PROJECTILE FOR USE IN AN ELECTROMAGNETIC LAUNCHER AND METHOD THEREFOR

Abstract: A projectile (52) for use with an electromagnetic launcher has an armature (82) for conducting current between conducting rails (66, 68) of the launcher. The armature has a plurality of curved trailing arms. During launch of the projectile, the current flowing through the trailing arms (84) of the armature, interacts with the magnetic fields generated by current flowing through the rails. The interaction causes the armature, and thus the projectile, to spin about its longitudinal axis.

Description: PROJECTILE FOR USE IN AN ELECTROMAGNETIC LAUNCHER AND METHOD THEREFOR FIELD OF THE INVENTION This invention is directed generally to a projectile for use with an electromagnetic launcher In one aspect, the invention relates to a projectile for use with an electromagnetic launcher which comprises a means for causing the projectile to spin along a longitudinal axis as the projectile travels along the barrel of the electromagnetic launcher BACKGROUND OF THE INVENTION Electromagnetic launchers or railguns utilize magnetic (i e , Lorenz) forces induced by a current carried between spaced, generally parallel electrically-conductive rails to launch a projectile at a high rate of speed A typical electromagnetic launcher also has a barrel, which guides the projectile as it is being launched and which stabilizes the guide rails, and a source of high electrical current The conductor used to pass the current across the space between the rails is known as an armature and, in general, four types of armatures are used A solid armature is a body, typically composed at least partially of metal The body conforms to the rails to make a sliding contact with the rails during launch A plasma armature is made of ionized gases and is typically triggered by vaporizing, via the launching current pulse, a metal foil spanning the gap between the rails After having been triggered, the heat of the plasma discharge generates additional ions from surrounding surfaces, perpetuating the ionized gases which carry the current from one rail to the other A transitioning armature is designed to function as a solid armature until it melts through bulk joule heating, creating a plasma armature which takes over automatically A hybrid armature will typically start as a solid armature but is designed to complete the launch by the establishment of a layer of plasma discharge between it and the rails in lieu of a sliding contact In electromagnetic launcher operation, an armature is accelerated from the breech of the launcher toward the muzzle end of the barrel It travels in the bore defined by the rail surfaces and by insulators which are disposed between the rails to prevent current flow from one rail to another without passing through the armature The armature may push a projectile or other payload ahead of it, or the armature itself may serve as a projectile It also may be integrated with one or more projectiles and/or other payloads The use of launchers and projectiles of this type are used as an alternative to more conventional chemical propellant-based guns and projectiles In conventional weapons, it is often advantageous for the projectile to spin about its longitudinal axis Such spinning increases the flight stability of the projectile, causing the projectile to travel more predictably and accurately toward its target In a conventional weapon, a plurality of helical grooves, known as rifling, is formed into the inner surface of the weapon's barrel As the projectile travels along the length of the barrel, these grooves induce a spin in the projectile Similarly, it is often beneficial for a projectile used in an electromagnetic launcher to spin as it travels to its target Rifling can be used in an electromagnetic launcher, however, mechanical difficulties are encountered at the region in which the rifling groove transitions from the conductive rail to the insulator due to discontinuities in material properties and relative movement between the two materials Other features and methods must be used to induce a spinning action in the projectile U S Patent 5,189,244 to Weldon discloses a railgun in which one or more solenoid- type magnet coils are placed exteriorly to the barrel of the rail gun and coaxially with the longitudinal axis of the railgun During launch of the projectile, an electric current is passed through the magnet coil so as to establish a magnetic flux field which intersects the projectile path through the barrel As the projectile travels along the barrel during launch, it encounters the magnetic field caused by the magnet coil This interaction results in a force tangential to the armature, causing rotation of the projectile The rate of spin is directly related to the strength of the magnetic field applied by the solenoidal magnet A major disadvantage of this type of launcher is that major modifications, in the form of added magnet coils, are required in the launcher itself Further, additional equipment to provide and control current to the magnetic coils