GB1571010A

GB1571010A - Supersonic projectiles

Info

Publication number: GB1571010A
Application number: GB1103277A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-03-26
Filing date: 1977-03-16
Publication date: 1980-07-09
Also published as: FR2345696A1; IL51505A; FR2345696B1; DE2712807A1; BE852625A

Description

(54) SUPERSONIC PROJECTILES (71) We, ABRAHAM FLATAU and JOSEPH HUERTA, both citizens of the United States of America, of 2003 Stockton Road, Joppa, Maryland 21085; and 399 Clover Street, Aberdeen, Maryland 21001; both in the United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to supersonic projectiles of tubular shape.

From the earliest known time, weapon designers have sought to increase the effect of projectile impact. This effect is dependent on many factors, particularly projectile mass, impact velocity, and the striking surface or area of contact. In addition, other factors such as total weight, case of handling, recoil, accuracy, and the launching means must be considered, evaluated, and optimized. To produce an acceptable projectile design, trade-offs are frequently made.

Air resistance or aerodynamic drag has plagued projectile designers since the mideighteen hundreds. High drag creates increased velocity decay and, in turn, reduces both the target striking power and the effective range of the projectile. To reduce the drag, many projectile design approaches have been taken. They extend to the development of long slender projectiles, and the development of projectiles with a longitudinally drilled air passage hole. These have been known as hollow or tubular projectiles.

If the high drag could be reduced by a hollow type design, a number of additional advantages were then to be gained. Among them were increased range, a reduced trajectory height for a given range as compared to a conventional projectile, and increased hitting power on target.

For a better perspective of our invention and the background thereof, figures 116 of prior art have been provided.

Whitworth, an English inventor, designed projectile 16 of Figure 1 about 1857.

It has hole 17 therethrough and multisided external configuration 18. Apparently, it met with little success.

In 1893, Professor Hebler of Switzerland conducted a series of experiments on projectile 19 of figure 2 and variants of this design. This projectile configuration was derived from a conventional projectile with a longitudinal perforation or aperture 20 provided therein. These experiments came to be known as Krnka-Hebler experiments.

Not long thereafter, in 1894, United States interest was aroused. Experiments were conducted at Frankford Arsenal in Philadelphia, Pennsylvania. These experimental bullets are described in "History of Modern U.S. Military Small Arms Ammunition," by F. W. Hackley et al, and published by MacMillan and Company in 1967. Conclusions of the work indicated that a conventional projectile with a through hole was of no benefit when considering air resistance or drag.

Between the years of 1944 and 1956, United States interest in tubular projectiles was rekindled and then discarded for lack of any noticeable benefits had thereby. It was concluded during this period that a well-designed conventional 20mm projectile functioned as well as a through-hole tubular 20mm projectile when comparing their air resistance or drag characteristics.

However, following World War II a great deal of information was developed concerning the internal aerodynamics of supersonic flow, both in ducts and diffusers.

This material now forms the basis for the analytical foundation in support of the design of tubular projectiles. The theory and previous studies indicated that under certain Mach number and configurational design conditions, the normal shock could be "swallowed." This meant that a normal shock would not be present at the nose of the projectile nor would it be located within the internal section, allowing for mass flow efficiency through the duct. Thus, a properly designed supersonic tubular projectile would have only supersonic flow internally. Hence, a normal shock would not be present either externally or internally. This situation would result in the desired low drag flight condition. This internal flow condition is established by proper projectile design with regard to duct size and contour and by launching the projectile at a suffi ciently high Mach number.The supersonic internal flow and consequent low drag is retained as the projectile initially decelerates during flight. However, at a Mach number of about 2.0, the internal flow experiences an abrupt change resulting in a normal shock wave appearing on the nose of the projectile and subsonic flow through the duct. This conditions is referred to as "choking" and results in a large increase in drag.

During 1969--1975, the US Army again ventured into the tubular projectile area.

