When Chuck Yeager flew NASA’s first rocket plane, the X-1, past the sound barrier for the first time in October 1947, confirmation of his feat rang out across the desert in the form of a sonic boom — the thunder caused by compression of sound waves at the bow of the plane as it reached Mach 1. In the seven decades since, the boom has remained an impediment to widespread supersonic travel, outside of the military. The Concorde, the French-British partnership that provided the only supersonic passenger service to date, took off for the last time in 2003 and landed in a museum in part because regulators required it to slow down over land.
NASA is trying to revive supersonic travel with its X-59, a single-pilot demonstration plane that is designed to produce a kinder, gentler boom than the Concorde’s. Lockheed Martin’s design, which NASA approved in August, is powered by a GE F414-100 engine and uses a slender fuselage that in theory produces several small shock waves that are eight times quieter than a typical sonic boom — hopefully small enough to mitigate the loudest effects of supersonic speeds. The point of building the X-59 is to find out how well theory works in practice, and to see if it passes muster with people who live under the plane’s flight path.
(GE also is helping Aerion, another aerospace company seeking to build a supersonic plane together with Lockheed Martin, “explore the feasibility of a joint development of the world’s first supersonic business jet.”)
Whereas Yeager’s X-1 used four rocket engines to accelerate beyond Mach 1, the X-59 will need only one GE F414-100 engine, adapted from the F414-400 that powers the Navy’s F/A-18 Super Hornet fighter plane.
The F414 was developed in the 1990s for the Super Hornet, which is manufactured by Boeing. Since then, GE’s Riverworks aviation facility in Lynn, Massachusetts, has produced more than 1,600 of the engines, which have collectively logged 4 million flight hours. GE got the X-59 contract last year from NASA to build two engines — one for the single-engine demonstrator plane, one for a spare — and plans to ship them in 2019.
“The reason to use the F414-100 is largely thrust and the single-engine safety features,” says program manager David Prescott. The F414 is a turbofan engine equipped with an afterburner. Its compressor blades pressurize air flowing into a combustion chamber, where it is mixed with fuel. Ignition makes the incandescent air rapidly expand and turn a second set of turbine blades that spins the fan and provides most of the engine’s thrust. The engine’s afterburner briefly turns the vehicle into a rocket plane by dumping a large amount of fuel directly into the exhaust. Fighter pilots use afterburners when they need a sudden burst of speed. In the case of the X-59, the afterburners will be useful in keeping the plane at high speeds for testing its aeronautics and to study its sonic boom.
Prescott has worked at the Aviation facility for 17 years, starting with an earlier version of the F414. The facility has about 40 engineers working on the F414-100 program. Chad Sutter, the model engineer in charge of adapting the F414, is now working on integrating the engine into the airframe of the X-59. Before coming to GE five years ago, Sutter worked as an automotive engineer in Michigan. “It’s not common to make that switch,” he says. “But it’s an excellent transition because the engineering worlds are so different.” Whereas high volume and low cost were top priorities in automotive work, military aviation puts a premium on quality: “As an engineer,” Sutter says, “you get to think a little more outside the box.”
The X-59 project is also a chance to contribute to a revival of supersonic commercial travel. NASA has said that it intends to share as much data as possible with commercial firms, which, if the project is successful, may follow through with designs for supersonic passenger jets. If all goes well, the X-59 will demonstrate that supersonic travel can be quiet enough for the U.S. Federal Aviation Administration to drop its ban on supersonic travel over land.