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Science spectrum: j-20 black technology -- conformal antenna, radar absorption, stealth, phase control, fire control, photoelectric aperture, Flight Helmet

Release date:2021-12-28Author source:KinghelmViews:562

With the service of China's heavy stealth fighter j-20 and the formation of initial combat effectiveness, as well as the aircraft's increasingly high-profile participation in joint exercises and practical military training at sea, its high-definition images are also emerging more and more. During the army building day on August 1, four new high-definition photos of the j-20 appeared on the Internet, giving us a rare opportunity to better understand some design details of this "game changer" stealth fighter.

The j-20 is the latest yellow leather aircraft. The fuselage surface has not been painted with gray camouflage coating. It is exposed with yellow protective primer and gray absorbing material structure at the front and rear edge of the wing, highlighting many design details that could not be observed before. It can be seen from the photos that there are a large number of embedded conformal antennas on both sides of the front fuselage and the lower skin surface of the j-20. It is no longer like the third generation aircraft to use a large number of knife antennas protruding from the fuselage, which is a basic skill for stealth aircraft. In addition, gray invisible composite structures are also widely used at the j-20 air inlet, front and rear edges of wings, which may be related to the fact that the j-20 fighter has been applied with metamaterials developed by private enterprises, which was confirmed by Yang Wei, chief engineer of j-20 during the two sessions.

The skin of the j-20 has been carefully stealth treated. Except that obvious joints and screw structures can be seen at the edge of the daily maintenance cover, the other skin joints and rivets are covered with microwave absorbing material fillers, and the surface is very smooth, which can maintain a unified impedance transition on the whole fuselage surface and avoid discontinuities, so as to minimize the radar cross-section of the whole machine.

The photo also shows the j-20 supersonic inlet (DSI) without boundary layer partition in detail, and the invisible composite structure on the compression drum can be seen. This 3D compression drum can separate the turbulent boundary layer air from the upper and lower lip edges of the inlet and maintain high inlet efficiency in a large speed range. At the same time, because the complex boundary layer separation structure and supersonic adjustable structure are eliminated, it has obvious advantages over the traditional supersonic inlet in weight and stealth performance.

From the taxiing deceleration attitude of j-20 after landing, it can be seen that the reason why the aircraft can cancel the pneumatic deceleration plate on the traditional fighter is that it can apply the upper and lower differential of the wing trailing edge lifting aileron and the full moving vertical tail to deflect outward at the same time, forming a pneumatic deceleration surface, and its equivalent deceleration area even exceeds the traditional deceleration plate. The canard wing of the aircraft does not participate in deceleration operation in flight, but is only used for taxiing and deceleration after landing. The huge forward deflection canard wing is like an elephant's ear at this time, which can provide huge aerodynamic deceleration resistance and reduce the wear of tires and brake discs. At the same time, the huge size also shows the excellent mobility of the j-20.

At the lower left of the belly of the j-20, we can see a Longbo lens. This is a radar echo enhancement device similar to angle reflector, which is used to help ground radar and air traffic controllers track j-20 during flight test and training to ensure flight safety. Of course, another important role of the device is to cover up the real radar characteristics of the aircraft and avoid disclosure.

In the nose of the j-20, in addition to the large aperture active phased array radome, two windows of the distributed photoelectric aperture system on both sides of the nose can be seen. Similar windows are also distributed in front of the windshield, behind the cabin cover and on the right side of the belly, forming a 360 degree spherical full coverage. In addition to being used as an advanced missile approach warning system, the distributed photoelectric aperture system of j-20 is also an important photoelectric sensor of the aircraft, which can be used to find air targets and night vision navigation. Combined with the advanced helmet mounted display of the aircraft, the photoelectric aperture system can provide the pilot with external high-resolution infrared images, realize "perspective" of the fuselage, and greatly improve the pilot's situational awareness.

In addition to the distributed photoelectric aperture system, another important photoelectric sensor of the j-20 is located below the nose. Most of the previous j-20 prototypes did not install this equipment, and the lower part of the nose is an opaque polyhedron structure. The new photos show that the photoelectric sensor under the nose of j-20 has only four pieces of glass in the forward direction, and lacks backward and downward vision. Therefore, the device should be used for air search and tracking, similar to the infrared search and tracking sensor in front of the j-10c and j-16 windshield. The infrared search and tracking sensor enables the j-20 to have the capability of passive search and tracking in the air when the radar is turned off and the radio is silent. This capability has become more and more important for detecting stealth targets in the air, which will make the j-20 better against other advanced stealth fighters in the future high threat air combat environment.

With the development of China's photoelectric sensor technology and the multi-purpose development of j-20, this infrared search and tracking sensor may eventually be replaced by the advanced photoelectric aiming system to increase the ground aiming capability on the premise of maintaining the existing air-to-air detection capability, so that j-20 can independently throw precision guided ground ammunition. At that time, its polyhedral window should also be modified to increase the field of view of the lower hemisphere.

These high-definition photos show that the j-20 is very mature in design and can be confidently displayed in front of the world. The various design details disclosed in the photos also show that in the development of stealth fighter, China has entered the world's advanced ranks, becoming the second country in the world to start the R & D projects of two kinds of stealth fighter, which fully shows China's significant progress in aerospace materials and fighter manufacturing technology. (signed by Armstrong)

The air force has released a very powerful news. Our j-20 stealth fighter has completed the actual combat training in the sea direction for the first time. In the photos of this training released by the military media, we were surprised to find that the J20 pilots wore a new type of Flight Helmet, which is compared with the old helmet used in Zhu rihe's military parade, This new helmet uses ar Augmented Reality Technology and holographic waveguide display technology. It can not only "see through" the aircraft to achieve an unobstructed field of vision, but also directly cross-linked with air-to-air missiles to achieve the purpose of aiming, locking and launching when the pilot finds it.

