Effect of Angle of Attack on Roll Characteristics of 65-Degree Delta Wing

Results are presented of an analysis that defines the flow physics behind the experimentally observed dramatic change of the roll-trim characteristics of a 65-deg delta wing when the inclination of the roll axis is increased from 30 to 35 deg. The big difference between the Cl(phi) characteristics at sigma = 30 and 35 deg is shown to be a direct consequence of where vortex breakdown occurs at phi = 0; 60 percent chord for sigma = 30 deg compared for 25 percent chord for sigma = 35 percent. Thus, in the former case the vortex-induced lift forward of breakdown dominates, generating a stable trim point at phi = 0, whereas in the latter case the movement of vortex breakdown creates the dominate loads, generating a statically unstable Cl(phi) slope at phi = 0. (Author)