TEMATIC CHANGES IN WINGS AND TAILS V. EFFECT OF AIRPLANE RELATIVE DENSITY

The reported tests are-a continuation oj an i?. A. C. A. investigation being made in the free-spinning wind tunnel to determine the effects oj independent variations in load distribution, wing and tail arrangement, and control disposition on the spin characteristics oj airplanes. The standard series oj tests was repeated to determine the efect oj airplane relative dendy. Tests were made at values of the relative-density parameter oj 6.8, 8.4 (basic), and 12.0; and the reswlts were analyzed. The tested variations h the relative-density parameter may be considered either as variations in the wing loading of an airplane spun at a given altitude, with the radii oj gyration kept constant, or as a variation. oj the altitude at which the spin takes place jor a given airplane. The lower values oj the relative-density parameter correspond to the lower wing loadings or to the lower altitudes oj the spir~. For all tail and wing arrangements, the lower values oj the relative-density parameter gave jaster recoveries jrom steeper spins and the higher values gave slower recoveries jrom jlatter spins than for the basic loading condition. In general, as the relative-density parameter decreased, the rate oj vertical descent decreased, the spin coefficient f)b/2V increased, and the sideslip became more outward. The importance oj airplane relative density, wing arrange-ment, and control manipulation increased as the elective-ness oj”the tail unit decreased