The bow can truthfully be said to have been man's universal weapon, down through the ages. With it he procured food for himself and his family and defended himself from his enemies. Australia is the only large land mass where the bow was unknown to the aborigines. The Bush man of Aus­tralia is at the bottom of the scale of civilized man; and it is interesting to note in reading history, that from ancient times to the advent of firearms, the nations who reached the highest degree of civilization also excelled in the use of the bow as a military weapon.

Lacking modern means of communication and transportation, the ancients were unable to exchange either commodities or ideas, and although the bow was almost universally known, it was constructed by necessity of materials indigenous to a local­ity and readily available to the inhabitants. Thus from the high steppes of Asia and the Far East where timber was scarce and almost non-existent over large areas, came the earliest counter­part of the modern composite bow. Fabricated from horn, wood, and sinew, it was used by the armies of Assyria, by the Mongols, the Chinese, and the Turks.

The wooden long bow of Western Europe was probably introduced into England from the Scandinavian countries, and underwent little change or improvement until the present cen­tury. Discarded by the English speaking peoples as a military weapon, it was relegated to a minor role in sport and no sincere effort was made to improve its performance.

The efficient modern bow has evolved through scientific re­search in many fields of material, and its characteristics and the application of the findings have been utilized to improve per­formance. For discussion purposes, bows may be divided primarily into three groups: the wood self bow of which the English long bow is the prototype; the composite bow, a bow constructed of several different materials; and the all-metal bow, and the fibre-glass bow, the most recent developments of the bowyer's art.

At first, efforts to improve the cast of the self bow, without at the same time increasing the drawing weight proportionally, were confined to the search for a suitable wood that would pro­duce the desired results when processed into a bow. Little or no attempt to change the cross section of the bow was made at this time. The principal bow woods are: yew, osage orange, lemonwood, and hickory. Lancewood, a straight grained, tough, elastic wood of the family annonaceac obtained from the West Indies and Guiana was at one time a favorite bow wood of the English bowyers, but is little used today. Lemonwood is imported from Cuba. It receives its name from its color to distinguish it from lancewood. It is a very reasonably priced bow wood and makes an efficient, serviceable, and nice appearing bow. Machine tools can be used in manufacturing a bow from lemonwood and this accounts in part for the low price of the finished article. Yew is rated as the preferred bow wood, with osage orange second. Yew is a softer wood than osage orange, and a bow constructed of yew is considered to have a smoother cast than one made from osage orange. For this reason it is the preferred bow wood of many target archers. Osage orange is more durable than yew and is very fast in action. It can be called the universal bow wood, as it is suitable for the construction of both target and hunting bows of all kinds. Yew and osage orange bows are made almost entirely by hand, and this accounts, in part, for the high cost of this type of bow. Hickory makes a very durable bow, but it rates lowest in cast of the bow woods. However, when carefully made of selected and well seasoned stock it is a good low priced bow.

 Having exhausted the possibilities of the different species of wood to increase the performance of the self bow, a craftsman began experimenting with changes in design of the conventional English long bow. Gradually the best features of the long bow and the short flat bow of the American Indian were combined to produce the modified flat bow, Figure 19 and 21.

            Figure 19.

Let us digress for a moment and examine the physical changes which take place in the fibres of the bow when it is flexed or drawn, and study the resultant internal stresses that are set up in the bow. These internal stresses or forces are what gives the bow its casting power. Wood has the property of elasticity. Within certain limits, when an external force is applied, it can be elongated or compressed; and when the ex­ternal force is removed the wood fibres, which have been sub­jected either to tension or compression, will return to their original shape.

 In Figure 20, the dotted line ab represents the cross section of one of the limbs of a stacked bow, which is a bow that is nearly as thick as it is wide in cross section. The solid line represents the modified flat type bow, which is considerably wider than it is thick. When the archer flexes or draws the bow, he applies the external force which sets up the stresses in the wood fibres. The line CC represents the neutral axis of the cross section of the bow, or the plane of no internal stress, which always passes through the center of gravity of the sec­tion. This axis may also be defined as, the plane on one side of which the wood fibres are under tension, and on the other side compression. The amount of tension or compression in the fibres at any point of the draw varies in direct proportion to the distance of the fibres from the neutral axis. Since the back of the bow is under tension in the draw, it follows that the fibres at point d, which is the greatest distance from the neutral axis, are under the greatest tension.

