US3846878A

US3846878A - Method of making an underwater projectile

Info

Publication number: US3846878A
Application number: US00101431A
Authority: US
Inventors: F Monson; K Mueller
Original assignee: AAI Corp
Current assignee: Textron Systems Corp
Priority date: 1968-06-04
Filing date: 1970-12-24
Publication date: 1974-11-12
Anticipated expiration: 1991-11-12

Abstract

An efficient underwater projectile is disclosed having a frustoconical nose end, a long thin shank and a shroudless, stepped parallel side wall finned rear section with a forward facing abrupt shoulder formed thereon between two parallel longitudinal edge surfaces, the forward edge surface terminating at a sloped edge surface connecting with the shank, and the fins being joined at the shank body by a rearwardly tapered body section with triangular tapered and rearwardly inwardly sloping outer separation surfaces between the fins.

Description

United States Patent Monson et al.

[ 1 Nov. 12, 1974 METHOD OF MAKING AN UNDERWATER PROJECTILE [75] Inventors: Franklin A. Monson, Glen Arm;

Kenneth E. Mueller, Baltimore, both of Md.

[73] Assignee: AAI Corporation, Corkeysville, Md. 22] Filed: Dec. 24, 1970 [21] Appl. No.: 101,431

Related US. Application Data [62] Division of Ser. No. 734,291, June 4, 1968.

[52] US. Cl. 29/12 [51] Int. Cl B21k 21/06 [58] Field of Search 29/12, 1.22

[56] References Cited UNITED STATES PATENTS 1,131,973 3/1915 White 29/1.2

2/1919 Hawkins 29/12 8/1944 Bardell ..29/1.2

Primary E.taminer-Francis S. Husar Assistant Examiner-Leon Gilden Attorney, Agent. or FirmReginald F. Pippin, Jr.

[57] ABSTRACT An efficient underwater projectile is disclosed having a frustoconical nose end, a long thin shank and a shroudless, stepped parallel side wall finned rear section with a forward facing abrupt shoulder formed thereon between two parallel longitudinal edge surfaces, the forward edge surface terminating at a sloped edge surface connecting with the shank, and the fins being joined at the shank body by a rearwardly tapered body section with triangular tapered and rearwardly inwardly sloping outer separation surfaces between the fins.

1 Claim, 5 Drawing Figures In the prior art, various projectile arrangements have been employed for underwater ammunition, the most common being spear gun projectiles and shot shell power heads, as well as combined shot shell and spear projectiles. Such prior configurations have been substantially less than fully effective, due to such deficiencies as cumbersome size, limited velocity, limited effective range and small terminal energy for target penetra- Still other objects, features and attendant advantages will become apparent to one skilled in the art from a reading of the following detailed description of a single preferred embodiment constructed according to the invention, taken in conjunction with the accompanying drawings wherein:

FIGS. 1 and 2 are perspective views of a flechett projectile according to the invention.

FIG. 3 is a fragmentary longitudinal side view of the rear section projectile of FIGS. 1 and 2, showing its stabilizing fin construction.

FIG. 4 is a rear end view of the underwater projectile of FIGS. 1 and 2.

FIG. 5 is a viewof the projectile during manufacture, and showing the fins in full line prior to final formation, and the broken line in the final configuration of FIG. 3.

Referring now in detail to the Figures of the drawings, the projectile 11 includes a cylindrical shaft or shank 13 having a frusto-conical nose section 15 with a flat tip end 15a, and a stabilizing tail section including canted stabilizing fins 17 each having parallel

opposite side walls

17k, 17k.

The overall length B of the fins 17 is approximately four shaft diameters and the overall length A of the frusto-conical nose section 15 is approximately three and one-half shaft diameters.

The four stabilizing radial fins 17 are integrally formed with the shank 13, as by hot or cold metal working of the shank body to form the desired configuration, as through the medium of a suitable forming die, to an initial configuration as shown in full lines in FIG. 5, with the curved outer edge 17f of the fins resulting from the amount of material disposed from the shank cylindrical blank into the fin formations when the die is pressed in to form the substantially flat or concave triangular rearwardly and inwardly tapered connecting surfaces 17g between'the fins l7t. Surface grinding of t the radially outer surface of the fins is employed to effect the desired intermediate and rearward radial surface final configuration as shown at 17a, 17b, 17c in FIGS. 3 and 5. Each of the respective parallel-walled fins is preferably canted at an angle of approximately 2 with respect to the longitudinal axis of the shank 13. It will be appreciated that the canted fins l7 contribute to trajectory accuracy by imparting spin to the projectile, whereby for a given yaw angle the canted fin projectile dispersion is helical and has a smaller radius of error dispersion than that which would be obtained by a straight finned configuration with a uni-directional dispersion. The fins 17 are formed by the initial die forming step with an inclined forward face 17d. The intermediate forward-reduced span or diameter section having a radially outer surface 17a of substantially constant diameter and the enlarged span or diameter rear section having its radially outer surface 170 also of sub stantially constant span along its length areinitially die formed and then surface ground as discussed above. At

