The “Long Pole in the Tent”: China’s Military Jet Engines
December 07, 2012
By Andrew Erickson and Gabe Collins
Much has been made of Beijing’s growing military might. Developing and producing high-performance jet engines could be the toughest -- but most rewarding -- advance.
a.. U.S. Navy Take Notice: China is Becoming a World-Class Military Shipbuilder
b.. Why China Military Watchers Got It Wrong
c.. Indian Military Goes French
d.. China’s Enigmatic Military
e.. China’s Military Gets Expeditionary
The PLA Navy surprised many foreign observers yet again when an indigenously-produced J-15 fighter became the first known fixed wing aircraft to take off from and land on the aircraft carrier Liaoning since its refitting and commissioning. Yet a critical question remains unanswered: how rapidly and to what extent will the J-15 and other Chinese military aircraft be powered by indigenous engines?
As in so many other areas, China’s overall development and production of military aircraft is advancing rapidly. Yet, as with a tent, it is the “long pole” that is essential to function and undergirds performance. In the case of aircraft, the most critical and difficult-to-produce component—the “long pole”—is the engine. Given the wide array of market-tested alternatives, nobody will buy a unit in which this central component is flawed. Hence, China’s currently significant efforts to make progress in this area. Still, the outcome and impact of these efforts remain uncertain.
As part of a larger effort to consolidate and enhance the industry, China’s jet engine makers, led by Aviation Industry Corp. of China (AVIC), are expected to invest 100 billion yuan (US$16 billion) in jet engine development in the near term, and perhaps up to 150 billion yuan (nearly US$24 billion) by 2015. According to Reuters, “Some Chinese aviation industry specialists forecast that Beijing will eventually spend up to 300 billion yuan (US$49 billion) on jet engine development over the next two decades.” With this level of capital investment, which is many times larger than previously-reported levels, China is finally deploying the financial wherewithal needed to enable major breakthroughs. For context, the Pratt and Whitney F135 powering the F-35 Lightning II, which is the world’s most advanced and powerful tactical aircraft engine, is estimated to cost around US$8.4 billion to develop (at least in terms of officially-reported funding sources). On this basis, China has deployed funds sufficient to potentially support the parallel development of several advanced high-performance jet engines and large turbofans.
China’s defense aerospace industry has shown the ability to successfully manage parallel projects, as it is simultaneously developing at least four different types of tactical fighter and strike aircraft, including two low observable fighters, the J-20 and the J-31. No other nation is working simultaneously on so many distinct modern tactical jet programs. Yet this very progress also highlights an additional reality of China’s military aircraft sector—while airframe design and construction capacity have advanced significantly in recent years, China remains unable to mass-produce a jet engine capable and reliable enough to give its new fighters truly 5th-generation performance characteristics such as the ability to cruise at supersonic speeds without afterburners. Even if the J-20 and J-31 prototypes are flying with Chinese-made jet engines, this by no means demonstrates that such engines have a sufficient service life and can be produced on a scale suitable for equipping a large tactical aircraft fleet.
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
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.
China has made progress in recent years with metallurgy and manufacturing techniques, leaving components and systems design, integration, and management as the most probable weak points that are holding back engine production. Chinese engines have suffered blade warp and destruction and other problems, both during ground testing and apparently also under high RPM, rapid turn conditions in flight that produce high centrifugal and g-forces (e.g., in J-11B aircraft). In order to remedy this, China’s military jet engine makers need to achieve some of the same production and process management breakthroughs that the personnel and facilities making the airframes and avionics have attained over the last two years. To facilitate such efforts, AVIC Engine has been recruiting experienced engine designers. Given the progress elsewhere in the sector and China’s continuing acquisition of technical and process management information through trial and error, research, and industrial espionage, the probability is rising that China’s jet engine makers will surprise the outside world in the next few years with a reliable, mass-produced version of the WS-10 engine.
The WS-10 has the potential to deliver performance in the same class as the Pratt & Whitney F100 turbofans that power the F-15 and some of the F-16 fleet, and thus might be able to capably power the J-11B, J-15, and J-16 aircraft, which are in the same size range as the F-15. China’s ability to series-produce an engine powerful and capable enough to give the J-20 true 5th-generation performance probably lies at least 2-5 years in the future.
