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Home > Books > Archery: The Technical Side > Physics of Bows and Arrows
Considerations in Bow Design
Part 3 of 3

A bow designed according to these principles performs very much as one might expect from theoretical considerations. The limbs may be made shorter than those of the English type longbow by 15 or 20 percent, with less hazard of breakage. The shorter, thinner limbs have greatly reduced virtual mass, and consequently the bow has much higher efficiency than the old style bow. Where, in the older design of bow a rigid section was used barely long enough to provide for a hand grip that gradually merged into the bending limbs, the new design employs a long rigid section which, in fact, may be made of such length that the over-all length of bow is still that of the English longbow. It may be said parenthetically that the force-draw curve for a longbow is nearly linear. The experienced archer likes the "feel" and behavior of such a bow. The long rigid section with the shorter limbs makes it possible to use limbs of equal length and have the arrow "nocked" at the midpoint of the string. In the English longbow design the lower limb was usually made 2 in. shorter than the upper and considerably stiffer, so that neither the undrawn nor the drawn bow manifested symmetry of its limbs with reference to the axis represented by the arrow.

Tests of many bows showed substantially increased cast and efficiency for the new design. An interesting side light is the fact that as late as 1932 practically all bows used in tournaments were of the English longbow type. The design had come down through generations of bowyers from the period in English history in which the archer was the invincible warrior. A tradition of such long standing dies hard. Nevertheless, the following five years, as a result of the publication of a number of articles pointing out the defects of the traditional design and the advantages of the new, witnessed a gradual change at the tournaments to bows in which the rectangular cross section was used. Today the English design of longbow is a rarity at American tournaments.

Limitation of space excludes many details that might prove interesting, particularly about the elastic properties of different kinds of wood with specific reference to their utility in bows. It must suffice to say that in America we have only two or possibly three native kinds of wood which are particularly well suited for the making of bows. They are the western yew, the osage orange and, for the lighter bow, the Tennessee red cedar. Ash, hickory and other kinds of wood are inferior because of large hysteresis and because they take a permanent set much more quickly than the other kinds of wood mentioned. Beginners' bows are usually made of a Cuban wood—degame—called lemonwood because of its color. It is the cheapest of the bow woods but yields bows of fair quality, though quite inferior to those of yew and osage orange. We cannot dwell on the merits of the individual species of wood. A stave of sufficient length to make a bow of either yew or osage orange, free from knots, pins, bear scratches, wind shakes and other imperfections and with proper physical characteristics, is a rare and beautiful article. An archer-craftsman will readily pay anywhere from $5.00 to 20.00 for such a stave in the expectation that from it he may be able to fashion a superlative bow. Sometimes he succeeds; more often he is disappointed.

In addition to the so-called self bows which are made of a single kind of wood throughout, there are laminated bows in which several kinds of wood may be glued together in strips with the purpose of utilizing the tensile and compressive strengths of each to best advantage. Then there are composite bows in which fibers of high tensile strength, such as shredded sinew laid in glue, constitute the back, while horn—superb material for compressive strength—is used for the belly. The bows of Ghengis Khan and his hordes were of the composite type. The superior properties of sinew and horn over wood make it possible to use much shorter limbs and to bend them on a much smaller radius than can be done with bows made solely of wood. Turkish bows of four centuries ago still hold the record for distance. In terms of the concept of virtual mass any bow, whatever the shape of its limbs, has very high cast only if its virtual mass is small. In a strongly reflexed bow such as the short Turkish type, the seemingly massive ends of the limbs are moving with small velocity at the instant the arrow leaves the string; notwithstanding the apparent massiveness, the virtual mass is small.

A major contribution to improvement in the straight type of bow is that of Hickman's, who recognized the virtue of the elastic properties and strength of silk, and devised a method of producing backing strips consisting of unspun silk fibers laid in glue. In 1934 the writer pointed out that when sinew or rawhide are used for backing, they should be applied and secured under tension, to assure their best contribution to the performance of the bow. The same procedure is employed in applying silk as backing. The silk replaces a larger mass of wood than its own and stores more energy per unit mass; hence it makes possible a bow of smaller virtual mass. Further reduction of virtual mass may be expected from the use, both for tension and compression, of synthetic materials which have been and are being developed during the war years. A synthetic material having the compressive strength and elastic properties of water buffalo horn—which is difficult to obtain and more difficult to process—would be a great contribution to bow making.