is required Increased requirements of equipment in the battlefield can produce serious burdens on infrastructure and support personnel, as well as the launcher operators themselves U S Patent 4,741,271 to Delvecchio et al teaches a projectile having an armature and a conductive open loop, wherein the loop is attached between the projectile body and the armature or aft of the armature While the open loop can be configured to either prevent spin or induce spin in the projectile, the reference teaches that when brush elements are positioned in a plane perpendicular to the plane of the open loop, a rotational torque is applied to the projectile As the projectile spins, the brushes are intermittently in contact with the conductive rails of the launcher, resulting in irregular spinning action To overcome this deficiency, multiple open loops and brush pairs are symmetrically placed around the projectile Additional non-warhead projectile weight only serves to decrease the projectile's effectiveness, due to decreased range and increased handling weight The projectile disclosed in the Delvecchio patent has both additional structure and weight as compared to a conventional electromagnetic projectile Other configurations in which a spinning action has been observed in round-bore electromagnetic launcher projectiles have resulted in random, unpredictable spinning which has typically been limited to one-fourth revolution BRIEF SUMMARY OF THE INVENTION The present invention is a new and advantageous spinning projectile for use in an electromagnetic launcher and method therefor for inducing a spin in an electromagnetically- launched projectile One object of the present invention is a projectile for use in an electromagnetic launcher wherein the projectile spins about a longitudinal axis of the projectile during launching of the projectile without the use of devices external to the launcher to induce the spinning action Another object of the invention is a projectile for an electromagnetic launcher which spins during launch in a predictable, reliable fashion A further object of the invention is a projectile which has an armature with features for inducing a spinning action in the projectile along a longitudinal axis of the projectile Yet a further object of the invention is a projectile wherein features in the armature for inducing a spinning action in the projectile along the longitudinal axis of the projectile add little or no additional non-warhead weight to the projectile In one embodiment of the present invention, a projectile is provided for use with an electromagnetic launcher having a plurality of conductive rails which are electrically connected to at least one power source The projectile comprises an armature for conducting electrical current between the plurality of conductive rails The armature comprises a plurality of spaced apart trailing arms connected with one another and are curved about a rotational axis of the armature In a further embodiment of the present invention, the curvature of the trailing arms is a helical curvature Current flowing through the rails of the electromagnetic launcher produce magnetic fields which interact with current flowing through the trailing arms, and thus the armature This interaction produces a torque on the projectile, causing the projectile to spin along its longitudinal axis as it is being launched BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features of the invention will become more apparent with reference to the following detailed description of the presently preferred embodiment thereof in connection with the accompanying drawings, wherein like reference numerals have been applied to like elements, in which FIG 1 is a perspective view of an electromagnetic launcher barrel and a projectile for use with an electromagnetic launcher having an armature of the present invention, FIG 2 is an end view of the electromagnetic launcher barrel and the projectile of FIG 1 as viewed from the armature end of the projectile, FIG 3 is a perspective view of an electromagnetic launcher barrel and a projectile for use with an electromagnetic launcher having an armature of the present invention and showing the magnetic fields and the current flows generated during projectile launch, FIG 4 is an end view of the electromagnetic launcher barrel and the projectile of FIG 3 as viewed from the armature end of the projectile, and FIG 5 is a schematic view illustrating the features of a helix DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, and FIGS 1 and 2 in particular, shown therein is an electromagnetic launcher barrel 50 with a projectile 52 in accordance with a preferred embodiment of the present invention disposed therein Like reference numerals within the figures described herein refer to like elements of the present invention The barrel 50 has an outer surface 54 which is depicted as being generally cylindrical but can be of any suitable shape The barrel 50 further has an internal bore 56 which is generally cylindrical and has a diameter 58 which is sized to appropriately