Electromagnetic launcher foreseen for UAVs UK NAVAL PROGRAMMES
T
HE UK Ministry of Defence (MoD) and Converteam formally inaugurated an
Electro Magnetic Kinetic Integrated Technology (EMKIT) unmanned air vehicle (UAV) launch technical demonstrator at the Bruntingthorpe airfield test site in Leicestershire, UK, on 20 March 2007. Funded through the Ministry of Defence’s
Director Equipment Capability (Above Water Effects) research programme, the EMKIT project covers the design, build, and testing of a high-speed high-acceleration system, and will be used to prove electromagnetic (EM) launch technology. Converteam was awarded a £2.6 million
contract by the MoD’s Research Acquisition Organisation in April 2005, for the design, build, and testing of the EMKIT demonstrator system. Testing, due to conclude in mid-2007, will include full speed dynamic acceleration and stopping tests on a range of test masses, at a range of speeds, within a short launch length, in order to demonstrate the flexibility and scalability of the technology. The Ministry of Defence and Converteam
had previously completed a study on the core technology required to launch aircraft from an aircraft carrier using an Electro Magnetic Catapult (EMCAT). This effort, completed in March 2003, used simulation and stall testing of an Advanced Linear Motor (ALIM) to prove thrust density and other core technology components. Furthermore, the EMCAT project showed that the technology had real potential for wider exploitation, and with scalability, had a broader application to any form of linear launch. Although a specific UK requirement for an EM
launch system has not yet been formalised, the wider electrification of naval propulsion, auxiliary, and weapon systems has gathered momentum for future platforms. Also, with the increasing use of UAVs, there is an acknowledged need to ensure that EM launch technology is available, with the correct level of maturity and within the UK equipment supplier base, to meet the potential future needs of the Ministry of Defence and Royal Navy. EMKIT is a full-scale land-based demonstrator,
intended to prove the launch of a medium to large UAV from a naval platform. The notional operational requirement envisages an EM launch system capable of launching UAVs such as the Hermes 180, Hermes 450, Eagle-1, I-Gnat and Predator-A. The requirement for a short launch length and high-g acceleration is predicated on launch from the flight deck of a frigate or destroyer-size vessel. To explore the potential of EM launch within
the boundaries of potential target platforms and UAVs, a set of indicative technical requirements has been developed for the demonstrator rig. These include a variable launch mass of 0kg- 500kg at rated speed, a variable end speed of 0ms-1 _ 50ms-1 at rated mass, a 15m launch length, a duty cycle of five launches per hour, and a maximum acceleration of 10g. Building on previous ALIM work undertaken
as part of the EMCAT project, the EMKIT demonstrator comprises of two 3.2MJ, 6000rev/
42 EMKIT technology demonstrator (source: Converteam).
min two-pole pulsed alternator energy stores, two insulated gate bipolar transistor 6000A, 0V-730V high power converters each with a 7.5MVA peak output, eight 2.2m ALIM stator pairs, a 4.4m reaction plate and a catapult frame with friction brake. Additionally, the demonstrator system has a test vehicle and track, diesel generator, transformers, switchboard, and a data logging system for the purpose of system demonstration. The high-pulsed energy demands and short
duty cycle of the system require the use of energy stores to provide the power requirements to the catapult. This maximises the system economy, reduces disturbances on the power system of the platform, and provides a near self-contained system requiring minimum interface to the prospective platform. The converters drive the energy stores up to
their rated speed by taking power slowly and at a low level from the local supply, which in this case is the diesel generator, representative of the vessel power system. Once the energy stores are at rated speed, the charge/launch contactors swap over and the converter’s supply bridge now effectively becomes the motor bridge, transferring the stored energy by a Variable Voltage Variable Frequency supply to the ALIMs. The use of low-slip ALIMs and suitable control algorithms allow them to be controlled open loop and apply constant thrust to the launch vehicle. Eight pairs of ALIMs provide the required
thrust for the catapult accelerator section at 27kN of thrust. A total of 54kN of thrust is transferred to the reaction plate (given that two pairs of motors are on load at any one time). Due to safety constraints at the test site, the test launch vehicle takes the form of a trolley restrained on a track (adopting basic roller coaster principles).
EMKIT topology (source: Converteam).
Once the vehicle is launched, the converters
then retract the shuttle to the start position, automatically reverting to their recharging configuration and bringing the energy stores back up to their rated speed, using closed loop vector control, ready for any subsequent launches. The EMKIT launch demonstrator was
installed, set-to-work, and commissioned at Bruntingthorpe in the latter part of 2006. Performance testing began in March, with initial work addressing low power trials (using diesel generator output as a direct energy source) to prove mechanical systems, converter control, and the data acquisition and measurement system. On satisfactory completion of low power
trials, the system will be reconfigured into the principal energy store mode for high-speed full- power trials. At this point, with the basic ALIM and system control proven, trials activities will concentrate on achieving full thrust, rated energy, and profiling of the system. Testing is planned to run through to July/August this year, with a final technology report, including a summation of system performance, to be submitted at the end of the contract in September 2007.
WARSHIP TECHNOLOGY MAY 2007
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