Electromagnetic Aircraft Launch System

EMALS

End speed	28–103 m/s
Max. peak-to-mean tow force ratio	1.05
Launch energy	122 MJ
Cycle time	45 seconds
System weight	< 225,000 kg
System volume	< 425 m³
Endspeed variation	−0 to +1.5 m/s

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.

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 conventional 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. Navy's newest Gerald R. Ford-class aircraft carriers. A somewhat similar system, Westinghouse's electropult had been developed in 1946 but not deployed.^[1]

Linear induction motor

The EMALS uses a linear induction motor (LIM), which uses electric currents to generate magnetic fields that propel a carriage down a track to launch the aircraft.^[2] The EMALS consists of four main elements:^[3] 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 down 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 knots (240 km/h).^[2]

Energy storage subsystem

The induction motor requires a large amount of electric power; more than the ship's own power source can provide. The EMALS energy-storage subsystem draws power from the ship and stores energy (up to 484 MJ) kinetically on rotors of four disk alternators, and then releases that energy in 2–3 sec.^[4] Each rotor can store 121 megajoules at 6400 rpm, and can be recharged within 45 seconds of a launch, faster than steam catapults.^[2]

Power conversion subsystem

During launch, the power conversion subsystem releases the stored energy from the disk alternators using a cycloconverter.^[2] 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.^[4]

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 the launch stresses on the plane’s airframe.^[2]

Program status

The Electromagnetic Aircraft Launch System at Naval Air Systems Command, Lakehurst, launching a United States Navy F/A-18E Super Hornet during a test on 18 December 2010

1–2 June 2010: Successful launch of a T-45 Goshawk at Naval Air Engineering Station Lakehurst.^[5]
9–10 June 2010: Successful launch of a C-2 Greyhound at Naval Air Engineering Station Lakehurst.^[6]
18 December 2010: Successful launch of a F/A-18E Super Hornet at Naval Air Engineering Station Lakehurst.^[7]^[8]
27 September 2011: Successful launch of an E-2D Advanced Hawkeye at Naval Air Engineering Station Lakehurst.^[9]^[10]
18 November 2011: Successful launch of a F-35C Lightning II.^[11]

In June 2014, the Navy completed EMALS prototype testing of 450 manned aircraft launches involving every fixed-wing carrier-borne aircraft type in the USN inventory at Joint Base McGuire-Dix-Lakehurst during two Aircraft Compatibility Testing (ACT) campaigns. 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). On completion of ACT 1, the EMALS demonstrator was reconfigured to be more representative of the actual ship configuration on board 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.^[12]

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 614 kilograms of steam per launch, have extensive mechanical, pneumatic, and hydraulic subsystems.^[4] EMALS uses no steam, which makes it suitable for the Navy's planned all-electric ships.^[13] The EMALS could be more easily incorporated into a ramp.^[4]

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.^[13] EMALS can also deliver 29 percent more energy than steam's approximately 95 megajoules, increasing the output to 122 megajoules.^[4] The EMALS will also be more efficient than the 5-percent efficiency of steam catapults.^[2]

Systems that use or will use electromagnetic aircraft launch systems

EMALS is a design feature of the Ford-class carrier.^[14] 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 A4W reactors on board the ships of this class could not provide. ^[15] 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." ^[16] Therefore the newer Ford class' carriers were equipped with powerplants that produce more power than the ship actually needs as of now. This allows unforeseen 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.^[17] 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 (CV) take off and landing aircraft utilizing the UK-designed non-steam EMCAT catapults.^[18]^[19]

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 the General Atomics Company of San Diego to develop EMALS for the Queen Elizabeth-class carriers.^[17]^[20] 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.^[21]

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.^[22]

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.^[23]