Abstract:
In accordance with one aspect of the invention, a system, method and apparatus for a boat-tail device is described herein. A body section for a projectile having a deployable portion is provided. Gun gases may pass through an orifice at an aft end of a piston and pressurize a volume in a plenum within the body section. Depressurization at muzzle exit may allow the gas pressurized in the plenum to push the piston aft deploying the deployable portion. A stopping and locking mechanism such as a complementarily tapered piston and opening may engage at the end of the stroke of the piston to stop and lock the piston at a predetermined location. A releasable protective cover may be used to protect the structure of the deployable element and other elements from gun gases and launch loads.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application relates to the same subject matter as co-pending provisional patent application Ser. No. 61/230,527, filed by the same applicant on Jul. 31, 2009. This application claims the Jul. 31, 2009 filing date as to the common subject matter. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of Invention 
       [0002]    The present invention relates to a system, method and apparatus for the reduction of drag, resulting in decreased time of flight and increasing range, of a projectile. It applies particularly to a system, method and apparatus incorporating a device deployed on a projectile after launch, and will be described with particular reference thereto. 
       SUMMARY OF THE INVENTION 
       [0003]    A system, method and apparatus for a boat-tail device is described herein. 
         [0004]    In one embodiment of the invention, a gun gas deployed boat-tail element was developed. An appropriate amount of available gun tube gas pressure is captured to deploy a boat-tail deployable element with a piston that may be locked subsequent to muzzle exit. 
         [0005]    In another embodiment of the invention, an appropriately sized orifice in a support for the deployable element allows the intake and pressurization of an ullage volume behind the piston. 
         [0006]    In another embodiment, the piston may be lockable, thereby precluding the need for ongoing pressurization or sealing to maintain the boat-tail shape of the deployable element during flight. 
         [0007]    Residual pressure may be vented through the piston shaft after deployment. 
         [0008]    A cover may protect the boat-tail components during handling and gun launch. 
         [0009]    The protective cover may be ejected at muzzle exit. 
         [0010]    The mass of the cover may be minimized for safety, for range extension or for other purposes. 
         [0011]    The deployable element may be attached to an outer mold line of the base structure to minimize air flow disruptions. 
         [0012]    In yet another embodiment, an opening within the base may be sized to pressurize gas entering a cavity such as a plenum when the opening is exposed to gun base maximum and minimum pressure profiles such that the piston has the force necessary to extend the deployable element and lock into place at the end of stroke. The opening may be sized appropriately with the inclusion of an element with a cross section narrower than the opening leading to the cavity. 
         [0013]    Proper pressures may be achieved for either low-zone or high-zone gun charges—ullage pressure does not experience a significant change from low-zone to high-zone cases due to the limited orifice area and the shorter tube time at high charges. 
         [0014]    In another embodiment, the present invention is a system, method and apparatus incorporating a boat-tail device which deploys a deployable element after the launch of a projectile, wherein the deployable element may be tapered to reduce drag and increase range. The leading edge of the deployable element may generally conform to an aft surface of the projectile and may be generally shaped as a conical frustum. The frustum may be right circular or otherwise. The device may decrease in cross sectional area after the attachment of it to the projectile to increase streamlining. The device may be attached to the projectile so that it reduces disruption of the air flow over the projectile such that air flow stays close to the device until the terminal end of the boat-tail is reached. The base area of the deployable element may be generally smaller than the base area of the projectile to which it attaches without the deployable element. 
         [0015]    Generally, a partial vacuum behind a moving projectile acts on the base area of the projectile. Therefore, by reducing the base area with a boat-tail which has a smaller base area than the diameter of the projectile, the “Base Drag” is reduced over the period of time the projectile is in flight. 
