The U.S. Navy is presently pursuing electromagnetic launch technology to replace the existing steam catapults on current and future aircraft carriers.
The steam catapults are large, heavy, and operate without feedback control. They impart large transient loads to the airframe and are difficult and
time consuming to maintain. The steam catapult is also approaching its operational limit with the present complement of naval aircraft. The inexorable
trend towards heavier, faster aircraft will soon result in launch energy requirements that exceed the capability of the steam catapult. An
electromagnetic launch system offers higher launch energy capability, as well as substantial improvements in areas other than performance. These
include reduced weight, volume, and maintenance; and increased controllability, availability, reliability, and efficiency.
Pros of EMALS (electromagnetic aircraft launch system)
The introduction of EMALS would have an overall positive impact on the ship. The launch engine is capable of a high thrust density, as shown by the
half scale model that demonstrated 1322 psi over its cross section. This is compared to the relatively low 450 psi of the steam catapult. The same is
true with energy storage devices, which would be analogous to the steam catapult's steam accumulator. The low energy density of the steam accumulator
would be replaced by high energy density flywheels. These flywheels provide energy densities of 28 KJ/KG. The increased densities would reduce the
system's volume and would allow for more room for vital support equipment on the host platform.
Another advantage of EMALS is that it would reduce manning requirements by inspecting and troubleshooting itself. This would be a significant
improvement over the present system, which requires substantial manual inspection and maintenance. The EMALS, however, will require a transition of
expertise from mechanical to electrical/electronic.
EMALS eliminates the complexity of the present system's conglomeration of different subsystems. The steam catapult uses about 614 kg of steam for a
launch, it uses hydraulics extensively, water for braking, and electromechanics. These subsystems, along with their associated pumps, motors, and
control systems tend to complicate the launch system as a whole. With EMALS, launching, braking, and retraction would be achieved by the launch motor,
thereby reducing all the auxiliary components and simplifying the overall system. The hydraulic oils, compressed air, etc. would be eliminated as well
as the cylinder lubricating oil that is expelled into the environment with each shot. The EMALS would be a stand alone system, completely independent
of the ship's main plant. This will allow greater flexibility in the design of the ship and more efficient ship propulsion schemes.
One of the major advantages of electromagnetic launch is the ability to integrate into the all electric ship. The Navy has directed substantial
research into its Advanced Surface Machinery program that is developing electric derived propulsion schemes for the next generation of surface
combatants. There has also been a good deal of work in high power electric weapon systems -. As such, more and more of a ship's systems will
evolve into the electrical counterparts of old mechanical systems. This is true of the launch, and eventually, the arresting gear. The average power
required by EMALS is only 6.35 MVA. Taking these power levels off the grid should not be a problem in an all electric ship, considering multimegawatt
pumps already exist on carriers for various applications.
Perhaps the most interesting aspect of electromagnetic launch is the flexibility it offers in the way of future aircraft and ship designs. An
electromagnetic launcher could easily be sized down to perform as a launch-assist system, augmenting the short takeoff of a STOVL aircraft. It can
also be easily incorporated into the contour of a ramp, which provides a more efficient fly-away angle for the aircraft being launched. This reduces
the required endspeed, the commensurate energy supplied, as well as the stresses on the airframe. Overall, an EM launcher offers a great deal of
flexibility to future naval requirements and ship designs
The Downsizes of EMALS
On the other hand, there are drawbacks to the EMALS. One of these is that high power electromagnetic motors create electromagnetic interference (EMI)
with electronic equipment. As in the case of an electromagnetic launcher, there would be sensitive aircraft equipment sitting directly above the
launch motor. Along with the aircraft equipment is the ship's own equipment, which may be affected by the electromagnetic emissions. Through proper
EMC design and a "magnetically closed" motor design, EMI will be minimized.
Another drawback of an electromagnetic launcher is the high speed rotating machinery associated with pulsed power applications. The disk alternator
rotors are spinning at 6400 rpm, each storing 121 MJ, for a total of 484 MJ. In a laboratory, this is not a problem, but put these rotors on a
heaving, jarring platform and it becomes more complicated. In order to ensure safe operation, the flywheel and bearings are to be a stiffer design
Due to the inherent high level of elegant control of electronic equipment, it is possible to reduce the stresses imparted to the aircraft. The present
steam catapult has relatively high peak-tomean acceleration profiles (nominally 1.25, with excursions up to 2.0). This results in high stresses in the
airframe and generally poor performance. With an electromagnetic system it would be possible to correct for deviations in the acceleration profile in
typically hundreds of milliseconds, which would result in low peak-tomeans. A simulation was conducted that analyzed the level of controllability of
the proposed design. The acceleration profile is smooth and flat, compared with a typical steam catapult profile. The simulation shows that for
various load conditions, the EMALS is capable of operating within the 1.05 max peak-to-mean acceleration requirement. The result of this reduced
peak-to-mean is reduced stress on the airframe. To quantify the effects of a reduced peak-to-mean, a Fracture Mechanics analysis was conducted on the
airframe  with both the steam catapult and EMALS peak-to-means. The results from this analysis show a peak airframe life extension of 31% due to
the reduced stresses on the airframe. This is becoming more important as tight budgets are forcing the Navy to procure fewer aircraft. This also has
the benefit of a safer operational environment, since when the EMALS experiences any unforeseen problems during a launch, it has the capability to
quickly adjust and correct for them, even if a component fails during the launch
company that is working on it website
What this tells me is the key things the navy wants of future technolgies are reduced weight, volume, and maintenance; and increased controllability,
availability, reliability, and efficiency. I think in some ways the whole military wants that, thats why were beginning to test EM (electromagnetic)
armor for our vehicles. EM armor is a lot lighter then regular armor, but still offers a lot of protection, but the reasons of course are different.
We want lighter vehicles for more speed, and deployabilty. Thats one of the major problems with the M1 Abrams, they can only fit like one on a C5
Globemaster. And thats where electricty comes in, the main pros of it are effiency, less maintenance because of that, which of course reduces crew
size, which in turn saves the navy a lot of money, because of less salaries it has to pay. Thats why I think the US military of tommorow is gonna be
able to deploy faster, because it smaller, more like a collection of strike groups. But I'll get some more links up here about how it works, and the
[edit on 2-7-2005 by blue cell]