A very detailed report on the Tejas. I'm guessing most people just don’t read up enough before passing comments on how the Tejas cannot be compared to the "incomparable" Gripen.
When reading about FBW FCS on the Tejas, keep in mind that the Gripen team skipped most of this development effort and time by having BAE Astronics and LM supply the FBW FCS for the Gripen and there was none of the sanctions and extra effort that was needed for the Tejas due to that.
Fly-by-wire Control Laws
One of the most ambitious requirements for the LCA was the specification that it would have "relaxed static stability." Although Dassault had offered an analogue FCS system in 1988, the ADA recognised that digital flight control technology would soon supplant it.[5] RSS technology was introduced in 1974 on the General Dynamics (now Lockheed Martin) YF-16, which was the world's first aircraft to be slightly aerodynamically unstable by design. Most aircraft are designed with "positive" static stability, which means they have a natural tendency to return to level and controlled flight in the absence of control inputs; however, this quality tends to oppose the pilot's efforts to maneuver. An aircraft with "negative" static stability (i.e., RSS), on the other hand, will quickly depart from level and controlled flight unless the pilot constantly works to keep it in trim; while this enhances maneuverability, it is very wearing on a pilot relying on a mechanical flight control system. What made RSS practical on the YF-16 was a new technology — the "fly-by-wire" flight control system — which employs flight computers to electronically keep the aircraft's instability in check whenever it is not desired.
Development of a FBW flight control system requires extensive knowledge of flight control laws and the expensive writing of a considerable amount of software code for the flight control computers, as well as its integration with the avionics and other electronic systems.When the LCA programme was launched, FBW was a state-of-the-art technology and such a sensitive one that India could find no nation willing to export it. Therefore, in 1992 the LCA National Control Law (CLAW) team was set up by the National Aeronautics Laboratory to develop India's own version. The CLAW team's scientists and mathematicians were successful in developing their control laws, but could not test them since India did not possess advanced real-time ground simulators at that time. Accordingly, British Aerospace (BAe) and Lockheed Martin were brought in to help in 1993, but the effort required for the Aeronautical Development Establishment to code the control laws into the FCS software proved a much larger job than originally anticipated.
Specific control law problems were tested on BAe's simulators (and on HAL's, once theirs became available). As it was being developed, progressive elements of the coding were checked out on the "Minibird" and "Ironbird" test rigs at the ADE and HAL, respectively. A second series of inflight simulation tests of the integrated flight control software were conducted on the F-16 VISTA (Variable In-flight Stability Test Aircraft) simulator in the U.S. in July 1996, with 33 test flights being carried out. However, Lockheed Martin's involvement was terminated in 1998 as part of an embargo enacted by the U.S. in response to India's second nuclear tests in May of that year.
The NAL's CLAW team eventually managed to successfully complete integration of the flight control laws indigenously, with the FCS software performing flawlessly for over 50 hours of pilot testing on TD-1, resulting in the aircraft being cleared for flight in early 2001. The LCA's maiden flight was made by TD-1 from National Flight Test Center(NFTC), near Bangalore, on 4 January 2001, and its first successful supersonic flight followed on 1 August 2003. TD-2 was scheduled to make its first flight in September 2001, but this was not achieved until 6 June 2002. The Tejas' automatic flight control system (AFCS) has been highly praised by all of its test pilots, one of whom said that he found it easier to take off with the LCA than in a Mirage [2000].[9]
BTW, the LCA's FBW was almost entirely coded, verified and tested by Indian engineers after they were basically thrown out of the US and their equipment seized in 1998.
Airframe
The LCA is constructed of aluminium-lithium alloys, carbon-fibre composites (CFC), and titanium-alloy steels. The Tejas employs CFC materials for up to 45% of its airframe, including in the fuselage (doors and skins), wings (skin, spars and ribs), elevons, tailfin, rudder, airbrakes and landing gear doors. Composites are used to make an aircraft both lighter and stronger at the same time compared to an all-metal design, and the LCA's percentage employment of CFCs is one of the highest among contemporary aircraft of its class.[34] Apart from making the plane much lighter, there are also fewer joints or rivets, which increases the aircraft's reliability and lowers its susceptibility to structural fatigue cracks.
The tailfin for the LCA is a monolithic honeycomb piece, an approach which reduced its manufacturing cost by 80% compared to the customary "subtractive" or "deductive" method, whereby the shaft is carved out of a block of titanium alloy by a computerized numerically controlled machine. No other manufacturer is known to have made fins out of a single piece. ...means we even innovated new concepts which never existed for other planes [35] A 'nose' for the rudder is added by 'squeeze' riveting.
The use of composites in the LCA resulted in a 40% reduction in the total number of parts compared to using a metallic frame. Furthermore, the number of fasteners has been reduced by half in the composite structure from the 10,000 that would have been required in a metallic frame design. The composite design also helped to avoid about 2,000 holes being drilled into the airframe. Overall, the aircraft's weight is lowered by 21%. While each of these factors can reduce production costs, an additional benefit — and significant cost savings — is realised in the shorter time required to assemble the aircraft — seven months for the LCA as opposed to 11 months using an all-metal airframe.[6]
The airframe of the naval variant of the Tejas will be modified with a nose droop to provide improved view during landing approach, and wing leading-edge vortex controllers (LEVCON) to increase lift during approach. The LEVCONs are control surfaces that extend from the wing-root leading edge and thus afford better low-speed handling for the LCA, which would otherwise be slightly hampered due to the increased drag that results from its delta-wing design. As an added benefit, the LEVCONs will also increase controllability at high angles of attack (AoA).
