Asia is an arms race hotbed right now - and depending on who you talk to, the People's Republic of China is the specific reason why. The PRC military has many strategic goals, some more publicly acknowledged than others. Whether or not the PRC has invasion plans for the Republic of China (Taiwan), they do have clear military and strategic goals on being able to counter the RoC military if necessary. The PRC also seeks military parity with the United States, if for no other reason than that this results in the PRC having greater regional and global strategic influence. The PRC is also highly invested in feeding the arms race directly by providing the arms that feed it. Arms manufacturers in the PRC - which are still highly influenced by the Communist government - are constantly trying to develop weapons that are at least competitive with their Russian and American counterparts but vastly undercut their price. In this way, they can be thought of as the Hyundai/Kia of the international arms world. Designing competitive cars that undercut the competition - and doing likewise for warplanes - are worlds apart and accusations of underhanded dealings have been thrown around as part of the PRC's technology development. These accusations have cultural and historical basis and include the PRC's development in stealth technology.
Above image sourced from The Battlefield Wikia
Chinese Stealth Pre-History
As covered before, the origins of the PRC's military aerospace industry lie largely in attempting to copy and mass-produce hardware given to them by the Soviet Union. This was a product largely of necessity as much as it was convenience due to the consequences of the Great Leap Forward and Cultural Revolution. These Soviet designs were, at the time, among the most advanced and sophisticated available to any military and it was thought that the People's Liberation Army Air Force (PLAAF) can expedite their arrival as a world-class airpower in not only copying them, but improving upon them. Despite long gestation periods that resulted in these designs reaching obsolescence soon after mass-production, the PRC was indeed able to implement many improvements.
Perhaps the most significant of these outright "copies" is the Chengdu J-7 (NATO reporting name "Fishbed" as with the original Soviet model), exported as the F-7 Airguard. The J-7 is not an unlicensed copy - it is an actual licensed derivative of the MiG-21, and has especially evolved in later variations to be distinct from the MiG-21 in several key areas. The difference is subtle, but illustrated in the photo above - instead of the perfectly triangular wing form of the MiG-21 and early J-7, this Pakistani Air Force F-7 Airguard has reduced wing sweep about midway along the leading edge. The most significant differences are invisible: from the time President Nixon warmed relations between the U.S. and the PRC until the Tienanmen Square incident of 1989, U.S. companies were able to export military electronic technology including radar directly to the PRC. This nearly revolutionized the PLAAF overnight. In the J-7's case, it meant more sophisticated electronics than the original MiG-21 and being able to forego the MiG-21's characteristic "hump" in favor of "shrunk" avionics of American origin. The J-7 was therefore allowed to keep its WWII-style "bubble" canopy and maintain a much cleaner look. It is also said that the J-7 - and all Chinese warplanes - are built to lighter standards. This reduces the lifetime usefulness of the aircraft, but results in an aircraft that is lighter yet able to withstand the same G-Force loading as Western aircraft during that useful lifetime (and in fact, leads to mass reduction which aids maneuverability). Given the school of thought in which an aircraft becomes outdated as soon as its electronics outfit does, this is hardly a flawed approach.
The Chinese were also able to develop the J-6 (a copy of the MiG-19) into the Nanchang Q-5, called the "Fantan" by NATO and the A-5 when exported. The MiG-19 was originally designed as an interceptor for use against early jet bombers (hence its heavy multi-gun autocannon armament) but found success in the Arab-Israeli Wars as a ground attack and light strike aircraft. The Chinese capitalized on this success to developed the Q-5 into a dedicated strike aircraft with the inclusion of a small bomb bay and a redesigned nose profile, initially for aerodynamic reasons but later proving useful for housing laser designation for precision-guided armaments.
Perhaps the best example of an early, truly indigenous PRC military aircraft design is the Shenyang J-8, called "Finback" by NATO. Even here, the MiG-21 origins are obvious, though they ultimately only share a superficial resemblance. Unlike the MiG-21 or J-7, the J-8 is primarily designed as a heavy interceptor, tasked with shooting down bombers or other aircraft with long-range missiles. Its closest Russian and American equivalents would be the Su-11/Su-15 heavy interceptors and the F-106 Delta Dart. The J-8 also features twin engines; it was later redesigned with a larger nose housing larger radar, necessitating intake splitters along the sides of the fuselage.
