Why a Mach 5 passenger plane is a crazy idea that might just work

Almost two decades since Concorde retired, interest around supersonic travel has been picking up pace, and several super-fast planes are under development. Airlines seem interested: United has already committed itself to offering supersonic routes as early as 2029. But what about hypersonic travel, which happens at speeds of Mach 5 -- five times the speed of sound -- and above? That would get an aircraft from New York to London in just 90 minutes, compared to about three hours for Concorde, and between six to seven hours for a regular passenger jet. Is it even possible? Hermeus, an Atlanta-based startup whose goal is to develop hypersonic aircraft, believes so. It's already testing a new type of engine it says will eventually be capable of reaching Mach 5 (over 3,000 mph). The engine is designed for a small, unmanned hypersonic aircraft Hermeus is currently creating for the US Air Force, but scaled to a bigger size, it will be able to power a passenger plane. That passenger plane is a long way away -- Hermeus hopes to get it in the air for the first test flight before the decade is out, in 2029 -- but because its technology has to be built almost entirely from the ground up, the company is already planning it out. For a start, it will be much smaller than current airliners and even Concorde, which had a capacity of around 100 passengers. "To help us size the aircraft, we basically built a business model for an airline," says AJ Piplica, CEO of Hermeus. "We focused on the business class and first class travelers, and then played around with some parameters such as speed and operating costs. What came out of that was an aircraft with a 20-passenger cabin," he adds. That's not far from the capacity of a large business jet, which means there will be just one class.<br/>