                        Figure 20.

In Figure 20, units of stress are indicated by opposing arrows; this stress is greatest at d and is pictorially represented as decreasing around the circumference as the distance to the neutral axis decreases until it reaches zero stress at the neutral axis. Thus it is evident that the major weakness of the stacked bow is that the tensile stresses are unequally distributed over the bow's cross section; and when the limit of elasticity is reached first in the wood fibres at point d, these fibres will rupture and the whole stress will be thrown on the remaining fibres, and pro­gressive destruction of the fibres will occur. When a wood is stretched beyond its elastic limit, it does not immediately frac­ture, but it no longer has the property of being able to return to its original shape, when the external force is removed. Archers express this condition by saying that a bow has let down, meaning that it has weakened to the extent that it has lost the power to cast an arrow.

The wood fibres of a bow may be ruptured in two ways: elongation of the fibres beyond their elastic limit, which results when a bow is overdrawn. This will inevitably result in a broken bow if done repeatedly, and it can occur the first time that a bow is overdrawn. Repeated flexing, or draw­ing and shooting the bow, will finally weaken the fibres until they begin to break down. The fibres will stand only so many distortions before they may be said to have worn out. The same physical laws apply to bows made of metal or any other material. For this reason the life of every bow is limited.

 Reducing the amount of material in the stacked bow, Figure 19, and changing the shape of the back from round to flat produced the back now used in the manufacture of the modified flat bow. The extreme outer fibres of the back of the modified flat bow, being equi-distant, Figure 20, from the neutral axis, are stressed in equal amounts when the bow is drawn. In this type of back there is, therefore, no single point of greatest stress on the surface, and consequently no weakest point.

We have discussed the forces that act on the back of the bow. Let us now examine the action of the internal forces which are set up in the draw and act on the belly of the bow, which is the side toward the archer. When the bow is flexed, and the fibres of the back of the bow are elongated, the fibres in the belly of the bow are placed under compression. In Figure 20, the plane of the neutral axis indicated by the line CC divides the mass of the back of the bow from the mass of the belly. The law of elasticity applies equally to wood under compression as it does to wood under tension. When the bow is flexed or drawn, the wood fibres of the belly of the bow are compressed, and within limits; when the external force is re­leased the fibres will return to their original position. The prop­erties of wood are such that it has greater compressive strength per unit area than tensile strength. Consequently when a bow is broken it generally fails by fracturing the fibres in the back of the bow rather than crushing the fibres in the belly.

The bowyer's aim is to achieve a nice balance between the forces of tension in the back of the bow and the forces of compression in the belly. Working together, these forces give the bow its cast, or propelling power.

Since the compressive strength of wood is much greater per unit of area than its tensile strength, excess wood was gradually removed from the belly of the bow to achieve a balance of the two forces. In this manner the modified flat bow evolved.

Self bows of the modified flat type are popular among archers, and the same basic design has been used in the manufacture of laminated bows. Self bows of the modified flat type are dur­able, smooth in action, and have an excellent cast.

                                    Figure 22.

In the increasing and unceasing effort to develop better bows, archers with scientific training have made use of their knowl­edge of stresses in materials, and have improved the modified flat type bow by recurving the ends of the bow limbs, Figure 22. Because wood has greater compressive than tensile strength, the ends of the limbs of the bow were recurved to take ad­vantage of the compressive strength of the wood. In the re­curved bow, application of external force created by the draw results in compressing the wood fibres in the back of the bow at the recurved portion. This is a reversal of the stresses which occur in the ends of the limbs in the modified flat type bow, and is advantageous because of the greater compressive strength of wood. The ancient Persians were familiar with the recurved bow, but probably had no knowledge of the underlying prin­ciples involved, although they fully understood the advantages gained by recurving the ends of the limbs and backing the bow with rawhide or sinew to improve the cast.