accommodate the projectile 52 Two slots 60 and 62 interrupt the surface of the bore 56 and produce a shape within the barrel 50 which has a dimension 64 that is greater than the diameter 58 The slots 60 and 62 are configured so as to be capable of receiving and holding two conductive rails 66 and 68, respectively Each of the rails 66 and 68 have outer surfaces 70 and 72, respectively, which are shaped so as to match the dimension 64 of the bore 56 Each of the rails 66 and 68 are sized to fit within the slots 60 and 62, respectively, so that, when disposed within the slots 60 and 62, the inner surfaces 74 and 76 of the rails complement the bore 56 of the barrel 50 to form a generally contiguous cylindrical internal surface The rails are connected to an electrical power source 77 such that current flows through the rails Current flow is depicted in the conventional manner with a circled dot indicating current flow out of the sheet and a circled "X" indicating current flow into the sheet The projectile 52 has an outer surface 78 which is shown in FIG 1 to be generally frustoconical in shape, however, the shape of the outer surface 78 of the projectile 52, as well as other physical characteristics of the projectile 52, can be any which are suitable for an outer surface of an electromagnetic projectile and which suitably cooperate with the bore 56 of the barrel and the inner surfaces 74 and 76 of rails 66 and 68 The projectile 52 has a main body portion 80 and an armature 82 The main body portion 80 of the projectile 52 houses any warhead or armaments which are carried by the projectile 52 The armature 82 is a conductor which conducts current across the space between the rails 66 and 68 Current is only conducted between the rails 66 and 68 when the armature 82 is positioned between the rails and is in contact with both of the rails 66 and 68 The armature 82 has a plurality of trailing arms 84 which are spaced apart from one another and extend from near the main body portion 80 of the projectile 52 to the rear of the armature 82 For clarity reasons, only one of the trailing arms 84 is indicated in FIGS 1 and 2 According to the present invention, the trailing arms 84 are curved and, in one embodiment, are curved into the shape of a helix or, when the armature 82 is not a right circular cylinder, a quasi-helix A helix is defined as a line so curved around a right circular cylinder that it would become a straight line if the cylinder were unfolded into a plane A quasi-helix is defined as a curve around a surface, which is not a right circular cylindrical surface, wherein the curve has an appearance similar to that of a helix An example of a surface which is not a right cylindrical surface is the non-planar surface of a frustum of a cone In the case where the outer surface 86 of the armature 82 is not a right cylindrical surface, a quasi-helix may be developed on the outer surface 86 by projecting a helix from a right circular cylinder having a diameter similar to, for example, the major diameter of the armature 82, onto the outer surface 86 of the armature 82 Any method for producing a suitable quasi- helical curve on the armature 82 is considered acceptable for the present invention Each of the trailing arms 84, at the aft end of the armature 82, has a contact portion 88 The aft end of the armature is the end which is last to pass a fixed point in the bore 56 during launch of the projectile The contact portions 88 are constructed so as to conform to the inner surfaces 74 and 76 of the rails 66 and 68 and thus make electrical contact with the rails 66 and 68 so that current can flow between the rails 66 and 68 When the armature 82 is positioned between the rails 66 and 68, one or more, but not all, of the contact portions 88 come into electrical contact with the inner surface 74 of the upper rail 66 At the same time, one or more, but not all, of the contact portions 88 come into electrical contact with the inner surface 76 of the lower rail 68 At this point in time, current begins flowing between the two rails 66 and 68 Referring now to FIGS 3 and 4, wherein the interaction of the current flow between and through the two rails 66 and 68 and magnetic fields due to these current flows are illustrated In the illustrated embodiment, current flows through the upper rail 66 toward the forward end of the barrel 50, as indicated by a circled "X" on the aft end of the upper rail 66 in FIG 3 FIG 4 is a view from the aft end of the barrel, thus, the current in the upper rail 66 is moving into the page, as indicated by a circled "X" on the rail 66 The magnetic fields due to the flow of current through the rails 66 and 68 are indicated by the broken lines 90 and 92, respectively. The flow of current between the rails 66 and 68, through the armature 82, is shown for two of the trailing arms 84 by the phantom line 94 As current flows from the upper rail 66, through the contact portion 88 and the trailing arms 84, to the lower rail 68, the current 94 in the trailing arms 84 interacts with the magnetic fields 90 and 92 The