In the autumn of 1985, the Soviet General Staff’s Intelligence Directorate obtained astonishing intelligence from the Pentagon. In this plan led by William Perry, in addition to upgrading Chinese fighter jets, exporting F-16s, Black Hawk helicopters, and E-3 early warning aircraft to China, it also attempted to establish reconnaissance, early warning, and air defense fronts against the Soviet Union in China, as well as heavy weapon storage and repair bases. However, the rational Chinese government would absolutely not take the bait and unhesitatingly rejected Washington’s proposal to turn China into an anti-Soviet outpost. Apart from introducing Black Hawk helicopters, China and the U.S. only advanced the “Peace Pearl” plan for the J-8 modification, which was led by Gu Songfen, the chief designer of the J-8 at the Shenyang Aircraft Design Institute. The U.S. would provide China with radar and fire control systems for 55 J-8 II fighter jets to intercept the Tu-22 supersonic bombers invading from the north. Meanwhile, China was also engaged in another aviation cooperation with the U.S., with Tu Jida, the chief engineer of Chengdu Aircraft Industry Company, leading the cooperation on the “Super 7” fighter jet with General Electric’s F404 engine, and the Super 7 was the predecessor of the JF-17 fighter jet.
During the honeymoon period between China and the U.S., China’s military industry laid bare its assets to the U.S., so much so that it could be said that they were completely exposed. The U.S. military not only visited the Qingdao naval base, Dalian nuclear submarine forces, and Xichang satellite launch base, but also visited research institutions such as the 14th Institute of the Ministry of Electronics Industry in Nanjing. At that time, the wind tunnel group at the Aerodynamics Research Center in Mianyang was already conducting research on the DSI inlet of the Super 7, but due to limitations in computing power and processing technology, it could not be further advanced. They could only share the wind tunnel test data of the DSI inlet with the U.S. in the hope of jointly developing it when cooperating on the F404 engine. Grumman also proposed suggestions for the Super 7’s underwing air intake and large leading-edge wing.
However, after spending $550 million and five years on U.S.-China aviation cooperation, the cooperation came to an abrupt halt, and China did not gain anything. The fighter jets remained behind, so that after 2000, the J-8F only met the Air Force’s combat requirements. By this time, the U.S. military had already begun equipping the F-22, a fighter jet that was almost science fiction for China.
Regarding the DSI inlet, the year after the interruption of U.S.-China aviation cooperation, Lockheed began research in 1990, and in December 1996, modified an F-16 with a DSI inlet for 12 intensive test flights over 9 days, covering the entire flight envelope of the F-16, and undergoing severe acceleration in both level and maneuvering flight to determine the compatibility between the inlet and the engine, achieving a maximum speed of 2 Mach. The results showed that under all angles of attack and sideslip conditions, it was very close to the production F-16, with two flights experiencing engine restart and 164 afterburner ignitions without any failures, including 52 afterburner ignitions performed during high-difficulty maneuvers, and the new inlet also demonstrated its subsonic performance, particularly in remaining power, outperforming the production F-16’s inlet, proving that the cancellation of the boundary layer separation was beneficial to the entire system. Considering that there were no modifications made to the F-16’s fuselage for the DSI inlet at that time, the entire test flight program aimed only to validate the viability of this new inlet technology, and the results were astonishing.
Years later, the Lockheed X-35 and Boeing X-32 prototypes, both utilizing DSI inlets, competed, with the X-35 ultimately winning the Joint Strike Fighter program bid, becoming the main stealth fighter for the U.S. military and its allies, the F-35.
Chengdu Aircraft began engineering the practical application of DSI as early as 1998. The “Fortune One” FC-1, equipped with the “A cup” DSI inlet, was suddenly revealed in 2005. On April 28, 2006, the fourth prototype of the JF-17 took off lightly on the runway at Chengdu, and less than a year later, on March 12, 2007, the world’s first fighter jet using a DSI inlet officially entered service. Without stopping, the J-20 entered the research and development phase as a key model project in 2007, while the J-10B equipped with DSI successfully flew for the first time in 2008.
