PL-20 / PL-21

The PL-21 (Thunderbolt-21) missile is considered to be an active radar-guided ultra-long-range air -to - air missile independently developed by China . It can be used to kill enemy early warning aircraft and aerial tankers at long distances , and fundamentally weaken the opponent’s air combat system. And even the capabilities of the entire combat system. In the early years, some air-to-air missile development pedigrees circulated on forums showed the PL-21 model. The missile has wedge-shaped inlets on both sides, so it can be determined that it uses a ramjet engine . However, no similar missiles have been exposed yet. In 2016, a group of photos of an unknown missile mounted on the F-16 took off on the Internet. The missile is estimated to be close to or more than 6 meters in length. It is judged from the appearance that it is a long-range air-to-air missile driven by a rocket engine . Therefore, some media and netizens believe that this model is the rumored PL-21. As of 2021, Chinese officials have not disclosed any PL-21-related information, nor had it officially confirmed the existence of the number. Some sources claim the PL-20 and PL-21 are the same missile, though the provenance of the two designators remains unclear. The Chinese Military Aviation website reported that a new long-range active radar homing AAM is under development, based on the PL-12 technology. The new PL-21, is said to be similar to the British Meteror Beyond Visual Range Air-to-Air Missile (BVRAAM). Meteor is a new concept in air to air weapons, employing advanced air breathing motor technology and state of the art electronics to provide optimum performance against increasingly complex threats. Conventional rocket motor powered missiles rely upon an initial boost phase to achieve the high speed required followed by a 'coast' phase to intercept the target. Latest generation, highly manoeuvrable aircraft, are able to out run conventional missiles at the extremes of their range. The air breathing motor proposed for Meteor provides sustained power, following the initial boost, to chase and destroy the target.

METEOR is a fast and highly manuverable Beyond Visual Range air-to-air weapon. Meteor uses a 'stealthy launch' technique, giving the enemy less time to take evasive action and it can engage multiple targets simultaneously - no matter what the weather conditions. METEOR provides the largest No Escape Zone of any air-to-air weapon, resulting in a long stand-off range and high kill probability to ensure air superiority and pilot survivability. Guidance is provided by an active radar seeker benefiting from enhanced technologies drawn from the MBDA Aster and Mica missile programs. METEOR is capable of engaging air targets autonomously by night or day, in all weather and in severe electronic warfare environments. The BVRAAM is equipped with both a proximity and impact fuse to ensure total target destruction in all circumstances.

The PL-12 features an active radar seeker and an integrated ramjet/solid rocket motor with a entral air inlet. As with the Russian R-27/AA-10, the PL-21 features 4 small stabilzing fins behind the active radar seeker. Two-way datalink antennas may be installed in the tail section for mid-course correction. The effective range of PL-21 is expected to be greater than 100km. The missile might be carried by the new J-11B and J-20 fighters for long-range interception. Chinese Military Aviation reports that the first ground launch test took place in March 2010, with development projected to be completed by 2012. Such a two year development cycle seems rather brief, considering the five years that elapsed between the first test flights of the METEOR in 2005 and first deliveries in 2012.

The US media said that China's new ultra-long-range air-to-air missile codenamed "PL-21", which is 5 meters long, uses a high-thrust ballistic and double-pulse solid rocket engine, uses active radar and infrared imaging dual-mode guidance, and is guided by a two-way data link. Ballistics can be launched by mounting on the J-16 and J-20. The US Air Force believes that the air-to-air missile has a range of 400 kilometers and can pose a huge threat to US military early warning aircraft, electronic warplanes and other special aircraft. China should not underestimate the new long-range air-to-air missile being developed by the US Air Force, Chinese military experts said on Wednesday after the development of the new US weapon was revealed. The US Air Force is working with arms manufacturer Lockheed Martin and other branches of its military to develop a new long-range air-to-air missile called the AIM-260, which is expected to enter military service by 2022, US media outlet the National Interest reported on 24 June 2019. The motivation behind such a development is to counter China's top long-range air-to-air missile, the PL-15, which was made public in 2016, the National Interest reported, quoting US Air Force Weapons Program Executive Officer Anthony Genatempo.

Having a maximum range of about 160 kilometers, the US' current air-to-air missile the AIM-120 is apparently inferior to China's PL-15, judging by the US military's decision to create a new weapon, the National Interest report said. The PL-15 is equipped with active electronically scanned array radar and is thought to have a range of about 200 kilometers. China's top stealth fighter jet J-20 displayed its weapons including what analysts said was the PL-15 missile at Airshow China in Zhuhai, South China's Guangdong Province in November 2018. China is also developing a new missile known as the PL-21, which could reach targets 300 kilometers away, the Business Insider report said. Some Chinese military observers said the US, once a forerunner in weapon development, is now chasing China, and the new AIM-260 could be a copycat of the PL-15 in terms of applied technologies.