         [0016]    In another embodiment, the present invention is a deployable element, deployable by means known in the art. As mentioned above, the deployable element may reduce the base area and thus the drag. In addition, the boat tail of the invention may be flexible and be able to occupy a reduced volume in the stowed condition. By occupying a reduced volume, the amount of propellant to propel the projectile may be maximized. In still another embodiment, a piston or piston assembly using several connected elements may be used with the support for the deployable element which itself has elements which admits gun gasses into a plenum within the body section and stored within the plenum. The stored gases then may be used to push the piston which erects or deploys a support for the deployable element and the deployable element. The piston assembly may also include elements for arresting the movement of the piston. Additional elements may be used in the invention to accommodate manufacturing and performance variations. Furthermore, additional elements may be used to reduce or prevent the creation of a vacuum inside the boat-tail. Also, additional elements may be used to insure a generally conforming and strong connection between the boat-tail and the projectile. In one embodiment, the connection is not so disruptive to the flow of air from the body of the projectile to the boat-tail that the flow separates from the projectile negating the utility of the boat-tail. The connection may also be sufficiently strong to transmit set-back, set-forward, and balloting loads during gun launch and carry aerodynamic loads throughout the flight of the projectile. In one embodiment, the present invention accomplishes the connection through the use of a conformal attachment technique. In one example, the attachment maintains a constant profile through the use of a groove in the body for attachment of the flexible element and a relieved zone, distal to the groove, which accommodates the thickness of the fabric. The deployable element may be interfitted with the body element such that the proximal end of the deployable element lies at the proximal edge of the groove. A strong tensile element may then be wound over the top of the flexible element compressing it into the grove in the projectile body. The wrapping of the tensile and epoxy element may then continue until the groove is filled and flush with the profile of the projectile. In another embodiment, secondary operations known in the art for smoothing the profile of the projectile may be carried out to minimize protrusions or depressions at or near the connection between the that would disrupt the even air flow from the body of the projectile to the boat-tail. 
         [0017]    The system, method and apparatus may be intrinsic with a projectile or may be a device attached to a projectile. 
         [0018]    The system, method and apparatus allow for reduction of drag and increase in range for a projectile. The system may be a producible, reliable, and cost effective solution with a low risk of system failure consistent with schedule constraints. 
         [0019]    The system of this invention may also provide a robust design applicable for ramming, set-back, set-forward and balloting loads. The invention further may provide minimal impact on current designs. The invention may also have a relatively low part count. The system may be light weight and may use gun pressure that is already created within the system for firing a projectile. The system may also provide consistent performance over its operational range. The invention may also provide a locking device to restrain the extended piston in the deployed position. The system provides for no insensitive munitions impact and there are minimal discards to the system for safety. 
         [0020]    Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
           [0022]      FIG. 1  is a cross-sectional view of one embodiment of the invention before deployment. 
           [0023]      FIG. 2  is a cross-sectional view of another embodiment of the invention before deployment. 
           [0024]      FIG. 3  is a cross-sectional view of another embodiment of the invention after it has been deployed. 
           [0025]      FIG. 4  is a perspective view of another embodiment of the invention after it has been deployed. 
           [0026]      FIG. 5  is a cross sectional view of another embodiment of the invention showing gas flow during deployment. 
           [0027]      FIG. 6  is a cross sectional view of another embodiment of the invention. 
           [0028]      FIG. 7  is a detail view of another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The invention, shown generally as device  10  in  FIGS. 1-7 , comprises a boat-tail device  10  for use with a projectile having elements to be deployed after the launch of the projectile. The device  10  before deployment is shown in  FIGS. 1-2 , and  6 . The device  10  after deployment is shown in  FIGS. 3 ,  4 ,  5 , and  7 . The device  10  may be connected to the aft end of a projectile or may be intrinsic with the projectile. The connection of the device to the projectile may be releasable or fixed. 
         [0030]    The device  10  may be embodied in a number of ways. One embodiment connects to a projectile and is illustrated in  FIGS. 1 and 2 . The boat-tail device  10  includes a body section  12 , a piston  14  and a support  16 . The piston is located within a passage  18  located generally centrally through the body section  12 . The piston has a proximal end and a distal end. The piston  14  is attached from a distal end of the piston to the support  16  at a proximal end of the support  16 . The support  16  itself may define the distal end of the boat-tail device  10  when deployed, as shown in  FIG. 3 . The support  16  may be generally disk-shaped, although other geometry such as a hemisphere or other spherical cap may be used. The support  16  may be fixedly attached to the piston  14  or other elements such as extenders may come between the piston  14  and the support  16 . Alternatively, the piston  14  may telescope as it is deployed within the passage  18 . 