New helmet

As can be seen from the new helmet photo above, its overall shape is very similar to the batter helmet display used by BAE to back up the F-35 fighter. The shading mirror on the face is large and has multiple layers. The middle layer is obviously a transparent layer. According to the batter's structure, this layer is a holographic display layer. The image display source on the helmet takes the transparent layer as the display screen, projects the image onto the transparent "display screen" through the miniaturized optical system, and then superimposes it with the external target scene, so that the pilot can obtain the aircraft flight information and target aiming information without looking at the head up display and display. This can not only greatly reduce the burden on pilots, but also take the lead in close combat. Compared with the previous refraction / diffraction helmet display, this waveguide helmet display has simpler optical structure, lighter weight, better display effect and larger observation range.

The old J20 helmet does not have display capability

In addition, we can also find that there are many protrusions at the rear of the helmet. These protrusions are actually led infrared light sources. They are mainly used to locate the pilot's head in cooperation with the camera at the rear of the fighter cockpit. The purpose of this positioning is to determine the aiming normal of the helmet display in real time, so as to guide the infrared combat bomb with large off-axis angle to lock, The pilot can launch missiles by "staring" at the target.

According to previous reports of various domestic media, the bidding for the j-20 integrated display helmet should have started in 2012. Due to the rich accumulation of helmet display technology in China and many universities and research institutes doing research in this field, the results are also very fast. In the second year, that is, 2013, the winning team completed the R & D and trial production, Design qualification was completed and delivery started in 2014 (quite fast). At the Zhuhai Air Show in that year, various helmet mounted display products began to appear, and many of them may be schemes or products that failed in the bidding. According to the information disclosed at Zhuhai Air Show, the new HMD also has the function of seeing through fighters like the F-35 HMD when cooperating with the J20. In other words, it can also use the image sensors around the J20 fuselage to obtain the surrounding unobstructed real-time picture, which is also very useful for Fighter reconnaissance, search and close combat.

With the distribution of the j-20's new helmet mounted display in place, its combat capability and deterrence capability in the air have reached a new level, and the large off-axis angle launch capability of the new generation thunderbolt 10 infrared imaging combat projectile can also be brought into full play. The combination of the two makes the J20 not afraid of any strong enemy in close combat. The sea combat training also marks that our army's J20 has begun to invest in real combat readiness tasks, which is not only a strong deterrent to the stubborn forces on the other side of the Strait, but also a silent deterrent to the surrounding parties who are equipped with F-35.

△ j-20 has a large nose size and can accommodate large active phased array fire control radar. Similar radars of F-22 can accommodate 2000 small antennas (T / R modules), and it is believed that j-20 can also do so

In the structural design and layout of modern fighter, there are three radar wave intensity scattering sources, one of which is the airborne fire control radar cabin at the nose, and the other two are the inlet and cockpit respectively. Therefore, for the design and R & D personnel of stealth fighter, how to reduce the radar wave reflection cross-sectional area of airborne fire control radar cabin as much as possible is one of the key points to ensure the stealth performance of the whole aircraft.

The radar wave scattering formed by the airborne fire control radar cabin mainly has two parts: one is the structural reflection caused by the internal structure of the radar cabin, such as frame, structural accessories and connectors; The second is the scattering formed by radar antenna. For the former, fighter design and R & D personnel can take certain measures to suppress or eliminate it. For the latter, we need the technicians in charge of the research and development of airborne fire control radar such as Nanjing Institute 14 to find a way.


△ tilt mounted F-35 fighter airborne active fire control radar

First of all, we can note that the antennas of active phased array airborne fire control radars equipped with stealth fighters of China and the U.S. air force, such as F-22, F-35 and j-20, are inclined upward at an angle, which is to reduce the reflection cross-sectional area of radar waves. According to the research results, if the upward tilt angle of the airborne fire control radar antenna reaches 15 degrees, the radar wave reflection cross-sectional area can be reduced to one fifth of the vertical state, or even lower.

Of course, the greater the inclination, the better. Too large antenna inclination will adversely affect the detection azimuth and accuracy of airborne fire control radar. Therefore, at present, the most suitable inclination is generally 15 ~ 30 degrees.

△ the technical level of klj-7a airborne active fire control radar exhibited in China has reached the latest level in the United States    

However, for most non stealth fighters equipped with phased array airborne fire control radar, due to its large radar wave reflection cross-sectional area, it is not of great significance to simply reduce the radar wave reflection cross-sectional area of airborne fire control radar, so basically all adopt vertical angle.

Secondly, the use of absorbing materials in the structural design of airborne fire control radar antenna can also reduce the radar wave reflection cross-sectional area. For example, the APG-81 radar of the U.S. F-35 fighter plane is equipped with large radar absorbing material shielding plates around and behind the active phased array antenna, which can effectively block the irradiation of forward radar waves to the rear structure and avoid the generation of strong scattering effect.

△ j-10c also adopts airborne active radar, and most of the active radars of Chinese fighters are from institute 14    

In addition, the shape of the airborne fire control radar antenna shall be parallel and consistent with the shape of the radome mounting frame as far as possible, so as to improve the processing accuracy of the antenna radiation array and keep it consistent. The reflection array surface of the radar antenna shall also use high-performance absorbing materials as far as possible, etc. Only by comprehensively using multiple means can we achieve the final satisfactory effect.

From the pursuit of antenna details, the efforts of the j-20 in stealth are obviously beyond the imagination of the outside world. Therefore, we have every reason to rest assured about the stealth ability of the j-20

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