The naval Tejas will also have a strengthened spine, a longer and stronger undercarriage, and powered nose wheel steering for deck manoeuvrability.[11][36] The Tejas trainer variant will have "aerodynamic commonality" with the two-seat naval aircraft design.[37]
Now, regarding the landing gear- Gripen's landing gear is made by BAE Systems, not by Saab.
Landing gear
The Tejas has a hydraulically retractable tricycle-type landing gear with a pair of single inward-retracting mainwheels and a steerable, twin-wheel forward-retracting nose gear. The landing gear was originally to have been imported, but following the imposition of trade sanctions, HAL developed the entire system independently.
India's Nuclear Fuel Complex (NFC) led the team that developed the titanium half-alloy tubes that are used for hydraulic power transmission and they are critical components in the LCA. India is one of only six nations which have developed this technology, which also has space applications.[38]
quadruplex digital FCS against the triplex redundant FCS with 1 analog channel back up in the Gripen.
Flight controls
Since the Tejas is a "relaxed static stability" design, it is equipped with a quadruplex digital fly-by-wire flight control system to ease handling by the pilot. The Tejas' aerodynamic configuration is based on a pure delta-wing layout with shoulder-mounted wings. Its control surfaces are all hydraulically actuated. The wing's outer leading edge incorporates three-section slats, while the inboard sections have additional slats to generate vortex lift over the inner wing and high-energy air-flow along the tail fin to enhance high-AoA stability and prevent departure from controlled flight. The wing trailing edge is occupied by two-segment elevons to provide pitch and yaw control. The only empennage-mounted control surfaces are the single-piece rudder and two airbrakes located in the upper rear part of the fuselage, one each on either side of the fin.
The digital FBW system of the Tejas employs a powerful digital flight control computer (DFCC) comprising four computing channels, each with its own independent power supply and all housed in a single LRU. The DFCC receives signals from a variety of sensors and pilot control stick inputs, and processes these through the appropriate channels to excite and control the elevons, rudder and leading edge slat hydraulic actuators. The DFCC channels are built around 32-bit microprocessors and use a subset of the Ada language for software implementation. The computer interfaces with pilot display elements like the MFDs through MIL-STD-1553B multiplex avionics data buses and RS-422 serial links.
I am yet to see ANY system on the Gripen that is "incomparable" to the Tejas. lets look at the avionics-
Avionics
The Tejas has a night vision goggles (NVG)-compatible "glass cockpit" that is dominated by an indigenous head-up display (HUD), three 5 in x 5 in multi-function displays, two Smart Standby Display Units (SSDU), and a "get-you-home" panel. The CSIO-developed HUD, Elbit-furnished DASH helmet-mounted display and sight (HMDS), and hands-on-throttle-and-stick (HOTAS) controls reduce pilot workload and increase situation awareness by allowing the pilot to access navigation and weapon-aiming information with minimal need to spend time "head down" in the cockpit.
The MFDs provide information on the engine, hydraulics, electrical, flight control, and environmental control systems on a need-to-know basis, along with basic flight and tactical information. Dual redundant display processors produce computer-generated imagery on these displays. The pilot interacts with the complex avionics systems through a simple multifunction keyboard and function and sensor selection panels.
Target acquisition is accomplished through a state-of-the-art radar — potentially supplemented by a laser designator pod, forward-looking infra-red (FLIR) or other opto-electronic sensors — to provide accurate target information to enhance kill probabilities. A ring laser gyro (RLG)-based inertial navigation system (INS) provides accurate navigation guidance to the pilot. The LCA also has secure and jam-resistant communication systems such as the "identify friend or foe" (IFF) transponder/interrogator, VHF/UHF radios, and air-to-air/air-to-ground datalinks. The ADA Systems Directorate's Integrated Digital Avionics Suite (IDAS) integrates the flight controls, environmental controls, aircraft utilities systems management, stores management system (SMS), etc. on three 1553B buses by a centralised 32-bit, high-throughput mission computer.
Self-protection
An advanced electronic warfare suite enhances the Tejas' survivability during deep penetration and combat. The LCA's EW suite is being developed by the Defence Avionics Research Establishment (DARE) — which was known as the Advanced Systems Integration and Evaluation Organisation (ASIEO) until June 2001 — with support from the Defence Electronics Research Laboratory (DLRL).[8] This EW suite, known as "Mayavi" (Sanskrit: "Magician"), includes a radar warning receiver (RWR), self-protection jammer, laser warning system, missile approach warning system, and chaff/flare dispenser. In the interim, the Indian Defence Ministry has revealed that an unspecified number of EW suites have been purchased from Israel's Elisra for the LCA prototypes.[39]
The ADA claims that a degree of stealth has been designed into the Tejas. Being very small, there is an inherent degree of "visual stealth", but the airframe's use of a high degree of composites (which do not themselves reflect radar waves), a Y-duct inlet which shields the engine compressor face from probing radar waves, and the application of radar-absorbent material (RAM) coatings are intended to minimise its susceptibility to detection and tracking by the radars of enemy fighters, airborne early warning and control (AEW&C) aircraft, active-radar air-to-air missiles (AAM), and surface-to-air missile (SAM) defense systems.
Escape systems
To improve pilot safety during ejection, the Armament Research and Development Establishment (ARDE), Pune, India created a new line-charged canopy severance system, which has been certified by Martin-Baker. This system, which is the first of its kind, can be operated from outside the aircraft, an important consideration when the pilot is trapped or unconscious.
The LCA has anyway been decades into development and is still, to this day, essentially a prototype.
