Jinmu ZF-21 Dragon

The Jinmu ZF-21 Dragon is a Zhenian single or twin-seat,, all-weather   developed for the Republic of Zhenia Air Force and the Republic of Zhenia Navy. Although originally intended as an when development began, it has been developed to carry out missions as a multirole fighter, capable of taking out both air superiority and precision ground strike missions, as well as  and  (ISR), although its design was largely streamlined towards air superiority missions. Although primarily built by Jinmu Heavy Industries, other contractors, including Signus Systems, took part in the development process as well.

A result of decades of continuous development that had been mostly in secret, the ZF-21 Dragon was first revealed to the public during its test flight on June 4, 1588 and was introduced to service in 1594. Later developed in tandem with the ZF-33 Black Eagle, later variants and upgrades introduced in the 1600s and 1610s feature a considerable amount of cross-development with technological input gained from developing the ZF-33 Replacing the ZF-7 Vanguard, the ZF-21 Dragon is planned to form the higher end of the RZDF's projected of combat aircraft. The Republic of Zhenia Air Force and Navy combined plans to field a combined total of up to 720 ZF-21 units in total by 1616.

Origins and concept demonstration
Shortly after the November Revolution, the Republic of Zhenia Air Force issued a requirement for a next-generation air superiority fighter aircraft that was to supersede the ZF-7 Vanguards that were being produced and fielded into the service. While many were skeptical regarding the need for a new air superiority fighter with the existence of the ZF-7 Vanguards in service, the service branch, then under the leadership of the then-Chief of the Air Force Kim Wonil, managed to defend minimal budgets needed for preliminary research into conceptual designs and characteristics for a future air superiority fighter. An array of rough, preliminary concepts emerged from the Jungchuwon's design bureaus and defense contractors, each with different characteristics and emphasis on different fields: however, many shared the denominator of taking advantage of new aviation technologies developed at the time, as well as large amounts of lightweight alloys and, advanced control systems and  technology that were merely being tested in deep secrecy. Among many preliminary concepts, those from Jinmu, Paragon and Hanshin were selected in 1576 AC and were given the way forward, being awarded contracts to bring a working by January 1582.

With the introduction of new ZF-7 derivatives in the late 1570s, however, particularly the multirole ZF-7E and ZF-7G "Super Vanguard", the purpose of what would become the ZF-21 came under attack, with additional budget cuts threatening the very existence of the program as a whole. The program, however, received the further go forward with the involvement of the Republic of Zhenia Navy, when they issued requirements to introduce a complementary replacement to the ZF-7 Vanguards within service aboard its aircraft carriers and land bases by 1595 AC. It was the Navy's involvement that ultimately changed the direction of the aircraft's development from a pure air superiority fighter to a multirole fighter with an emphasis on air superiority and survivability in contested airspace, as the Navy gave great emphasis to acquiring platforms capable of long-range naval and surface strike even in contested airspace. In the process, the key avionics that were to be included on the new aircraft were changed, with the addition of, electro-optical targeting systems and other augmentations to improve the aircraft's air-to-surface capacity, while the airframe was partly restructured to accommodate arresting gear and reinforced landing gears for operation aboard aircraft carriers. The concept was revised as the Next-Generation Air Superiority Fighter (NG-ASF) program in 1578 by the Ministry of Defense and the Jungchuwon, although most of the development before the technology demonstrators were made in secret.

The first technology demonstrators from the three respective contractors were revealed in 1582, although in deep secrecy. Each labeled ZX-20, ZX-21 and ZX-22 respectively by order of completion, they were evaluated across various fields within RZAF bases in Heuksu and Shingang Province, including flight performance and sensor fusion. Jinmu Heavy Industries' proposal, the ZX-21, was widely regarded as the most radical of the three and showed many design characteristics that would be on what would become the ZF-21 Dragon, such as the first practical use of the {{wp|divertless supersonic inlet}, while proposals from Paragon and Hanshin resorted to more conservative designs but still fulfilled the requirements issued by the Zhenian Ministry of Defense. Although the decision remains a considerable controversy among experts to this day, the Ministry of Defense selected Jinmu Heavy Industries as the primary contractor to develop what would become the ZF-21 Dragon, while also assigning other firms as secondary contractors to support its development.

Production, procurement and upgrades


The first pre-production prototype of the ZF-21 made its maiden flight on June 4, 1588, coinciding with the 150th National Day. It was during its maiden flight that the existence of the ZF-21 became known to the international media, as most of the development process remained shrouded by the Jungchuwon until then.

