The results of the computations are presented in the form of diagrams of variations of fin area with dihedral angle from neutral stability. The results indicate that ncreasing the values of wing loading and moments of inertia makes the attainment of lateral stability increasingly difficult and even doubtful in some cases for airplanes with flaps deflected. The fin area required for lateral stability is more dependent on fuselage size than on wing area.
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 analogy between the distributon of stresses in flat stiffened panels and the distribution of electric current in a ladder-type resistance network is used as the theoretical basis of an electrical computer for the rapid solution of shear-lag problems. The computer, consisting of variable resistors and multiple-current sources, is described; and typical examples are given of its use. The analogy is extended to include bolted-joint problems, and an example is also given.
When compared with most alloys systems for which diffusion data have been previously obtained, the diffusion rates of chromium in alpha cobalt-chromium solid solutions were found to be low.
