# Patent

## Title
Pyrotechnic fin deployment and retention mechanism

## Abstract

A fin retention and deployment mechanism includes a detent in each of a plurality of fins, a mechanism that engages the detent, and at least one spring clip that maintains each of the fins in a non-deployed position. The mechanism also includes a gas generator, a manifold, coupled to the gas generator and having a plurality of cylinders in fluid communication with gas from the gas generator, and a plurality of pistons disposed in the cylinders. A bottom of each of the pistons is coupled to each of the fins to provide deployment thereof when a corresponding top of each of the pistons is acted upon by gas from the gas generator. In response to the gas generator expelling gas, the pistons may move the fins to a deployed position.

## Background
STATEMENT OF GOVERNMENT SUPPORT
This invention was made with U.S. government support under Contract Number FA8681-06-C-0152. The U.S. government may have certain rights in the invention.


BACKGROUND OF THE INVENTION
1. Technical Field
This application relates to the field of fin deployment and retention, and more particularly to the field of fin deployment and retention for projectiles that are guided by fins.
2. Description of Related Art
Projectiles that are guided by fins, such as bombs dropped from aircraft, missiles, etc., may need to be stored in a relatively compact manner prior to deployment. However, the fins on the projectiles may limit the number of projectiles that may be stored in a given space. In addition, storage and transport of projectiles having fins may result in damage to the fins due to movement that can be expected in the course of transportation.
One way to address these issues is to manually detach the fins prior to deployment and then reattach the fins just prior to use. However, this may be impractical for a number of reasons. Manual reattachment may not be possible in situations when projectiles are being stored and then deployed in an automated fashion. For example, it may be desirable to store the projectiles in an aircraft bomb compartment that is opened while the aircraft is in flight.
As an alternative to manual fin deployment, the fins may be folded close to the body of the projectile for storage and transport and then automatically deployed just prior to use. However, for such a system, it is important that all of the fins be reliably deployed for the projectile to operate properly. In addition, it is also useful to avoid premature deployment (e.g., from jostling the aircraft) since premature deployment may cause the fins to be damaged and/or adversely affect deployment of the projectiles altogether.
Accordingly, it is desirable to provide a system that addresses the needs set forth above.
SUMMARY OF THE INVENTION
According to the system described herein, a fin deployment mechanism includes a gas generator, a manifold, coupled to the gas generator and having a plurality of cylinders in fluid communication with gas from the gas generator, and a plurality of pistons disposed in the cylinders, a bottom of each of the pistons being coupled to a fin to provide deployment thereof when a corresponding top of each of the pistons is acted upon by gas from the gas generator. The fin deployment mechanism may also include a valve coupled to the gas generator to control a flow of gas therefrom. The gas generator may be implemented using a chemical initiator. The fin deployment mechanism may also include a plurality of springs, disposed in the cylinders, to bias the pistons away from the fins. The pistons may be directly coupled to the fins or may be coupled to the fins through a padding element. The padding element may be made from a material that is softer than a material used for the fins. The fins may be made from 7075-T6 aluminum while the padding element 68 may be made from 6061-T6 aluminum.
According further to the system described herein, a fin retention mechanism includes a first detent in a fin, a mechanism that engages the first detent, and at least one spring clip that maintains the fin in a non-deployed position. The fin retention mechanism may also include a second detent that engages the mechanism. The fin may be maintained in a non-deployed position in response to the first detent engaging with the mechanism. The fin may be maintained in a deployed position in response to the second detent engaging with the mechanism and release of the fin from the spring clip. The mechanism that engages the first detent may include a ball and a spring that urges the ball toward the first detent. The mechanism that engages the first detent may include a plunger and a spring that urges the plunger toward the first detent.
According further to the system described herein, a fin retention and deployment mechanism includes a first detent in each of a plurality of fins, a mechanism that engages the first detent, at least one spring clip that maintains each of the fins in a non-deployed position, a gas generator, a manifold, coupled to the gas generator and having a plurality of cylinders in fluid communication with gas from the gas generator, and a plurality of pistons disposed in the cylinders, a bottom of each of the pistons being coupled to each of the fins to provide deployment thereof when a corresponding top of each of the pistons is acted upon by gas from the gas generator. The fin retention and deployment mechanism may also include a plurality of springs, disposed in the cylinders, to bias the pistons away from the fins. The pistons may be coupled to the fins through a padding element that is made from a material that is softer than a material used for the fins. In response to the gas generator expelling gas, the pistons may move the fins to a deployed position and a second detent in each of the fins may engage the mechanism to maintain the fins in a deployed position. The mechanism that engages the detents may include a ball and a spring that urges the ball toward the detents and/or may include a plunger and a spring that urges the plunger toward the detents.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the system are described with reference to the several figures of the drawings, in which:
FIG. 1 is a schematic diagram of a fin assembly in which the fins are in a non-deployed position according to an embodiment of the system described herein.
FIG. 2 is a schematic diagram of a fin assembly in which the fins are in a deployed position according to an embodiment of the system described herein.
FIG. 3 is a schematic diagram showing a fin retention mechanism according to an embodiment of the system described herein.
FIG. 4 is a schematic diagram illustrating a fin deployment mechanism according to an embodiment of the system described herein.
FIG. 5A is a schematic diagram illustrating in more detail a fin deployment mechanism according to an embodiment of the system described herein.
FIG. 5B is a schematic diagram illustrating in more detail an alternative fin deployment mechanism according to an embodiment of the system described herein.
FIG. 6 is a schematic diagram illustrating a manifold of a gas deployment mechanism according to an embodiment of the system described herein.
FIG. 7 is a schematic diagram illustrating additional fin retention mechanisms according to an embodiment of the system described herein.
FIG. 8 is a schematic diagram illustrating a spring clip used for fin retention according to an embodiment of the system described herein.
FIG. 9 is a schematic diagram illustrating a plunger used for fin retention according to an embodiment of the system described herein.



DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
Referring now to the figures of the drawings, the figures comprise a part of this specification and illustrate exemplary embodiments of the described system. It is to be understood that in some instances various aspects of the system may be shown schematically or may be exaggerated or altered to facilitate an understanding of the system.
Referring to FIG. 1, a control actuated fin assembly 20 is shown as including a base 22, a plurality of fins 26a, 26b, and a plurality of fin holders 28a, 28b. The fins 26a, 26b are shown in FIG. 1 in a folded, non-deployed, position. The system described herein allows for the fins 26a, 26b to be maintained in the non-deployed position to facilitate storage and/or transportation. The base 22 may represent a portion of a missile, a rocket, a torpedo, a flying drone, or similar device (projectile) that uses fins for navigation. Note that, although only the two fins 26a, 26b and the corresponding fin holders 28a, 28b are shown in FIG. 1, any number may be used. In an embodiment herein, the base 22 includes four fins, the two fins 26a, 26b shown in FIG. 1 and two additional fins not shown in FIG. 1 that are perpendicular to the view of FIG. 1. For the discussion herein, it should be assumed that, unless otherwise stated, reference to the two shown fins 26a, 26b include reference to all the fins being used.
The fin holders 28a, 28b include pins 32a, 32b that retain the fins 26a, 26b to the body 22. The pin 32a retains the fin 26a while the pin 32b retains the fin 26b. As described in more detail elsewhere herein, each of the fins 26a, 26b rotates about a corresponding one of the pins 32a, 32b to move the fins 26a, 26b into a deployed position. The base 22 also includes electronics 34 that are used in connection with deployment of the fins 26a, 26b and/or possibly actuation of the fins 26a, 26b for navigation of the projectile. The electronics 34 may receive one or more signals (e.g., transmitted radio frequency electronic signals, signals from a coupled tether, etc.) and may cause deployment of the fins 26a, 26b by providing one or more signals to electromechanical devices (not shown in FIG. 1), as described in more detail elsewhere herein.
Referring to FIG. 2, the assembly 20 is shown with the fins 26a, 26b deployed. As described in more detail elsewhere herein, an appropriate mechanism may be used to retain the fins 26a, 26b in a deployed position. In some embodiments, the mechanism may be provided in the fin holders 28a, 28b. In addition, in some embodiments, the mechanism that retains the fins 26a, 26b in a deployed position as shown in FIG. 2 may share at least some components with a mechanism that retains the fins 26a, 26b in a non-deployed position as shown in FIG. 1. In some embodiments, once the fins 26a, 26b are deployed, the fins 26a, 26b may be actuated (tilted) in a conventional manner using, for example, the electronics 34 and/or other electronic flight controls coupled to one or more electro-mechanical servos (not shown) that move the fins 26a, 26b. 
Referring to FIG. 3, the fin 26b and the corresponding fin holder 28b are shown in more detail to illustrate a mechanism for retaining the fins 26a, 26b in a non-deployed position as shown in FIG. 1 and for maintaining the fins 26a, 26b in a deployed position as shown in FIG. 2. The fin 26b is shown as including a first detent 42 that accepts a ball 44 that is urged into the detent 42 by a spring 46. The ball 44 and the spring 46 may act as a retaining mechanism to retain the fin 26b in a deployed position.
The ball 44 and the spring 46 may be provided in a shaft 48 that is part of the fin holder 28b. In other embodiments, at least part of the shaft 48 may be part of the base 22. The shaft 48 may be cylindrical, although other shapes may also be used, including, without limitation, a shaft having a square, rectangular, oval, etc. cross section. In addition, instead of the ball 44, it may be possible to use other appropriate mechanisms, including using a plunger, as described in more detail elsewhere herein.
The fin 26b may also include a second detent 52 that engages the retaining mechanism formed by the ball 44 and the spring 46 when the fin 26b is in a non-deployed position as shown in FIG. 1. Just as with the deployed position, the spring 46 urges the ball 44 into the detent 52 to retain the fin 26b in a non-deployed position. Note also that other appropriate retaining mechanisms may be used in place of the ball 44 and the spring 46. Furthermore, as described in more detail elsewhere herein, additional retaining mechanisms may be used in conjunction with the mechanism that engages the detent 52.
Referring to FIG. 4, the fin 26b is shown in a non-deployed position. The body 22 contains a deployment mechanism 62 having a gas generator 64 and a manifold 66. As described in more detail elsewhere herein, the manifold 66 has a separate outlet for each fin and each outlet is in fluid communication with the gas generator 64. As set forth below, each outlet may contain a piston that is acted upon by the gas from the generator 64 to push on and deploy all of the fins substantially simultaneously. The deployment mechanism 62 may be attached to the body 22 using any appropriate mechanism, including being bolted to the body through bolt holes (not shown) provided in the deployment mechanism 62.
