Catapult: Encyclopedia II - Catapult - Types

Catapult - Types

Catapults can be classified according to the physical concept used to store and release the energy required to propel the projectile.

The first catapult distinct from hand-held launchers (bows, crossbows, slings etc.) was the greek gastrophetes, a crossbow so large it was braced against the abdomen rather than being held in the hand, hence the nickname belly-bow. The next step from this was a larger form a crossbow mounted on a stand, including early versions of the oxybeles (Greek for bolt shooter) and the ballista (the Roman version of the oxybeles). The arbalette à tour is a medieval version of the stand-mounted crossbow. These catapults are tensional, in that the energy is stored as tension and compression of the bow. Although similar to a crossbow, a sling on the end of the rope meant these weapons could be used for firing all sorts of projectiles, from rocks to pots of Greek fire.

Subsequently, torsional catapults were developed: those with two torsion powered arms, the later versions of the ballista and oxybeles, and those with one torsion powered arm, the onager, known in medieval times as the mangonel. The bottom end of the throwing arm of the onager and the inner ends of both ballista arms are inserted into rope or fibers that are twisted, providing a torsional store of energy. Torsional ballistas were operationally equivalent to their tensional cousins, except the torsional energy store gave greater power. Onagers have an arm with a bucket, cup, or most often a sling to hold the projectile at one end.

Finally, the last type of catapult is a trebuchet, which uses gravity or traction rather than tension or torsion to propel the throwing arm. A falling counterweight or the effort of the operator(s) pulls down the bottom end of the arm and the projectile is thrown from a sling attached to a rope hanging from the top end of the arm, essentially like a sling attached to a giant see-saw. The counterweight is much heavier than the projectile.

Adapted from the Wikipedia article "Types", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki