A test and analysis method is presented for determining airplane lateral stability characteristics, including aerodynamic derivatives, from flight tests of scale models. The method of analysis utilizes the rotating time-vector concept and also a quasi-static approach. Data are presented at transonic speeds for three swept-wing rocket-propelled models differing only in vertical position and dihedral of the wing. The method proved to be adequate for delineating the major effects of the geometric variations on the aerodynamic lateral stability derivatives. The effects of Reynolds number on the linearity of the static stability data for an unswept wing configuration are illustrated.

Summary: The effects of negative dihedral on lateral stability and control characteristics at high lift coefficients have been determined by flight tests of a model in the Langley free-flight tunnel. The geometric dihedral angle of the model wing was varied from 0° to -20° and the vertical-tail area, from 0 to 35 percent of the wing area. The model was flown with various combinations of dihedral angle and vertical-tail area at lift coefficients of 1.0, 1.4, and 1.8. As the effective dihedral was decreased from 0° to -15°, the model became increasingly difficult to fly. With an effective dihedral of -15° the flying characteristics were considered to be dangerous because, when there was only a slight lag in the application of corrective control following a disturbance, the unstable moments resulting from spiral instability became sufficiently large to overpower the moments of the controls so that return to straight flight was impossible. Inasmuch as full-scale airplanes because of their greater size will diverge at a slower rate than free-flight models, the amount of negative effective dihedral that would constitute a dangerous condition is expected to be greater for full-scale airplanes.

The effects of large variations of lateral area on the lateral stability and control characteristics of a free-flying model when ailerons are used as the principal control have been determined by flight tests in the Langley free-flight tunnel. The effects of the lateral-force parameter (rate of change of lateral-force coefficient with angle of sideslip) were investigated for a wide range of values of the directional-stability parameter (rate of change of yawing-moment coefficient with angle of sideslip) and the rotary-damping-in-yaw parameter (rate of change of yawing-moment coefficient with yawing angular velocity).