The maiden arrested recovery of the LCA Navy Mk.1/NP-2 technology demonstrator on board INS Vikramaditya on January 11, 2020 and its following maiden takeoff a day later marked the attainment of a crucial milestone in the Indian Navy’s (IN) developmental process for obtaining a homegrown carrier-based multi-role combat aircraft (MRCA) solution. It may be recalled that Phase-1 of full-scale engineering development (FSED-1) for the LCA (Navy) technology demonstration project was sanctioned in March 2003 by the Government of India with grant-in-aid seed funding of Rs.949 crore and a planned completion date of December 2009. The IN contributed 40% of the development cost, with the rest being put up by the Defence Research & Development Organisation (DRDO), which controls the Aeronautical Development Agency (ADA)—designer and developer of the LCA family of L-MRCAs. The objective then was to develop a naval carrier-borne MRCA capable of Ski-Jump Takeoff with Arrested Recovery for landing (STOBAR concept). It was initially envisaged that converting the already flying Tejas Mk.1 to a naval aircraft would take about six to seven years, with structural changes restricted to about 15%. The two naval prototypes sanctioned were to be used primarily to demonstrate Carrier Compatibility and also to demonstrate Initial Operational Capability with air-defence configuration. However, contrary to initial assumptions, during the aircraft design and development phase, it turned out to be significantly different from the time of sanction in 2003 and challenges increased progressively. Further, the major constraint of design space due to the existing Tejas platform resulted in a sub-optimal design and compromises leading to the LCA Navy Mk-1 variant (NP-1) being heavier than anticipated. Consequently, Navy LCA (NLCA) Mk2 design powered by a higher-thrust turbofan was taken up in the FSED-II stage of the project, which was sanctioned in December 2009. However, by 2014, the IN realised that even the NLCA Mk.2 would have shortfalls in the full-mission capabilities.
This realisation had dawned after the IN had done a comprehensive assessment of flight operations with its twin-engined MiG-29Ks from the STOBAR flight-deck of INS Vikramaditya. To fully understand the assessment, one must first understand what distinguishes land-based flight operations from carrier-based flight-operations, plus the difference between STOBAR and CATOBAR flight-deck designs. Usually, there are three parameters relating to the takeoff of any type of shore-based aircraft: 1) thrust-weight ratio, 2) rolling distance, 3) the minimum liftoff safety speed. When an aircraft attains a certain rolling distance (usually much longer than the length of an aircraft carrier’s deck) at an acceleration produced by its thrust-weight ratio for takeoff, it reaches the minimum lift-off safety speed. Upon reaching this, the lift force of the aircraft is equal to the weight of the aircraft, and then the aircraft lifts off. So the lift force of an aircraft is proportional to the square of its speed. If the aircraft slides at acceleration for a distance which is shorter than the runway length when it takes off and fails to reach the minimum safety lift-off speed, the lift force produced by the aircraft’s wings will be less than the weight of the aircraft, so it cannot lift off. The landing, on the other hand, is accomplished in five stages: (1) glide; (2) flatten (when the wheel is 2 metres above the ground, throttle back to the idle speed, reduce the glide angle, and exit glide state at the height of 0.5 metres); (3) level flight at a deceleration (minimum level flight speed); (4) fall to touch down (at this moment, the aircraft’s speed is decreased to an extent that the lift force is no longer enough to balance the aircraft’s weight); (5) roll to land (under the action of wheel friction and air resistance etc, rolling at a deceleration until it halls).
