Hermeus is an American startup building a hypersonic airliner that could travel from New York to London in just 90 minutes (artist's impression).
(CNN) -
Nearly two decades since the Concorde was retired, interest in supersonic travel has accelerated and several ultra-fast aircraft are being developed.
Airlines seem interested: United has already committed to offering supersonic routes starting in 2029.
But what about hypersonic travel, which occurs at speeds of Mach 5, five times the speed of sound, and higher?
That would take a plane from New York to London in just 90 minutes, compared to roughly 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 planes, thinks so.
It is already testing a new type of engine that it says will eventually be capable of reaching Mach 5 (over 4,828 km / h).
The engine is designed for a small hypersonic drone that Hermeus currently builds for the US Air Force, but scaled up to a larger size, it will be able to power an airliner.
That airliner is a long way off (Hermeus hopes to get it airborne with a first test flight before the decade is out, in 2029), but because its technology must be built almost entirely from scratch, the company has already done so. it is planning.
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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 created a business model for an airline," says AJ Piplica, Hermeus CEO.
"We focused on business class and first class travelers, and then we played with some parameters like speed and operating costs. What came out of that was a plane with a cabin for 20 passengers," he adds.
That's not far from the capacity of a commercial jet, which means there will only be one class.
"We hope it will be profitable at today's business class prices," says Piplica, except that it is difficult to calculate how much people will be willing to pay to fly five times faster, because "you can't really answer that question. until there is a product and you have the real data. "
Faster than ever
The range of the plane will be about 4,000 nautical miles, sufficient for transatlantic routes such as New York to Paris, but not for trans-Pacific routes such as Los Angeles to Tokyo, which would require a stopover.
NASA X-43A is the fastest aircraft powered by an engine that "breathes" air.
Credit: NASA
Overland routes, like 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 daring the idea of a Mach 5 airliner is, it helps to look at the flight speed logs.
The fastest an aircraft with an engine has flown is Mach 9.6 (approximately 10,943 km / h), a record set in 2004 by NASA's X-43A, an unmanned aircraft that is approximately 3.6 meters long.
Because that flight only lasted a few seconds, the record for the longest sustained flight above Mach 5 belongs to the Boeing X-51, another experimental drone, which in 2013 flew for more than three minutes at Mach 5.1 ( around 5,471 km / h).
Both planes had to be launched from above by a B-52 bomber and then accelerated by a rocket, highlighting the complexities of this type of high-speed flight.
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For aircraft with humans on board, the current ground speed record is Mach 6.7 (7,274 km / h), set in 1967 by the X-15.
It was basically a rocket with a seat, designed to achieve the record, and also had to be launched from a height by a B-52.
For an air-breathing aircraft, that is, powered by jet engines rather than a rocket, capable of taking off and landing on its own, the speed record is "only" Mach 3.3 (about 3,540 km / h), 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 (2,172 km / h).
The proposed Hermeus airliner would therefore break the current record for the fastest air-breathing aircraft by a wide margin, and by flying for an extended time at Mach 5, it would surpass an achievement currently in the realm of non-experimental vehicles. manned (of course, other aircraft could break these records in the future before Hermeus).
'Mature technologies'
It's no wonder, then, 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 combat aircraft and manufactured by General Electric.
Hermeus uses hybrid technology in its engines.
Credit: Hermeus
It will be a hybrid of two traditional technologies: a turbojet, which is similar to that used by passenger planes, and a ramjet, a type of engine that only operates at supersonic and higher speeds.
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 through the front and is first compressed (to increase its energy potential) by rotating blades, then mixed with fuel and ignited.
The resulting hot gas is expelled through the rear of the engine, pushing the aircraft forward.
Above Mach 3, however, there is no need to compress the air - it will compress only as it enters the engine, simply from having to slow down so much.
Therefore, for speeds above Mach 3 and up to Mach 6, a type of motor called a ramjet is often used, so named because it literally collides with the air.
It has no moving parts, unlike turbojets, but it doesn't work at all at speeds below Mach 3.
Hermeus will use its hybrid engine in turbojet mode when taking off and landing, as well as at subsonic speeds.
The engine will then gradually reconfigure into a ramjet mode as it reaches Mach 3 and up to Mach 5.
"The turbojet part and the ramjet part themselves are mature technologies that we've been using for 50 years. The trick is putting them together, so we design our own architecture around a standard turbojet engine and then build from there." says Piplica.
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There are a host of issues Hermeus is not even working on at the moment, such as what kind of sustainable fuel to use, as the consumption will be much higher than current aircraft, and the extreme temperatures that the fuselage of a hypersonic aircraft must be able to resist.
Hermeus must withstand extreme temperatures.
Credit: Hermeus
The speed of the Concorde, which was traveling at less than half Hermeus' projected speed, was limited precisely by temperature, and windows and other internal surfaces became warm to the touch at the end of a flight.
The SR-71 Blackbird, on the other hand, had to be made of titanium, a rare metal that can withstand extreme heat, and the cockpit glass had to be made of quartz, with an outside temperature reaching 315 ° C. during a mission.
Responding to skepticism about Hermeus' chances of success and the need for huge amounts of funding, Piplica draws an analogy to Elon Musk's SpaceX.
"I think people asked the same questions about the new space industry in the early days of SpaceX," he says.
"People thought about going into orbit and said, this should cost a billion dollars, but SpaceX did it for $ 90 million with the Falcon 1."
Hermeus plans to finance itself by developing various aircraft en route to its airliner, similar to SpaceX's development of its Falcon 1, Dragon, Falcon Heavy and Starship rockets, which ultimately serve a vision of interplanetary spaceflight. while also generating income by working with NASA and business partners.
"There really is nothing like 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 transportation in the late 2030s, and the ticket price is in the business class range, then yes, that will be successful. But the odds of this happening are at. somewhere in the 1% range. "
And when a hypersonic airliner becomes a reality, what will it be like to fly in it?
"It will be quite similar to the Concorde," explains Piplica.
"You will accelerate for a longer period of time than on the current plane, where you will feel pushed back in your seat for about 30 seconds to a minute or so.
That experience will last perhaps 10 to 12 minutes.
But once you're at Mach 5, at 30,480 meters or so, it's going to be a really smooth ride.
There is not much air traffic there and the atmosphere is relatively benign. "
