Design features of the JAS-39 fighter

The JAS-39 has a center wing layout for optimal wing-body fusion, which also gives good ground clearance for external attachments. And in general, ground clearance for external attachments has been a bad problem for small airplanes. Due to the center-mounted wing, the main landing gear of the JAS-39 is mounted on the fuselage, and in addition, in order to obtain the best aerodynamic coupling with the main wing, the front wing has to have a certain mounting angle.The JAS-39 Hawker adopts a cutter-angle delta wing with a serrated leading edge and a 45° swept-back angle. The lift device consists of two sets of leading-edge flaps, which are connected to the elevator of the airplane through a full-authority three-odd degree fly-by-wire flight control system. The leading edge flaps are deflected downward at large angles of approach to delay the wing stall. When the trailing edge flaps are deflected downward, they allow the aircraft to lift, thus increasing the aircraft's maneuverability. This is different from conventional longitudinally stabilized aircraft, for which downward deflection of the trailing edge flaps causes the aircraft to develop a low head moment. The full-motion duck wing is also a tangent triangle, with a leading edge swept back angle of 43°.

One of the advantages of the JAS-39 Hawker's layout is that direct lift can be generated by simultaneously deflecting the duckwing and elevator. Differential deflection of the duckwing produces lateral force, which, in combination with rudder deflection, produces direct lateral force without changing the aircraft's heading. This "uncoupled" mode of flight is useful when air-to-air attacks are conducted using aerial guns, or when unguided weapons are dropped on ground targets. During the design process of the JAS-39 aircraft, the weight reduction of the aircraft was realized through the extensive use of new technologies and advanced computer simulation techniques, in which the use of composite materials accounted for 25% to 30% of the fuselage structure. Carbon fiber composites are mainly used for skins and wing beams, tail fins, elevators, landing gear hatches and some inspection port covers. The skins are not glued to the support structure, but are mounted with countersunk screws, and to eliminate leakage from the integral fuel tank, sealing material is used at the contact points. It is estimated that the JAS-39 aircraft*** has about 100,000 fasteners, and machine-added parts account for about 15 percent of the airframe structure by cost.

In accordance with modern aircraft manufacturing processes, the JAS-39's fuselage structure is built in several parts, with the wings divided into seven parts and the fuselage divided into three segments, which are permanently attached at the assembly stage, eliminating the weight increase associated with conventional transition joints. The center fuselage is subdivided into 3 parts: the gun pod, the landing gear section and the fuselage mounting section. The bending moment of the wing is transmitted to the fuselage through 3 small spaced spacer frames, with only one auxiliary mounting section at the leading edge wing root, a surprising design considering the long chord length of the delta wing's wing root. The reason for this was that the main fuselage bulkheads were limited by the main landing gear bay and engine inspection doors.The F404 engines were mounted and dismounted from the lower fuselage and this was to allow easy engine changes on crowded carriers. This situation forced Saab to design a very strong wing root reinforcement to transfer the bending moment of the wing centrally to the fuselage. The JAS-39 significantly reduced the pilot's workload through careful design of the cockpit display and maneuvering systems, significantly improving the operational effectiveness of the aircraft. The core component of the cockpit is Ericsson's EP-17 display system, which employs three 120mm x 150mm multifunction downward looking displays (HDDs), and one wide-angle holographic flat panel display (HUD) from Kaiser.The three monochrome downward looking displays (HDDs) are identical and interchangeable. During flight, the function of the displays can be adjusted to suit different flight phases or operational missions. The left HDD generally displays flight data, including data on the HUD and other self-defense equipment and sensors; the center HDD displays a computer-generated map of the surrounding area overlaid with tactical information; and the right HDD displays targeting information from radar, forward-looking infrared, and weapons sensors.

The HDDs, while based on existing TV technology, offer a major improvement in performance, providing a high-quality, high-definition picture in poor lighting conditions. According to the requirements of the Swedish Air Force, color displays may also be used in future aircraft. The use of diffraction gratings in the HDD allows high brightness images to be obtained.The HUD, with a field of view of 28° x 22°, can provide either computer-generated weapon targeting symbols or video images generated by optoelectronic systems (e.g., forward-looking infrared devices). All information displayed in the cockpit can be recorded on a standard magnetic tape for the pilot to consult.