When it comes to carrier-based aviation, due to the limited length of the flight deck of the aircraft carrier, there are mainly three take-off options for carrier-based aircraft: vertical takeoff (namely the vertical/short-range rolling takeoff), ski-jump take-off (or called sliding-tilted takeoff), and ejection takeoff (such as steam ejection takeoff, electromagnetic rail-launch ejection takeoff). For ski-jump takeoff, the aircraft first rolls at acceleration on the runway of the flight deck of an aircraft carrier only depending on its own power, then it leaps into the air through the upswept deck on the front part of the aircraft carrier, and then takes off. The principle is that the upswept angle of the deck (14 degrees) is regarded as the ejection angle, although the aircraft has not yet reached the takeoff speed when it rolls and leaves the aircraft carrier. The landing on an aircraft carrier is achieved by gliding to directly hook the arresting cable on the aircraft carrier (without the above stages of level flight at a deceleration, etc). A total of 3 or 4 arresting cables are installed on the canted deck of the aircraft carrier, in which the first one is arranged apart from the aft by 60 metres, and the remaining ones are arranged at an interval of 6 metres or 14 metres. The height of the arresting cable is 50 centimetres above the deck surface. The aircraft glides from upper right of the stern of the aircraft carrier, which is travelling rapidly, hooks the arresting cable with the tailhook, and then rolls on the deck within 100 metres to brake. The statistics show that 80% of aircraft accidents on board aircraft carriers occur in the course of touching down on to the top-deck but not in the air. The factors attributing to a complicated, difficult and risky landing process for the aircraft include: 1) short on-deck runway; aircraft carrier is limited in length, and the section for the carrier aircraft to land is more limited, while the length of landing area on the aircraft carrier is relevant to the safety in landing of the carrier-borne MRCA; 2) high landing speed; in the existing technology, when directly gliding to touch down onto the flight-deck, the MRCA does not throttle back to decelerate, but requires an appropriate force, so that it can immediately undertake a Bolter in case the tailhook misses all the arresting cables; 3) the accuracy requirement for pre-determined landing point is strict; for the accuracy of the landing point, none of longitudinal, lateral and height errors can be large, otherwise the MRCA may not hook the arresting cable, or may land on the aft or on the right side of the flight-deck, while the MRCA needs to, during gliding at high speed, finish hitting the landing position on the moving flight-deck; 4) control of the gliding angle (between 3.5% and 4%); 5) alignment with the centreline of the runway, because an alignment is more important than the gliding angle. Since the runway of the aircraft carrier is very narrow, if the aircraft deviates to the right, it may hit the superstructure (island) of the aircraft carrier, and if the aircraft deviates to the left, it may hit other aircraft on the parking apron. So during the landing stage, the MRCA should fly (glide) in a vertical plane where the centreline of the runway is located. However, the centreline of the canted deck-runway used for landing is not consistent with the heading direction of aircraft carriers, and presents an angle of between 6 degrees and 13 degrees (namely the canted deck and the longitudinal axis of the aircraft carrier form an angle of 6 degrees and 13 degrees). Such a design aims to allow the MRCA to roll after landing so as to avoid other deck-based MRCAs that are awaiting takeoff at the front portion of the flight-deck.
When a carrier-based MRCA takes off from a curved STOBAR deck it suddenly jumps into free air. The objective is to approximately reach the suitable speed and AoA at the end of the ski-jump, without exactly respecting the MRCA’s lift-to-weight equilibrium. It may well be in an infra-lift condition, but the overall strategy aims at keeping the longitudinal acceleration by maintaining engine thrust, and giving full control to the pilot who, until this moment has hardly intervened in the manoeuvre. An acceptable aircraft-vessel compatibility matching implies that the flight speed will reach a minimum value to sustain level flight before the aircraft altitude over the sea crosses below a certain safety threshold. The thrust-to-weight ratio at take-off must thus be appropriately matched to the available deck length and the ski-jump geometry, including wind-on-deck effects. The approach speed must be compatible with wind-on-deck and the available landing distance to completely stop the MRCA after engaging the last arrestor-cable. And lastly, the thrust-to-weight ratio at approach must be high enough as to allow fast acceleration and safe liftoff (Bolter) should the aircraft hook failing engaging the arresting pendants.
