Method of Conducting Tests
It was realized that in order to obtain results that could be reproduced at will, it would be necessary to mount the bow in a mechanical shooting device. He had previously designed such a device for testing arrows. This mechanical shooter is made in such a manner that it practically duplicates the conditions obtained in shooting by hand. The arm on which the bow is mounted is free to pivot in a manner exactly like the human arm, the fingers which grasp the string are locked into position by means of a trigger. The trigger is released pneumatically. In this manner there is no danger of disturbing the mechanism at the time the trigger is released. With this device, using good arrows, it is possible to obtain "golds" consistently at 50 to 60 yards.
A device of this type was equipped with a series of electrical contacts, so placed that they were closed by a silver pin on the arrow as it was leaving the bow. There was a sufficient number of these contacts to plot a space time curve from the chronograph readings.
The chronograph used was a modification of the Aberdeen chronograph developed during the war. This chronograph was modified and improved by the Ampico Research Laboratory. It was used in these tests and gave results that were very satisfactory. In addition to the space time curves which were plotted from the chronograph readings, the velocity of the arrow at the time it left the bow was also further checked by shooting the arrow through tin foil screens which were two feet distant from each other. The accompanying photograph shows a "set up" in the laboratory used in making these measurements.
Since it was desirable to determine the effect of shooting arrows of different weight, four different weights were used. These arrows weighed 230, 365, 545, and 635 grains, respectively.
The first bow which was tested was a 32 lb. fiber backed lemonwood bow, which was furnished by the Archers Company. The bow was carefully weighed and a curve plotted showing the force in pounds required to draw the bow as a function of the draw in inches. This is shown by curve 1, Graph A. This bow was then placed in the mechanical shooting device, and each of the arrows discharged, and chronograph records obtained showing the time required for the arrows to reach various positions, during their flight from the bow. From these data, space time curves were plotted. Curves No. 1 in Graphs B and F are for the lightest and heaviest arrows.
The bow was now removed from the shooting device and the fiber backing removed. Great care was taken to avoid removing any wood during this operation. This bow was carefully weighed and a curve plotted showing the force in pounds required to draw the bow as a function of the draw in inches. See curve 2, Graph A. The bow was then replaced in the shooting device and the arrows again discharged, obtaining, as before, chronograph records from which space time curves were plotted. These curves for the lightest and heaviest arrows are reproduced by No. 1, in Graphs C and G.