China’s J-20 stealth fighter has joined the People's Liberation Army Air Force's frontline squadrons, but questions remain about its readiness, especially its ability to fight at supersonic speeds.
China announced on Feb. 9 that the J-20 had been put into combat service last year, ahead of schedule, the South China Morning Post reported, but sources said the military used "stopgap" engines to get the jets in the air because of what it saw as increasing security concerns in the region.
The current engines limit the jets' maneuverability, fuel efficiency, and "stealthiness" at supersonic speeds, the Morning Post said, and the two independent military sources said problems with the jet's WS-15 engine, which first cropped up three years ago, have not been corrected.
"The WS-15 engine designed for the J-20 exploded during a ground running test in 2015," one source told the Morning Post. "The explosion indicated the WS-15 is not reliable, and so far there is no fundamental solution to overcome such a problem … that's why the J-20 is using WS-10B engines now."
The Business Insider reported the current engines prevent the J-20 from being able to supercruise and fly past the speed of sound without engaging its afterburners, as can the U.S. F-22 and the F-35.
"Afterburners do make any fighter much easier to detect, track, and target using infrared and electro-optical systems at closer ranges when in use," Justin Bronk, a combat-aviation expert at the Royal United Services Institute, told Business Insider.
Bronk said the J-20 won't be able to fire long-range missiles supersonic speeds because of the problem.
"The major drawback from not having the ability to supercruise in this case would be having to choose between using a great deal of fuel to go supersonic or stay subsonic and accept shorter effective range from the fighter's missiles and an inferior energy position compared to a supercruising opponent," Bronk said.
A senior scientist working on stealth aircraft who requested anonymity earlier told the Business Insider that the J-20's design had a decent stealth profile from the front angle but could be exposed from others.
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