A twin-engined naval MRCA operating from a STOBAR flight-deck can at best only take off with half-load (of either fuel or weapons payload), and the engine is in the state of thrust augmentation at the time of takeoff, thus shortening the aircraft’s service-life. The MRCA is also required to be added with some structural weights, such as increasing the wing area, just in order to improve the lift force for realising the ski-jump takeoff. The takeoff weight and takeoff efficiency of takeoffs from STOBAR flight-decks are thus less than that of the ejection takeoff, and the combat efficiency is thus poorer than that of the MRCA taking off from a CATOBAR flight-deck. The STOBAR flight-deck design thus limits MRCA takeoff weight and shifts the full burden of takeoff propulsion onto the aircraft, thus increasing the amount of fuel consumed at that stage. This in turn restricts the fuel and weapons payload that the MRCA can carry, thereby reducing its range, loitering time, and strike capabilities. STOBAR is also more affected by wind, tide, rolling, and pitching. Furthermore, it needs more flight-deck space for takeoff and landing, thus limiting the parking space and having an adverse effect on takeoff frequency–based crisis reaction. For instance, on all existing STOBAR aircraft carriers (Project 11430 INS Vikramaditya, Project 1143.5 Kuznetsov and the two PLA Navy vessels CV-16 Liaoning and CV-17 Shandong) there are two types of runway lengths—the shorter 115-metre one in a right-to-left orientation for launching MRCAs with greatly reduced weapons/fuel loads; and the longer 180-metre one in left-to-right orientation for launching MRCAs with greater but not maximum weapons/fuel loads.
In comparison, the CATOBAR design, which is mostly associated with large carriers, minimises aircraft fuel consumption on takeoff, thus enabling better payload, range, loitering time, and strike capability. Its runway requirement is also minimal, thus allowing more flight-deck parking and faster launches, even simultaneous launch and recovery, resulting in quicker crisis response. Lastly, unlike STOBAR flight-decks, CATOBAR flight-decks can also launch heavier fixed-wing AEW and ASW aircraft.
NLCA Developmental Milestones
The LCA (Navy) programme has involved development of the NP-1 tandem-seat operational conversion trainer and NP-2 single-seat multi-role combat aircraft, one structural test specimen for fatigue-testing, creation of Navy-specific flight-test facilities in Bengaluru and Goa, construction of a shore-based flight-test facility or SBTF at INS Hansa in Goa (for enabling arrested landing recovery, plus takeoff from a half-metal half-concrete 14-degree ski ramp and a flight deck ranging from 195 metres to 204 metres in length, and validating the simulation model for flight performance within ship-motion limits, validating the flight controls’ strategy with all-up weight and asymmetric loading, validating the load analysis methodology), and flight-tests/flight certification for aircraft carrier-based flight operations. The SBTF also has its integral flight-test centre equipped with line-of-sight telemetry/high-speed three-axis photogrammetric systems, systems for validating thrust measurement algorithms, systems for measuring wind-flow patterns, INS/DGPS-based trajectory measurement systems, RGS integration facility, plus a workshop.
