An interesting and comprehensive comparison between the JF-17 and the Tejas. The article appears to be neutral.
India's Tejas and China's Xiaolong Fighters Compared (Defense Aerospace.com)
Overview of the Aircraft
The HAL Tejas Light Combat Aircraft (LCA) was named by former Indian prime minister Atal Bihari Vajpayee. The development plan was approved by the Indian government in 1983. The government's requirements for the Tejas were to develop an all-weather supersonic LCA which could replace the MiG-21. Its main mission is to fight for control of airspace and to offer short-range support. The development of the Tejas wasn't a simple process, as it included a completely new engine, avionics and weapons systems, in line with global standards. The first test plane was unveiled on Nov. 17, 1995 and made its maiden flight on Jan. 4, 2001.
The design for the PAC JF-17 Thunder, also known as the FC-1 Xiaolong, began with the "Super 7" plan launched jointly by China and US aircraft maker Grumman to develop an upgraded version of the F-7, but Grumman left the project after sanctions were placed on China by the US in the wake of the Tiananmen Square Massacre in 1989. China and Pakistan subsequently signed a memorandum of understanding to design a new fighter together in 1995. The requirements for the fighter were that it make use of advanced technology, that it be a completely new design and that it approach the combat capabilities of third-generation fighters. It also needed to be light, cheap to produce and capable of carrying a large payload. The first plane took its maiden flight in 2003 and the third aircraft made a successful test flight in April of 2004. In the same year, the state-owned China National Aero-Technology Import & Export Corporation (CATIC) and the Pakistan Air Force signed a contract for the production of the FC-1 Xiaolong/JF-17 Thunder, the new designations of what had been the Super 7. On April 28, 2006, weapons systems and avionics were installed in the fourth aircraft and it made a successful test flight. The avionics systems were developed by China. On Sept. 10, 2006, the sixth JF-17 made its maiden flight.
Aerodynamic Configuration
There are clear differences in the shape of the two planes. The Xiaolong has horizontal tail-planes and a conventional aerodynamic structure, while the Tejas has no horizontal tail-planes on its triangular structure.
The lack of a (horizontal) tail is a unique feature of the Tejas, making it similar to the Dassault Mirage series of fighters. The plane also has a delta-wing configuration, which is the reverse of normal delta-wing fighters in that the angle of the sweep of the outer wing section is larger than the angle of the sweep of the inner wing section. The reverse configuration is normally used to balance supersonic and subsonic or transonic capabilities. The Tejas has an angle of incidence from the main axis of the wing, which gives the whole plane a larger dihedral force, improving its supersonic capabilities.
The Xiaolong has a trapezoid-shaped wing configuration, with a larger wing-aspect ratio and a smaller induced drag, therefore at high-altitude subsonic speed, the entire plane has a higher lift-drag ratio. The large wings that extend to the inlets on both sides of the plane's body not only improve the aircraft's lift during high-angle-of-attack flight but also help improve the maneuverability of the plane. The eddies created during high-angle-of-attack flight are also relatively stable, which reduces the chance of sudden drops in lift and improves the balance of the plane. It also improves the directivity of the nose of the plane in close-range combat.
In summary, in conventional air warfare, at an altitude of around 8,000 meters and a speed of Mach 0.8-1.2, the Xiaolong performs better in terms of acceleration, climb, stability and other combat capabilities. The Tejas' advantage lies in its low wing aspect ratio and its relatively low wave drag, which makes it superior to the Xiaolong in supersonic conditions.
Inlet Design
Both planes have intake cowls on both sides, but the Xiaolong's design is better as it is more functional, improves the plane's stealth capabilities and reduces its weight.
The Tejas uses the V-shaped air inlets typical of light fighters, the air inlets gather together towards the rear, sheltering the blades of the engine's axial compressor, preventing the scattering of radar, and adding to the craft's stealth capabilities. The oval air intakes are similar to the F/A-18C/D Hornet, with a diverter structure around them. All in all the design is in line with convention and has not shown much innovation.
The Xiaolong's air intake design is a little more imaginative and more advanced. It uses a diverterless supersonic inlet (DSI), scrapping the diverter structure used around the air intakes, as well as the air bleed and air bypass structures of most conventional supersonic aircraft. Through use of a three-dimensional compression surface to divert the boundary layer airflow at high subsonic and supersonic speeds, there is no longer a need for supplementary air inlets or bleed doors. This has the effect of lightening the structure, reducing drag and radar return. The air inlets are forward sweeping in a ramp formation, which reduces wave drag or surface interference.
Materials
As the Xiaolong was developed exclusively for export, to control costs, its body is mainly constructed with aluminum alloy as opposed to more popular composite material. The Tejas, however, has put an emphasis on reducing weight, and so it has used a lot of composite material. Forty-five percent of the plane's total weight is comprised of composite materials, including the fuselage, its vertical tailfin, the skin, the spars and the ribs of the wings, the elevons, the rudder, the air brakes and the landing gear doors. This cuts the plane's empty weight by 5.5 tons, making it almost 1 ton lighter than the Xiaolong, which means it can carry more fuel and a heavier load. The plane has a cargo-internal fuel ratio of around 30%, which improves its combat abilities.
Propulsion Systems
Although the Tejas' F414 engine is superior in terms of functionality, durability and life span to the Xiaolong's RD93 engine, it is also more expensive.
The choice of an engine has been problematic in the development of both aircraft. Those developing the Xiaolong had the choice of the commonly used F404, Pratt & Whitney's PW1216, the Turbo-Union RB199, the Snecma M88 and the Russian RD33. After considering different parameters, such as the combat radius, external storage and flexibility, they chose the RD-93 afterburning turbofan due to its low fuel uptake and its reasonable price.
The RD-93 is a variant of the RD-33 developed specifically for the Xiaolong, the main changes being the repositioning of the gearbox along the bottom of the engine casing and its mechanical turbine control. It employs a four-stage fan and nine high pressure stage compressor, with military thrust of 50 kiloNewtons (kN) and 81.3 kN thrust with afterburner, an augmented thrust ratio of 1.628, an overall pressure ratio of 21:1, a bypass ratio of 0.48:1, a normal gross takeoff weight of 9.1 tons and a thrust-to-weight ratio of 1, which gives it a longer range and better flying and propulsion capabilities.
The original plan for the LCA Tejas was that it would be fitted with the GTRE GTX-35VS Kaveri turbofan engine, but the development of the engine ran into a hitch, so they had to adopt the F414 instead. The engine was developed on the basis of the General Electric F404 and has an axial compressor with three fan and seven compressor stages and a turbine with one low-pressure and one high-pressure stage. Compared with the F404, the F414 has augmented thrust by 35%, pushing it to 60 kN military thrust and 98 kN with afterburner. Its thrust-weight ratio has been pushed to 9:1. India purchased the custom-made F414-GE-INS5 model, which has similar capabilities to the F414-GE-400, with a fully digital control system, more advanced than the RD-93's mechanical turbine control, making it quicker to react and more accurate.
End of part 1
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