Recently, there have been rumors circulating online that the two seater J-20 has undergone another test flight just after the arrival of the new year, and its appearance has also undergone significant changes. In addition to the number "2031" on the front of the fuselage, indicating that it is still in the prototype test flight stage, the black coating on the surface of the fuselage is quite similar to the current air force coating. These features are completely different from the yellow appearance of the two seater J-20 when it first flew two months ago. That is to say, after only two months of evolution, the test flight of the two seater J-20 has entered a new stage.

A new two seater J-20 that underwent test flights just after the New Year

As a development model based on the domestically produced single seater J-20, the dual seater J-20 is currently the only two seater stealth model in the world that has entered the prototype test flight stage. While creating new history, it is also destined to be like all explorers, boldly exploring and carefully verifying. However, due to the significant technological inheritance from the single seat J-20, it will no longer take more than five years from its first flight in January 2011 to small-scale production in 2016, as the J-20 did. But the transformation of stealth fighter jets from single seat to dual seat is not just about adding one pilot and expanding the rear seat space.

The number of J-20 in service is already considerable

As the design unit of the J-20, Chengfei had already demonstrated the plan for the dual seat J-20 to the outside world in its early years, and the original design also reserved space for later dual seat modifications to a certain extent. However, modern stealth fighter jets not only have unprecedented performance, but also have reached the ultimate level of detail control over fighter jets. For example, during the high subsonic to transonic phase, and then to the stable supersonic cruising phase at around 1.4 Mach, the center of gravity of a fighter jet will have a significant deviation. To ensure the stability of the supersonic cruising phase, the control system and balance capability of the fighter jet must be precise and controllable. After the J-20 changed from a single seat to a double seat, the rear seat pilot and the entire life support equipment, as well as the addition of a second set of display and control devices, brought hundreds of kilograms of weight gain, and the position was in the very sensitive front of the fuselage. How to ensure the balance between the nose and rear fuselage on the new platform, how to solve the decrease in maneuverability caused by hundreds of kilograms of weight gain, and how to improve engine thrust, increase the proportion of composite materials, optimize aircraft control software, etc., all require detailed and in-depth analysis, and gradually try to solve various problems during flight tests.

The two seater plan that was publicly announced a few years ago

In fact, the first yellow appearance twin seater J-20 that appeared at the end of October 2021 did not have many traces of green composite materials on its surface. Indicating that it is most likely a prototype modified from the early single seater J-20 prototype, mainly for flight testing and verification of the overall design of the modified dual seater J-20, to ensure the stability of the basic design performance. The recently emerged black twin seater J-20 is expected to focus more on testing subsystems such as avionics and engines, rather than testing flight performance.The first flight of "JF-17 Dragon" Block 3 took less than 20 minutes,At present, wind tunnel experiments still cannot achieve 1:1 simulation, and it is also impossible to truly reproduce the high-altitude and high-speed flight attitude. Some problems that are overlooked or not accurately displayed in the experiment ultimately need to be solved through actual test flights. As for the test flight cycle, it depends on the ability to identify and solve problems, including the number of prototypes, test flight frequency, and the technical level of the design unit. After the performance of the aircraft platform is basically stable, the unique full aircraft stealth tests of avionics equipment, engines, and stealth fighters will gradually be carried out, and problems will be gradually solved during test flights, ultimately creating a fighter jet with stable performance that meets the set goals.

Two somewhat extreme examples are the US F-15EX fighter jet and the Indian LCA "Glorious" fighter jet. The former is the final improved version of the US F-15, with the initial prototype F-15A entering service in bulk with the US Air Force in 1978, and later giving rise to the two seater trainer F-15B. After several years of service, the US Air Force improved the F-15A/B and evolved the main single seater F-15C and two seater F-15D. Given that in the mid to late 1980s, airborne radar began to develop towards multi-purpose applications, which could simultaneously meet the needs of air, sea, and ground operations. At the same time, rapidly developing flight control software can also effectively combine high-altitude high-speed and low altitude low-speed performance. Therefore, the United States officially launched the F-15E multi-purpose heavy fighter in 1987, achieving a transition from a single seat F-15C to a two seat F-15E, and the combat positioning evolved from an air superiority fighter to a multi-purpose model.

F-15E is a bold attempt in the iterative evolution process

The 1991 Gulf War proved the success of the F-15E's multi-purpose design concept, which sparked a global trend in the development of multi-purpose fighter jets. The popular J-16, J-10C, Rafale F3, Su-35, and others now belong to the category of multi-purpose fighter jets. Of course, for the US Air Force pilots at that time, due to the significantly lower operational quality and flight speed of the F-15E compared to the F-15C, its nickname within the US military changed from the well-known F-15C "Global Hawk" to the F-15E "Plowing Chicken". However, regardless, the stable and user-friendly F-15E was produced from the late 1980s until 2004, just before the mass production of the F-22A stealth fighter.

The subsequent improvements of F-15 have been uninterrupted

The F-15EX body is certainly the most problem free. Countless flights of thousands of F-15s around the world over decades have verified the excellent basic design of F-15s. As for the avionics equipment and engines, they have already been solved through research and development funds provided by external orders. The F-15EX, which ultimately emerged, was actually a highly mature model assembled on the classic platform of the F-15E, equipped with stable and advanced avionics equipment and engines. It is expected that it will only take more than two years to solve some compatibility issues in the subsystem and enter the mass production stage. This "easy to pick and assemble" modification method can be regarded as the most ideal state of fighter jet modification. The F-15EX is a highly mature model, while the Indian LCA "Glorious" fighter jet has taken it to the other extreme. The Indian Air Force officially launched the development of LCA fighter jets in the early 1980s. However, as India has never truly independently developed advanced fighter jets, it has hesitated for many years in the design of aircraft platforms, spending a lot of time and resources. In the end, it barely solved the problem by reducing the performance indicators of fighter jets, reducing range, payload capacity, and overload. However, this has also led to the awkward size of LCA at present. The original plan for LCA was to carry domestically produced avionics equipment and engines from India, but after more than 10 years of development, they were still unusable. Eventually, the F-404 engine was purchased from the United States and advanced radar was introduced from Israel to complete the assembly of the three major components.

The J-16D represents a new height for domestically produced fighter jets in the field of electronic technology

It is generally believed that the J-20 is equipped with the latest improved version of the domestically produced WS-10 turbofan, which can basically meet the requirements of supersonic cruise and super maneuverability under certain conditions. But it is difficult to say whether the thrust can still meet the demand after the improvement of the two seater model and the addition of hundreds of kilograms of weight. Based on existing information, it can be inferred that even if the WS-10 can meet the requirements of the dual seat J-20, it is still somewhat difficult. To fundamentally solve this problem, it may still require the new generation high-performance engine WS-15 that is truly prepared for the J-20.

The J-20 has not fundamentally solved its engine problems yet

As for the full body stealth testing of the dual seat J-20, due to the fact that the design and manufacturing of stealth fighter jets is already a systematic project, in addition to the stealth coating on the surface, the refraction and parallel design of the main body shape, every crease, opening and unevenness on the surface of the body need to be treated accordingly. Any negligence may significantly reduce the stealth performance of the fighter jet. Therefore, after the improvement of the dual seat J-20, the surface shape of the aircraft will inevitably be reprocessed, but this is actually a deepening and refinement of the previous J-20, which is not very difficult in itself.

Source: Military of Strong Countries