To date, the LCA Navy Mk.1 has demonstrated the following IN-specific technologies while operating from the SBTF: supersonic flight; takeoffs from the Ski-Jump was successfully demonstrated, including 12 Ski-Jumps when armed with R-73E SRAAMs missiles, plus night-time Ski Jumps; hot-refuelling; flying of 3-hour duration achieved in one sortie; in-flight jettisoning; Integration of AHS with the NP-2 airframe; and the development of a weight-optimised telescopic landing gear for high sink-rate landing with the help of consultancy from Airbus Military. In addition, a naval standard Structural Test Specimen (STS) has been built and integrated with the Main Airframe Structural Test (MAST) rig to test horizontal and vertical loads during a deck recovery, including 7.1 metre/ssecond sink rate and a 45-tonne load on an arrester wire. Compared to the Tejas Mk1, the LCA (Navy) Mk1/NP-2 is a technology demonstrator that features a drooped nose section, strengthened airframe structure, twin leading-edge vortex control surfaces or LEVCONS (for attaining lower approach speeds), main landing gear with higher sink-rate, increased internal fuel capacity, a Navy-specific avionics suite (including the locally developed autopilot and auto-throttle) and weapons package, and an arrester hook. The NP-2 is now being subjected to a carrier-based flight-test regime on board INS Vikramaditya, where seaborne wind conditions winds-on-deck envelopes (especially ship motion, cross-winds and high wind-on-deck speeds) are far more favourable than those around the SBTF. Integration with carrier-based support and weaponisation facilities, plus jettisioning of ventral stores, thrust data validation, and attaining hands-free and non-disorienting takeoff with supplied HUD symbology formats and high AoA are being demonstrated and validated in this phase of flight-tests. Incidentally, since the IN is involved for the very first time in its history with developing a carrier-based MRCA, it is resigned to the possibility of the NP-2 technology demonstrator ‘breaking up’ while in the process of subjecting the aircrafts’ main landing gears to arrested recoveries at sea. It must be noted here that the undercarriages of carrier-based aircraft collapse or break-up is not due to compression, but due to suspension.
Of utmost importance during the Carrier Compatibility Trials (CCT) are the data-points to be obtained for validating the flight-control logic during the NP-2’s carrier-borne flight operations. This in turn will help in the optimisation of the flight-control logic by the National Control Law Team (that comprises talents from FMCD, ADA, CAIR, and HAL and operating from the premises of NAL’s Flight Mechanics & Control Division, or FMCD). Data-points pertaining to boundary-limiting, automatic low-speed recovery, carefree manoeuvring, autopilot functionality (that supports hands-free takeoff mode , altitude and flight path select & hold mode, as well as auto level off features with both horizontal and vertical navigation modes) will be the most crucial. In addition, the service-life of the Arrestor Hook System (AHS)—designed and built by HAL’s Aircraft Research & Design Centre (ARDC)—too will be determined during the ongoing CCT. After having verified in-air operation of the AHS in Bengaluru on July 23, 2018, NP-2 fitted with the AHS has been operating from INS Hansa Goa, since July 28, 2018.
Due to limited area in deck landing zone and the demand for bolting and go-around, carrier-based MRCAs usually land on deck via impact method under high sinking speed and high engaging speed along a fixed glide-path angle. The impact load, braking load of arresting cable, and other loads at the moment when the MRCA touches the flight-deck put forward higher requirements for design and analysis of landing gears and airframe structure, especially for the structures closely related to landing. Gas-oil leakage in the shock absorber of any carrier-based MRCA’s landing gear is a frequent and common failure, which can deteriorate the absorbing performance. Since shock absorber performance varies with different gas-oil ratio caused by gas-oil leakage, this will be another crucial area of data-point assessment. Since the NP-2’s nose landing gear is comprised of the shock strut, drag brace, launch bar and power unit, all these major structural elements will be subjected to gruelling usage in order to determine their maximum operating limits. Presently, the landing gear assemblies of all fourth-generation naval MRCAs are built from Aermet 100 high-strength non-stainless steel, which is known for its damage tolerance and resistance to crack growth. However, this alloy is highly susceptible to both corrosion and hydrogen embrittlement, which can lead to stress corrosion cracking (SSC). This sensitivity makes SSC the primary failure mechanism for landing gear—a failure that often causes significant collateral damage to the aircraft, even though the failure usually takes place while it is parked. As a result, a number of aircraft components, such as landing gears, require a costly cadmium coating process to protect against corrosion. Cadmium, a known carcinogen, represents significant environmental risks in both primary manufacture and at MRO facilities. Eliminating this coating process thus has a tremendous potential for reducing long-term maintenance costs and eliminating environmentally hazardous processes. The US Navy is now experimenting with Ferrium S53 steel that provides much greater resistance to general corrosion and to SCC; excellent resistance to fatigue and to corrosion fatigue; and high hardenability. Its resistance to general corrosion is similar to that of 440C stainless steel, but it has much greater fracture toughness.
