US2721518A - Projectile - Google Patents

Description

1955 c. N. HICKMAN 2,721,518

' PROJECTILE Filed Jan. 26, 1945 //v we N TC) 1? By aid M WWAYrTO/ENEyJ United States Patent fiice 2,721,518 Patented Oct. 25, 1955 PROJECTILE Clarence N. Hickman, Jackson Heights, N. Y., assignor to the United States of America as represented by the Secretary of War Application .ianuary 26, 1945, Serial No. 574,642

7 Claims. (Cl. 10249) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to rockets and particularly to a rocket attachment for a projectile adapted to be fired from a rifled gun or mortar.

It is realized that the idea of adding velocity to a projectile fired from a gun by utilizing the action of a jet is not new. In fact, as early as 1917 tests involving this combination were conducted with encouraging results. The chief difficulty confronting the investigators, R. H. Goddard and Parker, was stabilizing the projectile in flight. Col. L. A. Skinner, U. S. A., later explored this particular field and obtained some very encouraging and interesting results. U. S. Patent No. 1,994,490 exempliiies Col. Skinners contribution to this art.

It is an object of this invention to provide an improved rocket projectile of the type disclosed in the above patent to C01. Skinner, by utilizing as a propellant for the rocket a plurality of stacked propellent discs each having an external diameter equal substantially to the internal diameter of the rocket motor chamber. The stack of propellent discs is also preferably characterized by being provided with a single axial and concentric perforation. The particular advantage of this propellent assembly is that the propellent laminations of any desired web thickness may be selected to provide a large controllable surface area for burning. Furthermore, the grains are supported in the motor chamber so as to resist the centrifugal forces present during the angular acceleration of the rocket, and since the burning of the propellent material is laminar, the stability of the rotating projectile will not be upset by changes in the mass of propellant as the burning proceeds.

In most instances where projectiles are adapted to be fired from a gun, the addition of a jet complicates the projectile construction; and since recoil forces are to be contended with, in all events, it is more feasible generally to obtain the increase in velocity by using a heavier gun. The projectiles adapted to be shot from muzzleloaded ordnance pieces constitute an exception, since the usefulness of this type of gun is dependent somewhat upon its weight.

One of the advantages of the mortar is its portability, and since the weight of the gun and its mount are factors affecting the portability of the mortar, any increase in muzzle velocity and range of this weapon is preferably made without a material increase in the size and weight of the gun or its mount. Obviously, if a larger propellent charge were used on the mortar shell, a larger and heavier gun would be required. The recoil forces would also be increased, requiring a heavier base plate to withstand these recoil forces. For this reason, therefore, I have illustrated the rocket attachment of my invention adapted for use specifically in combination with the 4.2" chemical projectile adapted to be fired from a rifled muzzleloading weapon. This invention is not necessarily limited for utility to the explanatory disclosure, but is applicable in combination with any projectile adapted to be fired from any rifled ordnance piece.

The 4.2" chemical mortar is a rifled, muzzle-loading weapon; and the shell, which is adapted to be fired from this mortar, is cylindrical in configuration and has its base equipped with a rotating unit, which includes a cupshaped annular disc of soft metal of the same diameter as the projectile body. Under the action of exploded powder gases transmitted through a pressure plate positioned to the rear of the cup-shaped member, the flange of the cup-shaped disc is forced outwardly into the rifiing grooves of the mortar barrel, thus performing the same function as the rotating band of other projectiles.

The development of an accelerator for a projectile which is to be rotated, entails considerable difficulty, since the propellent assembly must offer a sufficiently large and substantially consistent burning surface and must be of such a configuration that during burning the stability of the rotating projectile will not be upset by the change in mass of the propellent. Initially, I used a large cylindrical column of powder coated so that its outer surface would not burn. I was able to prevent burning on the outer surface by providing a cylindrical grain of an outer diameter substantially equal to the inner diameter of the combustion chamber and coating the outer surface of this grain with cellulose acetate. The centrifugal forces on the power keep the outer surface of the powder grain in contact with the inner chamber walls, thus effectively preventing the hot gases from contacting this outer surface of the propellent material.