This specific J-8II pictured collided with a US Navy EP-3 Aries on a reconnaissance mission in 2001, resulting in the destruction of the aircraft and the death of the pilot. The incident became highly sensationalized while U.S. diplomats worked for the return of the EP-3 and its crew which safely landed at a PLAN airbase. Image taken from Wikipedia.
Even when the J-8 was newly fielded in the early 1980s, it was arguably outdated compared to Western and Russian designs, which now included the F-14, F-15, F-16, F/A-18, Su-27 and MiG-29. PRC aerospace firms struggled to develop something actually competitive with these advanced Western types until the turn of the millennium.
The PLAN Enters the 4th Generation And Beyond
PRC military aerospace development was hardly stagnant in the 80s, but were largely still stuck with variations of 70s and even 60s technology. As such, these designs were canceled, having not progressed beyond the drawing board.
This rendering of the stillborn Chengdu J-9 (ultimately rejected in favor of the J-8) taken from Wikipedia shows both the stagnation of PRC military aircraft development and its eventual direction. The appearance bears resemblance to both the MiG-21 and the J-10, two aircraft that are lightyears apart in capability and technology.
The PRC response to the MiG-29 and F-16 and F/A-18 series of fighters became properly developed in the form of the Chengdu J-10, sometimes called the "Vigorous Dragon" and offered for export as the F-10 Vanguard. The J-10 is a true 4th Generation Fighter - combining an advanced radar and Beyond Visual-Range missiles, "Fly-By-Wire" controls and a high degree of maneuverability, all of which allow for the design to be equally flexible in close-in dogfights, far-away missile interception or precision strike bombing, all during the same mission if necessary. The J-10 also possibly incorporates low-level or subtle stealth characteristics, much like the F/A-18E Super Hornet for example.
This J-10A in aerobatic colors shows a planform generally similar to the Eurofighter Typhoon with canards at the front and the engine intake below the cockpit. Image taken from Wikipedia.
The J-10 continues to be developed; recently a version has been spotted with a reprofiled nose (possibly containing a larger, more powerful radar), a different intake and other subtle improvements. Image credit FreeRepublic.com
The appearance of the J-10 was as much of a shock for the West as the MiG-25 "Foxbat" had been back in the 60s. Although lacking the mythical attributes originally attached to the Mig-25, the J-10 nonetheless showed a technological development and manufacturing capability that many believed was out of the PRC's grasp. So much so that many believe outside help had to have been involved - specifically Israeli help, as Israel Aerospace Industries attempted to develop a very similar 4th generation fighter called the Lavi, allegedly canceled due to U.S. Congressional pressure in the interest of exporting more F-15s and F-16s built on American soil to the Israeli Air Force.
Image credit Wikipedia
The Xian JH-7/FBC-1 is, at least strictly by outer appearance, more inline with what many people expect out of the PRC. However, the full extent of its capabilities are not known - such as the possibility of terrain-following radar. The ability to carry long-range standoff missiles, particularly anti-ship missiles, also reduces any importance held on its somewhat outdated look. The JH-7 is operated solely by the People's Liberation Army Navy (PLAN) but is "multi-role" in that it can bomb both land and sea targets.
Image credit Wikipedia
The Chengdu FC-1, co-developed and produced in Pakistan as the Pakistan Aeronautical Complex JF-17 Thunder, has a very superficial resemblance to the MiG-21/J-7 (indeed, its origins lie in an extreme evolution of the J-7) but ultimately is an entirely new design meant to mimic the combat capability of the F-16 and other 4th generation fighters at a cheaper price point. Currently only used by Pakistan (as the PLAAF foresees their fleets filled out by even more capable J-10s and J-11s instead), the FC-1 is a clear indication of the PRC's export ambitions.
The most significant PLAAF 4th generation fighter, however, is once again a licensed copy of a Russian design - the J-11, based on (depending on the exact model of J-11) the Su-27 or Su-30 Flanker (the above image, from Wikipedia, represents an Su-30 derived design as indicated by its wingtip pods and twin seats). Despite being a licensed copy, the Russians accuse the PRC of abusing the license beyond the terms of their agreements including the development of the J-16, yet another (unauthorized) Flanker derivative with a larger, folding wing optimized for operation on the PLAN's future carriers.
