Fin-Opening Dynamics for an 8-Inch Gun Launched Extended-Range Guided Projectile
Final rept. Jul 1976-Dec 1978
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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The fin-opening dynamics for an 8-inch Gun Launched Extended-Range Guided Projectile ERGP were analyzed during the typical 20 to 30 millisecond time span immediately after the missile departed the gun barrel. Lagranges equations were used to develop a set of governing dynamic relationship using four generalized coordinates including missile roll angle, fin-opening angle and fin bending and torsion deflections. The latter two coordinates provided an elastic representation for accommodating the fins transient response during the fin-opening process. Sufficient details were provided so that the analytic model could be modified for other missile and fin configurations, including addition of more fin bending degrees of freedom. Comparison was made between the analysis results and a limited amount of experimental evidence. Agreement was reached with fin-opening times and an indirect conclusion was reached that initial fin- opening angle rates were in the range of 35 to 50 radianssecond. The fin elastic response was shown to be dependent primarily upon the fin bending mode. Peak stress encounters by the fin root beyond yield could be avoided by configuring the ERGP obturator rings to control initial missile roll rates to less than 15 revolutionssecond. This latter point is important since local yielding of the fins by excessive bending stresses, incurred during launch, can adversely effect the trajectory dynamics by contributing to the presence of a residual roll rate.
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