In order to keep the burning surface of this propellent charge substantially constant, I found that it was also necessary to coat the end surface of the grain to prevent burning at an end. Here again, I was able to utilize the forces of acceleration which help to keep the end of the grain tight against the trap plate at the rear of the combustion chamber to prevent the hot gases from contacting the end surface. This cylindrical grain was provided with a single concentric perforation and was of a length such that the increase in area, as the burning proceeded from the inside outwardly, was compensated for substantially by the decrease in area at the burning end.

The disadvantage of this construction, apart from the difficulties with inhibitors, was that the surface area, web thickness, and weight of propellent were fixed substantially for a particular length of combustion chamber, and the length of the charge was fixed somewhat by the diameter of the motor since the requirements of constant burning surface dictated a certain ratio of diameters to length.

The advantages, which the particular propellent assembly of this invention has over my first construction and any of the prior art constructions with which I am familiar, are that the particular propellent granulations which I use, while being supported within the combustion chamber so as to withstand the centrifugal force of the rotating projectile and while offering a burning surface which does not upset the stability of the rotating projectile, at the same time permit a wide choice in web thickness, total surface area, weight of propellent, and other factors affecting the internal ballistics of the rocket motor.

In the drawing accompanying this invention disclosure, there are shown two embodiments of this invention, as applied to the 4.2" chemical mortar shell, wherein Fig. l is an elevational view in longitudinal section of an embodiment having a multiple jet accelerator; and

Fig. 2 is a sectionalized longitudinal view in detail and assembly of an embodiment having a single jet.

Referring now to the drawing and particularly to Fig. l, the base 2 of the projectile 1 has a brass rotating disc 3 secured thereto intermediate the base of the projectile 1, and the chamber body 4, of the rocket accelerator indicated generally at 10. This cylindrical motor chamber body 4 is secured to the projectile 1 by being threaded to the adapter plug 5, which protrudes from the base of the shell. A plurality of washer-like grains of propellent material 6 are inserted within the motor chamber body 4 so that the outer peripheral surface of the stacked propellent charge 6 forms a tubular column whose lateral surfaces are in intimate contact with the inner cylindrical surfaces of the chamber body 4. These propellent washers are held in place by a metallic washer-like trap 7, which has an external diameter preferably about equal to the internal diameter of the motor chamber body 4, and which is held within the motor chamber by the end surface 8 of the charge supporting member 9. The charge supporting member 9 has a plurality of openings 11 drilled therein to provide a multiple jet for the gases liberated by the burning of the propellent charge 6, and has an elongated axial portion 12 which supports the propellent laminations 13 of the mortar. This elongated portion of the charge supporting member is perforated to provide an outlet for the flame from the ignition cartridge 14 supported in the axially drilled opening 15. The propellent 13 is held in place by the nut 16, which is threaded to the elongated portion 15 of the charge supporting member 9.

In Fig. 2, I have shown an embodiment of my invention as reduced to practice. As illustrated, the circular base 2 of the chemical mortar shell 1 has a rotating disc 3 secured thereon by the lock-nut 21. This rotating disc is provided with four equally, radially, and circumferentially spaced holes 22, each adapted to receive a pin 23, pressed therein to a tight fit. An adapter plate 24 for securing the rocket motor body 4 to the chemical shell 1 has its front surface provided with four similarly positioned recesses 25 for engaging the pins 23 projecting from the rotating disc 3 to hold the adapter plate to the shell base 20. This adapter plate is undercut to provide a cylindrical flange surface 26 which is threaded to receive the motor chamber 4. The adapter is also provided with a central stud 27, threaded to receive the ignition cartridge container 28. This container consists essentially of a cylindrical tube, internally threaded at each end and having a plurality of radial perforations 29 formed in the cylindrical surface thereof. This container 28 is adapted to receive the igniter 14 which in the modification illustrated consists of a blank 12 gage shot-gun shell. The shell is held in place within the container by the striker pin guide 30 threaded into the container end and supporting the striker pin 31.

