Effects of porous rings on the aerodynamic characteristics of a sphere

A number of design concepts were tested statically and dynamically to determine their ability to improve the stability characteristics and drag coefficient of a sphere. The most successful configuration tested was a thick (0.05d) porous ring, equatorially located. Results of static tests measuring axial force, normal force and pitching moment for this configuration are presented together with data from wind tunnel tests. The effects of the ring to sphere diameter ratio, ring porosity, and the location of the center of gravity on the directional stability are discussed. The influence of the hole cant angle on the roll rate is described.