Delayed Fin Deployment via Centrifugal Spring Restraint
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Solution Overview
Problem
Existing fin-stabilized projectiles lack a cost-effective, lightweight, and low-volume mechanism for delayed tail fin deployment, which is essential for avoiding interference with adjacent projectiles and mitigating boost-phase winds, without sacrificing reliability or requiring significant redesign.
Innovation Solution
A hold down device that uses a constant spring force to delay fin deployment until the projectile reaches a predetermined spin rate, allowing the centrifugal force to overcome the spring force and deploy the fins, with optional lanyard and cam mechanisms to ensure synchronized deployment and minimize dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If immediate fin deployment is used, then stability is achieved quickly, but interference with adjacent rockets or helicopter flow field occurs
Solution Approach 1:
The fin deployment mechanism is designed to deploy fins after a predetermined time delay following launch, allowing the rocket to clear the helicopter's flow field and adjacent rockets before fins are deployed. This preliminary timing action resolves the contradiction by scheduling the deployment event to occur after the harmful interference period has passed.
2Loss of time
If active-passive or active-active systems are used for delayed deployment, then deployment timing control is achieved, but cost, weight, and volume increase significantly
Solution Approach 1:
The system uses the rocket's own rotational motion (spin) generated during flight to trigger fin deployment. A centrifugal force mechanism automatically deploys the fins when a predetermined spin rate is reached, eliminating the need for external timing circuits, batteries, or control systems. The rocket serves itself by using its inherent motion characteristics to control deployment timing.
Solution Approach 2:
The deployment mechanism responds to changes in the spin rate parameter. As the rocket accelerates rotationally during flight, the centrifugal force increases until it overcomes the restraining force of the fin retention mechanism, automatically triggering deployment. This parameter-based control avoids complex timing systems while achieving precise delayed deployment.
3Speed
If spring loading is used to deploy fins quickly, then deployment speed increases, but deployment occurs immediately without delay capability
Solution Approach 1:
The fin retention mechanism applies a restraining force (preliminary anti-action) that counteracts the spring loading and centrifugal force during the initial phase of flight. This restraint prevents immediate deployment despite the presence of strong deploying forces. Only after the predetermined time delay, when the spin rate generates sufficient centrifugal force to overcome the retention mechanism, does deployment occur rapidly.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Provides a reliable, inexpensive, and lightweight solution for delayed fin deployment that minimizes interference and allows projectiles to clear aircraft flow fields or multi-tube launchers, with minimal redesign requirements and reduced dispersion at the target.
Implementation Method 1
a spring means for exerting a constant force to hold the fin in the stowed position
Implementation Method 2
When the spin rate reaches the target value, the rotational moment produced by the centrifugal force exceeds the opposing moment produced by the spring force and the hold down device releases the fin
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
A hold down device (100) 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 (102) 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 delayed deployment of multiple fins is attained by providing a plurality of like hold down devices or by providing a single hold down device that releases a lanyard (106) when deployed.