Defense: Leaving Steam Power in Its Wake
Navy Looks to Power Aircraft Carriers' Catapults With Electricity
Posted at Apr 20, 2012 6:45 AM
Frank Oliveri
@Frank Oliveri
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For half a century, Americans have marveled at launches from the massive aircraft carriers that are prime emblems of American military might. The roar of engines, the puffs of steam, the jarring and abrupt acceleration  -  and in a few blinks of an eye, a fighter jet is off on its mission.
What the public never sees are the miles of piping carrying the water and then steam that drive the pistons that catapult the planes off the bow. They don't see the energy required to convert salt water into freshwater steam. Or the hundreds of valves and other controls and dozens of people required to make the sophisticated steam engine work.
Effective? Sure. Efficient? Not so much  -  and especially not when compared with electric engines.
In 2015, when the first of a new class of aircraft carrier is complete, electromagnetic pulses are supposed to start hurtling fighter jets, propeller planes and unmanned aircraft from the deck of the USS Gerald R. Ford. That will be a fundamental change in naval warfare that will require less manpower and maintenance, improve reliability and save taxpayers about $250 million over one ship's lifetime. Beyond that, the innovation could herald the dawn of a potentially revolutionary set of ways that electricity is used by the military in coming decades. (The Navy is also testing ways that eletromagnetic pulses might replace gunpowder as the main propellant of shells fired at sea, for example  -  a switch that would significantly reduce the risk of explosion for ships in battle.)
The new generation of aircraft carrier catapult is known as the electromagnetic aircraft launch system  -  or EMALS, in the acronym-happy world of the Navy. The principles of physics on which it operates have been understood for decades, but it has only been within the past 15 years that the computer software and technological controls have come into being to manage the enormous energy field required to propel a 50-ton warplane to a speed of 150 miles an hour in about two seconds. Indeed, the same technology that drives many of today's roller coasters is behind the Navy's new approach  -  albeit with far more energy and hundreds of data checks every second to ensure that the electromagnetic pulses occur at exactly the right instant. Such precision is essential to keeping the pilots, as well as the F-18 Super Hornets and F-35 Joint Strike Fighters they're flying, from being plunged into the sea.
To be sure, the first four catapults to be put to use on the Ford will be costly: $1.1 billion has been committed to developing and building the new system and a coordinated landing apparatus. And the Government Accountability Office has raised concerns that too much development and testing remain to be done even as the carrier is being built. But the principal contractor, the privately held federal contracting conglomerate General Atomics, has signed a fixed production contract that ties its own financial future to meeting the catapults' price target. And the savings over the life of the program hold the potential to far outweigh the costs.
"Basically told the company that's building it, General Atomics, that if you're asking us to bet our ship on it, we're going to ask you to bet your company on it," Navy Secretary Raymond E. Mabus Jr. told the House Appropriations Subcommittee on Defense last month. "It's going to have to come in inside of a certain budget."
A New Age
Steam-powered engines were the dominant technology that powered the Industrial Revolution, increasing production while reducing back-breaking work for 19th-century man and animal. But the same sort of systems enable some of the most technologically dazzling feats of the early 21st century. Indeed, one of the most powerful weapons of war, the Nimitz class aircraft carriers that patrol the world's oceans and symbolize American power, depend on powerful steam pistons to dispatch bomb-laden fighter aircraft each and every day.
But soon the Navy expects its steam pistons to go the way of naval expansion engines and to be replaced by massively powerful and exceedingly efficient linear motors that use electromagnetic pulses to push fighters with enough energy to light a million 100-watt bulbs simultaneously.
"What replaced steam in the industrial sector and in the residential and commercial sector was electricity, and in a way we have been electrifying America for the last 100 years, and we're not done," said Fred Beach, an expert on electromagnetic technologies who was a naval officer and is now affiliated with the University of Texas. "Eventually, electrical devices will probably displace the internal combustion engine. This is basically because of their inherent efficiencies."
For the pistons on today's catapults, the original power source is the carrier's nuclear power plant. But enormous amounts of energy are wasted in the process of pumping salty seawater aboard, converting it to freshwater and then converting that to steam. Indeed, much of the desalinated water created onboard a carrier is used just once, to launch one jet. Every time the catapult is fired, all the steam in the pistons is discharged and soon evaporates. "With an electromagnetic device," Beach said, because the ship is "generating electricity anyway for radar, weapons, heating, lighting and ventilation, now you can use that more efficiently to drive the catapult."
And doing away with the current system means a less heavy and more energy-efficient ship  -  because there is less plumbing, less freshwater in storage and none of the bulky hydraulic and pneumatic systems. It also means a manifest with about 30 fewer sailors, who will no longer be needed to keep all of the pumps, valves, gears, wheels and rods in well-lubricated working order. The electromagnetic linear motor features an armature and some bearings, plus miles of cable, but not much else in terms of moving parts. It is quadruple redundant as well. Large motor generators store the energy below decks.
One other advantage to the electromagnetic catapult is its versatility: The steam-powered machines of today are designed to do their best work throwing the heaviest possible cargo (a fighter jet) and can only be minimally recalibrated to safely and efficiently throw something lighter (a drone, for example). And the steam pistons also almost instantly subject a motionless aircraft to four times the force of gravity  -  an enormous strain that even the best-built machines can live through only so many times.
An EMALS system, by contrast, can be adjusted so that it can throw both enormous and tiny aircraft with the force necessary, said Scott Forney, a vice president in the Electromagnetic Systems Group at General Atomics. And the system creates acceleration a bit more slowly, he said, which should help extend the life of the machine being propelled.
EMALS is really a linear motor. A typical electric motor is round, and it has a rotor and a stator. The stator is the outer shell and the rotor, often wrapped in wire, spins inside. But in a linear motor, the rotor is the aluminum armature to which the aircraft's front landing gear is attached. The stator is rolled out flat and runs the length of the catapult.
"As you pull the electrical current through that stator, it generates a magnetic field, just like in a regular motor, that interacts with that chunk of aluminium, which is now your rotor," Beach explained. "But instead of that armature spinning like a rotor, it runs along that linear stator."
Along the motor are a series of superfast on/off switches. As the aircraft moves down the runway, these switches emit pulses of energy that push the plane forward.
While the basic design is almost a century old, what's new is the computerized ability to time the pulses to the nanosecond, and also the advanced semiconductors capable of handling all of the electricity required. (The propulsion system is stopped merely by reversing the magnetic polarity as soon as the plane is off the deck.)
"High-powered silicon switches allow us to turn on and off extremely high levels of current and voltage instantly, and they didn't exist 20 years ago and 15 years ago to the level they do today," Beach said. "The rest is just copper and aluminum."
Because the system is sealed under the deck, the powerful energy fields pose no danger to sailors or other equipment.
The Pentagon says 134 tests using an array of aircraft have been successfully conducted on a land-based mock-up of the system and that 2,000 other tests were also conducted with dead loads.
Nonetheless, the GAO has raised some concerns. It cautions, for example, that the test results cannot be viewed as entirely reliable because it was impossible to fully emulate all of the variable conditions of a launch at sea. And so the agency is a bit wary that the first time a fully completed system will be used is after it has been installed on the $11 billion USS Ford.
But Forney, of General Atomics, is confident in EMALS' ultimate success aboard that carrier  -  which could mean millions of dollars more in sales for his company because the British navy is also interested in the system. The test catapult at the naval air station in Lakehurst, N.J., is almost identical to what will be on the ship, he said. "We recommended a  fixed price contract," Forney said. "I take 100 percent of the risk on the production hardware."