An electromagnetic catapult is a type of aircraft catapult that uses a linear induction motor system rather than the single-acting pneumatic cylinder (piston) system in conventional steam catapults. The system is used on aircraft carriers to launch fixed-wing carrier-based aircraft, employing the principles of electromagnetism and Lorentz force to accelerate and assist their takeoff from the shorter flight deck runways. Currently, only the United States and China have successfully developed electromagnetic catapults, which are installed on the Gerald R. Ford-class aircraft carriers (currently only the lead ship CVN-78 being operational), the Type 003 aircraft carrier Fujian and the upcoming Type 076 amphibious assault ship Sichuan (51).
Electromagnetic catapults have several advantages over their older, superheated steam-based counterparts. Electromagnetic operation recharges via electric energy and thus much faster than the pressurization process of steam systems, and does not suffer power loss with distance (where volume expansion within the steam catapult cylinder proportionally reduces pressure), temperature changes (which directly affects pressure according to ideal gas law) and leakages (which matters in pressure vessels but is irrelevant in electromagnet systems). The electromagnetic acceleration is also more uniform (unlike steam acceleration, whose accelerative force is always highest at the very initial phase, thus creating a distinct "jolt"), therefore reducing the stress upon the airframe considerably, resulting in increased safety and endurance as well as lower maintenance costs for the aircraft. Electromagnetic catapults are configurable and can assign varying power outputs to different sections, thus allowing them to tailor optimal acceleration to individual aircraft according to different payload weights and takeoff behaviours. Electromagnetic systems are more compact and also weigh less, have fewer linkage components and thus are expected to cost less and require less maintenance, and also require no fresh water boiling for their operation, thus reducing the need for energy-intensive desalination and sophisticated piping systems used in steam catapults, which take up significantly more space below the flight deck.