This work ranged from .30 cal to 70mm projectiles. The Canadians ran rests and collected data on tubular projectiles ranging from 20mm through 105mm. Figure 3 is an example of projectile 21 with externally configured surfaces 22 and 23 which was designed for reducing drag, etc. Figure 4 depicts projectile 25 with a constant external configuration and varying internal surfaces 26 and 27. The Canadians evolved a form of the configuration of Figure 5. Here they provided internal and external surfaces 29 and 20 in the forward section of a tube 28 per se.However, they did not appear to optimize the internal and external shaping in their final development design to achieve the best rrade-offs involving low drag When dealing with supersonic velocities of flow, it should be noted that a textbook theoretical model for a low drag tubular projectile has existed for years. Figure 6 depicts such a model. However, this type of projectile configuration is substantially impractical in military use because its wall thickness makes it of little utility due to the low projectile mass.

As set out above, and hopefully deduced, there has been considerable interest from time to time in tubular projectiles. However, each venture has in one way or another ended in failure because of the high drag characteristics and/or lack of know ledge or the cause thereof.

Basic knowledge in the area of apertured projectiles has been lacking until a breakthrough had been made by one of the instant applicants, Abraham Flatau, in the field of airfoil projectiles. United States Patents 3,877,383 and 3,898,932 are examples of apertured projectiles which by appropriate shapnng have attained low drag and low air resistance. These airfoil projectiles are for use in substantially sub sonic situations. Our interest in these types of projectiles has overflowed into the area of tubular projectiles.

As exemplified by the discussion of prior art set out in figures 1-3, each projectile configuration has a drawback of high air resistance of high drag at velocities above 1100 feet per second on to beyond Mach 4. Figure 6, if set out in proper parameters, does possess low drag; however, as aforesaid, same lacks mass; hence, no real utility is seen in the munition field for this configured projectile. Numerous approaches and failures have been had in this field because of the lack of knowledge about high drag and shock waves incident with supersonic velocities.

An ideal projectile would be one that could be launched at a velocity greater than Mach 3 with minimal velocity decay due to low drag. Conventional projectiles have relatively high drag coefficients. Hence, as of late, with ever present detection and defensive weaponry, a high velocity projectile with a low drag coefficient is and has been actively sought. As evidenced by past research, etc., with resultant cyclic interest, emphasis and then failure in the performance of the tubular projectile, munitions researchers have always felt success should be had in this area. Until our invention, only limited and marginal success has ever been had with low drag supersonic velocity tubular projectiles.

It is therefore an object of our invention to provide a low drag supersonic velocity projectile.

Another object of our invention is to provide a low drag, supersonic projectile of a tubular configuration having selected internal and external shape to minimize drag.

Still another object of our invention is to provide a low drag, supersonic projectile of a tubular configuration having selected internal and external shape to minimize drag and with sufficient mass to render utility at impact.

Still another further object of our invention is to provide a low drag, supersonic projectile of a tubular configuration having selected internal and external shape to minimize drag and with sufficient mass to render utility at impact, and with the internal and external shaping extended to form leading and trailing edges to further minimize drag.

SUMMARY OF THE INVENTION It has been found that the foregoing objects can be achieved by drastically departing from previous conventional tubular projectile design. What we have invented is a new tubular supersonic projectile of a relatively low length to diameter ratio having a practical mass, yet approaching the low drag coefficient performance indicated by the nonpractical theoretical model depicted in figure 6. Unlike the theoretical model depicted in figure 6, we have discovered the criticalities of the forward or leading edge portion both externally and internally. We have found the aft end or boattail end portion both internally and externally is so also critical. Notwithstanding, we have found for low drag that the body or throat portion of the projectile must complement the leading and trailing portions so that complete integrity is had.Hence, internal geometry in combination with nose/lip geometry and boattailing has resulted in a practical and never thought possible breakthrough in the projectile field. Our projectile configuration swallows the initial bow shock wave at Mach 3 and above, and will retain a low drag condition until it becomes choked at about Mach 1.95 or lower as the projectile decelerates along its flight path. Thus, due to its lower mass as compared to a conventional projectile, the projectile of our invention can be launched at much higher velocities and have a shorter time of flight to the target and a flatter trajectory.

