Chinese Hypersonic Aircraft - Mach 6.56!?

[Astronuc]

Scientists in China have announced that a jumbo jet prototype built by them had managed to reach hypersonic speeds (Mach 5 and above) during a flight test.

The scientists claim that the aircraft prototype with a rather bulky body reached the speed of Mach 6.56 (5,033 miles per hour approximately) during the test flight in 2021.

The test flight results had been kept a secret by the institute and authorities in China owing to the sensitivity of the project.

It was revealed by the Chinese Academy of Sciences through a post on social media in which they shared a video of the jumbo jet prototype’s lift-off. The post also contained a speech by Cui Kai, the project’s leader and a researcher at the Institute of Mechanics under the Chinese Academy of Sciences.

https://www.yahoo.com/news/china-hypersonic-jet-flies-blazing-103603904.html
https://interestingengineering.com/transportation/china-hypersonic-aircraft-mach-6-flight-test

Apparently, it has a name - Yunxing Hypersonic Jet


https://www.aviationpros.com/aircra...ghts-with-plans-for-concorde-beating-aircraft

 

[Flyboy]

“However, Cui or the Chinese Academy of Sciences did not reveal whether a full-scale model of the aircraft has been constructed, is under construction, or the time period for its first flight.

Cui is quoted as saying in the report that the team still faces multiple challenges that need to be addressed directly – “including issues related to power, materials and structure.””

In other words, they made a subscale demonstrator and proved it could reach that speed. Being able to scale up the design, and maintaining the speed long enough to be useful? That’s the unresolved challenge.
I suspect that whatever they flew cannot sustain that speed for anything close to a representative time, or even one to allow the airframe to undergo heat soak.

Tl;dr: Hypersonic hype is easy. Practical hypersonic is hard.

 

[Baluncore]

There is no way that the "artists impression" shown in the article could be supersonic, well, except in the ionosphere, or space.

China has had a bad run, of military failures in the news lately. Maybe this is supposed to compensate, to make China appear great again.

 

[FactChecker]

In other words, they made a subscale demonstrator and proved it could reach that speed.

I agree with everything in your post except for this. I don't know what type of "proof" they could have when they do not have the engine, materials, or structure figured out. I am especially skeptical of China's jet engine technology.

 

[Lnewqban]

I believed that we were moving away from burning more and more kerosene.

Copied from
https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Future

"Concorde, a supersonic transport, managed about 17 passenger-miles to the Imperial gallon, which is 16.7 L/100 km per passenger; similar to a business jet, but much worse than a subsonic turbofan aircraft. Airbus states a fuel rate consumption of their A380 at less than 3 L/100 km per passenger (78 passenger-miles per US gallon).
Newer aircraft like the Boeing 787 Dreamliner, Airbus A350 and Bombardier C Series, are 20% more fuel efficient per passenger kilometer than previous generation aircraft."

 

[Flyboy]

I’m not convinced of that. We may switch to a synthetic equivalent/replacement from renewable feedstocks, but a pound of Jet-A1 is still one of the best fuels for aviation use. Liquid at ramp temperature and at cruise, excellent energy density, great thermal performance as a coolant if needed, doesn’t need pressure tanks… and it leaves minimal deposits on turbine blades.

 

[Flyboy]

Okay, this is closer to a real Mach 6+ airframe, if subscale.

https://www.twz.com/air/china-launches-hypersonic-planes-from-drones-balloons

 

[boneh3ad]

"News" articles citing no sources other than Chinese state media should be treated as what they are: propaganda.

Interesting Engineering is not a serious source of journalism and has published loads of nonsense in the past.

 

[Astronuc]

"News" articles citing no sources other than Chinese state media should be treated as what they are: propaganda.

Interesting Engineering is not a serious source of journalism and has published loads of nonsense in the past.

I'm certain skeptical of the claim, but I was hoping to discuss hypersonic air craft technology and the various issues.

When I first read the headline/article, I reflected on "The X-15's highest speed, 4,520 miles per hour (7,274 km/h; 2,021 m/s), was achieved on 3 October 1967, when William J. Knight flew at Mach 6.7 at an altitude of 102,100 feet (31,120 m), or 19.34 miles. This set the official world record for the highest speed ever recorded by a crewed, powered aircraft, which remains unbroken."
From https://en.wikipedia.org/wiki/North_American_X-15

The fastest jet aircraft, SR-71, had a special design that allowed for differential thermal expansion of the hot and cooler surfaces.

 

[Flyboy]

I'm certain skeptical of the claim, but I was hoping to discuss hypersonic air craft technology and the various issues.

When I first read the headline/article, I reflected on "The X-15's highest speed, 4,520 miles per hour (7,274 km/h; 2,021 m/s), was achieved on 3 October 1967, when William J. Knight flew at Mach 6.7 at an altitude of 102,100 feet (31,120 m), or 19.34 miles. This set the official world record for the highest speed ever recorded by a crewed, powered aircraft, which remains unbroken."
From https://en.wikipedia.org/wiki/North_American_X-15

The fastest jet aircraft, SR-71, had a special design that allowed for differential thermal expansion of the hot and cooler surfaces.

If we are talking generic hypersonic aircraft , then why didn’t you lead with that?

Propulsion is definitely the largest hurdle at this point, but it is increasingly well understood. You have two well understood options (rockets and ramjets), a third promising option (scramjets), and a noisy new kid on the block who hasn’t proven itself just yet but looks very promising (rotating detonation). Gas turbines can be used for the initial kick into the mid to high supersonic range, but struggle past Mach 3.5 or so and become dead weight and drag to be accounted for if you’re doing combined cycle propulsion.