Prior to full introduction into service, the ZF-21 saw major changes as the course of development progressed closer to production. The angles of the leading edge extensions and sweep angles were adjusted for better plan form alignment and aerodynamic performance, while the location of vertical stabilizers and engines were pushed around 0.3 meters behind from what the prototype had been. Some design proposals, including the proposal to altogether remove the infrared search and track (IRST) sensor near the nose in favor of other sensors around the aircraft, as well as all-moving canted vertical stabilizers, were axed out in the initial production variants due to budgetary concerns and project deadlines, although accommodations were made to allocate space for future changes.

After its introduction to service, upgrades and improvements made to the ZF-21 drew significant inspiration and technology from the adjacent development of the ZF-33 Black Eagle. The cockpits on later variants of the ZF-21, for instance, are largely similar to the on the ZF-33, featuring a pilot-friendly interface centered around touchscreens rather than screens controlled by buttons. Upgrades to the ZF-21 also significantly leverage newer avionics introduced on the ZF-33, such as the Cheongu Distributed Aperture System, which augments and replaces the existing (IRST) mounted near the nose of the aircraft while also providing 360-degree situational awareness to the pilot. Mission computers, the electro-optical targeting systems, pilot interfaces and software updates are also key features of upgrades made to the ZF-21. Many of such upgrades are visible since the ZF-21C variants.

Overview


The ZF-21 Dragon is a line of primarily single-seat, twin-engine, supersonic, all-weather stealth multirole fighters. As the first capable of air superiority missions to be built and introduced in Zhenia, it combines low observability to radar and other sensors, high maneuverability,,  and new technologies considered revolutionary at the time into a single aircraft. It is also the first Zhenia-built fighter aircraft to include supercruise as a default in combat. Although nominally a multirole fighter aircraft, it is generally geared more towards carrying out air superiority missions in contested airspace rather than being a dedicated strike fighter, a role fulfilled by the later-introduced Jinmu ZF-33 Black Eagle: this is further supported with its supermaneuverability and significantly increased survivability compared to its predecessors.

The ZF-21 is equipped with four empennage surfaces, with the horizontal tail being an all-moving one rather than having rudders forming a part of the tail: this has increased the area of control surfaces available and has simplified parts needed on the stabilizers. The aircraft also has retractable tricycle landing gears, trapezoid delta wings with a reverse tailing edge sweep and leading edge extensions running just behind the rear end of the cockpit. The leading edge extensions, being situated above the inlets, are movable and control the aerodynamics around the aircraft in a way akin to found on other aircraft of previous generations, adding to its maneuverability. Other flight control surfaces include leading-edge flaps, flaperons, aileron and rudders on canted vertical stabilizers.

The ZF-21 is powered by two Li-Jien Dynamics AE-350S-200 turbofan engines, which are separated by a central extension of the airframe. Each providing a thrust of around 175 kN in full afterburner and 108.9 kN at maximum military power, it provides adequate power to allow the aircraft with capability, being able to reach speeds up to Mach 1.6 without using afterburners. The engines have also brought up the ZF-21's thrust-to-weight ratio at combat weight to around 1.3 in full afterburner, while the maximum speed in the same condition at altitude is around Mach 2.3. The engines also incorporate three-dimensional thrust vectoring nozzles consisting of three stealthy nozzle arms that have a range of ±20 degrees in all directions, increasing the maneuverability of the aircraft.

An aircraft geared toward increased survivability and combat in highly-contested airspace, the high cruising speed, maneuverability and stealth of the ZF-21 gives it an edge against both existing and emerging threats such as surface-to-air missiles, while also functioning as a force multiplier on the capability of its sensors and armament. The usage of internal weapons bays, while also eliminating drag from external stores, maintain the low observability of the aircraft, a characteristic critical in contested airspace. Its high cruising speed of the aircraft allows for rapid interception and escape without compromising the range of the aircraft, as aircraft of previous generations would require afterburners to achieve such speeds, while its high maneuverability ensures higher survivability against incoming enemy threats and maintain an edge against enemy aircraft at close-in encounters.

Armament


In order to preserve its stealthy shape, the ZF-21 is equipped with a total of three internal weapons bays - a large main bay running through the center of the aircraft and two smaller bays on the side of the fuselage, between the landing gear and the air intakes. Split along the center line of the aircraft, the large main bay is capable of accommodating up to six long-range air-to-air missiles at a time, while the smaller side bays are in theory capable of accommodating up to two air-to-air missiles each, although they normally carry only one in practice. Unlike the side bays, the main bay is also capable of carrying a broad range of air-to-surface weapons, being able to carry up to 1,300 kg of ordnance in each hardpoint. Ordnance in both the main bay and side bays are connected to the weapons bay via robotic arms, which are engaged when the weapon is set to be fired. The usage of internal weapon bays allow for non-stealthy ordnance to be carried within the airframe, minimizing radar signatures.