Image credit "Chinese Internet" via War is Boring
The Chengdu J-20 is a far greater development than the J-11 or J-16 - and is entirely indigenous. It represents a true 5th generation fighter aircraft with extensive stealth characteristics. It in effect resembles a "supersized" J-10 redesigned for twin engines and stealth and shares the characteristic canard configuration along with twin vertical stabilizers. The size is truly impressive - far larger than either the American F-22 or Russian T-50/PAK-FA.
This image, courtesy defense.pk shows that the J-20 is indeed very large for a tactical warplane - something that has lead some to believe that the J-20 might in fact be closer to a prototype stealth bomber or strike aircraft than an air superiority fighter. If so, it would likely be operated by the PLAN like the JH-7 (which it would probably replace) as a possible counter to US Navy aircraft carriers. A stealth aircraft would provide the best chance of evading the USN's AEGIS radar system, the USN's primary means of anti-air defense.
Image credit MigFlug
This suggests an obvious conclusion - that the true PLAAF's F-22/T-50 analogue is the Shenyang J-31, pictured above. Others speculate it may be closer to an F-35 analogue: a smaller, cheaper alternative to the J-21 that would be especially attractive to the export market. In either case, the J-31 (also referred to as the F-60) looks like an almost perfect mash-up of the F-22 and F-35, more closely resembling one or the other depending on the angle (for example, the radome especially bears an uncanny likeness to that of the F-22).
This image from UAS Vision shows yet a third type of PLAAF stealth aircraft - and the most significant development of all: an Unmanned Aerial Vehicle (UAV). The implications of a stealth tactical UAV are very important - removing the pilot has powerful ramifications for improved stealth, increased capability and potential ease of manufacture. USAF commanders envision future battles being fought not with squadrons of perfectly undetectable stealth drones, but with swarms of them, smart enough to evade surface-to-air missiles if detected and shoot down any attempt at interception, but also cheap enough to be expendable without having to write letters to loved ones. It should be assumed that PLAAF commanders have the exact same visions. PRC UAV/UAS development has exploded in the 21st century and includes numerous types, both stealthy and non-stealth types.
Where is China Getting This Technology?
Given the legacy of copying technology, there are accusations that the Chinese have stolen stealth technology from the Americans, Russians or (likely) both (and from anywhere else they can get it). It was revealed that the Chinese had in fact hacked their way into possession of F-35 blueprints. The appearance of the J-31 "coincidentally" lines up with this. The PRC has also been able to obtain examples of American technology recovered by adversaries: the Iranians allowed them access to an RQ-170 stealth drone that crashed in their territory, allowing the Chinese to copy it. It is widely assumed that wreckage of the still-classified stealth helicopter used on the Osama Bin Laden raid was shipped to the PRC by Pakistan (who has cooperated with the PRC extensively, including in the development of the FC-1 fighter described above). During the Serbian-Bosnian Conflict, wreckage from an F-117 stealth fighter shot down was also examined by the PRC.
One key area where the PRC is still lacking is in engine technology. Their best Flanker copies are powered by engines of genuine Russian manufacture, and this presumably applies to at least initial operational examples of the J-20 and J-31. The J-10 is also powered by a Russian engine, of the same type that powers their Flankers. The JH-7 is powered by a British engine design that dates back to the 60s and 70s and was in fact obtained by China to power civilian designs. The Chinese are working on a number of advanced engine designs from licensed (and unlicensed) Russian copies to true indigenous efforts, but all have fallen short of what they've been able to import.
That said, it's clear that the whole of PRC aeronautical ability has advanced immensely. The simple fact that they've been able to fly stealth prototypes puts them in a position to challenge the United States and Russia. Moreover, it puts them far ahead of almost every regional player, including the Republic of Korea and Japan which both have yet to fly stealth prototypes, and makes the Republic of China look hopeless in comparison. As to the realities of PRC stealth development - hopefully that will be a reality that remains untested.
However, given the PRC's export ambitions, testing their stealth designs may prove to be inevitable, even without direct conflict with the PRC.