In a projectile making one complete revolution about its major axis in every twenty-five calibres flight, any one elementary unit area or mass in that shell likewise makes one complete revolution in the same distance of travel, and the path traversed by that unit area or mass is that of a spiral of radius equal to the distance of that unit area or mass from the major axis of the shell, the diameter of which spiral would be the diameter of the shell in question—and the pitch twenty-five calibres—if said unit area were on the surface of the body of the shell.
Upon impact the tendency of this unit area would be to continue its flight along the continuation of that spiral or along the line ed of our theoretical shell of twenty calibres. The result would be for each disc element theoretically considered to crowd upon the next corresponding disc element and these two upon the third corresponding disc element etc., such crowding taking place along the line ed. Therefore the projectile must be designed not only to penetrate, as well as to withstand the great compressional stresses upon the advancing head of the shell but the body of the shell must be so designed as to give a maximum of integrity. The torsional stresses act along ed, and in order to resist these stresses the shell must be so designed that the resisting ability will be increased along that line, re-acting along de.
This the author advocates by means of a "twist forging," in which the grain of the metal will lie co-incident with the lines of the torsional stresses, and by the introduction of spiral ribs lying co-incident also with the lines of the torsional stresses and the grain of the "twist forging" manufactured by a process indicated in the patent herewith appended. By the introduction of the spiral ribs it will be seen that each disc is reinforced to withstand the tendency of the disc behind to crowd upon it and that by means of a properly designed shell of this type the whole energy of the shell can be better transmitted to the point of impact by means of the spiral ribs and twisted grain.
Furthermore, should any flaws be present in the ingot, their size would be reduced by the twisting, as are the spaces between the strands of a rope when twisted in the proper direction for so doing. Also, with a flaw in a finished projectile, and lying in a spiral direction the result of the compression stresses would be to jump across the flaw or to decrease the gap instead of acting wedgelike along the flaw causing it to open as before mentioned. Finally, an increase in integrity means an increase in penetrability, or in the percentage of complete penetration, with the ultimate necessity of increasing the thickness of armor-plate to successfully exclude the improved armor-piercing shell.
No. 863,248.
PATENTED AUG. 13, 1907.
C. DE ZAFRA.
PROJECTILE.
APPLICATION FILED DEC. 10, 1906.
United States Patent Office
Carlos De Zafra, Of New York, N.Y.