Catapult

I. Introduction

Catapult, device used to throw an object over a distance. A catapult can be as small as a rubber band slingshot used to skim rocks across a pond or as large as the 90-m (300-ft) long steam units used to launch airplanes from aircraft carriers. In Britain, aircraft carrier catapults are referred to as accelerators, which is perhaps a more accurate term for what these machines do.

II. Siege Engines

The catapult was a special type of siege engine, a large device used to attack a fortress or a city.

Catapults were used in ancient and medieval warfare until the introduction of the gunpowder cannon in the 14th century. A catapult could hurl large stones, spears, or other projectiles at an enemy, but was difficult to aim. A catapult was sometimes mounted on a wheeled cart, and as an army changed positions, the catapult could be moved accordingly. Some catapults were mounted permanently within fortresses and used for defense against attackers. Many different types of catapults were invented and used. Three of the most common were the ballista, the mangonel, and the trebuchet. See also Fortification and Siege Warfare.

The ballista and the mangonel used the energy created by twisting ropes to create torsion. The sudden release of this energy was used to launch large rocks, arrows, or flaming balls at an enemy. The earliest catapult was the ballista. It resembled a crossbow and originated in Greece in the 3rd century BC. Engineers working for Philip II of Macedonia, father of Alexander the Great, most likely invented the ballista. A ballista used two vertical groups of ropes that were twisted over and over again to create torsion. Wooden arms were inserted horizontally into the twisted ropes. A single cord attached to both arms pulled them back against the force of the twisted ropes, much like a crossbow as it is being cocked. A spear was placed in a pocket on the cord. When the cord was released, the twisted ropes pulled the wooden arms forward, thrusting the spear toward the enemy. The distance varied depending on how much and how tightly the ropes had been twisted.

The Roman mangonel also used twisted ropes to provide energy, but the mangonel had only one arm. The twisted ropes were stretched horizontally, and the arm was inserted vertically into the ropes. A scoop fitted on the end of the arm held a rock. The arm was pulled down against the force of the twisted ropes, loaded with a rock, and released. The arm flung forward and as it hit a wooden barrier on the mangonel, the rock would fly toward the enemy. The mangonel was less complicated than the ballista, but much energy was wasted as the arm collided with the wooden barrier.

Trebuchets, unlike mangonels and ballistas, did not derive their power from torsion. Trebuchets relied either on muscle power or gravity to hurl objects. A trebuchet was essentially a long wooden arm resting on a pivot point, and acted as a large class 1 lever. A stone would be placed on one end of the trebuchet, and soldiers would pull on ropes attached to the other end to swing the arm around and hurl the stone. Later designs used a counterweight on one end, rather than muscle power, to provide energy. Soldiers would pull the launching end down against the weight of the counterweight, load the projectile, and release the arm. The counterweight would pivot the arm around to launch the projectile.

III. Aircraft Launchers

The word catapult also refers to a device that is used on aircraft carriers to help launch airplanes. Catapults are built into the surface of a carrier's flight deck. A tow bar on the catapult slides into a holder on the forward wheel of an airplane. When the catapult is activated, the tow bar pulls the airplane down the catapult track and releases itself at the very end of the deck to allow the airplane to fly off the ship. Catapults of various designs have been used ever since the Wright brothers' first flight at Kitty Hawk, North Carolina, on December 17, 1903. The catapult used at Kitty Hawk was actually a small length of track running down a hill. This guide track helped the first airplane gain enough energy so that its small engine could take over and lift the airplane into the air.

The length of an aircraft carrier's flight deck is only a fraction of that of a commercial runway on land, which can run as long as 4,300 m (14,000 ft). An aircraft carrier of the USS Nimitz class has a flight deck only 333 m (1,092 ft) long and 77 m (252 ft) wide, and catapults give airplanes the extra boost they need to become airborne. Before jet aircraft came into service in the 1950s, the catapults aboard carriers were hydraulically powered. Hydraulic catapults used a pressurized fluid to release energy and accelerate an airplane attached to the moving tow bar. Hydraulic catapults were unreliable and dangerous, and the explosion of a hydraulic catapult aboard the aircraft carrier USS Bennington in 1954 killed nearly 100 crewmen. Hydraulic catapults were also not very adaptable, and as aircraft weights increased they were unable to launch airplanes effectively.

The steam catapult was invented in 1952 by Britain's Royal Navy to improve the launch of the era's new jet airplanes from carriers. Steam catapults draw their power directly from the heat of the ship's engines. Since aircraft carrier engines are large, they have an enormous amount of power. The steam catapult uses this power to fling airplanes weighing as much as 32,000 kg (71,000 lb) into the air using only 90 m (300 ft) of deck space.

Contributed By:

Andrew Bahjat

Consultant to U.S. Navy. Contributor to United States Naval Institute Proceedings. Coauthor of Chronology of the Cold War at Sea.

HOW TO CITE THIS ARTICLE

"Catapult," Microsoft® Encarta® Online Encyclopedia 2001

http://encarta.msn.com © 1997-2000 Microsoft Corporation. All Rights Reserved.

© 1993-2001 Microsoft Corporation. All Rights Reserved.