Image Number 7 for United States Patent #7628353.
A hold down device positioned on the projectile to exert a known spring force in opposition to the centrifugal force provides an inexpensive, light weight and reliable delayed fin deployment mechanism for boosted fin-stabilized spinning projectiles. When the forcing moment produced by the centrifugal force acting on the fin exceeds the opposing moment produced by the hold down device, the hold down device will release the fin allowing it to swing into its deployed position. Thus, proper selection of the spring force and positioning of the hold down device will cause the fins to deploy at a predetermined spin rate. The spin rate can be correlated to a time or travel distance of the projectile from launch. The incorporation of the hold down devices requires minimal design changes to existing rockets and may, in some cases, be retrofit to the existing base of rockets if desired.