A, section of bow. B, string in nock. C, arrow nocked but not drawn. D, arrow drawn 27 inches.
Fig. 9.—CHESTED ARROW.
Fig. 10.—STRAIGHT CYLINDRICAL ARROW.
The recoil of the bow, besides the motion in the direction of aim, impresses a rotary motion upon the arrow about its centre of gravity. This tendency to rotate, however, about an axis through its centre of gravity is counteracted by the feathers. For, suppose the arrow to be shot off with a slight rotary motion about a vertical axis, in a short time its point will deviate to the left of the plane of projection, and the centre of gravity will be the only point which continues in that plane. The feathers of the arrow will now be turned to the right of the same plane, and, through the velocity of the arrow, will cause a considerable resistance of the air against them. This resistance will twist the arrow until its point comes to the right of the plane of projection, when it will begin to turn the arrow the contrary way. Thus, through the agency of the feathers, the deviation of the point of the arrow from the plane of projection is confined within very narrow limits. Any rotation of the arrow about a horizontal axis will be counteracted in the same way by the action of the feathers. Both these tendencies may be distinctly observed in the actual initial motion of the arrow. In the discussion of these rotations of the arrow about vertical and horizontal axes the bow is supposed to be held in a vertical position.
If the foregoing reasoning be carefully considered, it will be seen how prejudicial to the correct flight of the arrow in the direction of the aim any variation in the shape of that part of it which is in contact with the bow must necessarily be; for by this means an additional force is introduced into the elements of its flight. Take for example the chested arrow, which is smallest at the point and largest at the feathers: here there is during its whole passage over the bow a constant and increasing deviation to the left of the direction of aim, caused by the arrow's shape, independent of, and in addition to, a deviation in the like direction caused by the retention of the nock upon the string. Thus this description of arrow has greater difficulty in recovering its initial direction, the forces opposed to its doing so being so much increased. Accordingly, in practice, the chested arrow has always a tendency to fly to the left. These chested arrows are mostly flight-arrows, made very light, for long-distance shooting, and they are made of this shape to prevent their being too weak-waisted to bear steadily the recoil of very strong bows.
As regards the bobtailed arrow, which is largest at the point and smallest at the feathers, the converse is true to the extent that this description of arrow will deviate towards the left less than either the straight or chested arrow; moreover, any considerable bobtailedness would render an arrow so weak-waisted that it would be useless.
There is another arrow, known as the barrelled arrow, which is largest in the middle, and tapers thence towards each end. The quickest flight may be obtained with this sort of arrow, as to it may be applied a lighter pile without bringing on either the fault of a chested arrow or the weak-waistedness of a bobtailed arrow.
If the tapering be of equal amount at each end of the arrow, the pressure will act and react in precisely the same manner as in the case of the cylindrical arrow, with the result that this arrow will fly straight in the direction in which it is aimed. The cylindrical and the barrelled shapes are therefore recommended as the best for target-shooting. And as the barrelled is necessarily stronger in the waist and less likely to flirt, even if a light arrow be used with a strong bow, this shape is perhaps better than the cylindrical.