US3745926A - Sabot spin-stabilized projectile - Google Patents

Abstract

In a preferred embodiment, a sabot-type spin-stabilized artillery projectile tapering from a pointed nose to a largerdiameter body of columnar shape continuous with a flare base of circular cross-section, the flaring base flaring preferably at a flare angle of between about 4.5* to about 9*, the length of the flaring base as measured along the projectile''s longitudinal axis ranging from preferably about 8 to about 22 percent of projectile length, where the length of the projectile ranges from about 8 to about 12 calibers with a body diameter (of the columnar shape) of about 0.8 to about 3 inches - where a ''''caliber'''' is the diameter of the columnar body.

Description

ilmted States Patent 1 1 1111 3,745,926 Mertz et al. 1 July 17, 1973 SABOT SPIN-STABILIZED PROJECTILE 3,566,528 3 1971 Musser 102 92.1

34,285 1 1s 2 M r [75] Dale R Mel; Ame! bmh 3,662,686 siw z laa ifiiii i i ii i i Assignee:

Filed:

of Dover; Edmund W. Falkowski,

Port Jervis, all of NJ.

The United States of America as represented by the Secretary of the Army, Washington, D.C.

June 21, 1971 Appl. No.: 154,797

Primary ExaminerRobert F. Stahl Attorney-Harry M. Saragovitz, Edward J. Kelly et al. v

[S 7] ABSTRACT In a preferred embodiment, a sabot-type spin-stabilized artillery projectile tapering from a pointed nose to a larger-diameter body of columnar shape continuous with a flare base of circular cross-section, the flaring 2% 5" base flaring preferably at a flare angle of between about 93 DIG 7 4.5" to about 9, the length'of the flaring base as mea- I 0 care 2 sured along the projectiles longitudinal axis ranging from preferably about 8 to about 22 percent of projectile length, where the length of the projectile ranges [56] References Cited from about 8 to about 12 calibers with a body diameter UNITED STATES PATENTS (of the columnar shape) of about 0.8 to about 3 inches 3,401,636 9/1968 Ciccone et al l02/DIG. 7 where a caliber" is the diameter of the columnar 3,l48,472 9/1964 Hegge et a! b d 3,111,902 11/1963 Taylor 102/1 R 5 Claims, 2 Drawmg Figures fie/.1 bit )3 l6 I? r 7 91 I20 6 v Y F (1 \1 PATENTED Y 7 3.745.926

HG. I

INVENTDRS DALE H. MERTZ ALFRED A. LOEB EDMUND W. FALKOWSKI ATTORNEY SABOT SPIN-STABILIZED PROJECTILE The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION The invention relates to a sabot-type spin-stabilized projectile, such as typically may be fired from any desired or conventional artillery piece to which sabot(s) is (are) adaptable, and the projectile may be employed for either peaceful or war-like purposes, peaceful purposes including, for example, the delivery of pesticide(s), marking dye(s), as well as being utilizable in sporting and game-like events and exercises. War-like uses include the delivery typically of high explosive charge(s) and/or of an armor-piercing mass to a target area, for example.

High-velocity, kinetic-energy type projectiles can be properly classified or divided into two groups. Either they are short spin-stabilized projectiles or the long finstabilized projectiles with the advantages and disadvantages conventionally associated with each group. A projectile of four, five, or six calibers (where a caliber is the missile s diameter) in length may be satisfactorily spin-stabilized. However, for projectiles of increasing lengths above about six calibers in length, spinstabilization is less and less complete and satisfactory i.e., the accuracy becomes less and less at the target area, i.e., very poor.

SUMMARY OF THE INVENTION A primary object of the invention was to develop a spin-stabilized projectile of a configuration adaptable to longer projectiles while retaining acceptable dispersion (accuracy) at the target. It should be noted that when such a configuration is found, for that particular configuration so long as all sections lengths remained proportionately the same relative to each other, for any test being conducted it typically could be expected that the shorter projectile(s) would give test results typically and normally considered more optimal; however, such test results for a short flared base missile (of this invention) would normally be much inferior to non-flared-base conventional spin-stabilized projectiles.

