Crossbow

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A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles, often called bolts. The medieval crossbow was called by many names, most of which derived from the word Ballista, a siege engine rassembling in mechanism and appearance to a crossbow.[1]

Crossbows played a significant role in the warfare of North Africa, Europe and Asia. They were developed in Ancient Greece and East Asia with Ancient China being the main source of archaeological evidence. The first textual reference to crossbows were found in the works of Mozi’s followers and Sun Tzu’s Art of War written in between 500 BC and 300 BC and from the 2nd century BC writer Biton referring to a 5th century work.

Crossbows are still being used in warfare. However, they are used today primarily for target shooting and hunting.[2]

A crossbow is a bow mounted on a stick (called a tiller or stock) with a mechanism in it which holds the drawn bow string. The earliest designs utilized a slot in the stock, down into which the cocked string was placed. To fire this design, a vertical rod is thrust up through a hole in the bottom of the notch, forcing the string out. This rod is usually attached perpendicular to a rear-facing firing lever called a trigger or ‘tickler’. A later design utilized a rolling cylindrical pawl called a ‘nut’ to retain the cocked string. This nut has a perpendicular center slot for the bolt, and an intersecting axial slot for the string, along with a lower face or slot against which the internal trigger sits. They often also have some form of strengthening internal ‘sear’ or trigger face, usually of metal. These ‘roller nuts’ were either free-floating in their close-fitting hole across the stock, tied in with a binding of sinew or other strong cording, or mounted on a metal axle or pins. Removable or integral plates of wood, ivory or metal on the sides of the stock kept the nut in place laterally. Nuts were made of antler, bone, ivory or metal (usually brass). A trigger system, (usually made of iron or steel from medieval times onwards), was used to retain the force of the cocked string in the nut and then release the nut to spin and the string to shoot the bolt. Sophisticated bronze triggers with safety notches are known to have been used on crossbows from ancient China. Complicated iron triggers that could be released with little strength are known in Europe from the early 1400s. As a result crossbows could be kept cocked and ready to shoot for some time with little effort, allowing crossbowmen to aim better.

The bow (called the “prod” or “lath” on a crossbow) of early crossbows were made of a single piece of wood, usually ash or yew. Composite bows are made from layers of different material—often wood, horn and sinew—glued together and bound with animal tendon. These composite bows, made of several layers, are much stronger and more efficient in releasing energy than simple wooden bows. As steel became more widely available in Europe around the 14th century, steel prods came into use.

The crossbow prod is very short compared to ordinary bows, resulting in a short draw length. This leads to a higher draw weight in order to store the same amount of energy. Furthermore the thick prods are a bit less efficient at releasing energy, but more energy can be stored by a crossbow. Traditionally the prod was often lashed to the stock with rope, whipcord, or other strong cording. This cording is called the bridle.

The strings for a crossbow are typically made of strong fibers that would not tend to fray. Whipcord was very common; however linen, hemp, and sinew were used as well. In wet conditions, twisted mulberry root was occasionally used.

Crossbows have a shorter draw length than bows, resulting in the need of a greater amount of draw force in order to store the same amount of energy. Very light crossbows can be drawn by hand, but heavier types need the help of mechanical devices. The simplest version of mechanical cocking device is a hook attached to a belt, drawing the bow by straightening the legs. Other devices are hinged levers which either pulled or pushed the string into place, cranked rack-and-pinion devices called ‘cranequins’ and multiple cord-and-pulley cranked devices called windlasses.

Crossbows exist in different variants, one way to classify them is the acceleration system, another the size and energy, degree of automation or projectiles.

The simplest acceleration system is a straight or bent prod and it is probably the earliest version of a crossbow.

A recurve crossbow is a bow that has tips curving away from the archer. The recurve bow’s bent limbs have a longer draw length than an equivalent straight-limbed bow, giving a more acceleration to the projectile and less hand shock. Recurved limbs also put greater strain on the materials used to make the bow, and they may make more noise with the shot.

Multiple bow systems (for example a Chu-ko-nu) have a special system of pulling the sinew via several bows (which can be recurve bows). The workings can be compared to a modern compound bow system. The weapon uses several different bows instead of one bow with a tackle system to achieve a higher acceleration of the sinew via the multiplication with each bow’s pulling effect.

A compound crossbow is a modern crossbow and similar to a compound bow, The limbs are usually much stiffer than those of a recurve crossbow. This limb stiffness makes the compound bow more energy efficient than other bows, but the limbs are too stiff to be drawn comfortably with a string attached directly to them. The compound bow has the string attached to the pulleys, one or both of which has one or more cables attached to the opposite limb. When the string is drawn back, the string causes the pulleys to turn. This causes the pulleys to pull the cables, which in turn causes the limbs to bend and thus store energy. The use of this levering system gives the compound bow a characteristic draw-force curve which rises to a peak weight and then “lets off” to a lower holding weight.

In size the smallest are pistol crossbows. Others are simple long stocks with the crossbow mounted on them. These could be shot from under the arm. The next step in development was rifle shaped stocks that allowed better aiming. The arbalest was a heavy crossbow which required special systems for pulling the sinew via windlasses. For siege warfare the size of crossbows was further increased to hurl large projectiles such as rocks at fortifications. The required crossbows needed a massive base frame and powerful windlass devices. Such devices include the oxybeles. The ballista has torsion springs replacing the elastic prod of the oxybeles, but later also developed into smaller versions.[3] “Ballista” is still the root word for crossbow in Romance languages such as Italian (balestra).