NACA-RM-A50K27

Abstract

INTRODUCTION <br>The effectiveness of wing sweep in delaying the detrimental effects of compressibility to higher Mach numbers is well known. One of the principal difficulties encountered in the use of swept-back wings of high aspect ratio is the low lift coefficient at which large changes of static longitudinal stability occur. Since this effect is attributed to stalling of the outer portions of the wing, it follows that increase in the lift coefficient at which large changes of static longitudinal stability occur might be realized by increasing the maximum lift coefficient of the wing sections. The use of camber is a familiar means of increasing the maximum lift coefficient as well as the lift-drag ratio of unswept wings. Research on the effects of camber and twist on the aerodynamic characteristics of swept-back wings has been reported in references 1 and 2. The present investigation was initiated to evaluate the effects of camber alone and also the effects of dynamic scale and compressibility on the aerodynamic characteristics of several wings having 35 of sweep back. <br>Six semi span model wings were tested: Three representing wings having an aspect ratio of 10, and three representing wings having an aspect ratio of 5. The stream wise sections of the three wings of each aspect ratio were the NACA 651a012, the NACA 641A312. and the NACA 64a1A612. According to simple sweep theory, the aerodynamic characteristics of sections perpendicular to the quarter-chord line determine the aerodynamic characteristics of a swept-back wing. The sections perpendicular to the quarter-chord line of the wings investigated were approximately 14 percent thick and had design lift coefficients of about 0, 0.37, and 0.73. Results of tests of airfoil sections reported in reference 3 have indicated that the addition of camber increases the maximum lift coefficient for airfoil sections having thickness chord rations of less than 12 percent, but that the effectiveness of camber in increasing the maximum lift coefficient diminishes as the thickness is increased beyond 12 or 15 percent. For the 14-percent thick wings tested in the present investigation, the increase in the maximum lift coefficient resulting from camber and hence the increase in the lift coefficient at which longitudinal instability occurs should be significant but may not be expected to be as great as that which would be anticipated for thinner wings. <br>The tests were conducted over a range of mach numbers form 0.25 to 0.92 at a Reynolds number of 2,000,000 and over a range of Reynolds numbers from 2,000,000 to 10,000,000 at a mach number of 0.25.