The “Long Pole in the Tent”: China’s Military Jet Engines (Page 2 of 6)

China is just now learning how to series-produce the WS-10 turbofan that powers some of its J-10 and J-11/J-11B fighter fleet, and remains unable able to produce the large, high-bypass turbofans it would need to power future indigenous large transport or tanker aircraft. While Global Times reports that the J-11B fighters now being produced are all outfitted with Chinese-made WS-10 engines, the latest jet engine import numbers suggest China’s fighter fleet remains heavily reliant on Russian engines, with Chinese-made engines now only powering about 20% of the country’s most modern fighters and strike aircraft as well as the JF-17 fighters it is exporting to Pakistan.

Reuben F. Johnson, a Russian and Chinese military aerospace analyst who writes for Jane’s, tells us that, based on interactions with foreign journalists and other experts at major international expos, of all the projects Chinese experts are working on, those concerning aeroengines appear to be some of the furthest behind their Western counterparts, with the least information available publicly.  At the 2012 Zhuhai Airshow, for instance, the WS-10 Taihang was not displayed in any form, although the lower-performance Ukrainian-derived Minshan turbofan (for the L-15 trainer) was displayed for the first time. A wide range of other jet engines are under development.

Technical challenges facing Chinese jet engine makers

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Jet engines used in tactical fighter and strike aircraft must be able to operate reliably under severe conditions. Jet engine compressor blades, for instance, can experience centrifugal forces as high as 20,000 times the force of gravity during flight. The challenge that a turbofan blade faces in surviving in this environment has been likened to stirring hot soup with a spoon made of ice.

With their complex, esoteric technologies and demanding performance parameters, aeroengines represent the pinnacle of aerospace development. According to Johnson, developing an engine core is almost always the “long pole in the tent” in fighter development, and the most likely source of program delays. Aeroengine materials are often simply “not machinable” according to industrial classification guidelines because it is not affordable to do so on an industrial scale. Alloys, powder metallurgy, and single crystal blades must all be mastered. It is important to note that of the five Soviet major higher research institutes devoted to aviation, one was dedicated to materials, and Soviet metallurgical research was extremely active. In Russian engine programs, mastering thermal barrier coatings proved a key step.

Despite these efforts, however, even Russia has not equaled the “Big Three” (Pratt & Whitney, GE, and Rolls Royce) in performance. Russian engines remain heavier, utilize less of the most sophisticated materials, suffer from higher fuel burn rates; have poorer acceleration, lower thrust-to-weight ratios, shorter lifespans, and less maintainability than the top U.S. and European-made jet engines;and also remain incapable of using the latest management technologies to best advantage. For example, while full authority digital engine control units (FADEC) are apparently available now for new Russian-made engines like the Salyut AL-31 and FADEC quality compared to non-Russian models has shrunk to fairly incremental levels, software quality remains a key difference. Even the first Su-27s flew with different engines because the AL-31 was not yet ready at the time.

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