Electromagnetic Aircraft Launch System

The Electromagnetic Aircraft Launch System (EMALS) is a type of aircraft launching system developed by General Atomics for the United States Navy. The system launches carrier-based aircraft by means of a catapult employing a linear induction motor rather than the conventional steam piston. EMALS was first installed on the United States Navy's Gerald R. Ford-class aircraft carrier, USS Gerald R. Ford.

A drawing of the linear induction motor used in the EMALS.

Its main advantage is that it accelerates aircraft more smoothly, putting less stress on their airframes. Compared to steam catapults, the EMALS also weighs less, is expected to cost less and require less maintenance, and can launch both heavier and lighter aircraft than a steam piston-driven system. It also reduces the carrier's requirement of fresh water, thus reducing the demand for energy-intensive desalination.

China is reportedly developing a similar system.[1]

Design and development

Developed in the 1950s, steam catapults have proven exceptionally reliable. Carriers equipped with four steam catapults have been able to use at least one of them 99.5 percent of the time.[2] However, there are a number of drawbacks. One group of Navy engineers wrote, "The foremost deficiency is that the catapult operates without feedback control. With no feedback, there often occurs large transients in tow force that can damage or reduce the life of the airframe."[3] The steam system is massive, inefficient (4–6%),[4] and hard to control. These control problems allow Nimitz-class aircraft carrier steam-powered catapults to launch heavy aircraft, but not aircraft as light as many UAVs.

A system somewhat similar to EMALS, Westinghouse's electropult, was developed in 1946 but not deployed.[5]

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.[6] The EMALS consists of four main elements:[7] The linear induction motor consists of a row of stator coils with the same function as the circular stator coils in a conventional induction motor. 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).[6]

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. 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.[8] Each rotor delivers up to 121 MJ (34 kWh) (approximately one gasoline gallon equivalent) and can be recharged within 45 seconds of a launch; this is faster than steam catapults.[6] A maximum-performance launch using 121 MJ of energy from each disk alternator slows the rotors from 6400 rpm to 5205 rpm.[8][9]

Power conversion subsystem

During the launch, the power conversion subsystem releases the stored energy from the disk alternators using a cycloconverter.[6] 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.[8]

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.[6]

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

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 onboard the USS Gerald R. Ford, which will use four catapults sharing several energy storages and power conversion subsystems.[10]

ACT Phase 2 began on 25 June 2013 and concluded on 6 April 2014 after a further 310 launches (including launches of the Boeing EA-18G Growler and McDonnell Douglas 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-center launches and planned system faults, to demonstrate that aircraft could meet end-speed and validate launch-critical reliability.[10]

  • 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.
  • May 2015: First full speed shipboard tests conducted.[18]

Delivery and deployment

On 28 July 2017, Lt. Cmdr. Jamie "Coach" Struck of Air Test and Evaluation Squadron 23 (VX-23) performed the first EMALS catapult launch from USS Gerald R. Ford (CVN-78) in an F/A-18F Super Hornet.[19]

Advantages

Compared to steam catapults, EMALS weighs less, occupies less space, requires less maintenance and manpower, is more reliable, recharges quicker, 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.[8] EMALS uses no steam, which makes it suitable for the US Navy's planned all-electric ships.[20]

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.[20] With up to 121 megajoules available, each one of the four disk alternators in the EMALS system can deliver 29 percent more energy than a steam catapult's approximately 95 MJ.[8] The EMALS, with their planned 90% power conversion efficiency, will also be more efficient than steam catapults, which achieve only a 5% efficiency.[6]

Criticisms

In May 2017, President Donald Trump criticized EMALS during an interview with Time, saying that in comparison to traditional steam catapults, "the digital costs hundreds of millions of dollars more money and it’s no good."[21][22][23][24]

President Trump's criticism was echoed by a highly critical 2018 report from the Pentagon, that emphasized that reliability of EMALS leaves much to be desired and that the average rate of critical failures is nine times higher than the Navy's threshold requirements.[25]

Reliability

In 2013, 201 of 1,967 test launches failed, more than 10 percent.

Factoring in the then-current state of the system, the most generous numbers available in 2013 showed that EMALS has an average "time between failure" rate of 1 in 240. [26]

According to a March 2015 report, "Based on expected reliability growth, the failure rate for the last reported Mean Cycles Between Critical Failure was five times higher than should have been expected. As of August 2014, the Navy has reported that over 3,017 launches have been conducted at the Lakehurst test site, but have not provided DOT&E [Director, Operational Test and Evaluation] with an update of failures."[27]

In the test configuration, EMALS could not launch fighter aircraft with external drop tanks mounted. "The Navy has developed fixes to correct these problems, but testing with manned aircraft to verify the fixes has been postponed to 2017".[28]

In July 2017 the system was successfully tested at sea on the USS Gerald R. Ford.[29]

A December 2019 DOT&E Report stated ”Through the first 747 shipboard launches, EMALS suffered 10 critical failures. This is well below the requirement for Mean Cycles Between Critical Failures” [30]

Systems that use or will use EMALS

China

Rear Admiral Yin Zhuo of the Chinese Navy has said that China's next aircraft carrier will also have an electromagnetic aircraft launch system.[31] Multiple prototypes have been spotted by the media in 2012, and aircraft capable of electromagnetic launching are undergoing testing at a Chinese Navy research facility.[32][33]

According to a report in July 2017, the construction of the Type 003 aircraft carrier has been rescheduled in order to choose between a steam or electromagnetic catapult and the latest competition results shows that the electromagnetic launchers will be used in the Type 003 aircraft carrier.[34][35]

China's military chief claims a breakthrough in electromagnetic launch systems for aircraft carriers has been made, and will utilize such a system in the third aircraft carrier that China will build after Type 002. The launch system is powered by fossil fuel via generators and capacitors.[36][37][38] The design on the Type 003 carrier is being led by Rear Admiral Ma Weiming.

India

The Indian Navy has shown an interest in installing EMALS for its planned CATOBAR supercarrier INS Vishal.[39][40][41] The Indian government has shown interest in producing the Electromagnetic Aircraft Launch System locally with the assistance of General Atomics.[42]

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.[43]

Russia

Russia's United Shipbuilding Corporation (USC) is developing new launch systems for warplanes based on aircraft carriers, USC President Alexei Rakhmanov told TASS on 4 July 2018.[44]

United Kingdom

Converteam UK were working on an electro-magnetic catapult (EMCAT) system for the Queen Elizabeth-class aircraft carrier.[45] 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 using the UK-designed non-steam EMCAT catapults.[46][47]

In October 2010, the UK Government announced it would 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.[45][48] 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.[49]

United States

EMALS was designed for and into the Gerald R. Ford-class aircraft carrier.[50] A proposal to retrofit it into Nimitz-class carriers was rejected. John Schank said, "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."[51]

See also

References
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