To date, the U.S. has only one fighter jet, the F-35, equipped with a DSI inlet, which cannot perform supersonic cruise and maneuvering. In contrast, China has the J-20, J-35, JF-17, and FH-97A unmanned wingman with side inlets, the J-10B/C with belly inlets, and the H-11 and H-20 with dorsal inlets, all utilizing DSI configurations. Even the “Sea Eagle” trainer-9G and the FTC-2000G, a low-cost export fighter jet, have adopted DSI inlets, which have become a design feature that everyone can see, with a level of technical depth that makes the U.S. envious. The delayed Su-75 is Russia’s first fighter jet to apply DSI technology, while India is attempting to adopt DSI inlets for the AMCA fifth-generation fighter, which has only just entered the prototype manufacturing stage after 20 years. The UK’s next-generation Tempest fighter and the sixth-generation fighter FCAS jointly developed by France, Germany, and Spain are also planned to adopt DSI. In contrast, South Korea’s so-called stealth fighter KF-21 and Turkey’s “Khan” fifth-generation fighter projects should feel embarrassed, as they all mimic the F-22’s Garrett air intake method, only able to look up to the J-20’s DSI inlet.
The full name of the DSI inlet is “Three-Dimensional Bump-Type Inlet without Boundary Layer Separation.” What magic does DSI have? Is the technical realization really that difficult? Let’s first fully understand the aircraft inlet.
We know that the inlet is a key component that introduces air into the propulsion system. It slows down the high-speed airflow entering from the front, pre-compresses the air, and adjusts the outlet flow rate of the inlet to meet the requirements of the compressor or combustion chamber. The total pressure loss during airflow compression in the inlet should be low, and the pressure, temperature, and velocity fields at the inlet outlet should meet the needs of the engine’s operation. It is important to note that a 1% increase in the total pressure recovery coefficient of the inlet can increase the engine’s thrust by 1.3% to 1.5% and reduce the specific fuel consumption rate by about 2.5%. In addition, the inlet is also one of the three major strong scattering sources in the aircraft’s forward direction, accounting for 30%-50% of the aircraft’s total forward RCS. Therefore, it is necessary to consider not only providing sufficient and stable airflow to the engine within the flight envelope but also the stealth requirements under overall layout constraints.
Lockheed’s designer Kelly Johnson once proudly stated: “The engine only provides 17% of the thrust needed for flight, while our own inlet and nozzle provide the rest.” The inlet of the SR-71 Blackbird, designed by him, accounted for 56% of the total thrust of the propulsion system after removing the external wall flow pressure and shock wave losses. This shows how significant the inlet’s impact is on the performance of supersonic aircraft.
The primary task of the inlet is to separate the boundary layer. At high speeds, the air can be regarded as a viscous fluid, and the flow speed of the “free air” moving away from the surface of the aircraft is relatively uniform, but close to the surface of the complex body, the flow is not laminar but chaotic and turbulent. Once it exceeds the transition point or is disturbed by the curved surface, resulting in a negative velocity gradient, it will cause boundary layer separation, leading to macroscopic turbulence. If these disordered low-energy airflows enter the inlet and feed into the engine, it will result in engine intake distortion, reduced total pressure recovery, compressor blade stall, etc. This could cause minor issues like cyclic stress and vibration on the engine blades, reducing engine life, or worse, lead to extremely dangerous engine compressor stall and surge, damaging the engine. Therefore, the inlet must isolate the boundary layer outside the inlet.
Early fighter jets used nose inlets, where there was no boundary layer airflow. As fighter jet noses were freed up to install large-diameter radars, the engine inlets had to move to the rear, and the boundary layer airflow became thick enough that simply separating the inlet from the fuselage could strip away the boundary layer. Different fighter jets have different boundary layer thicknesses at different speeds. For example, wind tunnel tests show that the boundary layer thickness of the F-16 at maximum speed is 4.5 inches, so the inlet must be separated from the fuselage by 4.5 inches. Some fighter jets even add small holes to further suck away the boundary layer. The YF-23 has achieved this to the extreme, ingeniously opening many small holes on the underside of the wing in front of the inlet, cleverly utilizing the pressure difference above and below the wing to suck away the boundary layer and release it to the upper surface of the wing, solving the boundary layer separation problem.
Clearly, the existence of a boundary layer separation structure increases the frontal area, adds structural weight, and the additional space and discontinuity in shape between the fuselage and the inlet becomes a new radar wave reflection source, which is the primary source of the F-22’s frontal signal characteristics.
Separating the boundary layer is just the beginning; more complex is that it must also convert supersonic airflow into subsonic through shock waves while achieving gas compression. Supersonic inlets must match the high back pressure conditions generated by the incoming flow and downstream combustion chamber, which will produce complex shock wave structures. As back pressure increases, shock waves may alternately appear to move forward slowly or quickly, and oscillation phenomena may occur, making it difficult to accurately predict their positions, which can lead to severe consequences like engine flameout.