In an embodiment herein, a padding element 68 is provided to cushion the force of the piston to prevent the piston from damaging the fin 26b. The padding element 68 may be made from a material that is somewhat softer than the material used for making the fin 26b. For example, the fin 26b (and all the other fins) may be made from 7075-T6 aluminum while the padding element 68 may be made from a somewhat softer 6061-T6 aluminum. Of course, other appropriate materials may be used for either the fins 26a, 26b and/or the padding element 68. Note that if the padding element 68 is too hard, the fins 26a, 26b may be damaged during deployment while if the padding element 68 is too soft, the padding element 68 may deform without the fins 26a, 26b being properly deployed.
Referring to FIG. 5A, the deployment mechanism 62 is shown in more detail as including a plurality of cylinders 72a, 72b in fluid communication with the gas generator 64. Gas from the gas generator 64 may be released into the cylinders 72a, 72b in a rapid manner using an appropriate valve 74 that may be controlled externally by, for example, the electronics 34 shown in FIG. 1 and FIG. 2. Thus, all of the fins 26a, 26b may be deployed simultaneously by actuating the valve 74.
In an embodiment herein, the valve 74 may be actuated by the electronics 34 and/or by some other appropriate mechanism. Note that the electronics 34 may also separately handle actuation of the fins 26a, 26b for navigation. In other embodiments, a sensor may be used to detect when the system is being deployed (e.g., released from an aircraft in flight) and/or an external signal may be provided to indicate when the system is being deployed. In some embodiments, actuation of the valve 74 is sufficient to deploy the fins 26a, 26b. Note that the valve 74 may be implemented using a squib that is configured so that detonation of the squib causes the gas in the gas generator 64 to be rapidly released.
The cylinder 72a includes a piston 76a while the cylinder 72b includes a piston 76b. A top of each of the pistons 76a, 76b is acted upon by the gas from the gas generator 64 so that the bottom of each of the pistons 76a, 76b extends outward from the manifold 66 to deploy the fins 26a, 26b. In some embodiments, the bottoms of the pistons 76a, 76b may be coupled directly to the fins 26a, 26b. In other embodiments, the bottoms of the pistons 76a, 76b may be coupled to the fins 26a, 26b indirectly through the padding element 68, discussed above.
In an embodiment herein, the piston 76a may be provided with a spring 78a and the piston 76b may be provided with a spring 78b. The springs 78a, 78b may bias the pistons 76a, 76b in a direction opposite to the direction the pistons are pushed by gas from the gas generator 64. The springs 78a, 78b may facilitate providing an appropriate force to deploy the fins 26a, 26b and, in addition, may facilitate assembly of the system by retaining the pistons 76a, 76b within the manifold 66 during assembly.
Referring to FIG. 5B, an alternative deployment mechanism 62′ is shown in detail as including the cylinders 72a, 72b in fluid communication with an alternative gas generator 64′. Just as with the deployment mechanism 62 of FIG. 5A, gas from the gas generator 64′ may be released into the cylinders 72a, 72b in a rapid manner to deploy all of the fins 26a, 26b simultaneously. However, the alternative gas generator 64′ may be implemented using a chemical initiator, such as that provided by Special Devices, Inc. of Newhall, Calif. under part no. 103377. The alternative gas generator 64′ includes a reactive powder 65 that rapidly releases a significant amount of gas when ignited. The powder 65 may be ignited using an electrical resistive element/squib 79 that is coupled to and actuated by the electronics 34. Operation of the pistons 76a, 76b and springs 78a, 78b may be like that of the deployment mechanism 62 of FIG. 5A, described above.
Referring to FIG. 6, the manifold 66 is shown from a top view as including additional cylinders 72c, 72d, additional pistons 76c, 76d, and additional springs 78c, 78d which operate in a manner similar to that discussed above in connection with the cylinders 72a, 72b, pistons 76a, 76b, and springs 78a, 78b. In an embodiment herein, there are four fins that are deployed although, as discussed elsewhere herein, any number of fins may be used. All of the cylinders 72a-72d are in fluid communication with the gas generator 64 (not shown in FIG. 6). Thus, sufficient gas pressure causes the pistons 76a-76d to traverse the respective ones of the cylinders 72a-72d to deploy the corresponding fins more or less simultaneously.
Note that if the size (pressure) provided by the gas generator 64 (or the gas generator 64′ or any other gas generator that is used) is too small, the fins 26a, 26b may not reliably deploy. On the other hand, if the size is too large, the fins 26a, 26b (and/or other components) may become damaged in connection with deployment. Accordingly, it may be desirable to determine a minimal size (pressure) for the gas generator and then choose a size that is a nominal percentage above the minimal size.
The amount of pressure, Pd, needed on the pistons 76a-76d to deploy the fins 26a, 26b, may be determined empirically. Similarly, the volume of the gas generator (e.g., the gas generator 64 or the gas generator 64′), the manifold 66, and the cylinders 72a-72d may also be determined. If V1 is the sum of the volumes of the gas generator, the manifold 66, and the cylinders 72a, 72d, and V2 is a reference volume used to test/spec the gas generator, then the following may be used to determine a minimum amount of pressure, Pg, for the gas generator at the reference volume V2:

