To prove that this was no flash in the pan, the same exercise was repeated multiple times over the next few days, culminating in what was probably an even more complete demonstration of the rapid progress that this programme has made in recent months. On 29th of the same month, the other LCA (Navy) prototype, NP-2 demonstrated a complete cycle of the core essential of aircraft carrier operations by launching off the ski jump and ‘trapping’ at the arresting gear site.

Of course, none of this happened by chance; in fact, quite to the contrary. Major achievements in aeronautics are often undertaken in a manner akin to climbing a formidable mountain. To ensure success, the ultimate achievement is broken into essential elements which are then tested and resolved in isolation. Only after all the different aspects are understood – and readiness for each has been convincingly demonstrated – is the final climb to the summit attempted. Being an absolutely pioneering effort in India, the ADA/NFTC design and testing teams have had to explore multiple hardware configurations and software concepts in the quest for the LCA (Navy)’s configuration, making it capable of STOBAR operations.

In the current analogy, such a major mountain was the LCA’s ‘arrested landing’, the launches of the ski ramp at Dabolim having already been demonstrated earlier. The landing exercise had to be broken into three major aspects of ‘Loads’, ‘Handling Qualities’ and ‘Performance’. Underpinning all these were a series of flight test concepts, aimed at achieving safety and efficiency in this exploration venture.

Brutality of an arrested landing

The structural brutality of an arrested landing is easily visualised – but little understood. This emanates largely from the very small flight decks that can be made available for aircraft flight operations. It is ironic that while Navies spare no effort to describe their carriers in terms like ‘Leviathan’ and ‘Colossus’, only a tailhook aviator can truly understand that even the largest of aircraft carriers do not afford him the luxury of a flared landing with its highly inaccurate touchdown scatter. A significantly steeper approach angle and unflared touch down are essential, which, coupled with the ship’s pitch and heave motions, results in a typical touch down at descent rates approaching 8-900 feet per minute (fpm) and could be as extreme as 1500 fpm. To this, one must add the deceleration forces generated by the arrestor hook. Even for an aircraft such as the LCA (Navy), these forces can be as high as 45 tons equivalent, radiating forwards through the black and white striped shank of the hook, to be progressively absorbed by the whole structure of the aircraft and of each component attached to it.





The ability of the aircraft to withstand these forces was therefore explored by isolating the vertical and horizontal loads. Vertical loads were explored by way of un-flared touch – and – go type landings, with sink rates gradually incremented in precise steps (often as small as 50 fpm). The LCA (Navy) has currently been tested up to 1100 fpm as one should discount the ship’s heave/pitch when operating on land.

Horizontal deceleration loads were explored by taxi-in arrestments at progressively increasing speeds. Variations in aircraft weight, engine thrust and arrestor gear settings were also conducted to clear the full envelope of expected loads up to the maximum arresting gear limit of 140 knots.





The LCA (Navy) stood up remarkably well to the loads imposed which were necessarily higher, individually, than those expected in the initial arrested landings. None of the expected problems like broken pipelines or blunt force butting of various parts was encountered. Not surprisingly however, several iterations were necessary to prepare the aircraft for a full-fledged arrested landing.





Amongst the first “problems” encountered at this stage were elements pertaining to the flight test instrumentation which apparently showed higher than expected loads (until these were analysed as an artefact of the sensor locations and orientations themselves). However, dynamic responses of the aircraft to arrestment with the nose wheel raised off the deck, indicated that the nose oleo was underdamped which caused nearly full stroke compression when the aircraft was de-rotated by the arrestment loads.





The hook itself needed several iterations to enable it to perform its unenviable task. These included reinforcement of the hook shank, deletion of the detachable wear plate, reduction in the trailing angle to reduce the time interval between wire pick up and main wheel touchdown - and of course at least three different variants of flight test sensor installations, not surprisingly as these were located at the exact point of origin of these smashing loads. Another major iteration was the need to provide additional room for hook swing up after it picked up the wire. Currently, the LCA (Navy) is operating with a ‘notch’ cut into the engine bay door to accommodate this extra swing.









Probably the most important lesson learnt during this test phase was that a “conservative” design does not necessarily generate additional safety. In the case of the nose oleo, the design case was for a virtually impossible three point landing at 1400 fpm. It emerged that typical landings at much lower sink rates were actually likely to be more stressful, requiring a large amount of energy to be absorbed. Notwithstanding increments to the nose oleo damping, it has, quite counter-intuitively, bred a much healthier respect for the avoidance of low sink rate arrestments as opposed to the slam-bam of a high sink rate landing!

The handling

The other obvious constraint imposed by an aircraft carrier environment is the need for extremely precision control of the aircraft. Accuracy in achieving of the touchdown point is quite obvious given limited confines of the flight deck. However, the need for precision extends far beyond that. Accurate touchdowns have to be achieved while maintaining equally precise control of the speed (to control deceleration loads), slope (to control loads due to high sink rate and dynamics arising out of low sink rates and, of course, to avoid that dreaded ‘ramp strike’) as also lateral displacement/azimuth (to prevent excursion from the safe landing area). Achievement of the required precision is as much a matter of skill as it is of proper design of the flight control software. While much of the macho swagger of the ‘tail hookers’ is based on possession of these heightened piloting faculties, being skill dependent results in a wider scatter in landing parameters. This, in turn, forces the designers to cater for more aggravated mis-landing cases.

In case of the LCA (Navy), the advanced skills gained by ADA in digital flight controls offered a unique opportunity to attempt unraveling of this knotty problem. A unique control strategy has been implemented by the ‘handling qualities brotherhood’ of control systems engineers and test pilots, which results in nearly halving the workload of piloting. This has been achieved by relieving the pilot from the task of controlling speed/angle of attack and also improving behaviour of the aircraft during lateral corrections and turbulence. Results of these endeavours have been outstanding, with many landings conducted to date being within just 1-2 knots of the limit speeds of the arresting gear itself. Arrestments have been confidently conducted in fairly severe crosswinds and even in extremely light surface wind conditions. The touchdown sink rate has also proven to be extremely well controlled. While the current LCA (Navy) has been designed without benefit of the enhanced accuracies achieved, future designs would surely be able to exploit these capabilities to reduce design margins and thereby achieve more efficient operational results.

The performance itself

Approach speeds are the single most critical parameter which drive the essential design of a carrier-based aircraft. Higher speeds necessarily result in higher landing loads which in turn require stronger and heavier structures to cope, which results in further increases in approach speeds thereby causing a vicious weight spiral. The key is to achieve high lift for approach while still permitting the desired optimisation at tactically relevant conditions. The LCA (Navy) has attempted to do this via the Leading Edge Vortex Controller device (LEVCON) which is deflected upwards to further destabilise the aircraft at approach speeds, controlled by drooping the elevons, effectively resulting in a more cambered, higher-lift wing profile. Several aerodynamic iterations (including different slat configurations and approach angles of attack) had to be explored to arrive at a suitable combination that yielded an acceptable approach speed. At the same time, precision on control had to be maintained. All these iterations, in combination with the enhanced precision of speed control, have resulted in an ability to cope with extremely low headwinds encountered at the SBTF, which will certainly pay rich dividends when operating afloat owing to the much stronger winds on deck generated on an aircraft carrier.

Carrier suitability flight tests

Conduct of the activities described thus far necessitated the development of an entirely new branch of flight tests for assessing the Type’s carrier suitability. As in all such endeavours, achievement of safe and efficient flight testing requires a combination of investments in test facilities, test crew and a clear concept of comprehensive testing.





