous pitching rotation about the lateral axis) which is also associated with semitailless airplanes. In addition, the center-of-gravity travel would not be as severely restricted for an airplane with horizontal tail. <br>Inasmuch as triangular-wing airplanes generally have stable pitching-moment characteristics through the lift-coefficient range, a horizontal tail would be expected to be necessary only as a control and not as a stabilizer, In the present investigation (which is a part of a research program being conducted in the Langley stability tunnel to determine the suitability of various types of controls for triangular wings), addition of a horizontal tail, however, resulted in serious instability for some tail positions. It was, therefore, desirable to determine an optimum, or nearly optimum, tail position with regard to static stability as well as control effectiveness. Thus, the effects of tail length, height, area, and aspect ratio on the low-speed static longitudinal stability and control characteristics of a 60&#176; triangular wing model having various all-movable triangular tails located behind the center of gravity of the model were studied in this investigation. The results for all-movable tails were compared with results for constant-chord flap controls and half-delta tip controls of the same area.