US2939318A - Apparatus for the determination of interior ballistics - Google Patents

Description

June 7, 1960 E. L. ARMI ETAL 8 APPARATUS FOR THE DETERMINATION OF INTERIOR BALLISTICS Filed May 26, 1953 i 2 Sheets-Sheet 1 INVENTORS EDGAR L. ARM! JAMES 1.. JOHNSON mama/v0 c. MAOHLER NORMAN E. POLSTER (Q. BWW ATTORNEYS June 7, 1960 E. L. ARMI ETAL 2,939,318

APPARATUS FOR THE DETERMINATION OF INTERIOR BALLISTICS Filed May 26, 1953 4 2 Sheets-Sheet 2 Illlll lll lllll\l ly l lllllll lillllll FIG. 5

DEGREES CENTIGRADE Tmve' in inches .25 1.0 3.0 I 54 .2: .50 L0 L5 2.0 31:49 so 54 Travel in inches 35 milliseconds L6 milliseconds INVENTORS EDGAR L. ARM! JAMES L. JOHNSON R Y MAOHLER ing X1 POLSTER States Patent APPARATUS FOR THE DETERMINATION OF INTERIOR BALLISTICS Edgar i. Armi, Santa Monica, cans, and James L. Johnice detailed description when considered in connection with son, Upper Darby, Raymond C. Machler, Philadelphia,

and Norman E. Polster, Southampton, Pa., assignors, by mesne assignments, to the United States of America 'as represented by the Secretary of the Navy Filed May 26, 1953, Ser- No. 357,468

3 Claims. (Cl. 73-167) This invention relates to an apparatus for determininginterior ballistic characteristics of a projectile and more particularly to a method and apparatus for accurately ascertaining the interfacial temperature changes induced by a bullet fired through a gun barrel bore.

Heat measurement apparatus and a method for determining frictional interfacial temperature between a bullet and a gun bore utilizing a freely falling Weight apparatus were disclosed in copending application Serial No. 295,624, filed June 26, 1952.

Advances in the ordnance art have necessitated accurate ballistic studies into the hitherto unknown variables inherent in propelling a projectile, in order to incorporate in a gun design compensating factors which will provide for greater accuracy. Interior ballistics relating particularly to the heat increment resulting solely from the frictional resistance between the periphery of a bullet and the lands and grooves of the rifling within the bore have not been determined accurately. The conventional ballistic tests produced a resultant temperature which included the summation of the heat input resulting from the frictional resistance from the propelled bullet, the heat input from the hot expanding powder gases, and other possible incidental heat from radiation, convection, and conduction. Furthermore, it is desirable to be able to determine accurately the individual contribution by each of the variables to the totalheat input and how the factors vary at determinable stages. Therefore, the present invention contemplates providing an accurate means for determining that heat increment of the summation of the total heat which is the effect produced 'solely by the frictional contact between the projectile periphery and the gun barrel. Furthermore, this inventionwill provide a means for measuring the temperature at the interfaces between the'projectile and the gun bore at predetermined intervals as the projectile is accelerated through the gun barrel bore during actual firing with actual powdercharges as distinguished from simple impact testing.

The present invention has as an object to provide an apparatus for accurately determining the frictional heat generated by a projectile passing through the gun barrel during actual firing. 1

Another object of this invention is to provide means for determining frictional heat generated at specific points and intervals by a bullet as it is projected through the barrel of the gun.

A further object of the invention is to provide means for accurately determining the frictional interfacial temperature at spaced intervals of projectile passage through the bore of a gun.

Still another object of this invention is to provide a sliding thermocouple capable of indicating the electromotive forces generated during propulsion of a bullet through the gun bore after actual firing.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following the accompanying drawings wherein:

Fig. 1 is a perspective view of a test stand embodying the present invention;

V Fig. 2 is a perspective view of one form of a projectile which may be used with the invention;

Fig. 3 is a longitudinal sectional view of the embodiment of Fig. 1 wherein a bullet is shown positioned for firing and schematically illustrates an electrical circuit with an electromotive sensitive instrument therein;

Fig. 4 illustrates a photograph of the oscilloscope screen which graphically shows the vital timing intervals of the fired projectile; and 1 Fig. 5 illustrates graphically the plotted temperatures versus time and position of the fired projectile.

Referring to the drawings, in which like numerals designate the sameparts throughout the several views, and

more particularly to Fig. 1, there is illustrated a device constructed in accordance with the present invention which comprises a base 10 rigidly mounted to support the gun assembly 11. The breech end 12 of the gun is securely mounted on the base 10 affording access to the breech bolt 13 and the firing mechanism 14. A barrel 15 with conventional rifiing or of a desired bore design is mounted on the gun assembly 11. Tests conducted indicate accurate results are obtained from foreshortened barrels and the difiiculty of maintaining an insulated conductor on a rapidly traveling projectile is substantially alleviated.

