NACA-TN-1378

Abstract

INTRODUCTION <br>The analysis of reference 1 shows that the use of sweptback wings for high-speed aircraft can greatly extend the range of flight Mach number attainable before the onset of serious compressibility effects on the wings. The National Advisory Committee for Aeronautics is therefore attempting to supply design data on the characteristics of swept wings. For the low-speed range in which the disadvantages inherent in the use of high degrees of sweep appear to be greatest, the Langley Laboratory of the NACA has supplied such data on the low-speed stability and control characteristics of sweptback wings in references 2 and 3 and has provided a collection and analysis of static longitudinal stability characteristics of sweptback wings in reference 4. <br>The analysis of reference 4 shows that the static longitudinal stability of isolated wings, particularly near the stall, is great dependent upon the aspect ratio and sweepback angle. A Summary chart based on these two parameters is presented in reference 4 for use in determining stable and unstable combinations of sweep and aspect ration. Other data presented in reference 4 indicate, however, that the problem of obtaining adequate longitudinal stability for wing-tail combinations is more complex than that for wings alone because of apparently large and unpredictable downwash changes in the region of the tail surfaces. <br>As an extension to the work of reference 4, the present paper provides a collection and brief analysis of downwash measurements made behind various sweptback wings. The data were obtained from tuft observations and force tests of wing-tail combinations in the Langley 7- by 10-foot tunnel.