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1、Electromagnetic Aircraft Launch System The Electromagnetic Aircraft Launch System (EMALS) is a system under development by the United States Navy to launch carrier-based aircraft from an aircraft catapult using a linear motor drive instead of the conventional steam piston drive. The main advantage i
2、s that this system allows for a more graded acceleration, inducing less stress on the aircrafts airframe. Other advantages include lower system weight, lower cost, and decreased maintenance requirements. It also will provide the ability to launch aircraft that are both heavier or lighter than the co
3、nventional system can accommodate. In addition the system has limited requirements for fresh water, reducing the need for energy-intensive desalination. Design and development The EMALS is being developed by General Atomics for the U.S. Navys newest Gerald R. Ford-class aircraft carriers. In June 20
4、10, the land-based prototype of the system passed initial tests, with the first aircraft launch from the system taking place at the end of 2010. Linear induction motor The EMALS uses a linear induction motor (LIM), which uses electric currents to generate magnetic fields that propel a carriage down
5、a track to launch the aircraft. The EMALS consists of four main elements: The linear induction motor consists of a row of stator coils that have the function of a conventional motors armature. When energized, the motor accelerates the carriage down the track. Only the section of the coils surroundin
6、g the carriage is energized at any given time, thereby minimizing reactive losses. The EMALS 300-foot (91 m) LIM will accelerate a 100,000-pound (45,000 kg) aircraft to 130 knots (240 km/h). Energy storage subsystem The induction motor requires a large amount of electric power; more than the ships o
7、wn power source can provide. The EMALS energy-storage subsystem draws power from the ship and stores energy kinetically on rotors of four disk alternators,and then releases that energy in a very short period of time. Each rotor can store more than 100 megajoules, and can be recharged within 45 secon
8、ds of a launch, faster than steam catapults. Power conversion subsystem During launch, the power conversion subsystem releases the stored energy from the disk alternators using a cycloconverter. The cycloconverter provides a controlled rising frequency and voltage to the LIM, energizing only the sma
9、ll portion of stator coils that affect the launch carriage at any given moment. Control consoles Operators control the power through a closed loop system. Hall effect sensors on the track monitor its operation, allowing the system to ensure that it provides the desired acceleration. The closed loop
10、system allows the EMALS to maintain a constant tow force, which helps reduce the launch stresses on the plane s airframe. Advantages Compared to steam catapults, EMALS weighs less, occupies less space, requires less maintenance and manpower, is more reliable, recharges more quickly, and uses less en
11、ergy. Steam catapults, which use about 614 kilograms of steam per launch, have extensive mechanical, pneumatic, and hydraulic subsystems. EMALS uses no steam, which makes it suitable for the Navys planned all-electric ships. The EMALS could be more easily incorporated into a ramp. Compared to steam
12、catapults, EMALS can control the launch performance with greater precision, allowing it to launch more kinds of aircraft, from heavy fighter jets to light unmanned aircraft. EMALS can also deliver 29 percent more energy than steams approximately 95 megajoules, increasing the output to 122 megajoules
13、. The EMALS will also be more efficient than the 5-percent efficiency of steam catapults. Systems that use or will use electromagnetic aircraft launch systems EMALS is a design feature of the Ford-class carrier. Such a launch system was also considered as a retrofit for carriers of the Nimitz class,
14、 but was not workable due to the high electrical power requirements of the EMALS catapults, requirements that the two Westinghouse A4W reactors on board the ships of this class could not provide. John Schank stated: “The biggest problems facing the Nimitz class are the limited electrical power gener
15、ation capability and the upgrade-driven increase in ship weight and erosion of the center-of-gravity margin needed to maintain ship stability.“ Therefore the newer Ford class carriers were equipped with powerplants that produce more power than the ship actually needs as of now. This allows unforesee
16、n technological advances to be implemented later, something which evidently was not possible with the Nimitz when the possibility for EMALS was considered on this class. Converteam UK were working on an electro-magnetic catapult (EMCAT) system for the Queen Elizabeth-class aircraft carrier. In August 2009, speculation mounted that the UK may drop the STOVL F-35B for the CTOL F-35C model, which would have meant the carriers being bu