An annular adapter sleeve assembly 16 is securely mounted to the muzzle end of the gun barrel 15 through insulator bushing 17. In the embodiment shown a pair of spaced parallel conductive bars 18 on sleeve assembly 16 are drilled at successive spaced intervals to accommodate a series of hardened steel wires 19 mounted in a plane normal to the axis of the barrel bore and in the path of projectile travel. However, a similar series of wires or comparable elements whether of a mechanical or electrical nature which will detect linear progression may be readily adaptable for use in conjunction with the barrel as by mounting thereon or external of the barrel for cooperation with the fired projectile. It will be readily appreciated that the severing of the wires 19 will be such as to cause imperceptible resistance to the flight of the projectile.

A bullet 20 conforming to the requisite tolerances and materials specified for the caliber gun to be used in the test is in the embodiment illustrated provided with an elongated slot 2 1 to accommodate a thermocouple lead wire 22. Securely mounted and projecting from the nose of the bullet is an elongated rod 23 which will protrude from the gun barrel 15 when the projectile is se curely seated in the breech end of the barrel. A wire severing disk 25 is mounted on the extreme end of the rod 23 and is aligned with the hardened wires 19.

A cartridge 24 containing the desired powder charge is loaded within the breech at the base of the bullet 20 after the bullet has been seated within the breech bore. A conventional firing mechanism 14 is interconnected with the firing mechanism operated sweep switch 41 which when actuated will fire the cartridge 24. i 1

It will be observed that the bullet 20 and the barrel 15 provide a sliding hot junction of a thermocouple and the lead wire 22 afixed to the bullet periphery will transmit the electromotive forces generated between the barrel 15 and the bullet 20 to a suitable indicating instru ment to be described. I

The impact received from an explosive powder charge from cartridge 24 will force the bullet assembly through the barrel 15 with a motion which is approximately a constant acceleration. Therefore, it is desirable to correlate the position and time cycle of the bullet traveling 7 after. a 7

in an accelerated path with a function of the electromotive forces generated at various positions in the gun barrel also to'obtain data for varyingpowder charges-and th re ultsfor wo s h te s us n a a t/gr m gram charge are plotted in Fig 5 and will be described'herein- Variouspyrometrid means known in the art are adaptable for recording Vtheltemperature V variations at the desiredjjintervals. However, in 'the embodiment illustrated, 'ai'cathode ray oscilloscope tube 35 is employed which willrihdicate the relative positions and the interfacialv electr'omotive forces generated by the traveling projectile, at the. respective. locations within the gun bore a a n rThe electrical circuits constituting the recording system will be designated. as the position-time circuit 40. and the telectromotive force temperature circuit 50. In the, position-time circuit 40; as the breech is bolted, a trigger operated sweep switch 41 closes the circuit 42 as the cartridge 24 is fired thereby completing the circuit 42 tothe horizontal swe'epplates 43 of the cathode ray oscilloscope. 35 through the sweep circuit energizing source 46 i Selector switch 36 is operable between the position-tirnecircuit 40 andjthe electromotive force temper-ature circuit '50 and when placed to close the positiontirne circuit. 40-the energizing current of battery 47 .Will flow from the ground 45 through the barrel 15 and the travelingwbullet assembly" and when the disk 25 at the end of rod 23 on bullet makes contact with each wire 19 in succession vertical deflections are produced on the cathode ray oscilloscope 35. A photographic record made ofthe oscilloscope screen, illustrated in Fig. 4, clearly indicates the successive wire contacts made by the disk as shown by the spaced peaks 60 relative to and measurable by spaced timing interval traces 61 which are placed on the oscilloscope screen 35. V

Inorder to determine the electromotive force temperature relationship at -the desired points within the bore 15 the selector switch 36 is placed in the electromotive force temperaturecircuit 50 (as shown by the dotted line positioned in Fig. 3) and a flexible insulated lead wire 22 is securely fastened to the periphery of a similar projectile 201in slot2 1 and the projectile is then seated .the gun barrel, bore. The free end of the lead wire 22 is passed through the bore and connected to a suitable amplifier 51. As in the position-time circuit 40 after the powder filled cartridge 24 is inserted in the breech, the bolt13 is locked and after the firing mechanism' 14 is actuated the firing mechanism sweep switch 41is closed thereby energizing the circuit 42 through the energy source 46 for the horizontal sweep circuit through plates 43,, of the oscilloscope 35. The electromotive force temperature circuit 50, which records the frictional electromotive 'force developed .at the interfacial contact between the barrel and the bullet passes from the ground 45 through the barrel15 to the sliding thermocouple which includes the barrel 15, the traveling bullet 20 and the lead Wire 22 through the amplifier 51 to influence the vertical deflecting plates 44 of the oscilloscope 35. A photographic record of the oscilloscope tube 35 will indicate the electromotive force generated during bullet propulsion through the gun barrel bore. Converting the electromotive forcevalues to corresponding temperature Obviously many modifications and variations of the present invention arerpossible in the light of thefabove teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than .as tspecifically described.