Why China wants to master production of high-performance jet engines
The lack of domestically-made jet engines represents a gaping hole in Chinese aircraft design and performance. Being able to mass-produce reliable and powerful jet engines is essential to perfecting and exporting indigenous aircraft; all major military aircraft producers save China have enjoyed solid engine design and production capabilities. Yet Russia, and to some extent Ukraine, are the only sources from which China can import military jet engines because the post-Tiananmen arms embargoes prevent companies based in the U.S. and European Union from selling such engines to China. Despite its considerable willingness to export, Ukraine lacks the engines that a 5th-generation fighter would need.
For its part, Russia has less and less reason to sell advanced jet engines to the Chinese military. First, Russia has its own ambitions to produce and export the Sukhoi T-50, a prospective 5th generation fighter, and would not want to undermine its position by helping the Chinese build a competing aircraft. Second, there will be political and economic pressure to keep advanced engines at home because Russia’s air force is attempting to modernize and aircraft being produced for the Russian military will need the late-model jet engines. Third, the last decade of Sino-Russian arms trade has been fraught with tension over technology transfer and illegal Chinese technology theft and reverse engineering of Russian systems. Finally, some Russian policy makers are increasingly concerned about China’s rising military and economic power and the growing presence of Chinese in the Russian Far East.
As such, it is increasingly unlikely the Russian government will want to sell its most advanced engines to China and risk having the Chinese reverse engineer them and then not only use the engines in their own aircraft, but also potentially make them available at a lower price on the world export market. In the 1990s and early 2000s, Russian jet engine makers gambled and won because China’s aerospace sector was relatively backward. However, rapid improvements over the last several years have put China’s aviation industry much closer to being technically on par with its Russian counterpart and the Russians are likely to be increasingly unwilling to sell engines on the assumption that China could assimilate the technology much more rapidly than before.
In September 2010, for instance, Reuben Johnson reported in Jane’s Defence Weekly that PLAAF Overhaul Plant Number 5719 had developed an upgrade for the AL-31F that extended its service life from 900 to 1,500 flight hours. Russian specialists viewed this achievement as “another example of how the technology sold to the Chinese during the 1990s has now been fully assimilated by them. It is only a matter of time before the engines that China produces will be as good as or better than anything designed here in Russia.”
Restricted engine supplies from Russia could also crimp China’s ability to train its pilots more intensively because realistic air combat training puts significant strain on engines and wears them out more quickly than the lower flight hour regime on which many Chinese pilots remain.
Su-35 Purchase Possibilities?
For now, however, Chinese engine programs have failed to deliver, and may currently be stuck at technical plateaus. Russia needs Chinese money to sustain its defense industry. China’s current pursuit of an Su-35 purchase agreement with Russia primarily reflects a desire to gain access to the NPO Saturn/Lyulka117S engine, a next-generation follow-on to the Su-27’s AL-31F engine, to try to reduce development time for Chinese engine programs. According to Reuben Johnson, while a final deal is unlikely before mid-2013, negotiations appear already to have risen to a new level, with Sukhoi having already acquiesced in principle to shifting from offering 48 aircraft for $4 billion to 24 aircraft at $1.5 billion.
Johnson stated that “sources within Russian industry insist that this back and forth negotiation with Beijing continues but several believe that China will end up ‘officially signing’ for 48 aircraft but only taking delivery of 24 Su-35s.There are precedents for this kind of arrangement in which China’s industry ends up actually procuring fewer aircraft than it orders, such as the 1996 Su-27SK/J-11 contract for 200 of these aircraft produced at the Shenyang Aerospace Corporation (SAC). Only about 100 of these aircraft were ultimately manufactured at SAC, at which time the Chinese firm began turning out pirated copies of the aircraft – the J-11B.”
Johnson added that Russian aerospace officials are leery of Chinese industry copying the Su-35 in the same manner. Meanwhile, at present Chinese officialdom is more sensitive than normal to the charge that its military aircraft industry is capable of only copying Russian designs following the recent first arrested landings of the SAC J-15 fighter aboard the Russian-designed and Ukrainian-built Liaoning aircraft carrier. The J-15, allege several Russian sources, is another illegal copy – this time of the Sukhoi Su-33 carrier-capable fighter.
In any case, the status of this potential purchase agreement bears watching, as the Su-35’s 117S engines are more powerful than the AL-31 engines that Russia has been selling to China. Having actual 117S engines physically available could help give Chinese jet engine makers an opportunity to attempt to reverse engineer them and/or and acquire insights into how they might be able to build a more powerful indigenous tactical turbofan engine.