magnetic field 90 has a significant radial component in this region, while the current flow 94 in the trailing arm 84a has a significant axial component The force generated by this interaction is the vector cross product of the current and the field and has a component tangential to the bore 56 This force is duplicated on the opposite side by the interaction of magnetic field 92 and the current flow 94 in the trailing arm 84b A torque couple, indicated by arrows 96, is thus established so as to cause the armature 82, and thus the projectile 52, to rotate In a preferred embodiment, the amount of torque produced by the interaction between the magnetic fields 90 and 92 and the current flow 94 is determined and regulated based upon the current flow 94 through the armature 82 and the helix angle of the trailing arms Referring now to FIG 5, the helix angle is defined as the angle A between the development of the helix and the centerline of the cylinder The helix angle of one of the trailing arms 84 is the angle between the edge of one of the trailing arms 84, which has been unwrapped from the outer surface of the armature 82, and the axis of rotation of the armature 82 In a preferred embodiment, a helix angle of approximately five degrees provides an acceptable projectile spinning speed A helix angle generally within a range of about four to about six degrees is preferable, however a desirable helix angle can be generally within a range of greater than zero to about forty-five degrees Embodiments in which an armature is integral with a projectile, as well as those in which an armature is an attachment to a projectile, are within the scope of the present invention While the armature of the present invention is most desirable when used as a solid armature, the use of the armature in other types of armature systems, such as hybrid or transitional armature systems, is within the scope of the present invention Other embodiments, such as those in which the main body of the projectile passes through the central region of the armature or those in which the armature is located forward of the main body of the projectile, are within the scope of the present invention. Although the present invention has been described with reference to a presently preferred embodiment, it will be appreciated by those skilled in the art that various modifications, alternatives, variations, etc., may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims: WHAT IS CLAIMED IS: 1 A projectile for use with an electromagnetic launcher, said electromagnetic launcher having a plurality of conductive rails, said plurality of conductive rails being electrically connected to at least one power source, said projectile comprising an armature for conducting electrical current between said plurality of conductive rails, said armature comprising a plurality of spaced apart trailing arms, wherein each of said spaced apart trailing arms is electrically connected with one another 2 A projectile as claimed in claim 1, wherein an outer surface of said armature is generally cylindrical in shape, each of said spaced apart trailing arms has a shape of a helix, and each of said spaced apart trailing arms further comprises a contact area which is shaped to conform to an internal surface of each of said conductive rails 3 A projectile as claimed in claim 2, wherein a helix angle of said helix is generally greater than 0 degrees 4 A projectile as claimed in claim 2, wherein said helix angle is generally no greater than 45 degrees 5 A projectile as claimed in claim 2, wherein said helix angle is generally within a range of about 4 degrees to about 6 degrees 6 A projectile as claimed in claim 2, wherein said contact area is on an aft portion of each of said plurality of spaced apart trailing arms 7 A projectile as claimed in claim 1, wherein an outer surface of said armature is generally frustoconical in shape, each of said spaced apart trailing arms has a shape of a quasi- helix, and each of said spaced apart trailing arms further comprises a contact area which is shaped to conform to an internal surface of each of said conductive rails 8 A projectile as claimed in claim 7, wherein a helix angle of said quasi-helix is generally greater than 0 degrees 9 A projectile as claimed in claim 7, wherein said helix angle of said quasi-helix is generally no greater than 45 degrees 10 A projectile as claimed in claim 7, wherein said helix angle of said quasi-helix is generally within a range of about 4 degrees to about 6 degrees 11 A projectile as claimed in claim 7, wherein said contact area is on an aft portion of each of said plurality of spaced apart trailing arms 12 A projectile for use with an electromagnetic launcher, said electromagnetic launcher having a plurality of conductive rails, said plurality of conductive rails being electrically connected to at least one power source, said projectile comprising a projectile body having an aft portion, and a conductive armature for conducting electrical current between said plurality of conductive rails, said conductive armature