To further minimize the pilot's workload, the Hawker uses a hand-operated throttle stick, with all the buttons for the radar and weapons controls placed on the throttle-stick.Saab studied both center and side-mounted sticks, and opted for a small center-mounted stick. This stick could be operated with either the right or left hand when required. In the Hawker's avionics system, there are more than 40 Ericsson D80 computers, which are connected by a three-degree MIL-STD-1553B data bus: one bus for basic aircraft and flight data, one bus for cockpit displays and radar, and one bus for tactical and weapons information. bus for tactical and weapons information. Subsequent batches of aircraft and export models have five data buses. The use of five data buses keeps the "load" on each bus low. The JAS-39 was designed as an air superiority fighter, but was first introduced into service as an attack aircraft. For ground attack missions, the Gripen can carry a variety of weapons, primarily Hughes AGM-65A/B ''Cub'' (Rb75) air-to-ground missiles and DWS-39 out-of-area bomblets. 39 Out of Defense Area (ODA) bomblet disperser. "The ''Young Animal'' missile is a battle-tested, TV-guided missile with a range of about 3km, carrying a 57kg combatant for attacking tanks and other armored targets.The DWS39 is unpowered and its range depends on the launch conditions.Prior to delivery, data on the target is transmitted to the weapon, and an inertial guidance system guides and control. Submunitions can be 24 anti-runway bombs, 96 cluster bombs, 120 anti-tank mines, 504 SB44 bomblets or 1,848 M42GP bomblets. Unguided weapons include 80kg M50 bombs, 600kg M60 bombs and ARAK70 rockets.

For anti-ship missions, the Hawker's primary weapon is the Saab Rbs-15F anti-ship missile. The missile carries a 200kg semi-armor-piercing blast warhead, has a range of 90km, and is guided by inertial guidance in the mid-range and active radar guidance in the beam section. For self-defense, the Hawker is equipped with electronic countermeasures, including radar warning receivers and an electronic countermeasures system consisting of a foil/tracer dispersal device mounted in an under-wing mount, a towed radar dummy target and a jammer. For reconnaissance missions, all sensors and photographic equipment are externally mounted.

Sweden had hoped to develop a successor to the Rb71 over-the-horizon missile, but after a number of years of work, the decision was finally made to go with Hughes' AIM-120 medium-range air-to-air missile, AMRAAM (Advanced Medium-Range Air-to-Air Missile). An important point was that the Swedish Air Force was allowed to flight test the missile. Since the Swedish Air Force has only ordered 100 AIM-120 missiles, the Hawker may also use Meteor air-to-air missiles. "The export version of the Gripen may also use the Meteor missile, which is interchangeable with the AIM-120 missile, requiring only minor software changes. Both missiles have the ability to discriminate between targets and use data chains and inertial guidance to maintain stealth for as long as possible after launch. The data chain is used to update information about the target, which can be provided either by the aircraft itself or by other aircraft (such as other Hawker or S100B AWACS aircraft). For short-range attacks, the Hawker can carry AIM-9L and AIM-9J Rattlesnake missiles. A 27mm Bk27 Mauser cannon is mounted in the lower left fairing of the belly. The JAS-39's avionics were designed and built by Ericsson and then integrated by Saab. The avionics of the JAS-39 were a vast improvement over those of the Saab-37 Thunder. The Ericsson/GMAv PS-05 radar was used, with three times the data processing power of the Ray's PS-46/A radar, but at 60% of the size and 50% of the weight of the latter, the PS-05A was a multi-operating modal pulse Doppler radar with a slit waveguide planar array. The PS-05A is a multi-operating modal pulsed Doppler radar with a slit waveguide planar array antenna and a liquid-cooled traveling wave tube transmitter. By using complex and variable waveforms and high, medium and low pulse repetition frequencies, it realizes multiple operating modes required for various missions. Frequency-modulated pulse compression is used to improve resolution and to enable detection of long-range targets.

The radar's operating modes are controlled by software and include the following: Air-to-air: long-range search and tracking; multi-target side search and tracking; short-range wide-angle search and tracking; and automatic control of artillery and missiles. Air-to-air: search and tracking; scanning and tracking of ground and sea targets; high-resolution mapping; air-to-air ranging. Adopting all programmable signal and data processors, it has good electronic anti-jamming ability and flexibility to adapt to future development. The PS-05A's flexible waveform avoids inaccuracies in radar ranging and optimizes performance in every operating mode. The planar antenna array scans with very little side flap, reducing sensitivity to interference and improving the radar's efficiency. The radar is also adapted to the data transmission requirements of guided medium-range air-to-air missiles (such as the AMRAAM Advanced Medium-Range Air-to-Air Missile (AMRAAM) and Meteor missiles), and has good applicability and low maintenance costs due to its modular design and in-flight self-testing capabilities. It utilizes the new active phased array technology, in which more than 1,000 transmitter/receiver units are used. In order to extend the radar's azimuth, the antenna is mounted on a movable chassis, which can significantly increase the radar's scanning range, a design approach that is relatively unique among phased array radars. AESA technology is used to improve the radar's target detection and tracking performance.

The Swedish Air Force has been using a Tactical Instrument Landing System (TILS), which is not only obsolete but also expensive to use and not suitable for decentralized wartime airfields. The need was to develop a system that relied solely on on-board sensors and equipment that could guide an aircraft to any airfield and guarantee a safe landing in all-weather conditions, all the time. The new system utilizes two new technologies developed for the Hawker-Lion aircraft, the New Integrated Navigation System (NINS) and the New Integrated Landing System (NILS). In addition, NINS can also use information from conventional navigation equipment such as Distance Measuring Equipment (DME), Very High Frequency Omni-directional Beacons (VOR) and TACAN if the pilot requires it.