(CNN) — Nearly two decades after Concorde’s retirement, interest in supersonic travel has accelerated and several ultra-fast aircraft are under development. Airlines seem interested: United has already committed to offering supersonic routes as early as 2029.
But what about hypersonic travel, which occurs at speeds of Mach 5 — five times the speed of sound — and more? This would allow a plane from New York to get to London in just 90 minutes, compared to around three hours for the Concorde and between six and seven hours for a regular airliner.
Is it even possible?
Hermeus, an Atlanta-based startup whose goal is to develop hypersonic aircraft, thinks so. He is already testing a new type of engine which he says will eventually be able to reach Mach 5 (over 3,000 mph). The engine is designed for a small unmanned hypersonic aircraft that Hermeus is currently creating for the US Air Force, but scaled up to a larger size it will be able to power a passenger aircraft.
That passenger plane is a long way off — Hermeus hopes to get it off the ground for the first test flight before the end of the decade, in 2029 — but because its technology must be built almost entirely from scratch, the company is already planning it.
For starters, it will be much smaller than current airliners and even the Concorde, which had a capacity of around 100 passengers.
“To help us size the plane, we basically built a commercial model for an airline,” says AJ Piplica, CEO of Hermeus. “We focused on business class and first class travellers, and then played around with some parameters such as speed and operating costs. What came out was an aircraft with a 20-passenger cabin,” he adds. -he.
This is not far from the capacity of a large business jet, which means that there will be only one class.
“We expect it to be profitable at current business class prices,” says Piplica, with the caveat that it’s hard to gauge how much people will be willing to pay to fly five times faster. because “you can’t really answer that question until there’s a product out there and you have the real data.”
Faster than ever
The NASA X-43A is the fastest aircraft powered by an air-breathing engine.
The aircraft’s range will be around 4,000 nautical miles, sufficient for transatlantic routes such as New York to Paris, but not for transpacific routes such as LA to Tokyo, which would require a stopover.
Overland routes, such as New York to Los Angeles, are out of the question due to noise regulations: breaking the sound barrier comes with a loud boom, which usually must occur over water .
To understand how audacious the idea of a Mach 5 passenger plane is, it helps to look at flight speed records.
The fastest aircraft ever powered by an engine is Mach 9.6 (about 6,800 mph), a record set in 2004 by the NASA X-43A – an unmanned aircraft measuring about 12 feet long.
Because this flight lasted only a few seconds, the record for the longest sustained flight above Mach 5 belongs to the Boeing X-51, another experimental unmanned aircraft, which in 2013 flew for more than three minutes at Mach 5.1 (about 3,400 mph). Both planes had to be launched from altitude by a B-52 bomber and then upgraded by a rocket, highlighting the intricacies of this type of high-speed flight.
For aircraft with humans on board, the current absolute speed record is Mach 6.7 (4,520 mph), set in 1967 by the X-15. It was essentially a rocket with a seat, designed to achieve the record, and was also to be launched from altitude by a B-52.
For an air-breathing plane — that is, one powered by jet engines rather than a rocket — capable of taking off and landing on its own, the speed record is “just” Mach 3.3 (about 2,200 mph), established by the SR-71 Blackbird, a military spy plane, in 1976.
The top speed of the Concorde, one of only two supersonic airliners to have flown commercially, was Mach 2.04 (1,350 mph).
The proposed Hermeus passenger aircraft would therefore beat by far the current record for the fastest air-breathing aircraft, and by flying for a long time at Mach 5, it would outclass an achievement currently in the field of experimental unmanned vehicles ( of course, other aircraft may break these records in the future before Hermeus).
Hermeus uses hybrid technology in its engines.
So it’s no surprise that the company’s initial focus is on the engine. Testing began in February 2020 for a new type of engine design, based on an existing model used in fighter jets and manufactured by General Electric.
It will be a hybrid of two traditional technologies: a turbojet, similar to what airliners use, and a ramjet, a type of engine that only operates at supersonic speeds and above. Initially, the engine will power Quarterhorse, the sleek hypersonic drone that Hermeus is developing through a $60 million partnership with the US Air Force.
Interestingly, when designing a jet engine to go faster, parts are removed rather than added. In a turbojet, air enters from the front and is first compressed (to increase its energy potential) by rotating vanes, then mixed with fuel and ignited. The resulting hot gas is expelled out the rear of the engine, pushing the aircraft forward.
Above Mach 3, on the other hand, it is not necessary to compress the air: it will compress as it enters the engine, simply by slowing down. Therefore, for speeds above Mach 3 and up to Mach 6, a type of engine called a ramjet is often used – so called because it literally soars through the air. It has no moving parts, unlike turbojets, but it does not work at all at speeds below Mach 3.
Hermeus will use its hybrid engine in turbojet mode during takeoff and landing, as well as at subsonic speeds. Then the engine will gradually reconfigure itself to ramjet mode as it reaches Mach 3 and up to Mach 5.
“The turbojet part and the ramjet part are in themselves mature technologies that we have been using for 50 years. The trick is to put them together, so we designed our own architecture around a standard turbojet, then built from there,” says Piplica.
Hermeus will have to withstand extreme temperatures.
There’s a whole host of issues that Hermeus isn’t even working on at the moment, like what type of sustainable fuel to use – since fuel consumption will be much higher than current jets – and the extreme temperatures at which the fuselage of a hypersonic the plane must be able to resist.
The speed of Concorde, which was traveling at less than half the projected speed of Hermeus, was precisely limited by temperature, with windows and other internal surfaces becoming hot to the touch at the end of a flight.
The SR-71 Blackbird, meanwhile, was to be made of titanium, a rare metal that can withstand extreme heat, and the cockpit glass was to be quartz, with its outside temperature reaching 600 F while on a mission.
In response to skepticism about Hermeus’ chances of success and the need for potentially huge funding, Piplica brings up an analogy to Elon Musk’s SpaceX.
“I think people were asking the same questions about the new space industry when SpaceX started,” he says. “People looked at orbiting and said it should take a billion dollars, but SpaceX did it for $90 million, with Falcon 1.”
Hermeus plans to finance itself by developing various aircraft on the way to its passenger plane, similar to SpaceX’s development of its Falcon 1, Dragon, Falcon Heavy and Starship rockets, which ultimately serve a vision of interplanetary spaceflight while by generating revenue by working with NASA and commercial partners.
“There really is no such thing as Hermeus, although many similar projects have come and gone in the past,” says Richard Aboulafia, aviation analyst at Teal Group. “It never seems to work. If they can magically create hypersonic transport in the late 2030s and the ticket price is in the business range, then yes it will be successful. But the odds of it occur are somewhere in the 1% range.”
If and when a hypersonic airliner becomes a reality, what will it be like to fly on it?
“It will be quite similar to Concorde,” says Piplica. “You’re going to accelerate for a longer period of time than on airplanes today, where you feel pushed back into your seat for about 30 seconds to about a minute.
“This experience will be maybe 10 to 12 minutes long. But once you get to Mach 5, around 100,000 feet, the ride will be really smooth. There’s not a lot of air traffic up there, and the atmosphere is relatively benign.”
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