         [0031]    The device  10  also includes a deployable element  20 . The packed material for the deployable element  20  can be folded in the form of concentric accordion folds which is accommodated because of the tapered shape of the fabric structure. The fabric may be bunched, folded or crammed into any form factor for packing volume, or stowed in any other manner known in the art. 
         [0032]    The support  16  may provide the load transmission path from a flexible deployable element  20  to the projectile. The piston  14  is movable axially and distally within the passage  18  of the body section  12  in the direction of the distal end  22  of the body section  12 . The piston  14  includes at least one orifice  24  that allows gas to enter the device  10 . The gas passes through at least one void  26  in the passage  18  into a plenum  28 . Alternatively, more than one plenum, either connected or separate, is contemplated. The orifice  24  may also include a restriction  30  having an aperture  32  of smaller cross section than the passage  18 . The restriction  30  may be a separate piece placed in the orifice  24 , as shown in  FIGS. 1-3 . However, the restriction  30  may also be formed directly into the orifice  24 . The restriction  30  allows collected gas to remain pressurized in the plenum  28  or move from the restriction  30  through alternative directions rather than escape unimpeded back through the orifice  24 . However, other means for restricting the outflow of the gas through the orifice  24 , such as one or more valve mechanisms, such as one or more reed and/or flapper valves, are also contemplated. 
         [0033]    The gas stored in the plenum  28  acts upon an area of the top  34  of the piston  14 . The gas stored in the plenum  28  passes through one or more gas flow elements  26  (shown in  FIG. 2 ) such as a castellation on the top  34  of the piston  14  or at the bottom of the recess  69  in  FIG. 5  in the body  12  holding the support  36  and then acts over the surface of the top  34  of the piston  14  which, once the projectile exits the gun barrel, is unrestrained. The gas flow elements may be one or more castellations on or attached to the piston which may be rectangular, rounded, or of other geometry which will allow passage of the gasses to the top  34  of the piston. As shown in  FIG. 5 , one or more gas flow elements  26  may alternatively be a part of the plenum  28 . In addition, gas flow elements  26  may be part of both the plenum  28  and the top  34  of the piston  14 . The gas acting on the top  34  of the piston will displace the piston  14 , pushing the support  16  aftwards. As the piston  14  and support  16  translate aftwards, they pull the flexible deployable element  20  aftwards with it. 
         [0034]    The deployable element  20  of the device  10  is deployed after the projectile has been fired from a gun. The deployable element  20 , supported by the support  16  creates a boat-tail element on the distal end  22  of the body  12 . Once the projectile leaves the gun, the gas within the device  10  is no longer countered by the pressure from the gun gasses. 
         [0035]    In addition, a cover  38  may be releasably attached to the body  12 . This cover  38  may be used to transmit launch acceleration loads without bearing acceleration on the deployable element  20 . The cover  38  may be of a material such as metal or plastic. The cover  38  is placed distally from the support  16  to protect the device  10  from heat and the gun gasses. The cover  38  would allow gasses to enter the passage  18  through at least one clearance hole  40  or by other means known in the art. As the projectile leaves the gun, the gasses would no longer press the cover against the support. Thus, the cover  38  does not impede deployment. Also aiding in the deployment is the fact that gas pressure behind the exiting projectile drops dramatically. 
         [0036]    The deployable element  20  comprises a flexible material that may unfold, expand or inflate as the piston  14  and the support  16  move in the direction of the distal end  22  of the body  12 . The deployable element  20  may be fabric, plastic or other suitable flexible and/or expandable material known in the art. For example, nylon or other similar fabric materials may be used. 
         [0037]    As shown in  FIGS. 1-3  and  5 , the piston  14  and the passage  18  include a stopping mechanism  42  for stopping the piston once the device  10  has been deployed. The stopping mechanism may include a locking mechanism. In one embodiment, shown in  FIGS. 1-3 , the stopping and locking mechanism includes a tapering end  44  to the piston  14  and a complementarily tapered end  46  to the passage  18 . Other stopping and/or locking mechanisms known in the art are also contemplated. 
         [0038]    As shown in  FIG. 4 , the distal end of the deployable element  20  may be located at over at least a portion of the top  48  of the support  16  or, as shown in  FIGS. 1-3  and  5 , it may be attached to one or more attachment points  50  such as grooves on or through the support  16 , or a groove around a circumference of the support. The deployable element  20  is also attached to the body section  12  at one or more attachment points  52  ( FIG. 1 ) such as grooves on or through the body section, or in a groove around a circumference of the body section. 