The earliest pitot-type inlets directly use normal shock waves to violently slow down the airflow to subsonic speeds, resulting in significant total pressure loss, causing a thrust loss of 13-15% for the engine, focusing on subsonic performance, with a maximum speed not exceeding 1.6 Mach. However, they excel in having no moving parts and a relatively lightweight structure, such as the U.S. F-100D, F-16, and China’s J-10A. Among them, the F-16 uses a carefully designed conformal inlet integrated with the fuselage and leading-edge wing to cleverly utilize the strong streamlining and pre-compression airflow effects of the forward fuselage and wing.
Subsequently, the industry developed shock cone inlets, such as Lockheed’s F-104, which was the first mass-produced fighter jet to use an inlet cone, and adjustable shock cone inlets on the MiG-21, China’s J-8, France’s Mirage 2000, and the Blackbird reconnaissance aircraft. When the shock cone inlet starts, the tip of the cone generates a uniformly distributed conical oblique shock wave, which falls exactly on the edge of the inlet. The oblique shock wave will also reflect multiple times inside the inlet; each time the supersonic airflow passes an oblique shock wave, it slows down a little. After passing through many oblique shock waves, it will finally become subsonic at a weaker normal shock wave, thus resulting in lower energy loss and higher efficiency compared to the normal shock wave in the pitot-type inlet.
However, as the speed of the fighter jet decreases, the angle of the shock wave increases, meaning the inlet cannot wrap around the entire conical shock wave, leading to insufficient airflow. Therefore, adjustable inlet cones can move back and forth, allowing the shock wave surface at different speeds to be fully wrapped by the inlet. For instance, the Blackbird reconnaissance aircraft begins moving the inlet cone back as it reaches 1.6 Mach, calculating in real-time the required distance for the inlet cone to move based on measurements from the pitot tube’s static pressure, pitch, roll, yaw, angle of attack, etc. Ultimately, at a cruise speed of 3.2 Mach, the increase in inlet pressure provides 58% of the usable thrust, with the compressor providing 17% and the afterburning combustion chamber only needing to provide 25% of the thrust, which is the optimal design condition for the Blackbird.
Following the shock cone inlets, a more advanced inlet type emerged: the dual-mode inlet, which allows for more complex control of airflow. Airflow passing over the adjustable sloped upper edge of the inlet generates an oblique shock wave, which, when adjusted, falls exactly on the lower edge of the inlet and reflects within the inlet. The adjustable slope allows the inlet to maintain high efficiency at different speeds.
For example, the adjustable panel on the upper lip of the F-15’s inlet can adjust the inlet angle, automatically ensuring optimal shock wave position and airflow control. The supersonic passenger aircraft Concorde has two adjustable sloped panels on its inlet. The supersonic bomber XB-70 pioneered the combination of external and internal compression in a dual-mode inlet. For a massive bomber with an inlet speed exceeding 3 Mach, the performance of a conventional dual-mode inlet is far from adequate, as eight oblique shock waves can only slow the airflow down to 1.6-1.8 Mach. The XB-70’s inlet, following the external compression structure, immediately adopts an adjustable internal compression structure, narrowing at supersonic speeds to enhance the deceleration effect. A 3 Mach incoming flow slows down to 0.4 Mach, with the total pressure recovery coefficient still maintaining above 80%, which is excellent for a 3 Mach inlet. However, the XB-70 ultimately fell into the typical American military-industrial development trap, spending massive amounts of money proposing ingenious solutions, but losing out to the Soviet Union’s unremarkable technical integration in terms of reliability and practicality.
The former Soviet heavy long-range air superiority fighter Su-27’s inlets are “attached” below the wing roots on both sides, with the inlet entrance located in a flat, wide area at the front and lower part of the wing-body fusion, thus ensuring that the airflow at the entrance remains stable even under large angles of attack and sideslip conditions, allowing the Su-27 to achieve unprecedented high maneuverability for contemporary fighter jets. It adopts a dual-mode inlet with adjustable sloped panels and a four-wave system, which is short and straight, providing high inlet efficiency at high speeds. The lower surface is equipped with a grating-type auxiliary air intake, and there are sloped boundary layer blowing ports on both sides. The inlet’s bottom has a hinged titanium alloy debris guard, which folds down and flattens against the inlet’s bottom during normal flight, automatically rising when the landing gear is lowered to prevent foreign objects from entering the inlet during takeoff and landing.