Pg=(Pd*V2)/V1

For example, if it is determined that 4800 p.s.i. are needed to deploy the fins 26a, 26b, and if V1 is 2.5 CC and V2 is 10 CC, then the minimum pressure needed for the gas generator at the reference volume is 1200 p.s.i. This minimum may be then adjusted (increased) to account for expected variances in tolerance that could require more than 4800 p.s.i. to deploy the fins 26a, 26b and/or variances in actual values for V1 and V2. For example, 10% may be added to the calculated minimum pressure to provide an operating pressure of 1320 p.s.i. for the gas generator. The reference volume may be a volume used by the manufacturer/reseller to specify the capacity of the gas generator (e.g., delivers 1200 p.s.i. at 10 CC).

Note that the operating pressure for the gas generator should be present at a minimum operating temperature of the system (e.g., −65° F.) and that the equation above may be used to determine the maximum pressure on the pistons 76a-76d at a maximum operating temperature (e.g., +160° F.). In instances where the pressure on the pistons 76a-76d is determined to be too high at the maximum operating temperature, the system may be adjusted by, for example, changing the volume of the gas generator and then determining a new operating pressure for the gas generator.
Referring to FIG. 7, the fin 26b is shown in a non-deployed position as being retained by a second retaining mechanism that includes a spring clip 82 and a third retaining mechanism that includes a ball 84 and a detent 86 in the fin 26b, The ball 84 and the detent 86 may be like the ball 44 and the detent 42 discussed above. The spring clip 82 may be a metal deformable clip, as discussed in more detail elsewhere herein.
Referring to FIG. 8, the spring clip 82 is shown in more detail in profile. The spring clip 82 exerts a force in a direction indicated by the arrows in FIG. 8 to retain an edge of the fin 26b that is shaped to be gripped by the spring clip 82. The spring clip 82 may retain the fin 26b in a non-deployed position until sufficient force is generated (e.g., by the deployment mechanism 62, discussed above) to pull the fin 26b away from the spring clip 82.
Referring to FIG. 9, an alternative implementation of the retaining mechanism of FIG. 3 is shown with the shaft 46 and the spring 48. However, instead of the ball 44 of FIG. 3, FIG. 9 shows a plunger 94 having a rounded end. The plunger 94 may be used instead of the ball 44 and/or instead of the ball 84 of FIG. 7. Note also that any or all of the retaining mechanisms illustrated herein may be used in any combination and/or eliminated so that, for example, it is possible to use only the retaining mechanism of FIG. 3, use the retaining mechanism of FIG. 3 in combination with the spring clip 82, use all of the retaining mechanisms described herein, etc.
Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

## Claims

1. A fin deployment mechanism, comprising:
a gas generator that generates gas used to deploy a plurality of fins by rotating each of the fins about an axis that is substantially perpendicular thereto;
a manifold, coupled to the gas generator and having a plurality of cylinders in fluid communication with the gas from the gas generator;
