The flat spin of axisymmetric bodies near the critical Reynolds number

Abstract

To study the steady state flat spin rate and yawing moment coefficient as a function of reduced spin rate, a series of flat spin experiments were conducted in a wind tunnel with circular cylinder, cone cylinder, and bicone cylinder models in the critical and supercritical Reynolds number regions using a free rotation method. Two modes of flat spin, a high spin mode and a low spin mode, were observed. The high spin mode occurred in a fairly narrow freestream velocity region near the critical Reynolds number. Once the high spin mode occurred, the spin rate increased in proportion to the freestream velocity. The spin rate of the bicone cylinder was erratic, being sensitive to small irregularities in the nose shape. The transient yawing moment coefficient of the circular cylinder model was a nonlinear function of the reduced spin rate, and varied in two steps. Slim triangular prism rods attached on the circular cylinder surface parallel to the body axis, effectively reduced the steady spin rate.