The dual-mode adjustable inlet has a complex structure and is heavy, with its rectangular cross-section acting as an angle reflector, making it highly likely to be detected by radar. This is where the Garrett inlet comes into play. The Garrett inlet, also known as the double-slope oblique shock inlet, is similar to a wedge-shaped oblique shock body. It forms an oblique shock wave through two slopes, then wraps it with a flat surface, making the pressure recovery of the inlet less sensitive to angle of attack and sideslip than conventional inlets, improving maneuverability and greatly expanding the working efficiency range of fixed inlets, breaking the limitation that traditional fixed inlets perform well at subsonic speeds but dramatically decline in performance in supersonic conditions. In terms of stealth, its cross-section can be designed as a parallelogram, thus avoiding the angle reflector effect of right-angled edges. The upper and inner sides of the inlet are equipped with front-edge rear-swept compression sloped panels, and the inlet lip can be designed with a rear-swept shape, which reduces radar scattering in the frontal view.
The Su-57 adopts a complex critical cross-section adjustable Garrett inlet, with the adjustable panels composed of two front and rear pieces with a gap in between, allowing the boundary layer to escape from the gap and enabling adjustments to the shock wave position, generating complex shock wave systems. The Su-57’s inlet also features large movable leading-edge flaps, allowing the aircraft to maintain a larger angle of attack at low speeds, while the leading-edge slats can assist engine intake at subsonic speeds.
The F-22, on the other hand, uses a non-adjustable Garrett inlet, which can effectively balance high and low-speed flight capabilities. However, at speeds exceeding 1.5 Mach, although it can improve the total pressure coefficient in supersonic conditions by adjusting the flow coefficient and using a large-area array of small holes to remove the boundary layer from the inlet, the inlet is ultimately non-adjustable overall. The total pressure recovery coefficient is only 0.88 at 1.8 Mach and drops to 0.80 at 2.0 Mach. The F-22’s Garrett inlet still employs a boundary layer separation structure, with exhaust outlets to expel boundary layer air, which brings some exhaust resistance and increases weight and structural complexity, compromising the aircraft’s stealth.
Now let’s return to the DSI inlet. DSI stands for “Boundary Layer Separation Free Supersonic Inlet,” elevating the design level of the wave inlet from two-dimensional to three-dimensional, integrating the design of the three-dimensional wave compression surface and the forward-swept inlet lip. It ingeniously combines boundary layer separation and supersonic airflow compression technology. The series of multi-stage conical compression surfaces before the inlet generates a transverse pressure gradient, driving the boundary layer to spill out towards the forward-swept inlet lip, achieving the removal of 99% of the boundary layer gas without the need for conventional boundary layer separation structures, nor exhaust or bypass systems, resulting in a significant weight reduction of up to 300 kilograms.
Additionally, the forward-swept inlet lip generates shock waves, and the three-dimensional convex surface forms double shock waves, causing the supersonic fluid to undergo continuous deflection, producing a series of continuous oblique shock waves, which eventually leads to a normal shock wave. The external shock wave at the inlet lip, continuous oblique shock waves, and a normal shock wave enable the inlet to achieve efficient airflow deceleration.
The DSI inlet not only avoids the cavity scattering of boundary layer separation structures and the angle reflection of dual-mode inlets, but the three-dimensional convex surface combined with the S-shaped internal inlet can also shield the engine blades in the frontal view, as the engine blades contribute significantly to the aircraft’s frontal radar cross-section. Therefore, DSI is the inlet with the best overall stealth effect. Of course, unlike the regular parallelogram design of the Garrett inlet, the complex forward-swept inlet lip and three-dimensional convex surface of the DSI inlet can generate electromagnetic scattering, which still requires the use of targeted stealth materials.
The performance of China’s DSI inlet today is certainly not achieved overnight.
As China’s first DSI inlet, the JF-17 was designed by Yang Wei, who succeeded Tu Jida as the chief designer. The 40-degree rear-swept leading-edge wing proposal from Grumman was retained, and the inward-tilted side inlet design improved high-angle-of-attack performance. The new DSI inlet design work took nearly two years, undergoing four rounds of high-speed wind tunnel tests and one round of low-speed wind tunnel tests, continuously improving and perfecting, resulting in a weight reduction of over 100 kilograms. Since it was the first application of DSI, to reduce risk, the JF-17 still added boundary layer array holes to enhance the effect of boundary layer airflow removal, and the new inlet design increased engine thrust by 2.6%-6%. Most importantly, the wide advantages of the DSI inlet in subcritical states were fully demonstrated, automatically adapting to changes in airflow, ultimately providing stability to the engine. The stability of the engine’s operation was greatly improved. The JF-17 is less prone to flameout regardless of whether it flies fast or slow.