The research chemists of the past decade have provided the modern bowman with backing far superior to the rawhide and sinew which had been the only materials widely used. Since we know that the fibres in the back of the bow are under tension in the draw, it follows that material selected for backing should have a high tensile strength and elasticity, so that it will be slow to yield to fatigue through repeated elongation and contraction of the fibres. The physical prop­erties of the material should be such that the material is im­pervious to changes in temperature and weather. Certain of the cellulose compounds and fibre glass products, marketed under different trade names, meet these requirements. When a strip of one of these materials is cemented to the back of the bow, the inherent power of the fibres, elongated by the draw, to return to their original position adds appreciably to the cast of the bow.

In the background we should always remember that the bowyer is searching for ways to improve the cast of the bow without a proportional increase in the amount of force re­quired to bring the bow to full draw. It is not difficult to build a self bow with an increased cross section that will have an improved cast. Unfortunately, if this is all that is done, the drawing weight will have increased proportionally.

 

The next logical step in bow design was to build a laminated bow taking advantage of the knowledge of the internal stresses in different materials, which vary in amount when the same external force is applied. A typical modern bow of this type has a fibre glass backing, a wooden core, and a fibre glass belly. In the draw, the fibre glass on the back elongates and that on the belly compresses or contracts. The internal stress built up in these materials during the draw is taking full advantage of the high tensile strength and elastic properties of the fibre glass on the back of the bow, and its compressive strength and inherent ability to return to its original shape when the external force is released. The high compressive strength of the fibre glass used on the belly of the bow permits a reduction of the cross sectional area from that required in a wood self bow. In consequence we find that the cross section of the laminated bow has assumed a rectangular shape with slightly rounded ends, Figure 23.


                                    Figure 23.

The principal difficulty encountered by the manufacturers of the laminated bows has been to develop a glue which will perform satisfactorily when it is used to bind to­gether two materials whose properties of elasticity are not equal. Certain combinations of materials which made a laminated bow of excellent shooting qualifications could not be used because their properties of elongation were at such variances that failure occurred in the glued joint. Until a glue is developed that has, in addition to its cohesive properties, the additional property of enlongating under stress, it is necessary to limit the materials used in building laminated bows to those materials that have relatively similar characteristics or properties of elongation. To gain additional propelling power by the con­tinued application of force over a greater distance than had been possible using a self bow, advantage has been taken of the greater elastic properties of the materials used in the face and belly of the laminated bows. The bow has been constructed so that it is reflexed when unbraced, Figure 24. This construc­tion permits the fibres in the backing of the bow to stretch farther when the bow is drawn, and act through a greater dis­tance in propelling the arrow when the drawing force is re­leased and the fibres return to their original position.

The author has been privileged to shoot several of these laminated bows over a period of several years. They have a smooth action and beautiful casting power. With an under-jaw anchor and using a bow sight, the author had a sight on the gold at 100 yards with a laminated bow which had a drawing weight of only 34 J4 pounds.

                                    Figure 24.

The Metal Bow

The elastic properties of metal are well known and the resilience of a metal bar under stress is the work done, upon the bar, in producing that stress, or in theory, the work the bar will do in regaining its original shape when the external force which has produced the stress is removed. These two properties of a metal are used to advantage in many articles in common use. The automobile spring and the main spring in your watch are examples. The processing of steel is so con­trolled that the strength of various properties of the metal can be varied to conform to the use which is to be made of the finished product. The terms: "hard" and "mild" steel are in common use.