More importantly, this flight performance is achieved while possessing the above same amount or greater hit power or kinetic energy at impact. At supersonic velocities, shock waves create high drag. So also, additional drag is created by skin friction at the projectile surface-air interface. The detached bow shock wave existing in front of a projectile will cause high drag. Our tubular projectile is designed and launched at high muzzle velocities to enable the projectile to "swallow" the bow shock. That is, the air flow must be properly established in the tube or internal portion of the projectile so as to have efficient flow continuity through the internal flow passage. When the bow shock re-appears in front of the projectile, "choking" occurs.Hence, an apertured projectile will then tend to act from an aerodynamic drag performance viewpoint as if no aperture or through passage exists. This is directly shown in diffuser theory for supersonic flow. Theory and previous studies indicate that under certain Mach numbers and configural design conditions, the normal shock can be "swallowed." The basis for a theoretical conventional low drag tubular projectile design is described in "Dynamics and Thermodynamics of Compressible Fluid Flow" by Shapiro as well as other known texts on supersonic flow. It will be elaborated upon below.Hence, by incorporating fluid flow theory for large bodies such as aircraft configuration, etc., and applying it to projectiles in conjunction with variable supersonic wind tunnel laboratory studies and aeroballistic range test firings, we have tnade our breakthrough in the tubular projectile field.

An extensive review of the technical state-of-the-art, its literature, and associated patent reference material reveals that although a number of tubular projectile designs have existed and been tested, none have achieved the sought for low drag coefficients.

Claims have been made that a tubular projectile could have an order of magnitude reduction of drag above the choking condition. This has not proven to be so. Based on the classical equations of fluid flow as related to skin friction, it is possible to be mislead into conceiving that an extremely low drag coefficient could be achieved.

However, this low value would not take into account the reality and contribution of the wave drag, skin friction drag, and base drag to the total projectile drag that actually exists as demonstrated by both Schlieren photographs in the wind tunnel, spark photo graphs taken of tubular projectiles in flight in an aeroballistic range, and drag measurements made during actual free-flight tests downrange following gun launch. In effect, wave drag and base drag are not virtually eliminated by a tubular design. The major portion of the actual drag coefficient of a tubular projectile is composed of the wave drag and base drag. Nonetheless, in comparing the magnitude of these drag values with those for a conventional projectile, there is a significant reduction in both the wave and base drag.To date, demonstrated tubular projectile designs have shown drag coefficients with a factor of 1/2 to 1/3 the drag coefficient of a conventional projectile, but not an order of magnitude.

Extensive wind tunnel testing resulted in low drag coefficient performance predictions. Actual aeroballistic range data measurements of gun launched tubular projectiles based on the inventive shaping then validated those predictions. This has produced a practical range of tubular projectile designs having performance characteristics that cannot be obtained by means of only the use of the theoretical equations.

Our breakthrough has enabled us for the first time to provide a low drag tubular projectile with sufficient mass for meaningful impact effects. This has been achieved by forming an elongated body or throat portion with substantial thickness while still maintaining a low drag shaping. This has been done by providing internal and external shaping both for and aft. Aside from the advantage had by increased mass, a concurrent feature of the design is a compatible throat length which enables swallowing of the initial bow shock over a large range of supersonic velocities. It is within the purview of our invention, of course, to modify the throat internal shape or size as one moves from the inlet end to the exhaust end if it provides a lower drag coefficient.

As will be seen below, our proiectile invention takes into account the inevitable choking that will occur as some point during deceleration. So also our unique compression section shaping optimized with a complementary designed throat section eliminates choking above Mach 1.95. With our new und unobvious projectile, we have provided a low drag projectile which functions at its optimum from a range of Mach 4 or higher through a lower Mach of 1.95. Our objective is to accept choking when it occurs because our projectile utility generally occurs before choking reduces the impact velocity and associated terminal ballistic features.

According to the invention there is provided a supersonic low drag projectile comprising a tubular structure defining an internal forward continuous convering conical surface, an internal elongate throat body section of substantially constant crosssectional shape and area throughout its length and an internal aft continuous diverging conical surface, the ratio of the internal throat length to the internal diameter of the throat section lying in the range of from 0.5:1 to 2.5:1, the ratio of internal inlet area of the projectile to internal cross-sectional area of the throat section lying in the range of 1.3:1 to 1.6::1, said projectile being boattailed on the exterior of the aft divergence section thereof and its junction with the internal aft divergence conical surface formed as bearing surface either fiat or curved, against which propellant forces act, in use, to give the projectile forward motion, the boattail portion and the internal divergence surface making an acute trailing edge angle up to 15 , and the internal and external inlet surfaces of the forward compression section making an acute leading edge angle in the range from 10 to 150 with the bisector of said leading edge angle being substantially parallel to the longitudinal axis of the projectile.