An anonymous Chinese military expert, however, told the Global Times 26 June 2019 that China should not underestimate the AIM-260 due to its late-mover advantages. The expert predicted that the US missile could use revolutionary technologies to boost range significantly without making it significantly larger, and these technologies will in return bring pressure to China's air-to-air missile development. US media used to hype that China made copycat weapons, which makes little sense as weapon designing tends to converge due to similar combat requirements, said the expert, suggesting the US is probably not trying to copy China's weapons.

From the picture published in the media, both sides of the PL-21 missile appeared inlets, suggesting that PL-21 uses a ramjet. The air-to-air missile system's main driving force is normally solid rocket motors. The advantages are simple structure, compact size, reliable operation, low cost, wide applicable height and speed range, and convenient maintenance. The disadvantages are low specific impulse, short working time, difficult thrust adjustment, and it is difficult to switch on and off multiple times. Solid rocket In order to increase the working time of the engine and increase the effective range of the missile, the single-chamber double-thrust method is used for the engine to generate two kinds of thrust in a fuel chamber through different charge designs or two kinds of grains with different burning speeds, that is, the take-off phase. The high thrust of high-speed combustion and the small thrust of low-speed combustion in the cruise section, but this increases the complexity and cost of the engine, especially the solid rocket motor needs its own oxidizer and fuel, so as the range of the missile increases, its weight and volume also increase.

For example, the American AIM-54 air-to-air missile weighs more than 400 kilograms, which is almost twice the weight of the AIM-7M Sparrow air-to-air missile of the same period. The heavier weight and volume of AIM-54 not only its own maneuverability, but also reduces the fighter aircraft. Therefore, the long-range air-to-air missile needs a new power system to achieve the unity of range and maneuverability. This is the ramjet, which is not enough with the solid rocket motor. The ramjet is an air-breathing engine. Oxygen is used as a combustion-supporting agent to mix fuel with the fuel carried by the missile itself to form thrust. Since there is no need to carry a combustion-supporting agent, compared with ordinary aspirated engines, ramjets use the static pressure generated by the missile's high-speed flight, thus eliminating the need for conventional Compressor required for jet engineTherefore, it has the characteristics of simple structure, low quality and low cost. Therefore, the missile with a ramjet can effectively control the volume and weight.

But the ramjet also has its own shortcomings; it cannot generate thrust when it is stationary, so it cannot take off by itself. The thrust system, in addition, has low thrust at low speeds, is not suitable for low-speed flight, and has high fuel consumption. In addition, it is more sensitive to changes in flight status. Changes in flight altitude, angle of attack, and speed will affect the performance and status of the ramjet engine. Based on the above shortcomings, an integral ramjet has emerged, which is to integrate the solid rocket booster and the ramjet, and use the combustion shell of the solid rocket booster as the combustion chamber of the ramjet to reduce the weight and volume of the ramjet. There are two types of ramjets used for air-to-air missiles, one is a solid rocket ramjet and the other is a liquid fuel ramjet. The former is the familiar meteor air-to-air missile. It is equipped with a gas generator using oxygen-poor solid propellant.

Using the oxygen-lean gas produced by the generator as fuel to supply the ramjet fuel chamber for secondary fuel, while the liquid fuel ramjet uses ordinary aviation kerosene as fuel, and the advanced mid-range air-to-air missile that competed with Meteor back then was The use of liquid ramjet has its own advantages in terms of the performance characteristics of the two. The solid rocket motor has the characteristics of simple structure and high reliability, but lower energy, while the liquid ramjet has higher energy, but the structure is more complex and the reliability is low.

