The steam-powered catapults that propel planes along aircraft-carrier flight decks may soon be replaced by electromagnetic launch systems
The crashing of the waves and the incessant roar of the fighter jets as, one by one, they are slung from the ship, make the flight deck of an aircraft carrier one of the more awe-inspiring sights of modern aviation. It is certainly a far cry from the dawdling taxiing and listless flick through the in-flight magazine that characterises most peoples’ experience of take-off.
While the performance of the fighter jets and the ship both play a critical role in this adrenaline-fuelled collision of marine and aviation technology, the key enabling technology is the immense catapults that accelerate the aircraft to take-off speed along a runway that is just a couple of hundred feet long.
While a typical steam catapult operates at a limit of about 95MJ, EMALS is reported to have a delivered energy capability of 122MJ, which means it should be able to cope with the heavier naval aircraft that are becoming more popular.
Conversely, the precise control that it allows means that it could also be used to launch aircraft that currently fall below the minimum weight limit allowed on steam-powered launchers. With unmanned aerial vehicles (UAVs) becoming increasingly important to military superpowers, this is expected to be a particularly useful capability.
The most visible of the system’s components is the moving shuttle that, in the same manner as existing catapults, provides the interface between the aircraft and the launch motor.
The shuttle is moved by an integrated linear induction motor that converts two- to three-second pulses of current into the electromagnetic forces necessary to accelerate the aircraft along the launch stroke. After the aircraft launches, the electric current in the motor will reverse to brake the shuttle to a complete halt and return it to its start position.
The required energy for a launch is drawn from the energy-storage devices, which are connected to the ships electrical systems and are recharged between launches. A power electronics system packaged in cabinets that are located below deck draw power from the energy store and convert it to the appropriate voltage and current to drive the shuttle along the launch stroke.
As well as the numerous short-term advantages claimed for the system, it could also offer some flexibility for the design of future aircraft carriers. For instance, unlike traditional steam-powered catapults, an EMALS could, in theory, be incorporated into a ramp, thus reducing the required launch speed and lowering the energy demand.
While the US Naval Air Systems Command (NAVAIR), GA’s customer for EMALS, appears keen to deploy the technology sooner rather than later, the UK appears undecided.
Although electromagnetic launch systems have reportedly been considered for the UK’s Queen Elizabeth-class future aircraft carrier (CVF), the Ministry of Defence (MoD) has not yet made a firm decision on the technology.
An MoD spokeswoman told The Engineer: ‘The UK’s new aircraft carriers… are being built to operate the short take-off and vertical landing [STOVL] variant of the Joint Combat Aircraft (F-35 Lightning) that does not require catapult launch or arrested recovery. Nevertheless, these ships have been designed to be adaptable and could, at some point in the future, be converted in refit to incorporate catapults and arrestor wires. The choice of catapult technology would be dependent upon an assessment of the options at that time.’
However, UK-based naval power and propulsion specialist Converteam told The Engineer that it is currently investigating electromagnetic launch systems for the MoD. The company, which is also part of the Aircraft Carrier Alliance (ACA), successfully trialled a prototype launch system for UAVs — dubbed Electro Magnetic Kinetic Integrated Technology (EMKIT) — back in 2007. Consisting of launch track, eight pairs of linear induction motors, a braking system, power converters, transformers, energy stores systems and a diesel generator, the system carried out more than 2,500 simulated launches, accelerating a dummy carriage along a 15m track to a speed of 51m/s.
A spokeswoman confirmed that the company is now working with further MoD funding on the development of a larger, more powerful system called EMCAT that may also be used to launch unmanned aircraft.