Accession Number : ADP009067

Title :   Flight Dynamics of a Spinning Projectile Descending on a Parachute.

Corporate Author : SANDIA NATIONAL LABS LIVERMORE CA

Personal Author(s) : Benedetti, G. A.

Report Date : SEP 1993

Pagination or Media Count : 12

Abstract : During the past twenty years Sandia National Laboratories and the U. S. Army have vertically gun launched numerous 155mm and eight-inch diameter flight test projectiles. These projectiles are subsequently recovered using an on-board parachute recovery system which is attached to the forward case structure of the projectile. There have been at least five attempts to describe, through analytical and numerical simulations, the translational and rotational motions of a spinning projectile descending on a parachute. However, none of these investigations have correctly described the large nutational motion of the projectile since all of them overlooked the fundamental mechanism which causes these large angular motions. Numerical simulations as well as a closed form analytical solution show conclusively that the Magnus moment is responsible for the large nutational motion of the projectile. That is, when the center of pressure for the Magnus force is aft of the center of mass for the projectile, the Magnus moment causes unstable (or large) nutational motion which always tends to turn the spinning projectile upside down while it is descending on the parachute. Conversely, when the center of mass for the projectile is aft of the center of pressure for the Magnus force, the Magnus moment stabilizes the nutational motion tending to always point the base of the spinning projectile down. The fundamental quantity related to stability of the nutational motion is the direction of the Magnus moment. Since this is determined from such a basic result, it is profoundly simple. Consequently, it is surprising that the large nutational motion for a spinning projectile during parachute descent puzzled many investigators and went unexplained for nearly twenty years.

Descriptors :   *ANGULAR MOTION, *PARACHUTE DESCENTS, *SPIN STABILIZED AMMUNITION, DIAMETERS, FLIGHT, GUN LAUNCHED, MOMENTS, PRESSURE, RECOVERY, SIMULATION, STABILITY, YAW, FIRING TESTS(ORDNANCE).

Subject Categories : Ballistics

Distribution Statement : APPROVED FOR PUBLIC RELEASE