Ball motion in a ball-obturated tubular projectile
By: R. H. Nunn, J. W. Bloomer, II
Contributors: Bloomer, James Wayne; Naval Postgraduate School (U.S.)
Publisher: Naval Postgraduate School
Published: 1981
Place of publication: Monterey, CA
Language: eng
Number of pages: 75
Subjects: Testing; Rotational motion (Rigid dynamics); Projectiles
Description: When a ball with a concentric hole through it is suspended within a spinning spherical cavity the ball will rotate in such a way that its hole is aligned with the axis of spin of the cavity. If it is mounted within a spinning tubular projectile, the ball can serve as an automatic obturator--plugging the projectile while the two bodies are within the gun barrel and rotating to open the tubular passage following exit from the muzzle. The motion of the ball is gyrodynamic in nature and highly dependent upon the external moments on the ball that arise because of its motion relative to the spinning cavity. This report presents the results of an analytical and experimental study to provide an understanding of such motions in as complete a sense as is possible. The general equations of motion are formulated together with appropriate mathematical expressions for the external moments. These moments have their origins in the forces acting on the ball (gravity and aerodynamic forces are considered) which, in the presence of relative motion between the ball and the projectile, lead to sliding friction torques. Torques due to fluid shear are also considered but these are found to be relatively insignificant. Exact solutions are obtained using standard numerical techniques. In addition, a linear form is developed and these solutions lead to useful approximations that are valid over a broad range of operating conditions.
Notes: Title from cover.

"Prepared for: Technology Programs Management Office (Code 3205) Naval Weapons center, China Lake, CA 93555."." -- Cover.

"January 1981."

"NPS-69-81-001."

Final report for period ending 31 December, 1980.

Includes bibliographic references (p. 72-73).

"Approved for public release; distribution is unlimited."

Technical report; 1981.