GB2089009A - Blast Equalizer for a Gun fired Ramjet Projectile - Google Patents

Abstract

A blast equalizer for use with a gun-launched ramjet projectile balances the pressure across the outer housing of the ramjet. By properly sizing the openings into the volume surrounding the ramjet casing and the opening into the internal cavity of the ramjet, the pressure increase associated with the explosive gases during firing reaches opposite sides of the ramjet casing at approximately the same instant. The equaliser may act as a bourrelet at the rear of the ramjet casing, and may include a plurality of notches or holes formed in a ring member that have a precisely determined area that opens into the annular volume around the ramjet casing, the ratio of the area of the notches to the area of the throat of the nozzle is matched to the ratio of the annular volume surrounding the ramjet housing to the internal cavity of the ramjet.

Description

SPECIFICATION Blast Equalizer for a Gun-fired, Ramjet Projectile Technical Field This invention relates to a projectile attached to a heat engine launchable from a gun, and more particularly, to a gun-launched projectile having a ramjet engine with a particularly designed blast equalizer to minimize sidewall stressing.

Background Art There has been a continuing attempt to increase the range and accuracy of projectiles fired from a gun in order to attack targets which are further and further away. Numerous different types of heat engine, such as a rocket engine or a ramjet engine, have been used in conjunction with a projectile fired from a gun with varying degrees of success to extend the range of a warhead. With this type of propelled warhead, the projectile is initially accelerated by the explosion of the charge in the gun to an initial velocity, this occurring as the projectile emerges from the gun barrel. The heat engine, is subsequently ignited and provides additional thrust to the projectile along its flight path.

One of the problems associated with a heat engine propelled, gun-launched projectile is the weight and stresses which act on the composite projectile during firing. As the projectile is being accelerated through the length of the gun by the explosion of the charge, the entire housing of the projectile is typically subjected to 5,000 to 10,000 G's of acceleration (one G equals the acceleration due to gravity). Because the sidewall of the heat engine is subjected to the pressure of the exploding gases that are necessary to creating this type of acceleration, the sidewall must inherently be relatively thick to withstand the hoop stress, axial crushing stress and buckling stress. Stressing of the heat engine sidewall can also cause shear stress in any fuel in the heat engine that is attached to the interior wall of the heat engine housing.

Disclosure of the Invention It is an object of this invention to provide a gun-launched ramjet projectile having a blast equalizing bourrelet.

A particular advantage of the blast equalizer of the present invention is to provide a gun-launched ramjet projectile in which the sidewall of the ramjet can be relatively thin and yet still withstand the high pressures associated with the exploding gases.

Yet another feature of the present invention is a blast equalizer positioned near the rear end of a ramjet, gun-launched projectile that functions both as a pressure regulating device and also as a bourrelet to stabilize the projectile in the bore of the gun.

A particular feature of the blast equalizer of the present invention relates to its use with a gunlaunched projectile to minimize the stressing of the sidewalls of the heat engine. In one embodiment, the blast equalizer functions as a bourrelet and has a plurality of notches or other apertures around the circumference of the obturator which is located at the rear of the ramjet. The sum of the areas of the notches or apertures has a specific relationship to the area of the nozzle. The ratio of the area of the notches or apertures to the area of the opening into the ramjet nozzle is the same as that of the annular volume between the ramjet housing and the gun bore and the volume in the cavity of the ramjet.

This causes the pressure associated with the exploding gases to enter the respective volumes at approximately the same rate resulting in the pressure differential across the ramjet engine sidewall to be minimized.

Brief Description of Drawings Fig. 1 is a view of a gun-launched ramjet projectile with one embodiment of a blast equalizer according to the present invention positioned at the rear portion thereof; Fig. 2 is a perspective view of just the ramjet engine showing the blast equalizer; Fig. 3 is a perspective view of the rear portion of a ramjet engine depicting a second embodiment of a blast equalizer according to the present invention; and Fig. 4 is a perspective view of the rear portion of a ramjet engine depicting a third embodiment of a blast equalizer according to the present invention.

Best Mode for Carrying Out the Invention Referring initially to Fig. 1, there is seen a gunlaunched ramjet projectile 10 positioned in the bore 12 of a gun 14 ready for firing. The gunlaunched projectile basically has two main component parts, a warhead assembly 16 and a heat engine, such as a ramjet 18, positioned axially adjacent the rear end of the ramjet projectile. As is known, a charge 20 is ignited to propel the ramjet projectile out of the gun, and, in so doing, accelerates the projectile to a sufficient velocity for operation of the ramjet engine 18.

Referring now to Fig. 2, in addition to Fig. 1, there is seen one embodiment of a blast equalizer 22 according to the present invention. The blast equalizer 22 of this embodiment performs the dual function of balancing the pressure differential across the outer casing or sidewall 26 of the ramjet and also acts as a bourrleet. The ramjet engine also includes an obturator 24 fixedly attached to the outer casing near the front end of the sidewall 26. The blast equalizer 22 is fixedly attached to, or integrally formed with, the rear portion of the casing and extends radially outward from the sidewall 26 toward the bore 12 of the gun. The ramjet 1 8 includes a nozzle 28 which forms an exit orifice from an internal cavity 30 where the fuel is burned.

A particular feature of the blast equalizer according to the present invention is that it balances the pressure differential across the sidewall 1 8 of the ramjet engine. This allows the sidewall to be thinner than the sidewall of prior art ramjet-driven projectiles formed from the same material. Accordingly, the center of gravity of the combined projectile is moved forward which enhances the inflight characteristics. As is best seen in Fig. 2, the blast equalizer 22 includes a plurality of apertures or notches 32 positioned around the periphery thereof. The notches form openings into the annular volume 34 which is the volume surrounding the casing of the ramjet 18 upto the obturator 24.The pressure balance across the sidewall 1 8 is maintained during firing by ensuring that the ratio of the sums of the areas formed by the notches 32 to the throat area of the nozzle 28 is the same as the ratio of the annular volume 34 (Fig. 1) surrounding the casing of the ramjet to the volume of the internal cavity 30.