In addition to the internal weapon bays, the ZF-21 is also equipped with three external hardpoints on each its wings, with a capacity of carrying up to 8,000 kg on each side of the wing. The external hardpoints can be used to carry large munitions that do not fit inside the main weapon bay, carry munitions in missions that do not require a stealthy configuration, or external weapon pods to increase its ordnance capacity while maintaining its stealthy configuration. Although only able to be installed at the internal hardpoints on each wing, the external weapons pod is capable of carrying up to four additional long-range air-to-air missiles. The ZF-21 is armed with a 20 mm Gatling gun mounted in the right-hand spot near the wings with 450 rounds for close-range warfare and strafing. The centerline of the aircraft, just behind the main weapon bay, has an additional hardpoint not for munitions but for multi-mission pods, including jammers and reconnaissance pods.

Sensors, electronics and countermeasures
The ZF-21 attempts through an integrated avionics system, often combining data acquired by various sensors and external input to draw the full picture for situational awareness. Key components of its sensor fusion include the Z/APG-88 (AESA) radar, which is integrated with the AJS-301A 'Leishen'  suite and jammers to maximize survivability, ultraviolet and infrared  (MLD) nad missile approach warning systems (MAWS), side-looking radars and other active and passive sensors to provide full coverage around the aircraft. The Z/APG-88 AESA radar, consisting of 1,552 T/R modules, is one of the most powerful phased array radars to be installed on Zhenian aircraft, and are augmented by two side-looking X-band AESA radars each with 360 T/R modules, providing a combined 250 degrees of radar coverage. Although the specifications of the Z/APG-88 remains a secret, there are estimations that it could identify and track a target 1 m2 in size from over 220 kilometers. The aircraft's leading-edge extensions also house the antennas of L-band radars, used to increase the resolution and detection range of the aircraft's radar system.

Another major element of the ZF-21's system is the Cheongu Distributed Aperture System designed and built by Signus Systems, a system consisting of multifunction infrared-range camera sensors installed around the airframe. Intended to provide 360-degree coverage around the aircraft in extended ranges, the Cheongu Distributed Aperture System is expected to allow for reconnaissance, threat detection and target acquisition in both air and the surface. The system is more or less the same with that seen on the ZF-33, with the ZF-21 having one more multifunction camera to provide higher coverage due to the larger size of the airframe: this is due to the fact that the ZF-21, unlike the ZF-33, did not initially come with the electro-optical targeting system installed.

While earlier variants of the ZF-21 required external or manual guidance of precision-guided munitions, most ZF-21s in operation today are equipped with the  (EOTS). Replacing the functions of existing targeting pods, and  (IRST) sensors, the EOTS provides the pilot with high-resolution imagery and targeting information. Due to its interconnections to the Cheongu DAS, the EOTS is often considered a component of the Cheongu DAS, with data from the EOTS often doubling as data needed to adjust the data for higher precision.

Cockpit
The ZF-21 uses a to maximize the pilot's situational awareness. Primarily centered around a 20-by 8-inch (50 by 20 cm) panoramic and the  at the top, the cockpit's information display system allows for flexible display of flight instruments, aircraft status, information on the aircraft's surroundings and incoming threats. The cockpit itself has been designed to reduce complexity and increase flexibility of screen usage at the end of the pilot, which has been factored into the lack of screen side buttons. While some have proposed to remove the head-up display altogether and replace its functions with a, it has been decided that all variants were to retain the head-up display to augment the pilot's own situational awareness.

Stealth
Although its exact remains a closely-guarded secret, there are speculations that the estimated radar cross-section of the ZF-21 without any external armaments is most likely smaller than 0.001m2 - roughly comparable to a metal golf ball. The ZF-21 was designed to minimize its radar cross-section and probability of being detected by enemy sensors. Such measures include planform alignment on the edges, curved vanes behind the to cover the engine turbines from external radar waves, extensive use of radar-absorbent material (RAM) and minimization of clear bumps and design irregularities that can possibly give a radar return. Reduction of radio emissions, infrared and acoustic signature has also been taken into account upon the ZF-21's design, with its saw-toothed three-dimensional designs both to scatter radar and heat signatures, active cooling on leading edges and other heat-concentrated areas to reduce heat buildup and the internalization of almost all antenna systems.

Although it takes extensive use of radar-absorbent material (RAM), the ZF-21 primarily uses more durable radar-absorbent fibermat skin modules that allow for less and easier maintenance than its predecessors, increasing its and availability in emergency situations. While its stealth is primarily focused on achieving very low observability (VLO) against threats, it is said to also have achieved at least low observability (LO) against S-band and L-band threats, among other lower-frequency threats. Although its exact remains a closely-guarded secret, there are speculations that the estimated radar cross-section of the ZF-21 without any external armaments is most likely smaller than 0.001m2 - roughly comparable to a metal golf ball. The aircraft can additionally mount a total of six reflectors to disguise its actual radar cross-section.