Lowering the Boom
Supersonic business jets are being developed, but their noise must be muffled before they can fly over land at full speed.
Though the fastest business jets approach the edge of supersonic flight, with top speeds exceeding Mach 0.9, no civilian aircraft has ventured beyond Mach 1—the speed of sound—since the Concorde fleet was grounded in 2003. But because supersonic speeds continue to entice travelers with their ability to cut flight times in half or more, a handful of fledgling and established aircraft companies, as well as NASA, are developing—or considering the viability of developing—supersonic business jets.
Building a jet that flies faster than the speed of sound is not the challenge for aircraft makers. Chuck Yeager first broke the sound barrier in 1947; Concorde, which could reach a cruising speed of Mach 2, made its first supersonic flight in 1969, and the fleet began flying the three-hour route between London and New York in 1976; and military aircraft fly at supersonic speeds every day. The challenge is building a supersonic jet that is relatively fuel efficient (Concorde aircraft, which consumed nearly 6,800 gallons of fuel per hour, became too costly to operate) and relatively quiet.
Public concerns about the ground-level noise and vibrations that Concorde’s sonic booms would create prompted the U.S. Federal Aviation Administration to enact a regulation in 1973 that bans civilian aircraft from flying over land areas of the United States at speeds greater than Mach 1. Similar regulations are in effect for most of the world’s inhabited land areas. They limit aircraft speed, or they prohibit sonic booms. No such rules exist for the airspace over international waters.
“We need a rule change,” says Robbie Cowart, the director of supersonic technology development for Gulfstream, the company that makes the G650 and other business jets. “This speed limit in the sky is holding everyone back.”
Gulfstream has been working for years—on its own and in partnership with NASA—to find ways to mitigate the sonic boom. The company has been conducting test experiments in wind tunnels and in the atmosphere, and collecting data on a variety of potential solutions. “It’s not just about the engines,” says Cowart. “It’s all of the aircraft that affects the noise signature. It’s the wing, the tail, the entire design.”
Peter Coen, the project manager for the Aeronautics Mission Directorate’s High Speed Project at NASA’s Langley Research Center in Virginia, says technology that would reduce the sonic noise to a tolerable level for people on the ground “looks promising.” He says that within five to seven years companies could produce experimental aircraft that are quiet enough to satisfy the public and the agencies around the world that regulate air travel. “The real devil is in how much it would cost and who’s willing to develop that technology,” Coen says. He also anticipates that it will take time before there can be any serious consideration to changing the regulations that prohibit supersonic flight. “That’s a slow process,” Coen says. “It’s a global geopolitical challenge.”
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