VISCOUS CONTRIBUTION TO THE HIGH MACH NUMBER DAMPING IN PITCH OF BLUNT SLENDER CONES AT SMALL ANGLES OF ATTACK

The dynamic stability derivatives of blunt cones for small variations in angles of attack have been previously derived by the current author . However, no account of the unsteady nature of the boundary layer was made in that work. In this paper closed form expressions for the incr ement in dynamic stability due to the presence of the boundary layer a re derived by considering the pressure distribution perturbations as t he boundary layer continuously adjusts to the enclosed oscillating bod y. The theory provides a first hand estimate of the complete pitch der ivative damping without having to resort to more rigorous and expensiv e computational methods. Calculations performed at Mach numbers of 7 t o 10 with axis positions ranging from 0.5 to 0.7 of the chord length f or cones of semi-angle 10 degrees and 20 degrees, indicate that the ef fect of boundary layer is to slightly reduce the magnitude of the invi scid damping derivative. For blunt cones at angles of attack less than 5 degrees, this was in good agreement with the limited experimental d ata available.