It is important to have a longer length spin-stabilized projectile, if a satisfactory degree of stability can be gained, particularly for armor-piercing projectiles since the greater length means that there will inherently be a greater mass to thereby enhance the armor-piercing characteristics.

Two of the major criteria that had to be considered in any attempt to advance the state of the art are: the projectile should consistently impact a 4 square foot target area (or less) at 1,000 meters; and the velocity decrease should be no greater than 225 feet per second (fps) per 1,000 meters.

In any projectile meeting the above criteria, a number of possible variables are involved which had to be considered, accounted for, and often put-up-with to one extent or another, as compromise with opposing consideration(s) in the opposite direction. Once the projected inventive projectile was arrived at by both the use of imagination and the benefit of experience and testing, th final embodiments of the invention had to be tested under simulated and/or actual firing conditions. Typical factors involved include the Normal force coefficient, the Normal coefficient derivative, the Magnus force coefficient, the Magnus force derivative, varying embodiments for these factors, spin rate, effect of velocity, the pitching moment coefficient, the angle of attack, the center of pressure, the Magnus moment jects apparent from the preceding and following disclosure and Figures, a sabot-type projectile capable of (susceptible to) being spin-stabilized by rotaty motion imparted to a sabot enclosing the projectile at the time of firing, was provided. The projectile is further clarified by its tapering from a substantially pointed nose to a columnar body of predetermined larger diameter (larger than the nose) which columnar body extends axially rearwardly to and is continuous with a flared base extending rearwardly from about the columnar body for an additional predetermined portion of the projectiles length, and the flaring surface being of substantially circular cross-section and of a predetermined angle of flare. Preferred embodiments serve to further enhance the accuracy (lack of dispersion) for a given (particular) long spin-stabilized projectile of this invention. As contrasted to a comparative control fin stabilized conventional projectile having a known im pact point of about 5 feet (at times) from the aiming point, the reduced pitch rate of the inventive projectile could result in an impact point of about 2 feet from the aiming point, based on the known fact of the reduced pitch rate of the inventive projectile. Such, for example, would be a clear and distinct major advance in the art, achieving considerably greater accuracy for spinstabilized long-length projectiles. Other typical evidence of improvements of varying embodiments are discussed in the following disclosure.

THE FIGURES FIG. 1 is a side elevation view of a typical projectile of the invention.

FIG. 2 is a side elevation view of a second typical embodiment-projectile of the invention, illustrating the inventive combination with the sabot shown in section extending along a longitudinal axis of the projectile and the sabot.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Although there may be intermediate subsections constituting a part of the columnar body section, for example the toothed subsection 1 (la & lb) of FIG. 1, and there may be typically a minor additional receding portion, or the like, as a final part of the base such as the receding section 2 of FIG. 2, the inventive projectile of this invention is composed of three basic sections. In particular, those sections are the nose section 3 or 3a, the intermediate columnar section 4 or 4a, and the third terminal-base section 5 or 5a. However, as noted above, there may be additional minor sections such as, for example a receding or columnar or conical or ogival section such as the section 2, orsome intermediate section, provided it does not amount to a major alteration in the shape such as to significantly alter the performance of the inventive projectile. Although the nose section 3 may vary in its shape in accord with desired and/or conventional shapes, a preferred shape is illustrated in each of FIGS. 1 & 2; in any event, the nose section is a conical (as defined below) and tapered shape, tapering from the substantially pointed nose to a larger-diameter projectile body 4 of substantially columnar shape extending aftly (rearwardly) toward the third terminal-base section 5, the latter base section enlarging to a greater diameter by virtue of flared outer walls 5 of substantially circular cross-section i.e., not mere flared pins, this inventive projectile having no fins but having substantially the entire circumferential surface-walls enlarging substantially consistently in diameter. The term conical is intended to include shapes such as a conventional cone and also such as an ogival shape, for example. Although the extent to which the flared walls (of the third section) increase in crosssectional diameter may vary as the flare extends from the beginning of the third section to rearwardly (toward the base), at least the overall flare is such as to define an average flare angle 8 relative to the longitudinal axis 6 of the projectile; thus the surface may be slightly curved, i.e., substantially straight, in forming the flared section, or may be preferably completely straight such as illustrated in each of FIGS. 1 and 2. The substantially straight surface, the average thereof being considered to extend along a substantially straight second axis 7, defines the flare angle 8, with the second imaginary axis lying in a longitudinal plane common to the longitudinal axis 6 of the projectile.

