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China successfully completed hypersonic engine test
By Deng Xiaoci Source:Global Times Published: 2019/1/7 20:53:40

China's home-grown turbine-based combined cycle (TBCC) engine system has completed its design and development stage and entered the aircraft-engine integration test phase, a major step toward the development of the country's next generation hypersonic drone.

An article published by the WeChat account of Chengdu Aircraft Research and Design Institute, a design facility of the Chengdu Aircraft Industrial Co, on Thursday said the TBCC engine flight test project is led by the institute's chief architect Wang Haifeng, who also led key national defense projects, such as the development of the J-20 and J-10 fighter jets.

The TBCC engine combines a turbine and a scramjet engine, which offers an ideal single-engine solution to achieving the shift from low speed to hypersonic speed, said Liu Xingzhou, a prominent ramjet expert and Chinese Academy of Engineering academician at the China Aerospace Science and Industry Cooperation, in 2011.

The TBCC engine will allow the aircraft to fly at speeds of up to Mach 6, which means five to six times faster than the speed of sound, said Wei Xudong, a Beijing-based military analyst.

The TBCC engine, which is bigger and more expensive than traditional ones, is primarily used in hypersonic cruise missiles and unmanned aircraft, including supersized reconnaissance drones and pilotless bombers, since no human could stand long periods of hypersonic flights, Wei told the Global Times on Monday.

Wei also stressed that once the TBCC engine technology matures, missiles outfitted with it will be impossible to intercept.

For years, US arms giant Lockheed Martin has been working on the development of the SR-72 using the TBCC propulsion system. The SR-72's top speed will be Mach 6. Its first flight is expected in 2023, and scheduled to enter service by 2030, US defense website airforce-technology.com reported.

The SR-72 is the successor of the fastest aircraft the world has seen, the SR-71, a Cold War reconnaissance jet that the US Air Force retired in 1998.

As Chinese firms rapidly develop their own TBCC engine, a Chinese version of the SR-72 will not be far off, Wei predicted.
 
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A very important post about Chinese military turbofans via jobjed from SDF:

Here are some background on the WS-10 and monocrystal turbine blade fabrication in China, as well as WS-15 updates and predictions.


About the WS-10, sources: here, here, here, here (2, 3, 4, 5, 6, 7):
  1. Its OPR is overly ambitious for a country starting off weak in material science, at around 32 whereas the AL-31's is around 24. A higher OPR means the turbine-inlet temperature and the stresses on the compressor stages are higher, putting greater demand on material quality. The OPR was that high because WS-10's core came from the CFM56, the same core as the F101 developed by GE which had a high OPR. Now GE didn't mind a higher OPR because they had the material science to back up their ambitions but the same could not be said for 606. The F110 uses monocrystal blades whereas the WS-10 uses directionally-solidified blades which are hugely inferior to moncrystals and don't last nearly as long meaning WS-10s today have a lifespan of ~1500 hours while F110s go upwards of 5000 hours. This resulted from China not having monocrystal turbine blade fabrication capability when WS-10 was under development. Additionally, 606 had to strengthen the WS-10's compressor stages to counter the stresses of a high OPR, making the WS-10 significantly heavier than the AL-31, some 250kg heavier according to gongke.
    • Another effect of the high turbine-inlet temp is the incorporation of large cooling channels in the WS-10's turbine blades. These channels bring up cool air to cushion the blades from the hot air of the combustion chamber but every litre of air used for cooling is a litre of air not optimally used to produce thrust. Therefore, most engine manufacturers try to minimise the amount of air passed through these channels to maximise efficiency. 606, on the other hand, had to enlarge these cooling channels to compensate for their directionally-solidified blades' inferior heat resistance. This means a relatively high portion of the WS-10's airflow is used for cooling and isn't optimally combusted.
  2. In the 1980s, 606 couldn't design components of an advanced engine independently so they copied the core of an American engine but adopted Russian design standards for the low-pressure compressor stage and afterburn section. This seems fine on the surface until you realise the Americans spin counterclockwise and the Russians spin clockwise. Why does this matter? In 4th-gen engines, the low-pressure compressor shaft is contained concentrically within the high-pressure compressor shaft meaning you'd want to minimise the relative velocity of the two shaft surfaces to reduce friction. In an engine where both the LP and HP shafts are spinning in one direction, the relative RPM between the two shafts would be something like 5000. For the WS-10, where the LP and HP shafts spin in opposite directions, the relative RPM is more like 20,000. For comparison, the F110's LP section has max RPM of 8500 and its HP section, ~15000, giving a relative RPM of 6500. If this was replicated on the WS-10, the relative RPM would be a ridiculous 23,500. This means the WS-10's compressors don't have as much margin to increase its RPM. As engine RPM increases, the bypass ratio decreases, see Figure 1. Unfortunately for the WS-10, it can't spin its engines above the RPM corresponding to a bypass ratio of 0.84 because its LP and HP shafts spin in opposite directions and a higher RPM would destroy the shafts, destroying the engine/aircraft. This means a minimum bypass ratio of 0.84, the highest of its contemporaries, is what the WS-10 has to work with. This isn't ideal because high-altitude cruising is most efficient with a bypass ratio as close to 0 as possible.
  3. 606 attempted to design the WS-10 to a modular architecture to facilitate rapid disassembly which is beneficial for maintenance, especially in the field and not the depot. This is also how GE designed the F101 and its derivatives. However, 606 didn't get everything right and the WS-10 ended up being only half-modular. This means while depot maintenance was simplified, field maintenance remains a hassle.
gvVBpZ7.png


