Striking Force of Arrows
In attempting to determine the striking force of an arrow I utilized one of the measures employed by riflemen in estimating the penetration of bullets, and used as a target a large cake of paraffin 2 X 12 X 24 inches, with a melting point of 54° C. To determine the striking force of an arrow, I discharged at this target arrows of various diameters, weights, and points, and the distance which they penetrated was measured from the extreme point to the face of the paraffin slab. This method was used, first, to ascertain the striking force; secondly, the penetration under varying conditions, such as weight, shape of head, size of feathers.
To establish a control, a birch dowel 3 inches long and of an inch in diameter was loosely set in a hole through a board and held perpendicular on the face of this slab of paraffin. A 10-pound weight was dropped on this blunt dowel, from distances of 1, 2, and 3 feet. A fall of 1 foot drove the blunt pin ½ inch deep in the paraffin. A drop of 2 feet drove it 1 inch deep, and a drop of 3 feet drove it 1½ inches.
The foregoing and all the following experiments were conducted at room temperature of about 30° C. It may therefore be assumed roughly that a bow which drives a 5/16 inch blunt shaft 1 inch into paraffin under these conditions has a striking force of 20 foot pounds, or approximately 10 pounds for every ½ inch penetration.
To measure the striking force of a 50-pound bow, an arrow made of a 5/16 inch dowel, having a similar blunt head, and weighing 1 ounce, was shot at this paraffin block at a distance of 10 feet. It penetrated just 1 inch, or had a striking force of 20 foot pounds.
A 75-pound bow, shooting the same arrow from 10 feet, drove it in 1¼ inches, or approximately 25 foot pounds.
This measurement may be taken as the maximum striking force of an arrow from the average English longbow, or the arrow of many Indian hunting bows. It is, of course, insignificant when compared with the striking force of a high powered rifle bullet, that is, 2445 foot pounds and 2700 foot seconds of the U. S. Springfield rifle; and yet, as we shall see later on, the damage done by an arrow may be quite as fatal as that done by a bullet.
To test whether a heavy missile strikes a greater blow than a light one, an arrow weighing 1½ ounces, having a diameter of 5/16 inch, blunt at the end, was shot from a 50-pound bow. It penetrated 1⅛ inches in the paraffin, or had a striking force of 22½ foot pounds. Increased weight of missile evidently results in increased penetration. This statement probably holds good only up to certain limits, which it is not necessary to define at present.
A similar arrow weighing 1½ ounces, having a blunt end ⅜ inch in diameter, shot from a 50-pound bow, penetrated the paraffin only ⅞ of an inch.