The projectile of FIG. 1 additionally illustrates toothed subsections la and lb, having a plurality of teeth such as tooth 9 or 9a, each of the teeth preferably being angled rearwardly at least the forward face being such that air turbulences are substantially avoided when the missile (projectile) is in flight, and such that a sabot such as sabot 10 may impart thrust to the projectile. The illustrated sabot 10 has a snugly-fitting body ll encasing the projectile and having meshing sabot teeth 12a interlocked with teeth 9a.

In FIG. 2, although a particular'sabot is illustrated, any conventional type of releasable sabot may be employed as a part of the combination. For the illustrated sabot, typical conventional parts thereof are: sleeve 13; the rotating band 14 (so-named because the barrelbore spiral grooves impart a rotary motion to it, and to the entire remaining portions of the sabot to which the rotating band is non-rotatably fixedly attached); the obturator 15; the rear thruster 16; the projectile support structure 18; the boot 19; and the centering band 20. Also there is the base section 17.

Broad ranges normally are as follows. The flaring surface continues to flare for a distance, as measured along the projectiles longitudinal axis 6, ranging from about 7 percent to about 30 percent of the projectiles length which for an artillery piece normally ranges from eight calibers to 14 calibers. In this disclosure, one caliber arbitrarily equals the diameter of the intermediate columnar body section; typically, the diameter caliber is about l.65 inches in models tested as discussed hereafter below. The diameter of the projectile, for an artillery piece to fire the encasing sabot, ranges normally from about 0.5 inches to about 5 inches. The length of the nose section, as measured along the projectiles longitudinal axis, normally ranges from about 25 percent to about 50 percent of the projectiles length, as measured along the projectiles longitudinal axis. The flare angle, as defined above, normally ranges between about 2 to about 10.

In preferred embodiments, the flaring surface extends along the projectiles axis for from about 8 percent to about 22 percent, and the nose section from about 35 percent to about 43 percent; the projectiles length ranges from about 8 to 12 calibers, the diameter ranges from about 0.8 inches to about 3 inches, and the flare angle ranges from about 45 to about 9.

The testing of the various influencing factors determining the above stated dimensions, ranges, shapes, angles of flare, and the like, was carried out in two separate phases, a set of preliminary tests to determine whether further development should be undertaken, and the thereafter more extensive tests in the further development.

In the preliminary tests i.e., the first phase, wind tunnel tests were performed on a number of configurations in order to verify the optimal shape and dimensions, etc. The data from these tests along with estimates I of other aerodynamic coefficients were then used in a computer analysis to help determine the optimal configurations. From the data at hand, further preliminary investigation was carried forth on two models, designated in this disclosure as model A & model C, the model A being a projectile generally similar in appearance to that of FIG. 1 and having a projectile length of about 10 calibers, a nose section of about 3.76 calibers, a flared section extending l caliber along the projectiles longitudinal axis, and a flare angle of 6, and the model C being also of similar appearance but of dimensions of about 12.8 calibers projectile length, 2.2 calibers flare-section length, the same nose-section length, and also 6 degrees flare angle, however subsequent models having different flare angles as noted for particular tests discussed hereafter. The further investigations included wind tunnel tests as well as range firings. Utilizing the coefficients and physical parameters thus obtained, 6-of-freedom trajectories were computed. A standard trajectory was obtained, with no initial disturbances, for an impact point at 1,000 meters. The muzzle velocity for the flared base projectiles of the invention was 5,000 fps, while for a control finned projectile, a 4,800 fps muzzle velocity was employed.