Prior to threading the cylindrical rocket motor body 4 to the adapter plate 24 the propellent laminations 6 of washer-like configuration are inserted within the chamber to rest against the back surface of the motor chamber where the walls project radially inwardly to form the throat 32 of the nozzle 33. The nozzle 33 has a cylindrical extension for the discharge of the combustion products liberated by the propellant 6 which is externally threaded and adapted to receive the mortar propellent bundles 13. These bundles are retained in place upon the cylindrical extension of the nozzle by a clamp nut 16 threaded thereon.

The mortar for firing the chemical shell is provided with a long firing pin extending inwardly from its breach end to engage the striker pin 31 when the shell is dropped into the mortar barrel from the muzzle end. Upon impact of the firing pin with the striker pin 31, the shot gun shell is fired igniting the propellent laminations 6 of the rocket. The hot gases liberated by the propellent laminations are ejected through the nozzle into the space at the breach end of the gun and ignite the propellent laminations 13 of the mortar shell. As is illustrated, the mortar propellent charge 13 is of smaller Web thickness than the rocket propellant so that the former will be completely consumed near the end of the travel of the projectile in the gun. The latter propellant, which is of a thicker web, continues to burn after the projectile has left the gun and the momentum of the gases liberated by the propellant and ejected through the nozzle 33 serves to give the projectile an added thrust, increasing its terminal velocity. Because the propellent laminations 6 are of an external diameter, substantially equal to the internal diameter of motor chamber body 4, the lateral surfaces thereof engage the inner surface of the chamber wall thus permitting the projectile to be rotated in flight without producing a break-up in the propellant and without causing the propellant to be moved outwardly during the rapid angular acceleration of the shell within the gun.

Suitable propellent discs are made of ballastite of the same type as used in propellent discs for the ordinary 4.2 mortar shell. Accordingly, there are no difficulties in the manufacture of the discs having a desired size by existing molding processes.

It has been found feasible to add considerable velocity to the 4.2" mortar projectile. The fact that the projectile is fired from a rifled mortar so that the projectile rotates simplifies the problem of stability. The added velocity due to the rocket motor jet considerably increases the range without drastic changes in design of the mortar or excessive additions in weight to the projectile. The rocket motor added to the mortar shell in accordance with the present invention gives an added weight of only about 5 to 8 pounds to a mortar shell of weighing about 25 pounds, and addition to the length of the projectile by the rocket motor is sufiiciently small to avoid interference with the efficiency of projection from the mortar. For example, the length of the rocket chamber need not exceed about 5 inches in length for a rocket propellent charge weighing about 2 pounds. The size of the rocket chamber nozzle may be varied; for example, if the nozzle is about 4 times the throat diameter it would preferably be only about 1.5 inches in length. For a 16 taper the outlet diameter would be only about 0.8 inch. Thus, it is possible to use the present powder bundles set about the nozzle for expulsion of the projectile from the mortar.

The rocket chamber body preferably has about the same external diameter as the shell, although smaller than the bore of the gun, so that pressure developed in the gun may be on the outside as well as on the inside of the rocket chamber. The burning time of the charge in the gun is so short (about 0.01 second) that very little of the rocket propellent charge is consumed while the projectile is in the gun, but the burning time of the rocket propellant may be adjusted to last about 0.5 to l or more seconds for a desired distance of flight.

It should be clear that various modifications may be made in the structure and arrangement of parts constituting the rocket accelerator for the chemical shell without departing from the spirit of this invention as defined in the suggested claims.

I claim:

1. A rocket projectile comprising in combination with a mortar shell, a cylindrical rocket motor chamber body having substantially the same external diameter as said shell, a threaded plug protruding from the base of the shell in threaded engagement with said chamber body, a rotating disc secured intermediate the base of the shell and said chamber body, a stack of intimately packed annular propellent discs of substantially equal diameters inserted in said motor chamber so that the outer peripheral surfaces are in contact with the inner cylindrical surface of the motor chamber body, a metallic washer-like trap pressing against an end disc of said stack to hold the stack of discs in place, a charge support member having openings for discharge of gas jets from the motor chamber secured to the chamber body to hold said trap in place, and an elongated hollow portion provided with and encircled by a plurality of propellent discs and projecting axially from said supporting member for holding an ignition cartridge inserted therein, said elongated portion being perforated to provide outlets for flame generated by an ignition cartridge inserted into the hollow portion and being provided with a threaded nut and being externally threaded for securing said propellent discs surrounding the elongated portion.