Each has inherent strengths and weaknesses:

• Gas turbines are very well understood, work at zero speed and altitude, and are respectably efficient, but as mentioned above, top out short of hypersonic speeds. Good as a reusable “first stage” of propulsion when paired with ramjets or scramjets.
• Rockets are the cheap, compact, and reliable way to accelerate an aircraft from subsonic to hypersonic, and have been for decades. Downside is the abysmal endurance. Suitable as a first stage, especially for disposable/attritable platforms, airframes where compact form factors are important, and for boost-glide systems. Most likely to be used for weapons systems and research programs in support of scramjet testing.
• Ramjets are pretty simple engines, and work from low supersonic to, iirc, maybe into the low hypersonic realm, although that’s pushing the concept hard. Strictly speaking, you only need a single moving part: a fuel valve. But that’s for a simplified version, optimized for specific conditions. You can get more complicated and have an adjust shock cone and diffuser, which allows you to adjust your performance to suit a wider range of conditions, but I don’t think many flight-proven ramjets used that approach.
• Scramjets have all the mechanical simplicity of their ramjet brothers with none of the aerodynamic simplicity. The tradeoff is much higher top speeds are now possible, but the minimum speed climbs well into the supersonic realm. They’re not as well understood as the preceding designs but they’re maturing quickly.
• Rotating detonation engines are still laboratory/test stand experiments afaik, but they are approaching the point where small-scale flight tests are possible. I don’t know much about them yet, but they look promising for a range of possible speeds and altitudes. I suspect that they will need optimization for a particular region of the envelope, though.

Realistically, you will want at least two of the above propulsion technologies working together to achieve and sustain hypersonic speeds.


Preventing the compression heating from cooking the systems in the airframe is honestly the other big deal breaker. For UAVs and missiles, it’s much easier as you can either opt for heat-tolerant avionics or active cooling, but anything carrying humans is inherently far more challenging. The Blackbirds burned through a sizable supply of liquid nitrogen to cool the cockpits, avionics, and sensors before supplying the nitrogen to the fuel tanks for inerting. Failure of that cooling system would (and on more than one occasion did) cause cockpit temperatures to spike to over 300°F in a few minutes. If the crewmember hadn’t been wearing their David Clark pressure suit, they would have been cooked alive.

Unless you can solve the heat buildup/rejection problem, I don’t foresee any airliners.

 

[Klystron]

Gas turbines can be used for the initial kick into the mid to high supersonic range, but struggle past Mach 3.5 or so and become dead weight and drag to be accounted for if you’re doing combined cycle propulsion.

[Bolding added]

Thanks for the synopsis on contemporary systems. The caveat on composite propulsion (and cooling systems nd other protective measures) strongly impacts practical commercial designs.

An air breathing stage becomes redundant as the atmosphere becomes tenuous with altitude, at least until reentry. Note programs such as the X-15 rocket planes used modified cargo jet aircraft to lift the experimental craft to altitude before separation.

Mission requirements for military versus commercial craft diverge sharply even as defense requirements define much cutting edge research. Recovering and reusing booster stages on current spacecraft provides an excellent example of commercial requirements improving overall performance while reducing costs.

 

[russ_watters]

I feel like [an update of] the SR-71/D-21 is already the best answer here. Two-stage, so no dead-weight(drag) engines, and no people to air condition or trade in a POW swap. I don't see much value in a human-piloted spyplane these days.

 

[russ_watters]

An air breathing stage becomes redundant as the atmosphere becomes tenuous with altitude, at least until reentry. Note programs such as the X-15 rocket planes used modified cargo jet aircraft to lift the experimental craft to altitude before separation.

Note that the SR-71 already often required multiple aerial refuelings on a mission anyway so what's the difference if the first refueling plane is also carrying the spyplane?

 

[Flyboy]

Agreed, there’s no real market for hypersonic vehicles in the civilian market. High supersonic is a maybe, but not hypersonic.

As for reconnaissance, the airdrop system is hands-down the ideal option. The US and China both have settled on that approach, with the US having fielded the high-supersonic D-21 using both the M-21 Blackbird (unsuccessfully) and the TAGBOARD B-52/rocket booster combo (also unsuccessfully), the B-52/Pegasus/X-43A combo from NASA, the B-52/rocket booster/X-51 Waverider, the Stratolaunch Roc/Talon combo… you get the idea.

China is believed to be working on an unmanned drone to drop from the underside of their H-6 bombers. They’re already supposedly ready to field the WZ-8 rocket drone in that manner but it’s expected to top out in the Mach 3-3.5 range, iirc.

 

[boneh3ad]

[Bolding added]

Thanks for the synopsis on contemporary systems. The caveat on composite propulsion (and cooling systems nd other protective measures) strongly impacts practical commercial designs.

An air breathing stage becomes redundant as the atmosphere becomes tenuous with altitude, at least until reentry. Note programs such as the X-15 rocket planes used modified cargo jet aircraft to lift the experimental craft to altitude before separation.

Mission requirements for military versus commercial craft diverge sharply even as defense requirements define much cutting edge research. Recovering and reusing booster stages on current spacecraft provides an excellent example of commercial requirements improving overall performance while reducing costs.

Speed actually helps you here. The air gets thinner, sure, but as you move faster, you can ingest a larger volume per second, which can at least partially make up for lower density. There's still a limit, of course.