Airframe
Basics: The LCA is the smallest and lightest combat jet in the world. Confusion may arise with respect to the South Korean T-50, but it must be remembered that T-50 is primarily a hybrid trainer, that can assume fighter roles when necessary. The T-50 has a higher height and longer wingspan than the LCA, while its length is shorter by 22 cms. Thus, overall the LCA is the smallest combat jet in the world.
It is much smaller than even the JAS-39, which is ~1 m longer. An effort was made to reduce the number of individual composite parts to the minimum and hence keep the plane light.
Detailed description: The LCA is a tail-less compound delta platform with relaxed static stability. Extensive wind tunnel testing on scale models and complex computational fluid dynamic analyses have optimised the aerodynamic configuration of LCA, giving it minimum supersonic drag, low wing loading and high rates of roll & pitch. The tailless compound delta platform helps in keeping LCA small and light. It also means fewer control surfaces, wider choice of external stores and better close combat, high-speed and high-alpha characteristics.
The LCA has 45% composite frame, which make it light and strong at the same time as compared to other all-metal aircraft. The configuration is a delta wing, with no tailplanes or foreplanes, and a single vertical fin. The LCA is constructed of aluminium-lithium alloys, carbon-fibre composites, and titanium. The design incorporates "control-configured vehicle" concepts to enhance manoeuvrability, and quadruplex fly-by-wire controls.
Among the most significant breakthrough is the use of advance carbon composites for upto 45% of the LCA air frame, including wings, materials fin and fuselage. This percentage of composites is one of the highest as compared to other contemporary aircraft of its class. Apart from making it much lighter, there are less joints or rivets making the aeroplane more reliable. Fatigue strength LCA studies on computer models optimise performance. National Aerospace Laboratory (NAL) has played a lead role. Materials include Aluminium-Lithium alloys, Titanium alloy and Carbon composites. Composites for wing (skin, spars and ribs), fuselage (doors and skins), elevons, fin, rudder, airbrakes and landing gear doors.
Special mention: The skin of the LCA measures 3 mm at its thickest with the average thickness varying between 2.4 to 2.7 mm. BAE was consulted. The fin for the LCA is a monolithic honeycomb piece. No other manufacturer is known to have made fins out of a single piece. The cost of manufacture is reduced by 80% from Rs 2.5 million in this process. This is contrary to a subtractive or deductive method normally adopted in advanced countries, when the shaft is carved out of a block of titanium alloy by a computerized numerically controlled machine. A 'nose' for the rudder is added by 'squeeze' riveting.
The use of composites results in a 40% reduction in the total number of parts (if the LCA were built using a metallic frame): for instance, 3,000 parts in a metallic design would come down to 1,800 parts in a composite design. The number of fasteners has been reduced to half in the composite structure from 10,000 in the metallic frame. The composite design helped to avoid about 2,000 holes being drilled into the airframe. Though the weight comes down by 21%, the most interesting prediction is the time it will take to assemble the LCA -- the airframe that takes 11 months to build can be done in seven months using composites.
Flight Envelope:
" AoA: 25 deg.
" Roll-rate : 290-300 deg/sec
" Sustained load G-limit : 8/-3.5g
" Short take-off and landing capabilities.
According to defence analyst B. Harry, the Naval LCA shall feature with LEVCONs or (Leading Edge Vortex Controllers). This shall require development of new control laws for it. These LEVCONs shall be control surfaces that extend from wing-root leading edge and thus afford better low-speed handling of the LCA which otherwise is slightly hampered due to increased drag that results from its delta-wing design. It shall also increase controllability at high AoA. At high speeds though, the delta-winged design offers better manoueverability than conventional winged-designs.
According to him, such a feature (as in the Naval LCA), has not been implemented on any other combat aircraft.
Stealth:It is expected that being the smallest combat jet, and coupled with a highly composite airframe (that do not reflect radar waves) and RAM (Radar Absorbent Material) coating, the LCA shall exhibit a very low RCS to radar detections from airborne enemy aircraft and AWACs. The Y-duct intake shields the engine compressor from radar waves.
LCA is expected to be highly maneuverable by virtue of its double delta wing and relaxed static unstability of its Fly-By-Wire system. Provisions for the growth of hardware and software in the avionics and flight control system, available in Tejas, ensure to maintain its effectiveness and advantages as a frontline fighter throughout its service life. For maintenance, the aircraft has more than five hundred Line Replaceable Units (LRSs), each tested for performance and capability to meet the severe operational conditions to be encountered.
Air intakes: The wing shielded side mounted bifurcated Y-duct air intake with optimised diverter configuration ensures buzz free air supply to the engine, at acceptable distortion levels.
Weapon stations: Seven weapon stations provided on Tejas offer flexibility in the choice of weapons Tejas can carry in various mission roles. Provision of drop tanks and inflight refueling probe ensure extended range and flight endurance of demanding missions.
Cockpit: The LCA has a glass cockpit with two Multi Function Displays, Head-Up Display, Multi Function Keyboard and Get-You-Home Panel.
Specifications ( HAL Tejas MK-I )
General characteristics
" Crew: One
" Length: 13.20 m (43 ft 4 in)
" Wingspan: 8.20 m (26 ft 11 in)
" Height: 4.40 m (14 ft 9 in)
" Wing area: 38.4 m² (413 ft²)
" Empty weight: 6,500 kg (14,300 lb)
" Loaded weight: 10,500 kg (23,100 lb)
" Power plant: 1× General Electric F404-F2J3 turbofan 80.5 kN (18,100 lbf),
1x F404-GE-IN20, 85kn (19,000 Ibf)
Performance
" Maximum speed: Mach 1.8, 1,920 km/h (1,195 mph) at high altitude
" Range: 850 km (530 mi)
" Service ceiling: 15,250 m (50,000 ft)
" Wing loading: 221.4 kg/m² (45.35 lb/ft²)
" Thrust/weight: 1.07