Under stress up to its elastic limit  (graph Figure  25), a metal bar will deflect in direct proportion to the external force applied. The resultant graph is a straight line between the points O and A. When the elastic limit, point A, is reached the stretch increases faster than the stress to point B on the graph which is designated the Yield Point. Stretched to and be­yond this point the bar will not return to its original shape when the external force producing the stress is removed. From point B to B1 on the graph, the result indicates that the stretch in the metal bar increases with little or no additional applica­tion of stress. If we continue to stress the metal, it will again resist the application of continued increase in increments of stress, but the corresponding stretch will be greater, until the ultimate strength of the metal is reached at the point designated


                        Figure 25.

C on the graph. Any increase of stress will now cause the bar to rupture at the point designated D on the graph. This ab­breviated course in Strength of Materials will permit a better understanding of physical properties of a recent addition to bow materials, in the appearance on the market of the metal bow. Certain steels and aluminum alloys have been used ex­tensively in recent years in the manufacture of metal bows and arrows.

Working within the elastic limit of the material; that is between the points O and A on the graph, the life of a metal bow in theory, would be limited only by the phenomenon known as the "fatigue" of the metal. The molecular structure of metal, under repeated distortions within the elastic limit, will finally crystalize and break down. This is a slow but inevitable process. The exposed cross section of a metal bow which breaks under these circumstances has the appearance under a microscope of a granular structure somewhat similar to cast iron.

 The sum of the maximum tension and maximum compression stresses in a bow which is subjected alternately to tension and compression is called the range of stress in the bow. For a given number of applications of the stress, the load required for rupture is least when the range of the stress is greatest. When, as in a bow, the stress is alternately tension and com­pression, rupture takes place more readily than if it is always tension or always compression. That is, it takes place with a less range of stresses applied a given number of times, or with a less number of applications of a given range of stress. For a given number of applications of stress, the most unfavorable condition is where the tension and the compression are equal. Rest between stresses increases the resisting power of a piece of material, which is the reason that the bow should always be unbraced when not in use, and the fistmele checked occasionally when used for long periods of time. The main spring in your watch finally breaks due to the fatigue of metal, not because it has any more or less work to do at a given time. This slow deterioration is progressive and can account for the spring in the old car breaking down when you hit one bump too many, although not necessarily a hard one. Theoretically, a metal bow should let down at the yield point rather than break when the bow is drawn beyond its elastic limit. So much for theory. In practice no two melds of steel can be exactly alike nor can the finished product be guaranteed free of im­perfections. A bow may rupture from a fault in the metal. So, although widely acclaimed by the manufacturers, metal bows have their limitations just as bows made of other materials.

Metal bows generally are light in weight. They have an ex­cellent cast and consequently a flat trajectory which can generally be said to exceed that of a wooden self bow with the same drawing weight. A flat trajectory is a decided asset in wooded areas when hunting game. The game may be in plain sight, but frequently the vertical clearance in the line of flight is insufficient to deliver an arrow to the mark. This is one of the reasons a good case can be made for the heavy drawing weight of a hunting bow. Bowmen are divided in their opinions as to whether the metal bows are as smooth shooting as some of the laminated and self wooden bows.

                                                Figure 26.

Some metal bows can be taken apart at the handle, which reduces the problem of transportation. One model known to the author has an adjustable lower limb. Limbs are replaceable on the metal bows, although it is the personal feeling of the author that re­placing one of the limbs of a metal bow would give results about equal to the old practice of replacing a single broken leaf in an automobile spring, now long discontinued.