The “independent” Song Wencai led the J-10B/C’s DSI inlet modification, dispelling the rumor that “belly inlets are not suitable for DSI modification, which will affect high-angle-of-attack flight performance.” The J-10B/C features primary and secondary inlet lips, with the lip edges gradually thickening upwards, and the bump also increasing correspondingly. It not only removed the boundary layer suction holes on the “JF-17” bump but also completely shielded the AL-31FN engine’s fan from the front, fully demonstrating Chengdu’s progress in DSI inlet research, with an average total pressure recovery coefficient close to 0.87 at 2 Mach and not less than 0.91 at 1.8 Mach. Although this value is slightly lower than that of the complex and heavy dual-mode four-wave adjustable inlets, it is significantly higher than the fixed pitot inlets of the J-10A and far exceeds the Garrett inlets of the F-22.
The Attack-11, designed by Liu Zhimin, deputy director of Shenyang Aircraft, and the H-20, continuing under Tang Changhong, the chief designer of the Y-20, both adopt a dorsal DSI inlet. Considering that the dorsal inlet cannot effectively utilize high-energy incoming flow at larger angles of attack, an integrated design with the swept wing must be conducted to utilize the leading-edge vortex of the swept wing to clear the low-energy airflow from the dorsal inlet.
The J-20’s DSI inlet is the culmination of China’s inlet technology. We know that the J-20’s aerodynamic structure has two distinct technical features: one is the coplanar canard and triangle wing aerodynamic layout, and the other is the bumpy supersonic boundary layer separation-free inlet. This allows the J-20, equipped with two relatively mediocre AL-31F engines, to achieve 50-60 degree high-angle-of-attack flight, excellent supersonic lift-to-drag ratio, subsonic maneuverability, and a range comparable to the Su-27.
The visual change of the J-20’s inlet bump from the “A cup” of the JF-17 to the “D cup” of the J-20 exemplifies that the J-20 is inherently a high-altitude, high-speed fighter jet, with air superiority being its core performance indicator. In the information maneuvering era, the physical domain still requires the J-20 to quickly approach or disengage from opponents, with higher altitude to increase height and energy advantage, excellent climb rate for stable interception or evasion of opponents in the vertical plane, and outstanding roll agility and turning maneuverability to obtain or prevent opponents from gaining firing opportunities, creating an unbreakable distance advantage in both offense and defense.
In the cognitive maneuvering era, although from an offensive perspective, the aircraft’s speed advantage over missiles will diminish with the development of long-range air-to-air missiles, speed and maneuverability remain the last line of survival for advanced fighter jets from a defensive perspective, being the most trusted means of survival for pilots, even though the frequency of use may decrease compared to fourth-generation opportunities.
Speed is the eternal pursuit of air superiority fighters. If the previous and contemporary air combat speed requirements for fighter jets were more derived from the engagement layer, future speed requirements for fighter jets will stem more from the mission layer. With the U.S. military taking a series of measures such as retreating, distributing, and reinforcing, it emphasizes that aircraft must initiate from farther distances, even from outside the anti-access operational distance. Greater launch distances will bring at least two significant changes: first, the sortie rate of the aircraft will drop significantly, and second, heavy refueling support will be needed to implement deep penetration. These two changes have a significant impact on the speed of fighter jets for both offense and defense. From the attacker’s perspective, maintaining a cruising speed of Mach 1.5-2.0 increases the sortie rate by 1.9-2.5 times compared to cruising at 0.8 Mach, greatly improving attack efficiency. From the defender’s perspective, based on hard-won intelligence, seizing fleeting opportunities to attack the opponent’s early warning and refueling support areas is crucial to cutting off the opponent’s task chain, which also urgently requires high cruising speeds for aircraft.
All of this places high demands on the J-20’s flight quality, naturally leading to higher requirements for the DSI inlet.