In other words, A1 V, ~=~=K A2 V2 where At=sum of the area of notches 32; A2=area of the throat of nozzle 28; V1=annularvolume around ramjet in gun bore; V2=volume of internal cavity within ramjet.

In operation, the explosive charges 20 are ignited and create an extremely high pressure which accelerates the projectile through the length of the gun. As the pressure of the exploding gases strikes the end of the blast equalizer 22, the opening formed by the notches 32 allows some of the expanding gases to enter the annular volume 34 surrounding the casing of the ramjet 18. In the same fashion, the nozzle 28 allows the expanding gases into the volume within the internal cavity 30. Because of the matched ratios between the areas and volumes, the increase in pressure occurs essentially simultaneously on either side of the sidewall 26.

As will be appreciated, this minimizes any pressure differential across the sidewall 26. In addition, this allows the presssure associated with the expanding gases to be directed to the obturator 24 located at the front end of the ra mjet.

Referring now to Fig. 3, there is seen a second embodiment of a blast equalizer according to the present invention. In this second embodiment a blast equalizer 38 is fixedly attached to or formed with, the rear portion of a ramjet in the same manner as just heretofore described. The blast equalizer 38 is shaped as a ring which protrudes outward from the sidewall of the ramjet 40. If desired, this second embodiment of the blast equalizer also can be sized and shaped to function as a bourrelet for stabilizing the projectile in the bore of the gun during acceleration. A plurality of holes 42 are formed through the ring so that the expanding gases can pass therethrough at a predetermined rate.

Referring finally to Fig. 4, there is se-en a third embodiment of the blast equalizer according to the present invention. In this embodime.t a blast equalizer 44 is positioned at the rear of the casing of a ramjet 46 in the same manner as heretofore described. This third embodiment is also ring-shaped and protrudes from the sidewall of the casing outward toward the bore of the gun.

However, the outward diameter of the ring will be sized such that it is sufficiently smaller than the internal diameter of the bore so that there is a space through which the expanding gases can enter the annular volume around the ramjet casing.

In the same fashion as heretofore described, a key feature of both these second and third embodiments is the balancing of the pressure differential across the casing of the ramjet during firing. This is achieved by ensuring that the ratio of the areas opening into the two volumes is matched to the ratio of the volumes. Accordingly, the pressure increase on the opposite sides of the ramjet sidewall occurs at approximately the same instant in time, thereby reducing the pressure stressing that the casing of the ramjet must withstand during firing.

Although this invention has been shown and described with respect to a preferred embodiment, it will be understood by those skilled in this art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.

Claims (7)

Claims

1. A gun-launched engine propelled projectile, comprising: a warhead assembly having a substantially cylindrical shape and sized to be positioned in the bore of a gun; a heat engine means having an outer casing with a cylindical sidewall sized to be positioned in said gun axially adjacent to said warhead assembly, said cylindrical sidewall having a diameter which is less than said bore such that an annular volume is formed between said cylindrical sidewall and said bore, said heat engine further including a rear opening into an internal cavity within said outer casing; obturator means positioned on said casing near the forward end of said sidewall, and formed from a material which seals against said bore when said projectile is fired from said gun, thus forming a gas seal;; blast equalizer means mounted on said casing near the rear portion of said sidewall and extending laterally outward toward said bore, said blast equalizer means having a diameter which is greater than said diameter of said sidewall but less than the bore of said gun, said blast equalizer having an aperture means opening into said annular area within said bore surrounding said casing of said heat engine; and whereby the ratio of the area of said aperture means opening into said annular volume surrounding said casing of said heat engine to the area of said rear opening is substantially the same as the ratio of said annular volume around said casing of said heat engine to the volume of said internal cavity within said casing of said heat engine.

2. A gun-launched engine propelled projectile according to claim 1, wherein said heat engine is a ramjet, and wherein said rear opening is the nozzle of said raMjet, and wherein said ramjet ignites subsequent to said projectile leaving said bore of said gun.

3. A gun-launched engine propelled projectile according to claim 1 , wherein said projectile is adapted to be positioned in the bore of a gun adjacent explosive charge, and wherein said explosive charge is fired creating explosive gases which propel said projectile through the length of said bore, and wherein said heat engine means is ignited subsequent to said projectile leaving said bore generating thrust propels said projectile along a trajectory.

4. A gun-launched engine propelled projectile according to claim 1 , wherein said blast equalizer is also a bourrelet.

5. A gun-launched engine propelled projectile according to claim 1, wherein said blast equalizer means includes a ring member extending radially outward from said sidewall of said heat engine, and wherein said ring member is sized and shaped to stabilize said projectile during acceleration in said bore, and wherein said ring member includes a plurality of notches, the combined area thereof forming said aperture means opening into said annular area surrounding said bore.

6. A gun-launched engine propelled projectile according to claim 1, wherein said blast equalizer means includes a ring member extending radially outward from said sidewall, and wherein said ring member is sized and shaped to stabilize said projectile during acceleration in said bore, and wherein said ring member includes a plurality of openings therethrough, the area of which forms said aperture means opening into said annular volume surrounding said casing.

7. A gun-launched engine propelled projectile according to claim 1, wherein said blast equalizer means includes a ring member extending radially outward from said sidewall, and wherein said ring is sized to be spaced from said bore of said gun by a predetermined distance, and wherein the area separating said ring member and said bore of said gun form said aperture opening into said annular area surrounding said casing of said engine.