Of the two flared-base projectiles, the model A most nearly approached the simulated performance of the control. It was significantly noted that for model A as compared to model C for which the angle of attack increased steadily as the projectile flew downrange, the model A increase in attack was almost insignificant at 007 at 1,000 meters as compared to the model C at 3 at L000 meters. Also it was noted that the velocity drop (decrease) of model A was less than for the control and for the model C. Also, from the results of the dispersion analysis, the angle of yaw build-up, and the velocity drop, the model A appeared to be the expected superior configuration, but with model C significantly being satisfactory. It is believed also that the flared shape of model A & C would result in less initial disturbance at the muzzle than for the control finned-missle, and as indicative of a pitch rate of 10 rad per sec., the control at times landed (impacted) at 5 feet from the aiming point; accordingly, if the inventive flared-base projectile due to its shape and spin only receives a 2 rad per second pitch rate at the muzzle, then its impact point would be a mere 2.2 feet from the aiming point. This would mean that a longor spin-stabilized projectile of the invention would be at least as good as the same long tin-stabilized projectile in its accuracy (lack of dispersion) this being in definite contrast to prior art spin-stabilized projectiles which lacked accuracy at longer lengths of the projectile.

Although conclusions may be drawn from various test data, many of the observations are consistent with what was expected insofar as typically shorter projectile lengths, for example, being for any particular design more optimal normally, the relevant observations and/or conclusions are not so much what is optimal and what is not optimal, but rather is whether for the greater length projectiles the many factors listed previously are nearly enough optimal or at least not fatal as to permit greater projectile lengths of the particular configuration of spin-stabilized projectile while having an acceptable stability and while thereby having a low dispersion (i.e., an acceptably high accuracy).

Typical conclusions from the preliminary data are as follows. The gyro stability for the model A at 2.1 is superior to that of model C at 1.6, but the 1.6 being acceptable. The decrease in velocity of the flared base models proved to be as good as (lack of decrease) the control, at 1,000 meters, the drop (decrease) being about 200 fps. Although the flared base models appeared to have a higher pitch rate, the negative effect on dispersion appeared to be more than compensated for by the lower disturbances at the muzzle for the flared base models (as compared to finned missiles), to give a lower overall dispersion.

in the second phase of tests, wind tunnel tests were performed at Mach numbers 4.0, 4.5 and 5.0 at angles of attack from 4 to The models consisted of varying projectile lengths of 8, l0 and 12.8 calibers, and for each of these some were absent (without) the flaring walls while others had flares of 4, 6 and 8 and with the flaring sections extending lengths of 1 and 2 calibers (along the projectiles longitudinal axis). A finned control was of a total length of 12.8 calibers. Such configurations were tested with'threads (teeth) and others without teeth (i.e., smooth) in the intermediate body section. For any comparative tests, the compared missiles had about identical body-section diameteis. Some of the projectiles tested were tested with reverse spin and others with forward spin. Thereafter, a

-of-freedom trajectory analysis was performed for two configurations and the influence coefficients determined.

T'he wind-tunnel test procedure was as follows. For each configuration, flow was established at the desired Mach numbers and zero degrees of attack; air was supplied to the models by an internal air motor and the model was rotated to approximately 50,000 rev/min.; the pens were dropped onto the x-y recorders and the model was allowed to coast to zero rpm. The procedure was repeated for all configurations at Mach numbers 4.0, 4.5 and 5.0 at angles of attack of 10, 8, 6, 4, 2, 0, -2 and 4; anexception was the rotation of the finned control to a maximum of 5,000 to 6,000 rpm.

To have an appreciation of conflicting factors, it is significant to note some of the following facts: for the control and all models, an increasing slope of the Normal force and pitching moment curves with increasing angle of attack and the constant center of pressure vs.

angle of attack; similarly Magnus coeflicient curves increased up to about 6-8 of attack; the Magnus force coefficient derivative decreases with increasing Mach numbers, while the center of pressure moves toward the nose; for the same flare, the Magnus force coefficient derivative increases with increasing body length and the center of pressure again moves toward the nose; in contrast, the Normal force coefficient derivative increases with increasing flare angle for the same flare length and body length, and the Normal center of pressure moves toward the base (away from the nose) with increasing flare angle. in further contrast, the Magnus force coefficient derivative decreases with increasing flare angle for the same flare and body lengths, and the Magnus center of pressure moves toward the nose as the flare angle increases. Although the Magnus center of pressure for bodies of opposite spin are approximately the sarne, the Magnus center of pressure for the smooth bodies tends to be closer to the base.

