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The Electromagnetic Aircraft Launch System (EMALS) is a type of aircraft launching system currently under development by General Atomics for the United States Navy. EMALS uses electrical energy to propel Aircraft by converting electric energy into kinetic energy. The system launches carrier-based aircraft by means of a catapult employing a linear induction motor rather than the conventional steam piston. EMALS was developed for the Navy’s Gerald R. Ford-class aircraft carriers and will be used in all future U.S. Navy aircraft carriers. US Navy has finished Load testing of the Electromagnetic Aircraft Launch System (EMALS) aboard the future aircraft carrier PCU Gerald R. Ford (CVN-78). The tests catapult “dead loads” placed on weighted sleds into the river.
Many countries are planning EMAIL systems for their future carriers. China will use one or more electromagnetic catapults for fighter jets on its third aircraft carrier, the Beijing-based Global Times has revealed, citing an anonymous expert within the military. Russia’s United Shipbuilding Corporation is reportedly external link developing a new aircraft launch system to be deployed on aircraft carriers. The company did yet not specify the characteristics of these systems or the timeframe of their development.
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. US has decided to release the crucial Electromagnetic Aircraft Launch System for the Indian Navy’s future aircraft carrier, according to the Trump administration.
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. This system allows for a more graded acceleration, inducing less stress on the aircraft’s airframe which could extend their lifetime and save maintenance costs. The EMALS will also be more efficient than the 5-percent efficiency of steam catapults.
Electromagnetic Aircraft Launch System (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. 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. It also reduces the carrier’s requirement of fresh water, thus reducing the demand for energy-intensive desalination.
The Ford class aircraft carriers, carry up to 90 aircraft, including the Lockheed Martin F-35C Lightning II, and Northrop Grumman’s new unmanned combat air vehicle, the X-47B. Due to its flexible architecture, the electromagnetic aircraft launch system can launch a wide variety of aircraft weights and can be used on a variety of platforms with differing catapult configurations, says GA.
However, EMALS system requires enormous electrical power requirements, hence is not considered workable on earlier Nimitz class of carriers. Therefore, the newer Ford class’ carriers were equipped with power plants that produce more power than the ship actually needs to cater for future EMALS requirements. The USS Ford is able to generate 13,800 volts of electrical power, more than three times the 4,160 volts that a Nimitz-class carrier generates. EMALS is also suitable for the Navy’s planned all-electric ships.
General Atomics was awarded a $573 million deal from the Navy in 2009 for EMALS development. The ground-based EMALS catapult tests have launched EA-18G Growlers, F/A-18 Super Hornets, C-2 Greyhound planes and E2D Advanced Hawkeyes, and even F-35 Joint Strike Fighter. Hardware delivery is due to be complete by the end of the year. GA received a second contract this August to install EMALS and AAG on the second in class, CVN 79, which will be named John F. Kennedy and will be delivered in 2023.
Even before on-board installation began on the Gerald R. Ford, GA-EMS trialled its EMALS systems at it’s specially designed Shipset Controls Lab (SCL) at its facility in San Diego, California, which accurately simulates Ford class catapult flight deck controls. Launches of a range of aircraft including an F-35C Joint Strike Fighter have been carried out using a land-based EMALS system at Naval Air Systems Command (NAVAIR) in Lakehurst, New Jersey since 2010.
The EMALS system is also engineered to work in tandem with the USS Ford’s new Advanced Arresting Gear, or AAG to safely bring landing aircraft to a halt. Similar to EMALS, the AAG is also designed to reduce stress on the airframe during the landing process. The other half of GA’s contract with the US Navy will deliver the Advanced Arresting Gear (AAG) to replace the hydraulic ram and rotary engines currently used. AAG uses energy-absorbing water turbines coupled with a large induction motor, provides fine control of the arresting forces and will work on Nimitz and Ford class carriers.
China’s third aircraft carrier to be equipped with EMALS catapult
China’s first aircraft carrier is in operation; the second carrier is currently under advanced stage of construction and third is in the planning phase. The third carrier shall be equipped with a Electromagnetically Assisted Aircraft Launch System (EMALS) catapult. Compared to steam catapautls, EMALS catapults are less maintenance intensive, mechanically simpler and have greater power and flexibility to launch aircraft of different sizes.
Hong Kong’s South China Morning Post newspaper, quoting sources close to China’s People’s Liberation Army, reported that a team led by China’s top naval engineer, Rear Adm. Ma Weiming, has developed a medium-voltage, direct-current transmission network to replace an earlier system based on alternating current. Forming part of an integrated propulsion system, the new system would allow a conventionally powered aircraft carrier to operate an Electromagnetic Aircraft Launch System, or EMALS, which conveys a number of advantages over traditional steam catapults that include increased efficiency, precision and shortening aircraft launch cycles.