The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of that set out below when related to the annexed drawings, wherein: Figure 1 depicts Whitworth's 1857 prior art projectile; Figure 2 depicts Hebler's 1893 prior art projectile; Figure 3 depicts a prior art test model with an external shape; Figure 4 is a prior art test model with internal shaping; Figure 5 is a prior art Canadian model; Figure 6 is a theoretical prior art model; Figure 7 is our invention; Figure 8 is our invention in a sabot; Figure 9 is our invention with an enlarged, for illustration purposes, rifling band; and Figure 10 is our projectile with a pusher or obturator disc.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings, wherein similar reference characters are utilized to designate corresponding parts throughout, our projectile of figure 7 comprises three portions designated "a" to "c". Compression or convergence section "a" of projectile in figure 7 defines leading edge 3 formed by outer surface 7 confronting internal surface 5. Moving farther to the right as we view figure 7, we see that surfaces 5 and 7 engage internal surface 10 and external surface 9, respectively, to define the throat section "b". The third section "c" is a divergence or expansion section defined by surfaces 6 and 8 forming the trailing portion 4. At launch, for example, projectile 1 would be rotatably thrust from the launch mean, not shown, at a velocity exceeding Mach 3 with leading edge forward most.

Our projectile 1 of figure 7, though depicted as solid, can as well be entirely hollow or have hollow portions therein. It is within the purview of our invention to have part or full partition walls disposed in any fashion to contain a payload and to keep the mass from displacement and define in the entirety or in part at least, the abovementioned portion or portions.

Our projectile 1 invention has critical dimensions throughout. The lip geometry is very significant. The total angle, i.e., from surface 7 to surface 5 in the compression or convergent area "a" should not exceed 150. The preferred embodiment for the total leading edge angle is 15". However, the leading edge angle can have a range from 10 to 15 with acceptable performance. Further, the desired alignment of the total leading edge angle is with the bisector of the leading edge angle parallel to the longi tudinal axis of the projectile. The divergence or expansion area "c" defined by surfaces 6 and 8 should likewise not exceed 1S" for the Mach regime in which our invention is used.Although our preferred embodiment for the trailing edge angle is 140, a range of 8" through 1S" will be satisfactory. In the preferred embodiment the boattail surface and the internal divergent surface may he at substantially 100 and 4" respec tively to the longitudinal axis of the projectile. Trailing edge 4 is contoured as with a radius or flat so as to provide a bearing surface for launch or propulsion purposes.

The prcferred embodiment for the propulsion surface has a width relative to the maximum thickness of the throat portion in a ratio of .167:1. The design will also be satisfactory for this surface in a range wherein the ratio will be within .150:1 and .250:1. Aside from the dimensions or parameters set out above, our internal throat portion "b" of figure 7 has a range of internal length to internal diameter ratio from 0.5:1.0 through 2.5:1.0. However, the preferred ratio of throat internal length to internal diameter is 1.95:1. Further, the preferred ratio of the maximum thickness of the throat portion "b" to the external maximum diameter is substantially .167:1. A range of this ratio which will provide satisfactory results is .10:1 and .20:1.The thick ness of the throat portion may also be defined by a preferred ratio of the maximum thickness of the throat portion may also be defined by a preferred ratio of the maximum thickness of the throat portion to the throat internal diameter as .250:1. A functionally satisfactory range for the aforesaid ratio is .15:1 and .35:1.

The projectile 1 of figure 7 has a preferred overall external length to maximum external diameter of 3.0:1. However, this ratio can be within a satisfactory range of 2.5:1 and 4.0:1.

The mass of our projectile 1 is also governed by the material same is made of.

We have made our projectiles of various metals such as "bearcat" steel (which is heat treated tool steel for hardness), and tungsten alloy though it is within the scope of our invention to use numerous other available metals. The terminal ballistic character istics as regards armor penetration is one primary factor in determining the type of material our new tubular projectile should be comprised of, though economic, manufac turing, and payload dictates play a part as well, Figure 8 shows our projectile 1 contained within a launch means comprising a sabot 11 and pusher/obturator 13 disposed aft therefrom. In operation, sabot 11 engages the refling of the barrel and transmits the spin to projectile 1. Upon muzzle exit the sabot 11 and obtruder 15 are shed from the projectile by aerodynamic drag caused by surface 12 on sabot 11 as well as due to centrifugal force.Although it is understood that sabot 11 and obturator 13 are not essential to our projectile's utility, it is one means by which launching occurs. In the event that it is desired to incorporate a combustible sabot, i.e., one wherein same disintegrates during launch, divergent surface 6 also serves a beneficial end.