A 6-of freedom dispersion analysis showed that the inventive flared base models of these greater lengths are at least as good as the control in accuracy; in addition to the advantages previously pointed out, very clear advantages of the inventive flared base projectile also include greater lethality due to th higher crosssectional density delivered at the target, less sensitivity to the muzzle blasts (such as are experienced with large-finned models), and consequently better accuracy, ease of production due to its external simplicity, ease of handling and storage, and less sensitivity to damage while handling.

In a comparison of Control Y (no flare) with a model B, the following observations were made: Pitch moment slope of increase as charted against increase in angle of attack, about matched the Control at each of 4.0, 4.5 and 5.0 Mach within the range of about 2 to +2 degrees angle of attack, and also within that range the Magnus and the Normal :force center of pressure lower (as measured from th base) than the Magnus center of pressure, and with the Magnus center of pressure increasing with increasing Mach.

In a plotting of Normal force coefficient derivative against Mach numbers 4.0 to 5.0, for each of Model A (8 calibers in length), Model B (10 calibers in length),

and Model C (12.8 calibers in length), all at 1 caliber flare length, 4 flare, and identical diameters, and compared to corresponding controls without flares, th 'following results were observed. The flared models compared favorably to the controls, and the Model B was more constant than the Model C or th Model A. in a similar plotting for Magnus Force Coeflicient Derivative, the results were opposite, with the Model A being the lowest in value (best showing) and most constant as chartered against Mach, with the Model B being next best, but with Model C being acceptable; this relationship continued relatively at flare lengths of 2 calibers and a flare angle of 6.

In a plotting of Magnus force center of pressure against Mach, the Model A favorably was more constant than either of the controls or the Models B & C which were of at least acceptable values, at 1 caliber flare length and identical diameters at each of 4 and 6 flare angle, and also at 2 caliber flare length at 6 flare angle, with the Magnus force center of pressure being more constant at 2 caliber flare length (at 6 flare angle).

In a plotting of Magnus Force Coefi'icient derivative against body length, for l caliber flare length at each of 6 and 8 flare angles, the results were about the same at 6 and 8, with a slightly lower Magnus force coefficient derivative at the 8 angle, and at both 6 and 8 flare angle the Model A being of lower value than the models B & C which were of at least acceptable values; the range of about 8 to 10 calibers length appeared optimal.

In a plotting of Magnus force coefficient against projectile length, at l caliber flare length and identical diameters, and each of 4 and 6 flare angles, the Model A compared favorably to the control and was of favorably lower value, and the range of 8 to 10 calibers length appeared optimal (lower in value), but with the l2.8 appearing at least acceptable.

For each of Models A, B, C, i.e., 8, l and 12.8 caliber projectile lengths, at identical diameters (of the intermediate body-section), at l caliber flare length, in a plotting of each of: (a)" Normal Force Coefficient Derivative, (b) Normal Force Center of Pressure, (c) Magnus Force Coefficient Derivative, and (d)" Magnus Force Center of Pressure, as plotted against flare angle, the results were as follow:

a. projectile length of Model A, and flare angle 4 and projectile length of Models ranging from 8 to calibers (i.e., A & B) appeared optimal; 12.8 (C) appeared acceptable;

b. projectile length A at 4 flare angle and range of 4 to 6 flare angle appeared optimal; B & C appeared acceptable;

c. projectile length A at 8 flare degrees and a flare angle range of 6 to 8 appeared optimal, with B & C being at least acceptable at these angles; and

d. projectile lengths of Model A & B (i.e., 8 to 10 calibers) in a flare angle range of 4 to 6 appeared optimal, with C appearing at least acceptable.