Figure 1: WS-10 Bypass Ratio vs RPM, x-axis 1.00 = 100% RPM








Monocrystal turbine blade situation in China, sources: here, here, here, here.
  1. As stated above, active service WS-10 do not use monocrystals. A few examples were built using monocrystals manufactured by 170 Factory but test results were disappointing and nothing came of it. The WS-10IPE is an attempt to use better materials including new monocrystals to squeeze more performance out of the WS-10 but the improvements are not significant enough to convince the PLA to invest more into the project.
  2. Chinese turboshaft technology is the least behind of all aeroengine areas. In fact, turboshafts are most prominent users of monocrystal blades in China at the moment. The WZ-9 uses monocrystal turbine blades manufactured by the 331 Factory, or AECC South Industry Company Ltd. Their blades are pretty good quality and their yield factor is decent. However, the small physical size of their products limit their use to turboshafts.
  3. Guizhou 170 Factory, now acquired by 621 Institute, achieves a monocrystal-growing batch yield factor of around 70% and is 606th's monocrystal supplier. For comparison, Western engine manufacturers typically achieve 95% yields.
  4. The Chinese Academy of Sciences' Institute of Metal Research also manufactures monocrystal turbine blades with a yield factor of around 70%.
  5. A private company, the Hangyu Superalloy Technology Company Ltd (航宇超合金技术有限公司) achieves the highest yield factors in China (~90%), comparable to Western manufacturers. However, their catalogue range is smaller than 170 and Institute of Metal Research's so their products aren't as widely used.
  6. 170 Factory's catalogue includes the latest 3rd-generation monocrystal blades such as DD32. The WS-15 does not use the DD32 because its design predates the arrival of the 3rd-gen blades. However, it definitely uses monocrystals of some kind, probably 2nd-gens.







Now, updates about the WS-15:
  1. Half a year ago, Dr Liu Daxiang predicted the WS-15 will achieve design certification within 3 - 5 years. Gongke also said an engine can achieve design certification 3 - 5 years after first flight if testing goes well. This means the WS-15, if it wants to achieve design certification within 5 years as predicted, should be flying within 2.
  2. An experienced Chinese aeroengine enthusiast wrote an article analysing the billboard of accolades (see Figure 2) that got posted last month. The statement about Batch 3 of prototype WS-15s is the main attraction. Looking back at the WS-10 program for hints, its Batch 1 and 2 prototypes were exclusively for ground tests, beginning delivery in 1995 while Batch 3, consisting of seven prototypes, was delivered from 2000 - 2001. In June 2001, a J-11 with its starboard AL-31F replaced by a WS-10 took off, marking the first flight of the WS-10. Flight verification of the WS-10 was subsequently conducted using Batch 3 and Batch 3S engines. Beginning in March 2004, the WS-10 began its design certification process, eventually being granted design certification in October 2005. In other words, a few months after WS-10 Batch 3 was delivered, the WS-10 had its first flight and after little more than four years, it got design certification. And now we know the WS-15 Batch 3 has or will soon be completed and delivered. However, we must remember that the testing of the WS-15 is far more rigorous and comprehensive than the WS-10's so the visible progress may be slower as 606 takes their time doing things right this time.
  3. In March 2018, someone asked gongke if the WS-15 was at a stage where 606 could just cram it in an airframe and make it fly for ten minutes. Gongke replied it definitely could. From this we know the WS-15 was already in flyable state almost a year ago, and probably considerably sooner than that taking into account the travel delay of news from 606 to Liyang.
The conclusion I get from this is we should expect a first flight of the WS-15 aboard the Il-76LL testbed within two years, quite possibly occurring this year.

OmP99nj.jpg


Figure 2: Billboard of achievements by young aeroengine designers
 
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