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For the typeface, see Trebuchet MS
. For the chess term for a situation in which the side to move loses, see Zugzwang
Trebuchets at Château de Castelnaud
Trebuchet constructed on the design of the "Warwolf"
traction trebuchet (also called a perrier) next to a staff slinger
A trebuchet[nb 1]
) 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 90 kg about 300 metres 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 trebuchet is a compound machine—a combination of simple machines. The trebuchet makes use of the mechanical advantage of a lever. Most trebuchets are powered exclusively by the force of gravity. Potential energy is stored by means of an extremely heavy weight box attached (by a hinged connection) to the counterweight portion of the throwing arm. Some earlier trebuchets stored potential energy as traction force (traction trebuchets).
- When the trebuchet is fired, the weight box is permitted to fall and the force of gravity causes rotational acceleration of the attached throwing arm around the axle (the fulcrum of the lever). The throwing arm is usually four to six times the length of the counterweight portion. These factors multiply the acceleration transmitted to the throwing portion of the arm and its attached sling.
- The sling is affixed to the end of the throwing portion of the throwing arm (opposite the counter weight portion). The sling contains the projectile and transmits the forces generated at the end of the throwing arm to the projectile. The sling also changes the trajectory, so that, at the time of release from the sling, the projectile is traveling in the desired speed and angle to give it the range to reach the target.
- It launches 90kg projectiles over 300 metres using a fixed counterweight
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.