a plurality of pistons disposed in the cylinders, a bottom of each of the pistons being coupled to a respective fin of the plurality of fins to provide deployment thereof when a corresponding top of each of the pistons is acted upon by the gas from the gas generator, wherein the deployment of each of the fins is from a non-deployed position to a deployed position after the top of each of the pistons is acted upon by the gas from the gas generator, and wherein the deployment of the plurality of fins is actuated by an electronic signal received by the fin deployment mechanism from an external source; and
a fin retention mechanism that maintains the fins in a non-deployed position prior to actuation of the gas generator and maintains the fins in a deployed position after actuation of the gas generator;
wherein the fin retention mechanism includes in each of the fins a first detent corresponding to the deployed position and a second detent corresponding to the non-deployed position.

2. A fin deployment mechanism, according to claim 1, further comprising:
a valve coupled to the gas generator to control a flow of gas therefrom.

3. A fin deployment mechanism, according to claim 1, wherein the gas generator is implemented using a chemical initiator.

4. A fin deployment mechanism, according to claim 1, further comprising:
a plurality of springs, disposed in the cylinders, to bias the pistons away from the fins.

5. A fin deployment mechanism, according to claim 1, wherein the pistons are directly coupled to the respective fins.

6. A fin deployment mechanism, according to claim 1, wherein the pistons are coupled to the respective fins through a padding element.

7. A fin deployment mechanism, according to claim 6, wherein the padding element is made from a material that is softer than a material used for the fins.

8. A fin deployment mechanism, according to claim 7, wherein the fins are made from 7075-T6 aluminum while the padding element is made from 6061-T6 aluminum.

9. A fin deployment mechanism, according to claim 1, wherein the fins are made from 7075-T6 aluminum.

10. A fin deployment mechanism, according to claim 1, wherein the fin retention mechanism comprises:
at least one spring clip that maintains the respective fin in the non-deployed position by engaging the second detent in the respective fin using a plunger and a spring that urges the plunger toward the second detent.

11. A fin deployment mechanism according to claim 1, further comprising:
an electronic assembly that receives the electronic signal and that is coupled to the gas generator.

12. A fin deployment mechanism according to claim 1, wherein the gas generator is configured to provide that a pressure of the gas that acts upon the pistons is controlled to be between a minimum pressure for the deployment of the plurality of fins and a maximum pressure for the deployment of the plurality of fins.

13. A fin deployment mechanism according to claim 12, wherein the minimum pressure of the gas for deployment of the plurality of fins is a minimally-sufficient pressure to deploy all of the plurality of fins fully to the deployed position, and wherein the maximum pressure of the gas is a pressure beyond which at least one of the plurality of fins is damaged during the deployment.

14. A fin deployment mechanism according to claim 1, wherein the gas generated by the gas generator is used primarily for deployment of the plurality of fins.

15. A fin deployment mechanism according to claim 14, wherein the plurality of fins are deployed simultaneously.

16. A fin deployment mechanism according to claim 1, wherein the fin retention mechanism comprises:
a ball that is urged into the detents by a spring.