What is claimed is: i

1'; Ini aj ballistic "device fordetermining the frictional interfacial temperature between a; bullet, and the bore of a gun barrel as the bullet is. propelled therethroug h, a position-time indicator comprising; a cathode ray tube having two pairs of deflection plates disposed in' quadrature; a time trace generator connected to one of said pairs of plates, aplurality of conductive wiresconnected in parallel mounted on but insulated from said bore and spaced apart in a plane including the axis of said bore, means including a'pair of mutually spaced bars composed of electrical conducting material for supporting said wires in advance of the muzzle end of said gun barrel, an annular member composed of insulating material mounted on said gun barrel and carrying said wire supporting means for insulating said wires from the bore, an elongated rod composed of electrical conducting material and having one end thereof secured to the nose of said bullet coaxial with said bore axis, a disk composed of electrical conducting material carried at the other end of said rod in a manner such that the wires 7 lie in path of travel of said disk for progressively severvalues and; plotting them on the ordinate axis and the time-position values on the abscissa axis will present graphically a representation indicative of the interfacial temperature conditions during actual firing. Fig. 5 illustrates a combined graphical representation for test results using a 4 gram charge and an 8 gram charge. g

Various powder charges may be used to produce the desired result in propelling projectiles from guns of various calibers and theresults may be attained in a similar man er, srahq e-desc i edr ing said wires as the bullet is propelled through said bore, a gun trigger-actuated switch secured to the breech end of said gun barrel to initiate operation of said time trace generator, a voltage source connected between said plurality-of wires and one of said remaining deflection plates, and means including a conductor secured to said bullet for electrically connecting the other remaining defiectionplate to said elongated rod.

' 2,. In a ballistic device for determining the frictional interfacial temperature between a bullet and the bore of a gun barrel as the bullet is propelled therethrough, a position-time indicator comprising; a cathode ray tube having a pair of deflecting plates connected with a gun trigger-operated time trace generator, an annular member composed ofinsulating material secured to said harrel at the muzzle endthereof, a cylindrical sleeve mounted on said annular member and insulated from the muzzle of said gun barrel .by theannular member, a pair of spaced conductive bars carried by said sleeve parallel with the axis of said bore, a ring secured to the terminal ends of said pair of conductive bars for supporting and maintaining said bars in spaced relationship, a plurality of wires electrically connecting said bars and arranged in the? path of travel of said bullet in spaced-parallel re lationship, an elongated rod composed of electrical conducting material having one end thereof connected to the nose of said bullet and extending through said bore to a point. to the rear of said wires, a disk carried at the other end of said rod and normally disposed in spaced relation with respect to the muzzle end of the gun barrel and the innermost wire of said plurality of wires for progressively severing said wires as thebullet is propelled through said bore, and means including a conductor secured to said bullet for electrically connecting and completing a circuit from an additional pair of deflecting plates of said cathode ray tube to said rod and disk to detect contact of said wires by said disk as the bullet progresses through said bore and said wires are engaged andsevered by said disk.

3. In a position-time indicator for detecting the position of a bullet relative to thebore of a gun barrel as the Ibullet is propelled therethrough, a bullet extension means composed of electricalconducting material and carried by said bullet and. extending substantially the length of said. barrel bore, a disk element integrally formed on said bullet extension means and composed of bets supported in advance of the muzzle end of said gun barrel, means including a pair of mutually spaced electrical conducting bars for supporting said contact members on said gun barrel in advance of the muzzle end thereof in a manner to consecutively intercept said disk element, an annular member composed of insulating material mounted on the muzzle end of said gun barrel for insulatin-g said supporting means from said gun barrel and for supporting said supporting means thereon, and detecting means electrically connected between said bullet extension means and said contact members to register the interception of said contact members by said bullet extension means, and said detecting means having a time base for correlating said contact detections therewith.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Pages 34-37 and 82 of Feb. 15, 1950, issue of "Automotive Industries.

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