The above and other tests results and interpretations are not intended to unduly restrict the scope of the invention, but serve to at least illustrate some of the bases for and/or the support for the choice(s) of model configuration and ranges. Similarly, it should be noted that although the particular models illustrated in FIGS. 1 and 2 are preferred, such are nevertheless only illustrative of and not limiting on the broad scope to which applicants are entitled insofar as obvious substitution of equivalents, equivalent parts, and obvious modification(s) within the scope of the invention.

we claim:

1. A projectile device comprising a projectile and means thereon engageable with spiral launcher grooves during launch to rotate said projectile for spinstabilization thereof during flight, said projectile having a longitudinal imaginary axis, said projectile along said axis including three serially consecutive substantially continuous sections of differing outer-surface shapes comprising a first nose section, a second intermediate section, and a third terr'ninal'base section, said nose section being conical and tapering from a substantially pointed nose to a predetermined larger projectile-body diameter, which ranges from 0.5 inch to 5 inches, said second intermediate section being a body section of substantially columnar shape, and said third terminal base section including a flared substantially straight surface along an imaginary axis in a longitudinal plane common to said longitudinal axis, said surface being of a substantially circular cross section and flaring from about an aft end of said intermediate section rearwardly to about a terminating point of said base section, said flared straight surface defining a flare angle relative to said longitudinal axis ranging from about 2 to about 10, the overall length of said projectile being at least 8 calibers of said projectile-body diameter, said flaring surface being about 7 percent to about 30 percent of said projectile length as measured along said longitudinal axis.

2. A projectile device according to claim 1, wherein said projectile rotating means comprises a spinimpartable sabot mounted on said projectile.

3. A projectile device according to claim 1, in which said nose section is about 25 percent to about 50 percent of said projetile length as measured along said longitudinal axis.

4. A projectile device according to claim 3, in which said angle ranges from about 4.5 to about 9, in which said flaring surfaces axial measurement ranges from about 8 percent to about 22 percent of said projectile length as measured along said longitudinal axis, and in which said nose section is about 35 percent to about 43 percent of said projectile means length as measured along said longitudinal axis.

5. A projectile device according to claim 1, in which said body section includes a plurality of teeth extending annularly around said body section thereby providing a substantially circular cross section arranged consecutively along said longitudinal axis and engageable with meshable teeth of a sabot such that a sabots thrust is transmittable to said projectile means, and in which said projectile rotating means includes a spinimpartable sabot having a plurality of serially arranged teeth meshable and engageable with said body section 's teeth.

* i I t

Claims (5)

1. A projectile device comprising a projectile and means thereon engageable with spiral launcher grooves during launch to rotate said projectile for spin-stabilization thereof during flight, said projectile having a longitudinal imaginary axis, said projectile along said axis including three serially consecutive substantially continuous sections of differing outer-surface shapes comprising a first nose section, a second intermediate section, and a third terminal base section, said nose section being conical and tapering from a substantially pointed nose to a predetermined larger projectile-body diameter, which ranges from 0.5 inch to 5 inches, said second intermediate section being a body section of substantially columnar shape, and said third terminal base section including a flared substantially straight surface along an imaginary axis in a longitudinal plane common to said longitudinal axis, said surface being of a substantially circular cross section and flaring from about an aft end of said intermediate section rearwardly to about a terminating point of said base section, said flared straight surface defining a flare angle relative to said longitudinal axis ranging from about 2* to about 10*, the overall length of said projectile being at least 8 calibers of said projectile-body diameter, said flaring surface being about 7 percent to about 30 percent of said projectile length as measured along said longitudinal axis.

2. A projectile device according to claim 1, wherein said projectile rotating means comprises a spin-impartable sabot mounted on said projectile.

3. A projectile device according to claim 1, in which said nose section is about 25 percent to about 50 percent of said projetile length as measured along said longitudinal axis.

4. A projectile device according to claim 3, in which said angle ranges from about 4.5* to about 9*, in which said flaring surface''s axial measurement ranges from about 8 percent to about 22 percent of said projectile length As measured along said longitudinal axis, and in which said nose section is about 35 percent to about 43 percent of said projectile means'' length as measured along said longitudinal axis.

5. A projectile device according to claim 1, in which said body section includes a plurality of teeth extending annularly around said body section thereby providing a substantially circular cross section arranged consecutively along said longitudinal axis and engageable with meshable teeth of a sabot such that a sabot''s thrust is transmittable to said projectile means, and in which said projectile rotating means includes a spin-impartable sabot having a plurality of serially arranged teeth meshable and engageable with said body section''s teeth.

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