Experimental Validation of Elliptical Fin Opening Behavior

Report No. ARL-TR-2527
Authors: James M. Garner, Paul Weinacht, Robert P. Kaste
Date/Pages: September 2001; 31 pages
Abstract: An effort to improve the performance of ordnance has led to the consideration of the use of folding elliptical fins for projectile stabilization. A second order differential equation was used to model elliptical fin deployment history and accounts for deployment with respect to the geometric properties of the fin, the variation in fin aerodynamics during deployment, the initial yaw effect on fin opening, and the variation in deployment speed based on changes in projectile spin. This model supports tests conducted at the Transonic Experimental Facility, Aberdeen Proving Ground, Maryland, which examined the opening behavior of these uniquely shaped fins. A companion boat tail configuration is created by sectioning the projectile base and joining with the fin. The configuration is both space efficient and aerodynamic. Reduced drag coefficients have been documented for this configuration and it is employable on a variety of projectiles. The fins use the centrifugal force from the projectile spin to deploy. During the deployment, the fin aerodynamic forces vary with angle-of-attack changes in the free stream. Model results indicate that projectile spin dominates the initial opening rates and that aerodynamics dominate near the fully open state. Vibratory fin motions after elastic and inelastic collisions with the fin stop are also examined. The aerodynamics and initial state conditions correspond to a zone 7w artillery firing (roughly Mach 2.25) that uses a slip band obturator and with muzzle exit yaws of 0 and 5 degrees. The model results are examined to explain the observed behavior and to suggest improvements for later designs.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2001