Our invention projectile of figures 7-10 also encompasses, not shown, use of a traveling charge. Here the charge is located in the throat section and is actuated during or sometime after launch.

Figures 9 and 10 depict our projectile 1 invention with rifling band 14 located exteriorly thereof. Hence, the rifling of the gun barrel could be directly engaged by band 14 and the pusher/obturator 15 could be used to transmit propellant gas force to launch proiectile 1. In both figures, element 14 has been illustrated as being rela tively thicker than in actuality.

Comparisons are presented of the drag coefficients of our invention with two tubular configurations each having different inlet lip angles forming the compression section but of constant internal diameter thereafter, as well as lacking the exterior boattail shaping in the aft section. The data are based on wind tunnel testing between Mach 4 and Mach 2.

Configuration Drag Coefficient (CD) I I Test Tubular of constant internal diameter .240 1 Tubular internally shaped .143 Test Tubular constant internal diameter .183 2 Our invention internally shaped .103 Hence, it may be directly seen from the drag coefficient data that the internally shaped confieurations moduce a significant reduction in drag. The internal geometry in com- bination with the external nose geometrv and boattailing, results in a practical low drag projectile which may be applied to a variety of weapon sizes and systems.

Salient advantages of our invention are further spelled out now. In the 20mm area, our new invention projectile far out performs its conventional solid component counterpart. With a muzzle velocity of 4500 feet per second for our invention and a conventional projectile muzzle velocity of 3380 feet per second for the standard 20mm at a range of 1400 meters, comparisons indicate that our projectile reaches the target in one half the time. Our projectile has a flatter trajectory, having an apogee of one third that of the conventional 20mm, less mass, and four times the kinetic energy at impact.

An example of our invention with the configuration of figure 7 displayed which has low drag characteristics above Mach 1.95 while contemporaneously possessing adequate terminal ballistic capabilities, is described as follows, based on a projectile having an outside diameter of 1.125 inches and an overall length of 3.375 inches. The throat section length divided by the internal diameter of the throat should be a constant between 0.5 and 2.5. In this example using a throat section length to diameter ratio of 1.947, a .75 inch internal throat diameter will render a throat length of 1.460 inches.The convergent section forming the forward projectile portion is provided with a .9 inch diameter leading edge and a total inlet lip angle of 15 degrees with a .570 inch longitudinal dimension of the convergent section "a." Thus, the preferred embodiment has a ratio of inlet area to throat internal cross-sectional area of 1.44:1.

However, this area ratio can be within a satisfactory range of 1.3:1 to 1.6:1. Aft section is shaped with a 1.345 inch divergent longitudinal dimension "c" and a four degree divergence angle which is the angle that annular surface 6 makes with internal throat surface 10. The boattail defined by surface 8 is ten degrees as measured from the angle surface 8 makes with external surface 9.

Our new projectile is designed for supersonic speeds so that at launch at Mach 3 or higher the initial bow shock is "swallowed," and supersonic flow is established within the projectile. We have invented a new projectile configuration which is designed to function with optimum efficiency for a specific velocity range. We have optimized on trade-offs to accomplish this end. We are cognizant that the choking phenomenon always affects our projectile at some point during the trajectory, especially as it decelerates toward sonic velocity. The "choking" results in an abrupt drag rise as the projectile slows in its trajectory. However, our projectile functions at Mach numbers thereabove; hence, the effect has been diminished.

To eliminate choking at a given Mach number, particularly at and near the launch velocity, the ratio of minimum throat area to inlet area is determined by use of the theoretical equation. It may be applied to the model of figure 6, which is also known as the Busemann biplane. There element 31 represents a plane from which the inlet measurement is made and element 32 represents a plane from which the minimum throat area is made.

The formula below should be used. It is applicable to the shape of figure 6 as shown and can as well be used to design inlets such as ours.

