- Electromagnetic Aircraft Launch System
Electromagnetic Aircraft Launch System (EMALS) is a system under development by the
United States Navyto launch aircraft from carriers using a linear motordrive instead of steam pistons used in conventional aircraft catapults. This technology has the advantage of gradually increasing the aircraft's speed, thus reducing the stress the plane's airframehas to support. The EMALS is currently being developed for the U.S. Navy's newest "Ford "class aircraft carriers. It was also considered for the Royal Navy's new "Queen Elizabeth" class aircraft carriers (CVF), but the Royal Navy opted for a Vertical/Short Takeoff and Landing( VSTOL) configuration instead.
How EMALS works
The EMALS in based on the concept of the linear induction motor (LIM). This system uses large electric currents to generate strong magnetic fields, which in turn propel the carriage down a track to launch the aircraft.cite news
title=How It Works
accessdate=2008-02-18 ] The EMALS consists of [http://www.ga.com/atg/EMS/m1346.php four main elements] :
*Linear induction motor
Linear induction motor
The linear induction motor (LIM) is the main component of the EMALS. It consists of a row of stator coils that, when energized, accelerate the carriage (equivalent to a conventional motor’s rotor) down the track. Only the section of the
statorcoils surrounding the carriage is energized at any given time, minimizing reactive losses. The EMALS will use a convert|300|ft|m|abbr=on long LIM capable of launching a convert|100000|lb|abbr=on aircraft to convert|130|kn|km/h.
Energy storage subsystem
To power the LIM, the EMALS requires a large amount of electric energy to be used in a short amount of time. The ship’s power source can’t provide this kind of immediate energy, so the energy-storage subsystem is designed to accumulate power from the ship and store it kinetically on rotors of four disk
alternators. cite news
author=Doyle, Samuel, Conway, and Klimowski
title = Electromagnetic Aircraft Launch System - EMALS
url = http://www.lakehurst.navy.mil/nlweb/ieeerevc.pdf
accessdate=2008-03-12] Each rotor can store more than 100 MJ, and they are able to recharge within 45 seconds of a launch.
Power conversion subsystem
At the time of launch, the power conversion subsystem releases the stored energy from the disk alternators in a controlled manner by using a cycloconverter. The
cycloconverterprovides a controlled rising frequency and voltage to the LIM, energizing only the small portion of stator coils that affect the launch carriage at each instant in time.
The power used by the EMALS is controlled through a closed loop system to give the operators complete control over the system's performance. A number of
Hall effectsensors positioned on the track provide feedback to the control consoles, allowing the system to monitor itself and ensure that it provides the desired acceleration. The closed loop control system allows the EMALS to maintain a constant tow force, which helps reduce the launch stresses on the plane’s airframe.
The EMALS has a number of significant advantages over the conventional steam driven catapult system, including reduced weight, volume, and maintenance, and increased controllability, availability, reliability, and efficiency.
One of the most important advantages of the EMALS is its simplicity, compared to the existing catapult system. The steam catapult system, which uses about 614 kg of steam per launch, requires extensive mechanical, pneumatic, and hydraulic subsystems that complicate the launch system as a whole. With the EMALS, launching, braking, and retraction would be performed by the linear induction motor, eliminating a substantial amount of auxiliary components. The EMALS is an entirely stand alone electric system, requiring no steam to be pumped around the ship.cite web
title=Defense Tech: EMALS: Next Gen Catapult
first=Christian] This characteristic makes the EMALS easily suitable for integration into the all-electric ships the U.S. Navy is currently researching. Its simplicity also reduces the manpower necessary to operate and maintain the system.
The EMALS is also a much more flexible system. Its feedback control system allows operators to control the launch performance with greater precision. This ability makes the EMALS capable of launching a wide variety of aircraft, from heavy fighter jets to lightweight unmanned aircraft. The EMALS could also be easily incorporated into a ramp, which would reduce the aircraft’s required end speed and consequently the launch energy.
The EMALS offers the increased energy capability necessary to launch the next generation of carrier based aircraft. The current steam catapult system can deliver about 95 MJ of energy, while the EMALS is capable of 122 MJ, a 29% increase. The EMALS is also being designed to be much more efficient than the current system, which is only about 5% efficient. With a cycle time of only 45 seconds, the EMALS can launch planes much more quickly than the conventional launch system.
* [http://www.globalsecurity.org/military/systems/ship/systems/emals.htm "Electromagnetic Aircraft Launch System - EMALS"] , "GlobalSecurity.org"
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