Effects of Wing Position and Horizontal-tail Position on the Static Stability Characteristics of Models with Unswept and 45 Degree Sweptback Surfaces with Some Reference to Mutual Interference

Abstract : An investigation was made to determine the effects of wing position and horizontal tail position on the low speed static longitudinal and static lateral stability characteristics of airplane models having unswept and 45 deg sweptback surfaces. The results indicated that both the unswept and the sweptback low wing low-horizontal-tail configurations were the optimum configurations from the standpoint of longitudinal and lateral stability. The results indicated that, for all wing positions, moving the horizontal tail from the high to the low position resulted in configurations which were longitudinally stable throughout the angle of attack range. For the lateral case, the vertical-tail contribution to the directional stability was increased by moving the wing from the high to the low position because of the favorable sidewash at the vertical tail arising from the wing fuselage interference. The addition of a horizontal tail in the low position produced a further increase in directional stability. The results also indicated that at low angles of attack the effective dihedral due to wing-fuselage interference increased as the wing height was increased - that is, from approximately - 4 deg for the low-wing configuration to 5 deg for the high-wing configuration. This effect could be predicted with fair accuracy by available theory. At low angles of attack, the lateral force on the fuselage was increased because of the end-plate effect when a wing was placed in the high or the low position. However, the lateral force on the fuselage decreased for the low-wing configuration and increased for the high-wing configuration as the angle of attack was increased because of the variation in the distribution of sidewash on the fuselage with angle of attack.