         [0039]    In one embodiment of the invention, the deployable element  20  may be folded, stowed or packed in a volume  54 . As shown in  FIG. 1 , in one embodiment of the invention the volume  54  for the stowed deployable element  20  may be between the distal end  22  of the body section  12  and the cover  38 . In this embodiment, the impact of the deployable element  20  of the boat-tail device upon the space behind the projectile where propellant can be packed for launching the projectile may be minimized. 
         [0040]    In other embodiments, the deployment portion can be deployed with an internal inflation system and/or expansion system resident on the projectile. The deployment can be triggered using a number of conditions. The triggering mechanism may be a predetermined longitudinal or rotational acceleration at launch, increase in temperature due from the combustion of the propellant used to propel the projectile, an on board signal from the projectile or outside of the projectile source, or any combination of triggering mechanisms. 
         [0041]    Alternatively, the deployable element may be interfitted with or otherwise attached to the body element so that that the proximal end of the flexible element lies at the proximal edge of a groove on an outer surface of the body element. A strong tensile element such as Vectran, carbon fiber, fiberglass in an uncured or B stage cured epoxy matrix, or other materials known in the art, may then be wound or placed over the top of the proximal end of the deployable element, fixing or compressing the deployable element into the grove in the projectile body. The wrapping of the tensile element may then continue back and forth or as otherwise known in the art until the groove is filled and the wrapped tensile element is flush with the profile of the outer surface of the body element. In another embodiment, secondary operations known in the art for smoothing the profile of the projectile may be carried out to minimize protrusions or depressions at or near the connection point of the body element and the deployable element that would disrupt the even air flow from the body element to the boat-tail. 
         [0042]    In another embodiment, shown in  FIG. 7 , a small controlling orifice  56  can be employed radially through the piston  14  to equalize the pressure between an outer surface of the deployable element and an inner surface of the deployable element. Other means for minimizing the potential of the creation of a partial vacuum forming inside the deployable element which would inhibit deployment are also contemplated. 
         [0043]    Also illustrated in  FIG. 5 , the piston  14  may have one or more controlling orifices  56 , and the passage  18  may include one or more complementary orifices  58  into the plenum  28 . In addition, the support  16  may be comprised of two parts: an inner support  60  and an outer support  62 . In yet another embodiment, shown in  FIG. 6 , gun gas may directly enter into the plenum  28  via a channel  68  from the outside of the body section  12 . In still another embodiment, the body section  12  may be connected to a projectile by having threading on the body section  12  and complementary threading on the distal end of a projectile. 
         [0044]    Also as shown in  FIGS. 1-3 , one or more obturators  64  may be held in place between a projectile and the body section  12  by tension created by screwing the threaded sections together. In addition, the boat tail deployment device of the invention described herein may be made into a kit for modifying a projectile. In addition, folding glide fins  66  may be located on the body  12 . 
         [0045]    In other embodiments, gas may be introduced into the volume displaced by the deployable element  20  as the piston moves distally with deployment. In these embodiments, a gas is used to reduce the differential in pressure between the contained volume of the deployable element  20  and the outside surface of the deployable element  20 . 
         [0046]    In one alternative embodiment, shown in  FIG. 7 , a flow of gas is introduced into the volume displaced by the deployment element. In one embodiment, one or more vents  68  are located on the outside of the body element  12  leading directly to the volume being displaced by the deployable element. In another embodiment, a control orifice  70  is made through the piston at a location on the piston whereby gas from the plenum is vented into the displaced volume during deployment. In still another embodiment, a port  72  through the support  16  may allow gas to enter the displaced volume. Any of these systems may be used singly or together to control the amount of gas entering the displaced volume. The flow of the gun gas or air entering the displaced volume may then be used to control the rate of deployment of the deployable element. 