Over the next two decades, China’s jet engine demand will be massive. Buyers in China are expected to purchase 5,260 additional commercial aircraft valued at $670 billion from 2012-31 and more than 2,300 business jets in the next 20 years, a number of aircraft that could require more than 16,000 additional jet engines. What’s more, aircraft demand from China’s military could easily add another 500-1,000 engines to these totals.
Selling parts and services to companies who use the engines is an additional dimension of interest for Chinese engine makers. Servicing jet engines tends to be much more profitable than selling the engines themselves, leading some analysts to say that many engines makers “sell the hot air moving out of engines” as opposed to the engines themselves. For example, Citibank has estimated that some jet engine makers may derive seven times the profit from aftermarket service and parts sales for their engines that they do from the sale of the powerplants per se.
Key dual use technology
On the strategic side, government and company officials may also seek to be able to power future Chinese military tanker, transport, and airborne early warning (AEW) aircraft with domestically-made engines because they fear embargoes or disputes over prices and other issues with foreign suppliers. Such a strategy can only work if all critical subcomponents and parts are produced indigenously, which suggests that China will seek to create a full indigenous jet engine supply chain.
This has significant military implications because the same large high-bypass turbofans used in civilian airliners can, with little or no modification, power large military aircraft including tankers, transports, and AWACS. The major U.S. large transport aircraft (C-17 and C-5), tankers (KC-10 and KC-135), and AWACS and others (E-3A and P-8A) all either are, or can be, powered by engines that are essentially identical to commercial aircraft powerplants.
For example, the same CFM56 series engines like those that power the Boeing 737 and Airbus A320 single-aisle airliners are also used in the KC-135 tanker, E-3A AWACS, and P-8A maritime patrol aircraft. Likewise, the PW2000 turbofan that powers the Boeing 757 and Ilyushin IL-96 airliners is physically very similar to the F117 PW100 engine used in the C-17 transport aircraft, the backbone of the U.S. airlifter fleet.
Another use for jet engines—at least their cores—is propulsion of naval ships, since marine gas turbines tend to be based on aircraft engine designs. Having good reliable engine cores that were originally developed for aircraft application could have potentially significant implications for Chinese military shipbuilding, as gas turbine propulsion gives ships much better acceleration and combat maneuverability.
Conclusion: Exceeding China’s “80% Solution”?
In terms of raw numbers of aircraft being built, China has become the world’s largest producer of fighter aircraft over the past three years. Now observers are waiting to see if the newly announced investment plans can help bring China’s military jet engine manufacturing capabilities to a level commensurate with the country’s ability to build airframes. The stakes are high because once China masters indigenous production of high-performance jet engines, there will be few, if any, technical constraints on its ability to rapidly produce late-generation fighters for its own forces and for export markets.
This is a daunting task indeed. When it comes to future efforts to export aircraft with Chinese engines, Beijing may be burdened with an “80% solution” pattern. According to Reuben Johnson, China’s particular technological development approach produces a common pattern in performance parameters of the systems it develops: “Chinese always seem to be able to achieve around 80% of the performance of whatever they’re trying to mimic; the last 20% would be difficult and expensive to accomplish.” This approach may produce significant and even superlative performance in categories in which ‘quantity has a quality all its own’—as with missiles—but limits results in areas where workarounds are scarce or unavailable, as with aeroengines.
It will be hard to convince China’s military and export customers that they should accept a substandard Chinese engine when China has previously used imported engines (e.g., a Ukrainian engine in the L-15 trainer); asking them to accept an unfamiliar product represents a great leap of faith. Increasing indigenous efforts in this area may reignite previous tension between the interests of China’s aviation industry as a producer and the PLAAF and PLAN as end-users—just as the Indonesian Air Force opposed the ambitious efforts of Dr. B.J. Habibi and the state-owned enterprise Industri Pesawat Terbang Nusantara (IPTN)—now known as Indonesian Aerospace—and the Indian Air Force is often at loggerheads with Hindustan Aeronautics Limited over jet engine issues.
China is increasingly recognizing that aeroengines represent the “long pole in the tent” of military aircraft production, but has a long way to go before it can remove this as a limiting factor. Even with China’s existing resources and growing expertise, this process is likely to take time to even approach the accomplishments that the Big Three, secondary Western European, and Russian aeroengine manufacturers have achieved after many years of arduous development.
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