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The EMALS system is a multi-megawatt electric power system involving generators, energy storage, power conversion, a 1,00,000 hp electric motor, and an advanced technology closed loop control system
Folowing systems are currently being used for aircraft take off and landing on aircraft carriers:
Catapult-assisted take-off but arrested-recovery (CATOBAR). This system is meant for large, heavy and heavily armed aircraft. At present US, France and Brazil use this system. There are many means to power the catapult like air pressure, hydraulic and steam power. At present the use of electro-magnetic means to power the system is under development.
Short take-off but arrested-recovery (STOBAR). This system is limited for use with lighter fixed-wing aircraft with more limited payloads. At present Russia, China, and India use this system.
Short take-off vertical-landing (STOVL). This system can be used for STOVL aircraft like the Harrier Jump Jet family and Yak-38. At present it is in use with India and Italy.
Electromagnetic Aircraft Launch System (EMALS)
Steam powered catapults have many limitations. Being very large systems, they require large manpower to operate and maintain. They are reaching a plateau in power generation as such will not cope up with the future heavier aircraft. Steam catapult launch has an adverse effect on the life of the aircraft as it is not smooth. The weight of the aircraft dictates the amount of steam to be used but once the launch starts there is no way to fine-tune the quantity of steam. Excess of steam will rip off the nose wheel landing gear which is attached to the catapult. Too little steam will not provide adequate speed for take- off. Considering some of these limitations, EMALS is under development by General Atomics for the US Navy’s latest aircraft carriers, contract award of the Program Definition and Risk Reduction phase was given in 1999. Westinghouse had developed almost similar system in 1946 but which was not deployed.
The EMALS system is a multi-megawatt electric power system involving generators, energy storage, power conversion, a 1,00,000 hp electric motor, and an advanced technology closed loop control system with built in performance monitoring. It is planned to replace the current steam catapult being used on all US aircraft carriers. The Gerald R. Ford is designated to be the first carrier to use EMALS. The advantages as given out by General Atomics are:
EMALS is based on larger linear induction motors. The system works with the help of two 300-foot-long stationary beams, or stators which are spaced a couple of inches apart; a 20-foot-long carriage or shuttle which is sandwiched between the two beams and can slide back and forth along their lengths. Each beam is made up of dozens of segments. Along the two beams is the wiring sealed in a housing which turns the beams into an electromagnetic force to propel the carriage. When the beams are selectively switched on and off, they generate an attractive magnetic force at the carriage’s leading edge and a repulsive magnetic force at its rear. Only the segments around the moving carriage are energised, creating the effect of a magnetic field which while moving through the twin stationary beams, propels the carriage. The carriage and the aircraft are connected through the nose wheel landing gear and employs the same hardware as used by the current system. After the system is switched on, the aircraft is pushed and pulled electromagnetically down the catapult until airborne. The carriage releases the aircraft at about 200 miles (320 km) and comes to a stop in only 20feet (about 6 m) due to reversing the electromagnetic field which is also used to bring the carriage to the starting point for another launch. Major subsystems are:
Prime Power Interface
This system provides the interconnect with the ship’s electrical distribution system and delivers power to drive the energy storage generators.
This has been developed in a linear induction motor configuration which is compact and modular which is integrated with the flight-deck structure that converts electrical current into the electromagnetic forces to accelerate the aircraft for launching. The motor is designed to withstand the conditions existing on the flight-deck as well during launch operations. Power
Power Conversion Electronics
The power conversion electronics derive power from the energy stored and convert this power to a travelling wave of energy of the appropriate voltage and current to drive the carriage for launch.
The EMALS uses a state-of-the-art system to control the current into the launch motor in real time in which launch speeds cater for a wider range of aircraft types and weights as compared to steam catapults. The smoother acceleration for launch may extend the lifetime of the aircraft.
The required energy for a launch is drawn from the energy storage devices during each two- to three-second launch. The energy storage devices are recharged from ship’s power between launches. EMALS can launch every 45 seconds. Each three-second launch can consume as much as 100 million watts of electricity, about as much as a small town uses in the same amount of time. Such a system may use an acre of equipment but as per lab engineer Mike Doyle, “due to shipboard space limitations, we have to take that and fit it into a shoebox.”
Energy Distribution System
This system delivers the energy from the power conversion system to the launch motor. The ground-based EMALS catapult tests have launched EA-18G Growlers, F/A-18 Super Hornets, C-2 Greyhound planes and E2D Advanced Hawkeyes, among others. In fact, EMALS has even launched an F-35 Joint Strike Fighter at Lakehurst. The first ship borne EMALS system has been under construction for several years aboard the US Gerald R. Ford (CVN 78), the first in class of the new carriers expected to be delivered to the Navy in 2016.
Advanced Arresting Gear (AAG) programme
General Atomics was awarded this contract in 2003 to supply US Navy aircraft carriers with an electric motor-based system that will replace the current MK 7 hydraulic system for aircraft deceleration during recovery operations. AAG allows arrestment of a broader range of aircraft, reduces manning and maintenance, provides higher reliability, and safety margins. It replaces the mechanical hydraulic ram with rotary engines using simple, proven energy-absorbing water turbines coupled to a large induction motor, providing fine control of the arresting forces. AAG has many advantages over the current recovery systems as it is fully compatible with Nimitz class and Ford class carriers, has renewed service life margins, self-diagnosis and maintenance alerts and reduced manning and total ownership cost.
During his visit to US in December, Defence Minister Manohar Parrikar and Secretary Ashton Carter commended positive discussions at the Joint Working Group on Aircraft Carrier Technology Cooperation (JWGACTC), especially in the area of Aircraft Launch and Recovery Equipment (ALRE), and look forward to continued progress to be achieved at the second meeting of the JWGACTC in February 2016 in India. It is reported that INS Vikrant, which is currently under construction at Cochin, will have a catapult launch system instead of a ski-jump. India thus may be interested in EMALS and AAG.