         [0047]    In another embodiment, a gas source stored on or in the body element  12  may be triggered electrically, or gas may be introduced through the use of a mechanical impact igniter such as a percussion primer, hot gas from other on board systems, signal transfer lines such as detonation cords, deflagration transfer lines or tubing carrying pressure or hot gas or particles. The gas introduction system for inflation or expansion may also be a dedicated system such as a stored gas bottle, or pyrotechnic gas generator. Alternatively, the gas introduction system may comprise gas from one or more other on board sources which operated or control events other than deployment of the boat-tail device. Such gas may be derived from Arm-Fire and Safe-and-Arm devices or other stored gas systems or gas generation devices. In still other embodiments, on-board inflation or expansion systems are used, singly or in combination, and gun gasses are not be used. 
         [0048]    An alternate deployment scenario may harness the inertia of the components of the system to deploy the deployable element during the acceleration phase of launch or to store the energy from the acceleration for deployment. One energy storage device may be a spring or an equivalent that would be used to help deploy the device once the acceleration phase of launch has been completed. 
         [0049]    In yet another deployment scenario, the deployment element may include an inflating deployment element. For this embodiment, the material for the deployment element may be a sealed fabric inflatable which is impermeable or contains an impermeable element within it. Internal folds to the element such as internal concentric accordion folds can be used to control the inflation. The folding method such as an internal concentric accordion method may be used to prevent a fold which could block the inflation gas. 
         [0050]    In still another embodiment, a shaft or another internal mechanical erector uses stored energy, such as self generated or externally generated or stored pressurized gas or a mechanical storage device such as a spring, to actuate the piston  14  which acts on the support  16  to hold up the deployable element  20 . Some of the propelling charge gas may be captured and a flow path for the gas can be provided down the center of the shaft. 
         [0051]    Also, as described above, the stopping mechanism  42 , and potentially the locking mechanism, may be integrated into the design such that once fully deployed it will not collapse. This stop-lock mechanism can be accomplished using a ratcheted device, a wedging action, positive snapping action of one device into another or other means known in the art. 
         [0052]    The deployable element  20  of the deployment mechanism may also be made from a material of sufficient elongation capability to adjust for the variation in machining tolerances and energy variations from test to test. Such materials can be materials with naturally high maximum strains without failure such as many of the plastic based fabrics such as nylon. Also, the fabric may be cut on a bias to allow a mechanical deformation of the material at the macroscopic level. 
         [0053]    The material of the deployment device may have specifications to accommodate variations in manufacture or performance of the device while being able to be folded in an advantageous arrangement such as an accordion arrangement. Also, where sewn seams could be a hindrance to folding, a double layer fabric structure could be made where the seams are clocked out of phase and the layers are bonded together so the deployment element is consistent in thickness. 
         [0054]    An alternative to the elimination of sewn seams is a braided structure to the fabric where there are minimal or no longitudinal seams. Braiding in the fabric of the deployment element can help change the length of the deployment element by changing the angle of the braid. 
         [0055]    Attachment of the deployment element to the body section can be accomplished by a number of means. In one embodiment, the deployment element conforms to the shape of the projectile so that there is a minimization of any step up. Thus, the risk of the creation of a source of a high pressure zone or if traveling fast enough a shock wave is minimized. Conversely, the deployment element may conform with the shape of the projectile so there is a minimization of step down whereby air flow can be detached at the interface and the goal of reduced drag will not be achieved. Many attachment methods are possible; they may be capable of a load if inflated or erected by mechanical device as well as survive the air flow over the joint. 
         [0056]    Also, a “deadman” termination may be used for attachment. For example, an edge portion of the deployment element is mechanically trapped in a joint with the body section. Alternatively, the edge portion of the deployment element may be located within a shallow groove at the distal end of the body section. To connect the deployable element to the body portion, an overwrap of material such as a metal or plastic may be molded, crimped or otherwise used to connect the deployable element in place providing a smooth transition. Connection may also be accomplished using a wound filament in a curable matrix. A filament such as carbon fiber may be used so that there is little surface variance which could cause shocks to the attachment or gas flow separations from the body portion. Similarly, the deployable element  20  may be connected to a circumference of the support  16  using the same or equivalent means. By attaching the deployable element  20  to a circumference of the support  16 , the deployable element does not have to attach to the distal end of the support  16 , as shown in  FIG. 4 . 
         [0057]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. It should be noted that the accompanying drawings are not to scale. A variety of modifications, variations, shapes and sizes are possible in light of the above teachings without departing from the scope and spirit of the invention.