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Testing Begins on Combined Cycle Engine That'll Grow to Challenge SR-71 Blackbird Record

Hermeus testing F100 engine with in-house made precooler 18 photos
Photo: Hermeus
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Back in 1976, at the height of the Cold War, one of America's most secretive planes, the SR-71 Blackbird, managed to achieve a tremendous feat: it traveled at a speed of Mach 3, which is 2,193.2 mph (3,529.6 kph). That's the fastest speed any production, crewed aircraft managed to reach in the atmosphere of our world, but a record that'll probably be challenged soon enough.
There are many companies working on hypersonic aircraft, meaning a lot faster than the Blackbird, but the vast majority of them will be drones meant to be used for military purposes. A company called Hermeus is working on the same kind of stuff, but unlike most others, it ultimately targets the release into the world of a hypersonic civilian plane.

The plan is still in the early stages, as the company still has a lot of research and development ahead. But a major milestone in the development of the tech need to reach that goal was announced this week.

Last time we heard anything about Hermeus was back in March, when we were presented with the first look at a test aircraft called Quarterhorse Mk 1. The uncrewed vehicle is scheduled to be remote-controlled into an actual test flight scheduled to take place later this year at the Edwards Air Force Base in California.

The Quarterhorse Mk 1 is equipped with a General Electric J85 jet engine, the same kind currently in use on planes such as the T-38 Talon trainer, but its successor, the Mk 2, will employ the mighty Pratt & Whitney F100, best known for its use in fighter jets, including the F-15 and F-16.

The powerplant will not be installed as is on the Quarterhorse Mk 2, but it will use a precooler technology developed in-house by Hermeus. The extra hardware is meant to increase the maximum speed of the turbine, and it does this by lowering the temperature of incoming air.

Quarterhorse Mk 2
Photo: Hermeus
The company put the precooler through its paces at the same Edwards Air Force Base, in at sea-level static conditions. It's unclear what the test will show, but the data obtained this way will be used to inform the next test flight, which will use heated air to simulate Mach speed conditions.

This setup of the F100 engine, along with other pieces of hardware, will eventually form something Hermeus calls the Chimera turbine-based combined cycle (TBCC) engine. That would be a combination between a turbine and a ramjet, resulting in a hypersonic air-breathing engine.

When the aircraft it powers travels at low speeds, the Chimera will work in turbine mode with the F100 powerplant. When it will reach certain speeds, the ramjet will kick in. The precooler Hermeus has developed "helps bridge the gap between these two modes of operations by increasing the performance of the turbine."

In the Quarterhorse Mk 2 application the precooler-F100 combo should be capable of pushing the aircraft to speeds of over Mach 2.5 (1,918 mph/3,087 kph). If it works on this test machine, the Chimera will be developed and fitted on the Quarterhorse Mk 3. And that one should reach speeds as high as Mach 4 (3,069 mph/4,939 kph), which is just under the threshold of the hypersonic realm.

As for the applications of this technology, there are virtually few limits. The military is already mesmerized by what Hermeus is doing and has included the company in the High-Cadence Airborne Testing Capabilities (HyAT) program run by the Defense Innovation Unit (DIU). There, the Quarterhorse competes with the DART AE in the works over at Australian company Hypersonix, the Hypersonic Accelerator Suborbital Test Electron (HASTE) made by Rocket Lab, and an unnamed drone currently being developed by Fenix Space.

Quarterhorse drone rendering
Photo: Hermeus
All the Quarterhorses mentioned above are just test aircraft, and for military uses they should lead to something called the Darkhorse, the plane that will actually challenge the Blackbird record.

The plane should be able to travel at over Mach 5 (3,800 mph/6,100 kph), potentially with pilots on board, effectively making it the fastest of its kind in history. It is not exactly clear how soon we'll get to see the first Darkhorse in action, but work on its predecessors seems to be moving at a fairly rapid pace.

As for the ultimate goal of Hermeus, that of creating a hypersonic aircraft for passengers, that design is for now called Halcyon. In a nutshell, we're talking about "a passenger aircraft capable of accelerating 125+ trans-oceanic routes at hypersonic speeds – five times faster than any commercial aircraft today."

In words, we can all understand that would mean one of the world's most popular air routes, the ones linking New York to London, would be completed by the Halcyon in just 90 minutes.

The design is so insane in scope that at the time of writing there is no set date for when we should see it flying.
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About the author: Daniel Patrascu
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Daniel loves writing (or so he claims), and he uses this skill to offer readers a "behind the scenes" look at the automotive industry. He also enjoys talking about space exploration and robots, because in his view the only way forward for humanity is away from this planet, in metal bodies.
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