having a forward portion and an aft portion, said forward portion of said conductive armature attached to said aft portion of said projectile body, wherein said armature comprises a plurality of spaced apart curved trailing arms, and each of said spaced apart trailing arms being electrically connected with one another 13 A projectile as claimed in claim 12, wherein each of said spaced apart trailing arms is electrically connected with one another in an area at said forward portion of said armature 14 A projectile as claimed in claim 12, wherein an outer surface of said armature is generally cylindrical in shape, each of said spaced apart trailing arms has a shape of a helix, and each of said spaced apart trailing arms further comprises a contact area which is shaped to conform to an internal surface of each of said conductive rails 15 A projectile as claimed in claim 14, wherein a helix angle of said helix is generally greater than 0 degrees 16 A projectile as claimed in claim 14, wherein said helix angle is generally no greater than 45 degrees 17 A projectile as claimed in claim 14, wherein said helix angle is generally within a range of about 4 degrees to about 6 degrees 18 A projectile as claimed in claim 14, wherein said contact area is on an aft portion of each of said plurality of spaced apart trailing arms 19 A projectile as claimed in claim 12, wherein an outer surface of said armature is generally frustoconical in shape, each of said spaced apart trailing arms has a shape of a quasi- helix, and each of said spaced apart trailing arms further comprises a contact area which is shaped to conform to an internal surface of each of said conductive rails 20 A projectile as claimed in claim 19, wherein a helix angle of said quasi-helix is generally greater than 0 degrees 21 A projectile as claimed in claim 19, wherein said helix angle of said quasi-helix is generally no greater than 45 degrees 22 A projectile as claimed in claim 19, wherein said helix angle of said quasi-helix is generally within a range of about 4 degrees to about 6 degrees 23 A projectile as claimed in claim 19, wherein said contact area is on an aft portion of each of said plurality of space apart trailing arms 24 An armature for a projectile for use with an electromagnetic launcher, said electromagnetic launcher having a plurality of conductive rails, said plurality of conductive rails being electrically connected to at least one power source, said armature for conducting electrical current between said plurality of conductive rails, said armature comprising a plurality of spaced apart curved trailing arms, wherein each of said spaced apart trailing arms are electrically connected with one another 25 An armature as claimed in claim 24, wherein an outer surface of said armature is generally cylindrical in shape, each of said spaced apart trailing arms has a shape of a helix, and each of said spaced apart trailing arms further comprises a contact area which is shaped to conform to an internal surface of each of said conductive rails 26 An armature as claimed in claim 25, wherein a helix angle of said helix is generally greater than 0 degrees 27 An armature as claimed in claim 25, wherein said helix angle is generally no greater than 45 degrees 28 An armature as claimed in claim 25, wherein said helix angle is generally within a range of about 4 degrees to about 6 degrees 29 An armature as claimed in claim 25, wherein said contact area is on an aft portion of each of said plurality of spaced apart trailing arms 30 An armature as claimed in claim 24, wherein an outer surface of said armature is generally frustoconical in shape, each of said spaced apart trailing arms has a shape of a quasi-helix, and each of said spaced apart trailing arms further comprises a contact area which is shaped to conform to an internal surface of each of said conductive rails 31 An armature as claimed in claim 30, wherein a helix angle of said quasi-helix is generally greater than 0 degrees 32 An armature as claimed in claim 30, wherein said helix angle of said quasi-helix is generally no greater than 45 degrees 33 An armature as claimed in claim 30, wherein said helix angle of said quasi-helix is generally within a range of about 4 degrees to about 6 degrees 34 An armature as claimed in claim 30, wherein said contact area is on an aft portion of each of said plurality of spaced apart trailing arms 35 A method of inducing a spinning action in a projectile launched from an electromagnetic launcher, said projectile having a conductive armature with a plurality of curved trailing arms, said electromagnetic launcher having a plurality of conductive rails, said method comprising the steps of contacting at least two of said plurality of spaced part, curved trailing arms to at least two of said plurality of conductive rails, and applying an electrical potential to said plurality of conductive rails.

Inventors: TAYLOR ROBERT J, TAYLOR, ROBERT, J.
Applicants: LOCKHEED CORP, LOCKHEED MARTIN CORPORATION
Application year: 2000
Main classification: F41B6
IPC codes: F42B6