Compared to the J-20A, the J-20B’s DSI inlet bump has undergone significant changes in shape, position, and skin color. The bump position is higher and more forward, and the shape is sharper, replacing the rounder DSI bump of the J-20A. This change can significantly reduce drag during supersonic cruise. Additionally, the J-20B’s inlet lip has undergone further refinement, featuring perfect adaptive overflow control on both sides of the inlet, which can adaptively limit the forward projection of the normal shock wave at high Mach numbers, keeping the normal shock wave confined within a narrow channel, thus reducing drag and increasing total pressure recovery. The change in the color of the bump skin is also quite noteworthy; under prolonged supersonic cruise conditions, the DSI inlet bump can reach a high temperature of about 150°C due to aerodynamic heating. To address this challenge, the J-20B’s fully integrated DSI inlet bump has replaced its color with a darker supermaterial to improve high-temperature resistance.
From the shape of the J-20B’s bump, we can boldly speculate that it employs an isentropic cone guiding wave inlet. Compared to simple single-cone bumps, it can produce complex shock wave series, weakening the intensity of the cone-shaped shock wave, reducing total pressure loss in the mainstream and separation zones, thus improving the total pressure recovery coefficient of the bump’s external compression system. The more shock waves there are, the greater the enhancement, and this advantage becomes more pronounced at high Mach numbers like 2.5. Simulation calculations indicate that the performance of the isentropic bump improves significantly, with the total pressure recovery coefficient increasing by about 5%, while the distortion index decreases by about 0.03, resulting in an approximate 7.5% thrust increase at high altitudes and speeds. The J-20 has been optimized to the extreme for high-altitude and high-speed performance, making it truly reign supreme as soon as it enters supersonic flight.
In contrast, simulations of the F-35’s fuselage and inlet suggest that its maximum speed is around 1.6 Mach. If it exceeds 1.6 Mach, the angle of the oblique shock wave decreases, and the flow separation generated by the coupling of the oblique and normal shock waves will enter the inlet, significantly reducing intake efficiency.
It is evident that the difficulty in designing a DSI inlet lies in the fact that there is no boundary layer separation, and the fuselage’s disturbance to the airflow affects the inlet, necessitating an integrated design of the inlet lip and bump with the fuselage. The inlet bump is a three-dimensional complex surface, requiring extensive numerical simulation and optimization of both the fuselage and inlet. In an era of limited and expensive computing power, adopting a DSI inlet was infeasible. In contrast, traditional inlets with boundary layer separation structures can be designed separately from the fuselage and then assembled together. Furthermore, traditional inlets are typically two-dimensional or axisymmetric, making it easier to calculate shock wave systems using formulas without relying on computing power.
To further expand the operational speed range of fighter jets, the industry is researching variable geometry DSI inlets, which adjust the capturing surface or throat area of the inlet to achieve matching of intake and exhaust flow. Although there is insufficient evidence to suggest that the J-20B employs a more advanced variable geometry DSI inlet to accommodate the wider flight envelope of the WS-15 engine, we can still make reasonable speculations regarding the adjustable DSI inlet.
The first option is the simplest: the inlet bump is fixed, but adjustable panels are added to the sides of the inlet, allowing for changes in the shock wave system and throat area with speed variations, achieving excellent inlet control capabilities in the main speed range. The weight of the adjustable panels is less than that of traditional boundary layer separation panels and does not affect stealth performance.
Alternatively, shape memory alloys can be used to manufacture the bump. Shape memory alloys can remember specific geometric shapes and switch between austenite and martensite crystal structures driven by temperature changes, thus instantly reverting to their original shape without mechanical structures, even after repeating 5 million times without fatigue or fracture, with output capabilities exceeding 100 times their weight. Through technologies like laser additive manufacturing, complex curved shape memory alloy bumps can be produced. However, due to the complex mechanical properties of shape memory alloys, their deformation precision under non-uniform aerodynamic forces within the inlet is poor, and issues like the decline of the memory effect after multiple cycles also need substantial material and process research.
Another option is to use adaptive flexible smart skins, which are composed of elastic rubber membranes and high-elastic fibers, with strain sensors and displacement sensors arranged on the inner surface of the “flexible skin” that can smoothly adjust the shape of the bump or the throat area of the inlet based on speed.
Looking back, the J-8, which was “rolled out” by the first generation of aircraft designers in New China, such as Huang Zhiqian and Gu Songfen, is gradually fading away. Today, the J-20 has forced Americans to accelerate the development of sixth-generation fighters, and China’s DSI inlet has branched out, becoming the technical foundation for new sharp eagles. The failure of the “Peace Pearl” program has taught China many lessons: engaging in technological cooperation with Western countries must be based on a solid technological foundation; otherwise, one will face discriminatory ridicule. A defense research system centered on our own capabilities is essential to support the glory and dreams of an aviation power.
