At the 21st International Space Plane and Hypersonic Systems and Technology in Xiamen—a global forum of scientists and engineers researching hypersonic concepts and technologies—Chinese scientists provided key details on several little-known but game-changing scramjets, near-space planes, and super wind tunnels.
First, let’s talk about scramjets. These have air-breathing engines (like turbofans and piston engines), so they don’t need to carry a supply of oxidizer to combust their fuel. This makes them lighter and more efficient than rocket propelled missiles, as well as being more maneuverable. The first open source image of a Chinese scramjet test emerged in December 2015. It flew to an altitude of 30 kilometers (over 18 miles), and reached a Mach 7 speed. Interestingly, while American scramjet tests have generally been air dropped before firing their rocket boosters, the Chinese scramjet test was boosted from a land-based launcher. Scramjets could enable more efficient and easier forms of space launch and hypersonic airliners, just as they could be used for high-speed cruise missiles to replace ballistic missiles.
A hypersonic plane can fly in the «near-space» altitude of 12 miles to 60 miles, allowing it to shoot into orbit with integrated rockets, or fly civilian and military missions in near space. Such a hypersonic plane could circumnavigate the world in a couple hours, out of the reach of conventional air defenses. China has several programs researching hypersonic combined cycle engines, which consist of a turbofan stage for subsonic/low supersonic flight, and a ramjet stage for the transition from supersonic to hypersonic flight.
The most promising program is Beijing Power Machinery Research Institute’s turbo-aided rocket-augmented ram/scramjet combined cycle (a mouthful often abbreviated to TRRE), which uses integrated liquid-fueled rockets to boost the performance of the turbine and ramjet stages, thus making a safer and smoother transition from supersonic to hypersonic flight of Mach 10. With key components like the engine inlet, cooling, and combustion already developed, ground tests of the system are beginning later this year. The reported plan is for a full-scale TRRE testbed to begin flights by 2025, with a 2030 test flight.
And then there are the hypersonic wind tunnels. China has the world’s largest hypersonic wind tunnel, the detonation drive JF-12, and is working to build an even larger one. The 556-foot-long FD-21 hypersonic shock tunnel can reach speeds of Mach 10-15, well above the JF-12’s Mach 5-9 range. Clearly, China is not content to restrict its flight research to the lower end of the hypersonic speed range.
At the Xiamen event, Chinese engineers also reported on a wide range of other hypersonic technologies, such as plasma jets to steer hypersonic thrust, advanced heat resistant composites, and new fuels. The event was yet another indication that, with well established programs in spaceplanes and scramjets, China is set for a hypersonic flight boom.