When the Superman: Escape from Krypton roller coaster opened at Six Flags Magic Mountain theme park in Valencia, California, in 1997, it was the tallest ride in the world and one of the fastest. The coaster can shoot a 6-ton car carrying 15 people up a vertical tower 415 feet tall at 100 miles per hour. The Escape was the first ride in the world powered by an electric linear motor system, developed by engineers at GE’s Power Conversion business.
The engineers have now tested the latest version of the technology. Instead of fun ride cars, it can power an electric catapult that could fling fighter jets weighing as much as 37 tons (like a fully loaded F-35 Joint Strike Fighter) off the deck of an aircraft carrier at takeoff speed. The catapult can quickly accelerate to speeds in excess of 186 miles per hour and generate gravitational forces of 3.3g. For shorter launches the technology can reach as much as 12g. “In terms of force, this is probably the most powerful linear motor ever built,” says Mark Dannatt, director of naval business at GE Power Conversion.
The new electromagnetic catapult could replace steam catapults still used by even the latest American aircraft carriers. Steam-powered launch has a number of drawbacks. “It’s basically a tube with a piston inside,” Dannatt says. “You get a tremendous jolt at the start of the launch when you open the valve and let the steam out at full pressure. This does not do the aircraft or the pilot any good.” Worse, as the jet goes down the track, the steam leaks out and the pressure gradually dies away. “It’s a bit like a balloon going down,” Dannatt says.
But the electromagnetic catapult, the technical name for the technology is medium-voltage advanced linear induction machine, starts slow like a theme park ride and attains maximum speed at launch. “This is what you want,” Dannatt says. “The wear on the airframe is less.”
Access to power is not a problem. Many ships are switching to electric propulsion (Dannatt’s business has built power and propulsion systems for the UK’s aircraft carriers as well as the U.S. Navy’ first hybrid and all electric vessels). The new catapult could easily tap into that electricity.
The effect on the ship would be negligible, even though the catapult is providing most of the energy during the plane launch. (The jet’s engines contribute only a small amount.) “Although the amount of launch energy you need is high, the power that you need to charge the catapult is very small compared to the propulsion system,” Dannatt says.
The new catapult is essentially a common rotary induction motor that GE engineers cut open. They arranged the motor’s internal coils along a track several meters long. An automatic control system jogs electricity forward through the coils, and generates a moving electromagnetic field. A heavy steel the plate rides on the field along the track, kind of like a maglev train, and pulls the jet during takeoff. “There is an air gap between the plate and the track,” Dannatt says. “There are no bits wearing down. It’s much better for maintenance.”
Besides aircraft carriers and roller coasters, the technology could also power car parts, cars, and other vehicles during acceleration crash tests. It could also launch large unmanned aircraft from locations that were previously not feasible. Says Dannatt: “It’s a solution looking for a problem.”
It’s Bird, It’s a Plane: The technology behind the new catapult started like a motor for Superman fun ride. A GE Power Conversion’s catapult at the Bruntingthorpe test site in Leicestershire, England.