Next, a US Navy Carrier Suitability Test Team will audit all the data-points obtained from the CCT and its experience in developing and maintaining carrier-borne MRCAs will be most useful, since the IN wants to replicate almost all those flight-safety-related features that are now finding their way on board all US Navy carrier-based MRCAs. One such feature is the US Navy’s latest Maritime Augmented Guidance with Integrated Controls for Carrier Approach and Recovery Precision Enabling Technologies (MAGIC CARPET), a software package that makes a carrier approach nearly as routine as a runway landing. The system works with the carrier-based aircraft’s autopilot to maintain the approach using ‘direct lift control’. In other words, once the pilot sets the glide angle of the approach, it becomes the ‘neutral’ setting for the controls. The autopilot then tracks the position of the flight-deck, adjusting the throttle, flaps, ailerons, and stabilisers to keep the flight path and AoA on point. Instead of maintaining continuous pressure on the stick and making myriad inputs before landing, the pilot can instead relax. Any adjustments he/she does make are incorporated into the autopilot settings. However, the system is not fully automated, and pilots remain in control. MAGIC CARPET just simplifies the descent. And because it augments existing flight-control systems, it does not require hardware modifications. Pilots typically perform 300 corrections to their flight-path in the final 18 seconds of an approach. MAGIC CARPET drops that between 10 and 20. Beyond reducing stress, MAGIC CARPET also minimises the time and effort needed to train pilots for carrier deck landings, thereby allowing more time for tactical training. It also reduces the time and money spent on manoeuvring aircraft carriers into ideal landing positions. Lastly, the fewer aborted landings saves fuel, and fewer hard landings saves wear-and-tear on aircraft.
NLCA Timeline
July 6, 2010:The first NP-1 prototype is rolled out.
April 27 2012:NP-1 makes its maiden flight, nine years from the sanction of the programme.
2013: SBTF is built by Goa Shipyard Ltd along with the construction arm of DRDO CCER & D (W) Pune. Restraining Gear System (RGS) installation also successfully completed.
December 19, 2014:NP-1 takes off from the SBTF for the first time, piloted by the IN’s Chief Test Pilot Cmde Jaideep Maolankar of the National Flight Test Centre (NFTC). It was planned to have a minimum climb angle of 5.7 degrees for the first launch. However, there was an unexpected bonus in terms of excess performance and the actual minimum climb angle was in excess of 10 degrees. The AoA after ramp exit reached 21.6 degrees.
February 7, 2015:NP-2 prototype takes to the skies in Bengaluru, flown by Captain Shivnath Dahiya from the NFTC, who ensures that the 35-minute maiden sortie is smooth. NP-2 has been customised (plug & play) to incrementally accept modifications for landing aids like LEVCON Air Data Computer, Auto-Throttle, and internal/external AoA lights. NP-2 is the lead aircraft for AHS integration.
January 24, 2017: The IN releases a RFI for procurement of approximately 57 multi-role carrier-borne fighters (MRCBF) for its future aircraft carriers.
December 2, 2017:Then Chief of the Naval Staff Admiral Sunil Lanba states that the IN is scouting for another carrier operations-compatible MRCA besides the MiG-29K, since both the existing NLCA Mk.1 and the projected NLCA Mk.2 lack the payload required to be effective when operating from an aircraft carrier.
September 19, 2018:NP-1 takes off from the Ski-Jump and then makes an arrested landing at the SBTF in INS Hansa, Goa. The same day, NP-2 accomplishes the same feat.
October 19, 2019: At the Indian Defence & Aerospace Summit, Chief of the Naval Staff Admiral Karambir Singh reveals that the IN wants ADA to develop a Twin-Engine Deck-Based Fighter (TED-BF) with MTOW of 25 tonnes.