the longitudinal junction of reduced span section 17a and enlarged diameter rear section 170 of each fin is radially extending forwardly facing flat surfaced shoulder 17b which is also formed by surface grinding, preferably during the grinding of the radially outer surfaces 17a and 17c. The diameter of the larger diameter rear constant diameter surface 17c substantially equal to approximately one and one-fourth to one and two-fifths diameters of the shaft or shank l3, and the smaller'diameter intermediate surface is approximately one and one-tenth to one and one-fifth shank diameters, the depth of the shoulder 17b being approximately onetenth to one-fifth shank diameters.

The cone angle of the frusto-conical nose section 15 is 10 (:1), included, and the flat tip end 15a of the frustum is approximately .30 to .35 of the diameter of the shaft or shank 13. V

The overall length of the projectile is equal to between 30 and 43 shaft diameters, with a preferred length of 43 diameters for minimum desired muzzle velocity of approximately 700 to 750 feet per second and associated launching propellant chamber pressures.

In one illustrative and preferred embodiment in which the shaft diameter is .100 inch, the shoulder has a depth of .010 inch, and the outer diameterof the rear fin surface 170 is .131 inch. Also, in this particular preferred embodiment, the projectile shank 13 is formed of tungsten, the overall weight being grains, and the overall length being 4.3 inches, with a frustrum cone angle of 10 and a tip diameter of .030 inches.

In operation, the launching velocity of the projectile is preferably near that of atmospheric pistol ammunition, being approximately 700 to 750 feet per second, and whereas drag forces render atmospheric bullet shapes and other fiechette shapes ineffective in very short ranges under water, the present projectile is far superior in its range capability under water. The high mass per frontala'rea and specific nose and tail proportions contribute mutually to an efficiently low coefficient of drag, and the stability of the projectile flight is also maximized by the same balance of proportions.

Prior copending application Ser. No. 650,374 filed June 30, I967 illustrates an ammunition arrangement through the medium of which similar, but shroudless shouldered finned underwater projectile is launched. A similar ammunition arrangement may be employed for launching the shroudless, shouldered finned underwater projectile according to the present invention.

In operation, as the projectile flies through the water the flat frustrum tip area 1521 separates a bulk of water normal to the trajectory, creating a cavitation envelope of specific shape and length relative to the instant projectile velocity and depth-The instantaneous cavitation envelope for velocities up to approximately 700 feet per second and depths up to 90 feet has an effective length extending well back of the rear finned section 17 of the projectile 11, and may be of a length up to several times the projectile length, dependent upon depth and instant velocity, before pressure can close the cavity. The cavity is difficult to precisely measure and define in structural contents; however, evidence indicates that the forward area of the envelope surrounding the projectile body is composed of water vapor of varying density levels, the density gradient increasing at a high rate of change from the zone immediately adjacent the projectile body to the zone at the edge of the cavitation envelope, and the lines of equal vapor density extending in something of an arcuate form from the zone of the flat tip a in a generally convex form along the length of the projectile and the remainder of the envelope rearwardly to the zone of closure where larger water droplets are forced into the envelope zone. It has been found that the density gradient of the water vapor increases so rapidly from the zone adjacent the projectile body that small increases of tail fin diameter or projectile length, with respect to shaft diameter, cause very large increases in drag with resultant decrease in velocity and effective range and terminal energy of the projectile. The tail configuration 17 raises a stabilizing force from collision with the vapor within the cavitation envelope, and as the water vapor thus exerts a drag force on the tail section at the same time, it will be appreciated that the tail section must be formed with the concept of minimizing contact with water vapor while insuring sufficient stabilizing force to accomplish stability or projectile flight. With the foregoing mentioned configuration and relative dimensions and weights, for muzzle velocities of approximately 700 feet persecond and depths up to 90 feet, the projectile is nearly free of boundary layer drag forces over its effective range except for the area of the frustrum flap tip end 15a, and the very minute drag force exerted on the tail section 17 by the low density water vapor in the central zone of the cavitation envelope cross section. The area of the flat tip end 15a is optimized for minimum drag and desired cavitational envelope vapor impingement for stability control on the tail section 17, a frustrum tip end 15a of smaller proportion producing erratic flight with severe yaw resulting in negligible effective range, whereas increase in the proportions of the flat tip end 15a results in higher drag forces at this zone, which also decreases the effective range. In addition, it has been found that increases in the cone angle of the nose section 15, and/or the outer diameter of the fins 17 also results in higher drag forces which decrease the effective range, as will be apparent from considerations of the rapid radial increase in vapor density of the water vapor within the cavitation envelope. While use of a shroud as disclosed in application Ser. No. 650,374 effectively minimizes yawing and increases flight accuracy of the projectile the shroud'also reduces velocity materially more than the present invention, particularly due to the inherently larger frontal and surface area of the shroud and the drag resulting from axially vectored impingement of the water vapor particles on this large frontal and outer surface area. The present intermediate shoulders l7b between thetwo constant diameter surfaces 17a, 17c on the fins 17 have surprisingly been found to be substantially equivalent in reducing and have resulted in further increased accuracy, apparently due largely to the materially less drag, and higher terminal velocities or longer effective range for a given initial velocity than that of the prior shrouded finned projectile. Further, while the shrouded projectile of Ser. No. 650,374 is quite satisfactory in shallow depths, this shrouded projectile has inadvertently decreased accuracy as water depth increases, and the present shroudless stepped shouldered. finned projectile has been found to afford materially better accuracy at increased depths than the shrouded projectile, due to its decreased prior shrouded finned projectile.