1/2 1 1/2 1 A min Amin = xl (2j1) 1+2 1x4 1x-1 inlet xel x-1 M22x M2 here x = cup = ratio of specific heats V A = area M - Mach number Further edification on internal flow parameters, etc., can be had from Professor Rudolf Hermann's 1956 book on "Supersonic Inlet Diffusers and Introduction to Internal Aerodynamics." Projectile designs based on the Busemann biplane, figure 6, will be limited in projectile wall thickness and hence the total projectile mass. This is due to the manner of the Busemann, or iinternal design, hollow projectile in which the inlet area is based on the maximum or outside diameter of the projectile.Thus, for a given area ratio of inlet area to throat area, as shown in the equation, substantially internal designs will always be limited in wall thickness and total mass.

The advantages of our invention projectile over that of the conventional projectile are manifold. Comparing our invention with a conventional projectile adaptable for use in the same gun, indicates that our projectile will be lighter in weight. The lighter weight can be utilized by launching the tubular projectile at a higher initial velocity without exceeding the gun recoil of the conventional projectile systems. The higher launch velocity in conjunction with the low drag results in shorter times of flights, flatter trajectory, and greater accuracy. This is done, of course, by utilizing greater than Mach 3 launch velocities. At this velocity range, our low drag characteristics are optimized by the use of a long throat section which can be internally contoured for bow shock swallowing.Our lip configurations, both internally and externally on the forward end of the projectile, provide a compression function for optimization of low draw features. Notwithstanding, our internal lip angle and inlet area is proportioned with that of the throat area for minimum drag and optimum flow. The aft or expansion section of our projectile is so also configured so that our low drag range of Mach numbers is had. Boattailing on the exterior coupled with the expansion portion on the interior enables the air to flow through the projectile from the throat with the least drag thereto.

For the same material and given diameter, the tubular projectile will be of lower weight than a corresponding conventional ballistic projectile.

Hence, the lighter tubular projectile can be launched at higher velocities. However, unless the external and internal geometry is properly shaped, the tubular projectile will not have the desired low drag.

To determine if the tubular projectile has achieved low drag, a standard ballistic measurement technique is utilized. That is, a series of velocity screens are installed along the flight path. As the projectile flies through the series of velocity screens, the relative velocity at each set of screens is measured.

The velocity data are then used in the following equation to calculate the drag coefficient. The value of the drag coefficient will then be directly indicative of whether the projectile is in a low or high drag conditions.

2m V Cg= in D pSds VO or for standard conditions (p=.G012 g/cmS) The equation reduces to: CD = - (21.22) in rd2 V0 where o=air density (g/cmS) m=projectile mass (grams) d=projectile diameter (cm) sd2 S=projectile area= (cm2) 4 s=range (calibers) r=range (meters) V,=initial velocity (fps or mps) V=downrange velocity (same units as V) The result of this work is a low drag practical tubular projectile design which provides for sufficient mass to result in a higher ballistic coefficient than would be obtained with the design known as the Busemann, or direct variants thereof, and a nose shaping which significantly improves the terminal ballistics against targets such as armor plate.

In this manner our invention is distinguished over the prior art.

Cartridge and tubular projectile combinations have long been known in the state of-the-art. United States Patents 2,433,334 and 3,621,781 are examples of tubular projectiles combined with cartridges and various types of propellant to form a round of ammunition. U.S. Patent 2,433,334 also includes provision for a combustible obturator. What has been lacking in the past and recent state-of-the-art is a tubular projectile design which, when launched from a gun barrel at sufficiently high velocity, will actually achieve low velocity decay because of the combination of low drag shaping and relatively high projectile mass and have a shaping geometry and mass which will produce significant damage upon target impact.Our design accomplishes these goals, which have been long saught for by many and claimed by some, but until our invention never actually proven until demonstrated by us and based on a substantial depth of experimental data.

WHAT WE CLAIM IS: 1. A supersonic low drag projectile comprising a tubular structure defining an internal forward continuous converging conical surface, an internal elongate throat body section of substantially constant cross-sectional shape and area throughout its length and an internal aft continuous diverging conical surface, the ratio of the internal throat length to the internal diameter of the throat section lying in the range of from 0.5:1 to 2.5:1, the ratio of internal inlet area of the projectile to internal crosssectional area of the throat section lying in the range of from 1.3:1 to 1.6::1, said projectile being boattailed on the exterior of the aft divergence section thereof and its junction with the internal aft divergence conical surface formed as bearing surface either flat or curved, against which propellant forces act, in use, to give the projectile forward motion, the boattail portion and the internal divergence surface making an acute trailing edge angle up to 15 , and the internal and external inlet surfaces of the forward compression section making an acute leading edge angle in the range from 10 to 150 with the bisector of said leading edge, angle being substantially parallel to the longitudinal axis of the projectile.