The Center Shot Bow

Since the arrow passes on the left side of the bow, and the string returns to the middle, it would appear that the arrow should fly far to the left. Actually well made arrows are spined for a particular drawing weight of bow. By spine we mean the quality of stiffness and resiliency of an arrow. Properly spined, an arrow actually bends around the bow in flight, and oscillates as it flies toward the target. During this change of direction the arrow loses some of its initial velocity. Dr. Clar­ence N. Hickman propounded the proposition that the arrow should be shot from a point nearer or at the center of the bow, rather than from the side. With such a bow, the arrow would leave the bow in a straight line of flight and thus lose none of its initial velocity through oscillation. Too, a bow of this de­sign would permit the use of lighter arrows, as there would be less chance of breakage from bending at the bow in flight. Consequently, increased distance and a flatter trajectory would be achieved without an increase in the drawing weight. The danger of personal injury from arrow shafts breaking at the bow is lessened and is a factor which increases the margin of safety to the shooter when this type of bow is shot. With these ideas in mind, Dr. Hickman designed a modern version of the center shot bow. The American Indian used a bow which employed this principle, but the design and construction of the bow were inferior to the modern product. This bow, Fig­ure 27, in its simplest form is reduced in width in the vicinity of the arrow plate by cutting out a section on the left side of the bow. The reduction in the amount of material at the sec­tion is made up by increasing the thickness of the bow, and the adjacent portion of the bow limbs are much wider than the limbs of the conventional type of bow. The bow is a bizarre looking affair, but it shoots smoothly and well. The bow has been manufactured and marketed  in recurved and reflexed models, and Dr. Hickman has had excellent results in flight shooting with a special bow of this type.

 To obtain the maximum efficiency at any drawing weight, bows are designed so that at full draw the material under stress is approaching the yield point, B Figure 25. This is true in both wood and metal bows. The expression commonly heard is that a bow at full draw is considered to be four-fifths broken.

                                    Figure 27.

Your bow should never be drawn past its proper arrow length. An added inch of draw may seriously damage or break the bow. Regardless of the excellent quality and workmanship of our modern bows, they do fail on the snooting line for reasons we have discussed. A broken bow limb striking the archer around the head or face produces painful results. If your new bow is equipped with a keeper, a short piece of elastic cord attached to the loop of the bow string and to the bow near the top nocking point, it will bear repetition to remind you to remove it before you use the bow. It may cause the upper limb to fly back and injure you if the bow should break. The number of bowmen who use protective head gear as a pre­caution against injury is increasing all the time. Stiff visored caps, sun helmets, GI helmet liners etc., are all seen at a shoot. Since the life of a bow is indeterminate, reason indicates that we should take the necessary safety precautions to insure against accidents. A blow from a broken bow limb can stretch an archer flat on the ground. Don't take chances.

The Ideal Bow

 At this point it is well to realize that the search for the ideal bow is not a process of groping in the dark for an unknown goal. The bowyer envisions a bow that has all the attributes of the best modern bows, and one additional quality. His aim is to build a bow, which at or just before full draw will have a drawing weight of X pounds, and will continue to draw or pull just X pounds when brought to full draw or slightly overdrawn. The solid line a in Figure 26, graphically represents the relation between the length of draw and the drawing weight of a modern laminated bow. In the illustration the pull increases at a constant rate as the bow is drawn until a pull of approximately 11 pounds has been exerted. From this point, less effort is required to continue the draw until approxi­mately 21 pounds of force have been exerted. From this point until full draw is reached it becomes increasingly difficult to draw the bow through a given distance. The dotted line b rep­resents the curve of a bow which has a theoretically ideal draw. In our ideal bow the length of the draw increases in direct proportion to the pull exerted on the bow string. The curves in the illustration each represent a bow which has a draw of 27 inches at a drawing weight of 32 pounds. In the ideal bow the drawing weight of 32 pounds would be reached just prior to full draw, and the drawing weight would remain constant through the full draw position and slightly beyond, as shown by the portion of the curve marked C. When we are able to construct a bow that will meet these requirements, the bowman will be able to release an arrow at any point between the limits marked C, with the knowledge that the arrow will be propelled by exactly the same force each time that it is released from the bow. Creep, the bane of every bowman, will have no effect on accuracy. Creep is the movement of the arrow during the interval necessary to slip the drawing fingers from the string. It is impossible to remove the drawing fingers instantly from the bow string, and consequently some variable amount of the propelling force that has been built up in the bow during the draw is lost each time that the string slips through the fingers during the release. The rifleman is not con­fronted with this problem. Regardless of the time spent in squeezing the trigger, there is the same initial velocity im­parted to the projectile at the instant of each discharge of the piece, because of the uniformity of the powder charge. The bowman is searching for a bow that will achieve a similar result.