2. A rocket projectile comprising a cylindrical mortar shell, a rotating disc secured to the base of the mortar shell by a lock nut, a plurality of pins projecting from the base of the shell with a tight fit through radially spaced holes in the rotating disc, an adapted plate having spaced recesses for engaging said pins projecting through the rotating disc, a rocket motor chamber body in threaded engagement with said adapter plate, a threaded central stud projecting from said adapter plate to receive a cartridge container, a cylindrical cartridge container attached to said stud, the cartridge container being disposed to hold an ignition cartridge in position for impact by a mortar striker pin on loading into a mortar, a column of intimately packed annular propellent discs in the rocket motor chamber surrounding the cartridge container in spaced relation thereto, a nozzle projecting from the motor chamber body for discharge of combustion products therefrom and entrance thereinto of a mortar striker pin, and means for loading a stack of propellent discs onto the nozzle.

3. A rocket projectile adapted for shooting from a rifled mortar comprising a cylindrical shell having a circular base, a cylindrical rocket motor body attached at its closed front end to the base of the shell, a rotating disc secured intermediate the base of the shell and said closed front end of the rocket motor body, a tubular column of laminated ballistite type discs intimately stacked together and of a size adapted to press against inner surfaces of the rocket motor body, a relatively narrow and elongated axial member extending rearwardly from the rocket motor body at its discharge end, and a bundle of laminated ballistite type discs secured to and concentrically encircling said elongated axial member and having a substantially smaller web thickness than the discs in said tubular column.

4. A rocket projectile comprising a cylindrical shell, a metal rotating disc means secured to the base of the shell, a cylindrical rocket motor body secured at its front end to said disc, a plurality of intimately stacked propellent discs each disc being in surface-to-surface contact with another of said discs and having an external diameter substantially equal to the internal diameter of the rocket motor body disposed within said rocket motor body, said stack of discs being provided with an axial concentric bore of constant diameter extending through the stack,

6 and a gas jet outlet at the rear end of said rocket motor body.

5. A rocket projectile comprising a cylindrical shell, a rotating disc secured to the shell, a cylindrical rocket motor body having in its rear end portion a gas outlet and being secured to the said rotating disc, a plurality of intimately stacked propellent discs provided with central perforations and snugly fixed in the rocket motor body and forming a laminated tubular column having its lateral surfaces engaged with the inner wall surfaces of the rocket motor body and its front and rear end surfaces engaging portions of the rocket motor body.

6. A rocket projectile adapted to be fired from a rifled mortar, said projectile including a cylindrical shell having a circular rotating disc of soft metal of substantially the same diameter as that of the shell secured to the base portion of the shell, a cylindrical rocket motor body attached at its closed front end to the said rotating metal disc and being provided at its rear end with a restricted gas nozzle portion, said rocket motor body having an external diameter approximately equal to the external diameter of the shell base and the rotating disc, a plurality of intimately stacked and centrally perforated propellent discs nicely fitted in said rocket motor body in a manner adapted to form a laminated tubular column having a central opening extending entirely through said column, and a bundle of centrally perforated propellent discs encircling and secured to the nozzle for discharging the projectile from a mortar.

7. In combination with a shell adapted to be fired from a rifled gun, a soft metal rotating disc secured to the base of the shell, a rocket accelerator including a cylindrical combustion chamber inclosed in a casing rigidly secured to the rotating disc and having in its rear end portion a constricted gas outlet orifice, a stack having a central bore extending therethrough formed of centrally perforated and intimately stacked washer-like grains of propellent material tightly packed in said chamber, and means for retaining said grans of propellent material within said chamber in a manner whereby said grans are kept intact in said chamber against the centrifugal forces produced by the rotation of said projectile and rapid angular acceleration.

References Cited in the file of this patent UNITED STATES PATENTS 826,293 Unge July 17, 1906 1,994,490 Skinner Mar. 19, 1935 2,069,794 Woodberry Feb. 9, 1937 FOREIGN PATENTS 14,000 Great Britain May 29, 1897

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