The Pili-21 missile adopts the normal aerodynamic layout, that is, the wings are in the front and the rudder surface is behind. The advantage of this layout is that the rudder surface is farther from the center of gravity of the missile, so a smaller area of ??the rudder surface can be larger. Torque, thereby reducing the volume and weight of the missile. At the same time, because the wings are fixed, the washing effect on the rear rudder surface is small, and the aerodynamic performance is better. The disadvantage is that the missile’s engine is generally located in the middle and rear part, so The installation of the steering gear and the control system is limited. In addition, the lift generated by the wings is sometimes opposite to the lift generated by the rudder surface. The responsivness of the missile is poor, especially when the weight and volume of the missile itself are relatively large, so the Thunderbolt-21 A set of fixed winglets are added to the warhead, whose role is to improve the stability and maneuverability of the missile's full ballistic flight. The advanced engine and reliable aerodynamic layout only solve the problem of the missile's flight distance. In order to effectively attack the target, A sophisticated guidance system is also needed. Our country has mastered the technology of the composite guidance system for medium-range active radar-guided air-to-air missiles. Therefore, the guidance system of the Jili-21 air-to-air missile will definitely develop from this system. Subsonic speed is used to ensure the stability of the fuel. During this process, the temperature in the fuel chamber rises sharply due to aerodynamic work. Therefore, the speed of the ramjet generally does not exceed Mach 4, so the missile needs to fly for nearly 2 minutes to enter the terminal guidance. Stealth aircraft is quite unfavorable, so I think it is necessary to transplant the composite terminal guidance system technology developed for the Pili-21 for the Pili-12B air-to-air missile, which is to add a passive guidance system. The passive guidance system uses the opponent’s radar signal to guide. The signal is only reduced in one way and the radar power of the early warning aircraft is larger, so the detection range of the terminal guidance system can be expanded, thereby reducing the dependence on fighter guidance. The development of ramjet engines in China started early. Since the 1960s, it has started to develop the supersonic anti-ship missile Haiying-3 with ramjet engines . Since the 1990s, it has broken through the integrated ramjet technology and successfully developed integrated liquids. Ramjet and integral solid rocket ramjet, then which one is used by Pili-21? From the characteristics of the two engines, I think it is more likely to be an integral solid rocket motor. I said that solid rocket ramjet is The high temperature and rich combustion gas produced by the combustion of the oxygen-lean propellant in the gas generator is used as a powerful fire source for the ram afterburner, so the engine can work under a wide air-fuel ratio. When the external atmospheric conditions and flight attitude change, it will not cause flameout, so that the missile can work at a larger angle of attack, which increases the mobility of the missile. This is very valuable for air-to-air missiles that often need to change their flight trajectory. For the shortcomings of insufficient energy of solid rocket ramjets, the emergence of fuel-efficient high-metal content propellants makes up for this shortcoming, which is why solid rocket ramming is used The main reason why the engine's meteor missile can win the competition is that the air intake of the Pili-21 missile is located under the side of the projectile on both sides, and the air intake is swept back to increase the area of ??the air intake. The purpose is to improve the ability of the missile to pre-compress the airflow with the missile body under the condition of a large angle of attack, thereby reducing the airflow turbulence in the intake duct, improving the intake efficiency, and avoiding the change of the ramjet working state and flameout caused by the maneuvering of the missile. The successful development of the Pili-21 long-range air-to-air missile has greatly improved China’s air defense capabilities. In particular, the Chinese Air Force has the ability to attack key system nodes such as the other’s early warning aircraft , which can fundamentally weaken the opponent’s air combat system and even the entire combat system. Ability. According to relevant data, the foreign early warning aircraft with the strongest detection capability is the E-3A early warning aircraft after the improvement of the radar upgrade (RSIP) plan . It claims to provide a detection capability of 550 kilometers for targets with RCS=0.5. If the RCS=0.05 of the overseas data J-20 is calculated, then the E-3ARSIP early warning aircraft has a detection capability of about 200 kilometers, so that the J-20 can already intercept it with the Thunderbolt-21, although there is news that E-3A’s improvements also include the addition of electronic support, missile approach warning, jammer launching and other systems. However, in the face of rapidly approaching air-to-air missiles, it may still be necessary to adopt a combination of route maneuvering and interference release. At the same time, it may also take radar Measures such as cutting off the high voltage, reducing electromagnetic signals or even shutting down will inevitably lose the ability to master the air situation in the theater, and lose the command, guidance and support of external air situation information, even stealth fighters like the F-22 cannot be displayed. With all its combat capabilities, if it cooperates with ballistic missiles and cruise missiles to attack its AWACS base, it will put the other AWACS in an embarrassing situation of "cannot fly and fall." The early warning and the joint combat system formed with the F-22 is the most powerful air combat system. It can be said that the maintenance of US theater air combat is the basis of joint combat capabilities. If it can threaten early warning aircraft, it can be fundamentally weakened from this. The air combat capability of the opposing theater. The Pili-21 can also effectively intercept cruise missiles . The main reason why the United States developed AIM-54 was to intercept the former Soviet Union’s anti-ship missiles. Against the background of flat seas, ballistic anti-ship missiles have become excellent targets for AIM-54. For our country, if the other party launches cruise missiles from the first island chain, the cruise missiles need to be on the sea. Flying for nearly an hour, then at this time, using the high-precision airborne AESA fire control radar, cruise missiles can be intercepted at a relatively long distance, and the depth of defense can be extended from the outside, thereby extending time and space for the inner defense. Another point is to take advantage of the stealth advantage of the J-20 and the long-range interception capability of the Pili-21. It can penetrate around the first island chain to intercept bombers carrying cruise missiles, because one bomber can carry more than 10 In this way, shooting down a bomber is equivalent to intercepting more cruise missiles. At the same time, it can also force the other party to launch cruise missiles at a greater distance. This increases the exposure probability of cruise missiles, thereby increasing our interception time and effectiveness. If the J-20 provides the material basis for the Chinese Air Force to fight out, then the Pili-21 converts this ability into combat effectiveness, especially with the ability to strike key information nodes such as early warning aircraft. The ability to fundamentally weaken the opponent’s combat capability is critical in modern air combat and even modern high-tech local wars [2] .