 | ||
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 is that this system allows for a more graded acceleration, inducing less stress on the aircraft's airframe.
Contents
- Design and development
- Linear induction motor
- Energy storage subsystem
- Power conversion subsystem
- Control consoles
- Program status
- Advantages
- Systems that use or will use electromagnetic aircraft launch systems
- References
Other advantages include lower system weight, with a projected lower cost and decreased maintenance requirements. The design includes the ability to launch aircraft that are heavier or lighter than the conventional system can accommodate. In addition, the system requires far less fresh water, reducing the need for energy-intensive desalination.
Design and development
The EMALS is being developed by General Atomics for the U.S. Navy's newest aircraft carriers. A somewhat similar system, Westinghouse's electropult, had been developed in 1946 but not deployed.
Linear induction motor
The EMALS uses a linear induction motor (LIM), which uses electric currents to generate magnetic fields that propel a carriage along 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 motor’s armature. When energized, the motor accelerates the carriage along the track. Only the section of the coils surrounding 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 kn (240 km/h; 150 mph).
Energy storage subsystem
During a launch, the induction motor requires a large surge of electric power that exceeds what the ship's own continuous power source can provide. As of 1994, the EMALS energy-storage system design accommodates this by drawing power from the ship during its 45-second recharge period and storing the energy kinetically using the rotors of four disk alternators; the system then releases that energy (up to 484 MJ) in 2–3 seconds. Each rotor delivers up to 121 MJ (34 kWh) from 6400 rpm (approximately one gasoline gallon equivalent) and can be recharged within 45 seconds of a launch; this is faster than steam catapults. A max launch using 121 MJ of energy from each disk alternator slows the rotors from 6400 rpm to 5205 rpm.
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 small 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 system allows the EMALS to maintain a constant tow force, which helps reduce launch stresses on the plane’s airframe.
Program status
Aircraft Compatibility Testing (ACT) Phase 1 concluded in late 2011 following 134 launches (aircraft types comprising the F/A-18E Super Hornet, T-45C Goshawk, C-2A Greyhound, E-2D Advanced Hawkeye, and F-35C Lightning II)using the EMALS demonstrator installed at Naval Air Engineering Station Lakehurst. On completion of ACT 1, the system was reconfigured to be more representative of the actual ship configuration on board the USS Gerald R. Ford, which will use four catapults sharing several energy storage and power conversion subsystems.
ACT Phase 2 began on 25 June 2013 and concluded on 6 April 2014 after a further 310 launches (including launches of the EA-18G Growler and F/A-18C Hornet, as well as another round of testing with aircraft types previously launched during Phase 1). In Phase 2 various carrier situations were simulated, including off-centre launches and planned system faults, to demonstrate that aircraft could meet end-speed and validate launch-critical reliability.
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 energy. Steam catapults, which use about 1,350 lb (610 kg) of steam per launch, have extensive mechanical, pneumatic, and hydraulic subsystems. EMALS uses no steam, which makes it suitable for the Navy's planned all-electric ships.
Compared to steam 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. Each one of the four disk alternators in the EMALS system can deliver 29 percent more energy than a steam catapult's approximately 95 megajoules; each disk alternator can supply up to 121 megajoules. 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, but was not workable due to the high electrical power requirements of the EMALS catapults, requirements that the two Westinghouse nuclear 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 generation 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 power plants that produce more power than the ship actually needs as of now. This allows unforeseen technological advances to be implemented later, something which was not possible with the Nimitz-class when the possibility for EMALS was considered.
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 built to operate conventional takeoff and landing aircraft utilizing the UK-designed non-steam EMCAT catapults.
In October 2010, the UK Government announced it had opted to buy the F-35C, using a then-undecided CATOBAR system. A contract was signed in December 2011 with General Atomics of San Diego to develop EMALS for the Queen Elizabeth-class carriers. However, in May 2012, the UK Government reversed its decision after the projected costs rose to double the original estimate and delivery moved back to 2023, cancelling the F-35C option and reverting to its original decision to buy the STOVL F-35B.
The Indian navy has shown interest in installing EMALS for its planned CATOBAR Supercarrier INS Vishal. The Indian government has shown interest to produce the Electromagnetic Aircraft Launch System locally with the assistance of General Atomics.
Rear Admiral Yin Zhuo of the People's Liberation Army Navy has said that China's next aircraft carrier will also have an electromagnetic aircraft launch system.
The concept of a ground carriage is intended for civilian use and takes the idea of an electromagnetic aircraft launch system one step further, with the entire landing gear remaining on the runway for both takeoff and landing.