2. A projectile as claimed in Claim 1 wherein the leading edge angle is substantially 150.

3. A projectile as claimed in claim 1 or claim 2, wherein said boattail portion and said internal divergence surface make an acute trailing edge angle having a value within the range of from 8" to 150.

4. A projectile as claimed in claim 3, wherein said acute trailing edge angle is substantially 140.

5. A projectile as claimed in claim 4, wherein the boattail surface and internal divergence surface are respectively inclined at substantially 100 and 4" relative to the longitudinal axis of the projectile.

6. A projectile as claimed in any one of claims 1 to 5, wherein said area ratio is substantially 1.44:1.

7. A projectile as claimed in any one of claims 1 to 6, wherein said throat length to diameter ratio is substantially 1.95:1.

8. A projectile as claimed in any one of claims 1 to 7, wherein said propulsion surface has a width relative to the maximum thickness of the throat portion defined by a width to thickness ratio within the range or from .150:1 to .250:1.

9. A projectile as claimed in claim 8, wherein said width to thickness ratio is substantially .167:1.

10. A projectile as claimed in any one of claims 1 to 9, wherein the ratio of maximum thickness of the throat portion to the external maximum diameter is in the range of from .10:1 to .20:1.

11. A projectile as claimed in claim 10, wherein said ratio of maximum thickness of the throat portion to the external maximum diameter is substantially .167:1.

12. A projectile as claimed in any one of claims 1 to 11, wherein the ratio of the maximum thickness of the throat portion to throat internal diameter is in the range of from .15:1 to .35:1.

13. A projectile as claimed in claim 12, wherein said ratio of maximum thickness of the throat portion to the throat internal diameter is substantially .250:1.

14. A projectile as claimed in any one of claims 1 to 13, wherein the ratio of the length of the projectile to the external maximum diameter is in the range of from 2.5:1 to 4.0:1.

15. A projectile as claimed in claim 14, wherein said ratio of the length of the projectile to the external maximum diameter is substantially 3.0:1.

16. A supersonic low draC proiectile substantially as described herein with reference to Fig. 7, or Fig. 8, or Fig. 9, or Fig. 10, of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Cartridge and tubular projectile combinations have long been known in the state of-the-art. United States Patents 2,433,334 and 3,621,781 are examples of tubular projectiles combined with cartridges and various types of propellant to form a round of ammunition. U.S. Patent 2,433,334 also includes provision for a combustible obturator. What has been lacking in the past and recent state-of-the-art is a tubular projectile design which, when launched from a gun barrel at sufficiently high velocity, will actually achieve low velocity decay because of the combination of low drag shaping and relatively high projectile mass and have a shaping geometry and mass which will produce significant damage upon target impact.Our design accomplishes these goals, which have been long saught for by many and claimed by some, but until our invention never actually proven until demonstrated by us and based on a substantial depth of experimental data. WHAT WE CLAIM IS:

1. A supersonic low drag projectile comprising a tubular structure defining an internal forward continuous converging conical surface, an internal elongate throat body section of substantially constant cross-sectional shape and area throughout its length and an internal aft continuous diverging conical surface, the ratio of the internal throat length to the internal diameter of the throat section lying in the range of from 0.5:1 to 2.5:1, the ratio of internal inlet area of the projectile to internal crosssectional area of the throat section lying in the range of from 1.3:1 to 1.6::1, said projectile being boattailed on the exterior of the aft divergence section thereof and its junction with the internal aft divergence conical surface formed as bearing surface either flat or curved, against which propellant forces act, in use, to give the projectile forward motion, the boattail portion and the internal divergence surface making an acute trailing edge angle up to 15 , and the internal and external inlet surfaces of the forward compression section making an acute leading edge angle in the range from 10 to 150 with the bisector of said leading edge, angle being substantially parallel to the longitudinal axis of the projectile.