• An adapted scramjet called a "sodramjet" could reach Mach 16 flight by leveraging sonic booms.
  • The experimental engine is Chinese, but based on American ideas dating back 40 years or more.
  • Turning sonic booms into combustion addresses a key, "fatal" flaw in scramjet designs.

A Chinese-made "sodramjet" engine has reached nine times the speed of sound in a wind tunnel test. The engine could power an aircraft to reach anywhere in the world within two hours, the makers say.

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Scientists say the sodramjet (short for “standing oblique detonation ramjet engine”) could be the first real hope for hypersonic flight—many times the speed of sound, and something that would bring both global travel and space travel much closer to home.

"With reusable trans-atmospheric planes, we can take off horizontally from an airport runway, accelerate into orbit around the Earth, then reenter into the atmosphere, and finally land at an airport," the scientists, from the Chinese Academy of Sciences’ Institute of Mechanics, write in a new study published in the Chinese Journal of Aeronautics. "In this way, space access will become reliable, routine and affordable."

The idea is a decades-old theoretical variation on a scramjet, itself a variation on the ramjet, building on generations of work on high-speed flight.

Many commercial aircraft today have turbofans or, for smaller jets, turboprops. These have descended from the idea of the turbojet, and on the family tree of jet propulsion, the turbojet and ramjet are something like cousins.

The same way that, say, researchers continue to work on stellarators along with tokamaks and salt-cooled along with lightwater reactors, research on the lower profile idea of the ramjet has continued since the interwar period. Because of their design, turbojets, turbofans, and turboprops work better in the zone we’ve decided is right for passenger flight. For the most part, that’s subsonic flight within Earth’s atmosphere.

The sodramjet is the latest bleeding edge of a completely different use case. The ramjet led to the scramjet, which was designed to go as much as 15 times the speed of sound. Like the fastest combustion and even rocket cars, the secret is in dropping a great deal of weight from the craft—the scramjet scoops up oxygen from the air instead of in condensed form from a tank.

But that means a more fragile cycle of combustion that, it turns out, can be woofed out by the very sonic boom the engine creates. The scramjet just never reached its full potential.


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South China Morning Post (SCMP) reports that the sodramjet follows decades of work on scramjets that began in the United States. But in China, development of scramjet concepts has continued, too. Even so, lead researcher Jiang Zonglin grew frustrated with scramjets and decided to go his own way, based on a theory published by NASA in 1980:

“Jiang and colleagues said they were fed up with scramjets’ fatal design weakness. The scramjet could barely generate any thrust at the speed of Mach 7 or beyond. The fuel consumption was so high that no commercial aviation company could possibly foot the bill. And the pilots—not to mention passengers—could suffer heart attacks if they were required to restart the engine from time to time during a flight.”
concept demonstration model of the sodramjet engine and its installation in jf 12 shock tunnel
Zonglin Jiang, et. al./Chinese Journal of Aeronautics
Concept demonstration model of the sodramjet engine and its installation in a wind tunnel.

The key difference in the sodramjet is that the new design uses the sonic boom to add combustion, not blow it out.

“Turning the shock wave from their enemy to their friend helped them sustain and stabilise combustion at hypersonic speed,” SCMP reports. “The faster the engine flew, the more efficiently the hydrogen fuel burned. The new engine was also much smaller and lighter than previous models.”

Nothing is certain about this design, which can’t even be tested in a full-speed wind tunnel yet—one simply doesn’t exist. A lot remains to be seen, studied, and proven.

The sodramjet, however, seems to be a hypersonic contender at the beginning of an era where this technology will be critical to travel and exploration.


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Caroline Delbert

Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all.