The People’s Liberation Army Navy, or PLAN, has been operating a pair of catapults at its carrier training base at Huangdicun since the second half of 2016. The pair are believed to consist of a single steam catapult and one EMALS. The service is evaluating both systems and carrying out test launches using a modified Shenyang J-15 (Flying Shark) carrierborne fighter jet.
Indian navy shown interest in installing EMALS for planned Supercarrier INS Vishal
The Indian Navy has initiated the first steps towards acquiring the Electromagnetic Aircraft Launch System (EMALS) for carriers as well as the long-range Predator B Guardian surveillance drone by sending Letters of Request (LoRs) to the Pentagon under government-to-government deals.
The Indian Navy’s second indigenous aircraft carrier, INS Vishal due by 2028, will be a 65,000-ton nuclear-powered, capable of carrying up to 55 aircraft and will be more than 300 metres long. The Predator B Guardian is a naval version for long-range surveillance over waters
EMALS technology
The projectile experiences a Lorentz force due to magnetic field (produced by the current flowing through rails) and current flowing
across the armature itself. The force applied by the shuttle on the aircraft is directly proportional to the current supplied by the energy conversion systems and the length of the rails. Greater the amount of current, more will be the force applied, leading to requirement of power
sources that can provide such amounts of current.
The EMALS consists of four main elements:
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.
The average power from the prime power is rectified and then fed to inverters. With power from the inverters, the four disk alternators operate as motors and spin up the rotors in the 45 seconds between launches. The disk alternator is a dual stator, axial field, permanent magnet machine. The rotor serves both as the kinetic energy storage component and the field source during power generation and is sandwiched between the two stators.
There are two separate windings in the stators, one for motoring and the other for power generation. The motor windings are placed deeper in the slots for better thermal conduction to the outside casing. The generator windings are closer to the air gap to reduce the reactance during the pulse generation. The use of high strength permanent magnets allows for a high pole pair number, 20, which gives a better utilization of the overall active area. The rotor is an inconel forging with an inconel hoop for prestress. The four disk alternators are mounted in a torque frame and are paired in counter-rotating pairs to reduce the torque and gyroscopic effects.
The rotors operate at a maximum of 6400 rpm and store a total of 121 MJ each. This gives an energy density of 18.1 KJ/KG, excluding the torque frame. 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. Cycloconverters amplify the Electrical power from energy storage systems which increases its voltage and frequency to provide sufficient launch energy. 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. The controls allow EMALS to operate at variable speed according to varying loads.
Linear induction motor
The linear synchronous motor takes the power from the cycloconverter and accelerates the aircraft down the launch stroke, all the while providing “real time” closed loop control. 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 linear motors are engineered to help create a sequentially activated rolling magnetic field or wave able to thrust or propel aircraft forward, Navy program officials explained.
The linear induction motor consists of a row of stator coils that have the function of a conventional motor’s armature. The aluminum plate runs in between stationary sections of 12-foot long linear motors. 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).
The motor itself is a dual, vertical stator configuration with the active area facing outwards. The rotor, or carriage, sits over the stators much like a saddle and protrudes through the flight deck to be attached to the aircraft. The carriage contains 160 full permanent magnets, the same type used in the disk alternator, NdBFe. The carriage is restrained in two axes by rollers. The rollers run in channels welded to the stator frame. This allows both the stator and trough to flex with the ship and the carriage to follow this flexure while maintaining a consistent air gap.
At the end of the 103 m power stroke, the front of the carriage enters the brake. This brake consists of shorted stator segments, which act as eddy current brakes. At the same point in time, the carriage is still covering a number of active stator segments. Two phases are switched in these segments so that reverse thrust is initiated to help with the braking force.
Thermal Management
With a projected efficiency of 70% and peak losses of 13.3 MW in the stator, active cooling will be necessary. Maximum coil action is 4.36e6 A2(squared)s, resulting in a maximum copper temperature delta of 118.2 Degrees C. The launch motor has an aluminum cold plate to remove this heat from the attached stator windings and back iron. The cold plates consist of stainless steel tubes in an aluminum casting. The peak temperature reaches approximately 155oC and, after cooling for the 45 second cycle time, cools to 75oC. The carriage that houses the permanent magnets will be cooled by convection, since there will be only slight heating from eddy currents in the carriage structure and magnets.
Control consoles
The launch profile is continuously monitored by the control systems in real time. Closed loop feedback control system allows the crew to keep a track of the various parameters even when the launch has initiated.
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.
General Atomics claims that there is a decrease in manning by 30% if the carriers are equipped by EMALS due to its self-diagnostic feature. The closed loop monitoring system also allows EMALS to adjust according to the weight of the aircraft which is very crucial for light unmanned surveillance aircraft. Being constructed modular in nature EMALS would be more efficient in terms of maintenance and future
upgrades
References and Resources also include:
https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launch_System
https://www.globalsecurity.org/military/systems/ship/systems/emals.htm