It has further been foundthat reduction of the overall length relative to diameter and tip end area results in less momentum with proportionate loss in effective range, unless the launching velocity is increased inversely proportionate to the length reduction. In this respect, the preferred length of the overall projectile 11 has beenfound'to be 43 diameters, and by a sacrifice of higher launching velocities and associated higher chamber pressures the length of the projectile has been successfully varied down to a length of 30 shaft diameters. It will, of course, be appreciated that such requirement for higher launching velocities and associated higher firing chamber pressures for launching the projectile'put severe requirements upon the weight and strength of the launching ammunition arrangement and/or barrel with consequent increase inbulkiness and the weight of the equipment and decrease in efficiency of power utilization.

It has been found that the terminal efficiency of the remaining energywhen the projectile is at a 30 foot range, which is the general visibility range in shallow water of up to 3 foot depth, equals normally better than approximately one-half that of the energy of the projectile at the launch location, and produces penetration force concentration of an extreme degree over a distance equal to and beyond this 30 foot visibility range.

- At the 90 foot depth the terminal efficiency of the remaining energy is about 25 percent of that of the launch location energy of the projectile, with consequent lesser but effective penetration force.

It will accordingly be appreciated that the critical interrelation of the various parameters of the projectile are effective overall to provide a highly desirable and useful underwater projectile which may be effectively used by underwater fishermen, divers, etc., with good results within the operating ranges of visibility in water depths up to feet, and using launching velocities conventional to atmospheric pistol ammunition in the vicnity of 700 feet per second.

While the invention has been described with respect to a single illustrative and preferred embodiment, it will be apparent to those skilled in the art that various modifications may be made without departing from the scope and spirit of the invention. Accordingly it is to be understood that the invention is not to be limited by the illustrative embodiment, but only by the scope of the appended Claims.

That which is claimed is:

l. The method of making an underwater projectile comprising:

forming a cylindrical shaft having opposite flat ends,

surface grinding the radial surfaces of the fins to a first substantially constant radius at all longitudinal points along a rearward section of said fins,

and surface grinding the radial surfaces of the fins to a second smaller radius substantially constant along a forward section of said fins while grinding a forwardly facing shoulder on each of said fins and adjoining said rearward and forward different constant radii sections.

Claims

1. The method of making an underwater projectile comprising: forming a cylindrical shaft having opposite flat ends, taper-grinding at one end of said shaft to a degree sufficient to leave a flat blunt end whereby said one end is frustoconical and flat-ended, impact die forming the opposite end of said cylindrical shaft by impact in a forming die and thereby working the cylindrical shaft material into a convex finned shape with the fins extending radially beyond the shaft diameter with the connecting shaft body being rearwardly inwardly tapered from the beginning to the ends of the fins, surface grinding the radial surfaces of the fins to a first substantially constant radius at all longitudinal points along a rearward section of said fins, and surface grinding the radial surfaces of the fins to a second smaller radius subsTantially constant along a forward section of said fins while grinding a forwardly facing shoulder on each of said fins and adjoining said rearward and forward different constant radii sections.