Trebuchet

A trebuchet (French trébuchet) is a type of siege engine most frequently used in the Middle Ages. It is sometimes called a counterweight trebuchet or counterpoise trebuchet, to distinguish it from an earlier weapon called the traction trebuchet, where men pulling ropes provided the power.

The counterweight trebuchet appeared in both Christian and Muslim lands around the Mediterranean in the 12th century. It could fling projectiles weighing up to 350 pounds (160 kg) at or into enemy fortifications. Its use continued into the 15th century, well after the introduction of gunpowder.

The three distinguishing characteristics of a trebuchet are:

The couillard is a smaller version with a single stem or platform instead of the usual double "A" frames. The counterweight is split into two halves to avoid hitting the center stem.

The earliest form of trebuchet, often called the traction trebuchet, utilized the power of the human body to pull down on the lever arm to launch the desired projectile. However, this was eventually deemed an inefficient method of warfare, which motivated ancient engineers to update the design. The next step in the development of this siege engine was the invention of the fixed counterweight trebuchet.

Ancient armies directly utilized gravity to launch projectiles at their enemies by placing a large weight on the short end of the trebuchet's lever arm and then letting it fall. This was a more efficient and powerful machine than the traction trebuchet because it reduced the number of men needed to operate it and could be fired repeatedly without wearing out.

As societies advanced, so did the trebuchet's design. While the fixed counterweight trebuchet was devastatingly effective, it was subject to a great deal of fatigue stress during operation. This led to a shortened operational life cycle. The counterweight was eventually placed upon a hinge. This allowed the counterweight to swing as it reached the bottom of its fall, thus reducing the stresses placed upon the frame and throwing arm. Not only did this improvement increase the usable life of the machine, but by propping the counterweight up on the hinge, the total distance traveled increased. By increasing the distance the counterweight fell, ancient engineers also increased the rotational speed of the lever arm. This, in turn, increased the launch speed and impact force of the projectile.

The trebuchet derives from the ancient sling, and originated in China. A variation of the sling, called staff sling (Latin: fustibalus), contained a short piece of wood to extend the arm and provide greater leverage. This evolved into the traction trebuchet in which a number of people pulled on ropes attached to the short arm of a lever that has a sling on the long arm. This type of trebuchet was smaller and had a shorter range, but was a more portable machine and had a shorter cycle time than larger, counterweight-powered types. The smallest traction trebuchets could be powered by the weight and pulling strength of one person using a single rope, but most were designed and sized for between 15 and 45 men, generally two per rope. These teams would sometimes be local citizens helping in the siege or in the defense of their town. Traction trebuchets had a range of 100 to 200 feet (30 to 61 m) when casting weights up to 250 pounds (110 kg).

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