Despite the evident maturity of the J-11D program, the Chinese military nevertheless appears to also be going ahead with plans to purchase Russian Su-35 Flankers. The Su-35 is far more maneuverable than the J-11 – which gives the Russian jet an advantage in short-range dogfights – can fly longer distances, and can take off and land with a larger payload. It is also equipped with new avionics and new cockpit displays. However, its radar is a less advanced passive electronically scanned array (PESA) than the AESA system on the J-11D. Moreover, the aircraft and its systems will be manufactured abroad. The Chinese government views its indigenous defense industry as a strategic asset; purchasing more planes from Russia will not help advance Beijing’s goal of developing a mature, self-reliant aerospace industry. Given the apparent redundancy of moving forward with two very similar aircraft programs, some analysts speculate that the PLAAF’s primary motivation for buying the Su-35 may not be for its value as a weapons system but rather because it is equipped with advanced AL-117S turbofans.
Engines are a critically important component of any fighter aircraft, and they present Chinese airplane manufacturers with a dilemma. Their new fifth-generation fighter prototypes, the Chengdu J-20 and Shenyang J-31, sport sophisticated airframes and avionics that are clearly intended to make them a match for the United States’ most advanced aircraft. However, China’s ability to manufacture jet engines has not kept pace with other sectors of its aerospace industry. Regardless of how capable other Chinese aircraft systems may be, without a reliable, high-performance turbofan engine to power them, both the J-20 and the J-31 will be crippled.
History is replete with examples of otherwise excellent jets that struggled because they were underpowered. Although the iconic P-51 Mustang is now best remembered for its sterling service escorting strategic bombers on missions over Germany, it was only after engineers replaced its original Allison engine with the much more powerful British Merlin that it could fly and fight at the altitudes necessary to keep station with the bombers it was protecting. Early models of the now-legendary F-14 Tomcat were equipped with turbofans so weak that Secretary of the Navy John Lehman blamed them for nearly 30 percent of all Tomcat crashes and described them as being “just…terrible.” The F-15 Eagle and F-22 Raptor both struggled through long, painful development programs before their massive engines finally matured and turned them into the highly maneuverable dog fighters that they are today.
The Chinese military has traditionally relied on Russian engines to power its jets. Unfortunately for the PLAAF, the foreign models it is currently using are no longer cutting edge. The designs of these fighter engines date back more than 30 years and they were intended to be used in aircraft that are much lighter than the new models being tested today. For the time being, prototypes of both the J-20 and the J-31 are flying with older Russian turbofans – the J-20 with the Saturn AL-31 and the J-31 with the Klimov RD-93. Analysts have speculated that both of these aircraft are facing performance limitations imposed by their vintage power plants. For example, the J-20’s current reliance on AL-31s may be preventing the aircraft from achieving super-cruise, one of the key performance characteristics that makes the U.S. F-22 such a capable fighter.
China’s airplane manufacturers have two options for acquiring more advanced engines: Buy them from the Russians or build them at home. Beijing’s clear preference is for the latter; engines have become a focal point of the PRC’s aerospace industry. One Russian commentator described domestic engine development as being as strategically important for the Chinese as the Apollo space program was for the United States during the 1960s. However, jet engines are notoriously difficult to develop, and pose unique design challenges due to the extreme forces they encounter during flight and the exotic materials and techniques used in their construction. In 2012, Andrew Erickson and Gabe Collins argued that engine manufacturing remained a “persistent Achilles heel” of the Chinese aircraft industry and one that lagged behind rapid progress in other aerospace sectors, such as airframe design and sensors.
Today, the most advanced Chinese-made military turbofan in operational use is the Aviation Industry Corporation of China (Avic) WS-10. The WS-10 provides power for many Chinese aircraft, including some of the PLAAF’s J-11 fleet and the new J-16 multirole fighter. Reports on its capabilities are mixed at best. Although many of the engine’s initial teething problems have apparently been overcome, Jane’s reported last September that the WS-10 still suffers from so many faults that the “number [of engines] sent back to the…plant exceeds the amount of new production units.” Some Chinese commentators have also speculated that the WS-10 lacks sufficient power for the J-16, which is heavier than other Chinese Su-27 variants, and will need to be upgraded to allow the new plane to meet its design potential.
Another clue pointing to potential problems with the WS-10 is the decision by the PLAAF to use the AL-31 to power the newest variant of the J-10 attack fighter, the J-10B. Although a prototype J-10B equipped with a WS-10 was seen flying as far back as 2011, the PLAAF has nevertheless decided to go forward with the AL-31 for the production version instead. This decision may indicate that the Chinese military is concerned about the WS-10’s capabilities and is opting for a tried-and-true Russian alternative.
Regardless of the WS-10’s current capabilities, the fifth generation J-20 and J-31 will need much more powerful and reliable engines if they are to maximize their performance. An upgraded WS-10 is one option for the J-20, but it would almost certainly still leave the aircraft underpowered for its size and weight. Two entirely new Chinese engines are currently in development: the Xian WS-15 for the J-20 and the Avic WS-13 for the J-31. The progress of the WS-15 is unknown and it is not being flown on J-20 prototypes, although one Chinese blogger recently suggested that positive test results may indicate an unexpected leap in progress for the engine. The WS-13 was displayed at the Zhuhai air show last November along with another afterburning turbofan, but according to Bill Sweetman “the identical engines were on show two years ago,” and the “the [WS-13’s] development pace so far contrasts sharply with the rate at which new missiles and radar systems are being produced.”
The questionable progress of both the WS-13 and WS-15 programs may help to explain China’s interest in the Su-35, the latest and most advanced variant of Russia’s venerable Flanker aircraft family. The Su-35 is powered by the AL-117S, a significantly improved version of the AL-31 also sometimes designated the AL-41.
With its domestic programs seemingly in limbo, some analysts have argued that an AL-117S purchase would be the fastest way for the Chinese to get their hands on a suitable turbofan for the J-20. Since Russia is reportedly unwilling to sell the new engine as a standalone product, the PLAAF will have to buy the Su-35 and acquire the AL-117S as a part of a complete weapons system. After a series of false starts, it seems that a deal for 24 Su-35s is now in its final stages and Chinese pilots have already begun training on the new aircraft in anticipation of the first delivery in 2016.
In the long-run, it would be foolish to bet against the Chinese aerospace industry ultimately achieving the capacity to develop competitive high-performance jet engines. In the near term, however, the AL-117S remains China’s best option for powering the J-20. Although resorting to Russian technology may not be the ideal solution from an indigenous manufacturing standpoint, lessons learned from the AL-117S will undoubtedly be incorporated into the WS-13 and WS-15. That may benefit the J-31, which will be stuck with older WS-10s or RD-93s until the WS-13 comes on line.
For the PLAAF, purchasing the Su-35 is a win-win. They will not only get a highly capable new aircraft, they will also acquire get an engine that has the power to make their sophisticated new J-20 a world-class fighter.