How the LCA is Different

[Zarvan]

by Sitaramarao Yechuri

If you look at the fighter jets used by the USA, Russia, France, the EU etc. you will notice that the shapes of the F-16, F-18, Su-30, MiG-29, MiG-21, Rafale, EuroFighter, Gripen and India’s LCA are all different. Common sense tells you that the designers of these aircraft did not actually believe that their design was necessarily the best fighter jet, instead they were responding to the needs of the airforce at the time and the constraints of the project that they were given. So essentially each country looks at the airpower of their enemy and then designs an aircraft to best take on the challenge. The cold war of course gave rise to most beautiful aircraft of the time, however even today the combat aircraft are still evolving because of new materials, and because of new challenges and new focus of the airforces of the world.

The aircraft with the largest number used by the Indian Air Force was the Soviet MiG-21 and so when the LCA was designed, it was meant to replace the MiG-21 when it retired. First produced in 1959 the MiG-21 has a small delta wing of only 250 square ft and a tail and it managed to achieve Mach 2 speed using a single engine of 70 kN. The MiG-21 was a classic produced in huge numbers. (As an aside the MiG-21 also had a feature you don’t see anymore, the use of a movable nose cone adjusting the air intake as a function of speed).

Now, the French Mirage 2000 which also India purchased (though not in large numbers) was introduced in 1982 and it also used a delta wing but had no tail, instead it had two very small fixed canards just in front of and above the wings. The Mirage 2000 had a much larger wing area of 441 square ft and although it weighs less than the MiG-21 it requires a larger 95 kN engine to achieve Mach 2.2 speed. The best example of the use of canards and no tail was in the earlier 1971 Swedish Viggen which had even larger 500 square ft wing area and needed an even larger 125 kN to achieve Mach 2.1 speed.

So if you compare the MiG-21 and the Mirage 2000 you see that the MiG-21 used a small delta wing area at 57° and has a tail, the more modern Mirage 2000 has no tail but requires a larger delta wing area at 58° and has very small and fixed canards which are nevertheless effective to improve airflow over the top of the delta wing. The Mirage 2000 has low-negative stability and it depends on the computer to control angle of attack, thus the pilot cedes some control to the computer but the Mirage 2000 is more maneuverable as a result. In general the delta wing is synonymous with high speed performance in a straight line but is known to have control problems at low speeds and thus even modern combat jets with delta wing use either a tail or canards. See for example, the single engine Gripen has delta wing and canards but no tail whereas the single engine F-16 has cropped-delta wing and a tail but no canards.

Now, the LCA weighs even less than the Mirage 2000, and uses a compound delta wing and appears to be unique among the combat fighters in that it has neither a tail nor canards. Like the Mirage 2000 it too has low-negative stability and depends on the computer to control angle of attack and is highly maneuverable. The wing area of the LCA is slightly smaller at 413 square ft than the Mirage 2000, and it’s engine is also smaller at 90 kN than the Mirage 2000, the length is shorter by about 4 ft. Larger angle of a delta wing tends to make the airplane go faster, and when a compound delta wing is used the inner part usually has a larger angle however the compound delta wing of the LCA uses a 50° and 62.5° angles and this seems to have reduced the top speed so that the LCA achieves Mach 1.6-1.8 speed. Perhaps the LCA designers chose these angles to allow safer landing in the absence of canards.

Luckily the LCA has room to grow because it is smaller and lighter than the Gripen, so maybe future generations of the LCA can include canards i.e. the LCA can grow in length and wingspan, the compound delta wing can adjust the angles for faster speed and the canards will give more control surfaces. Adding canards will almost definitely make the computer control a lot more complex because now the computer would have to control the angle of more control surfaces in tandem, so there is no question that adding canards is a big upgrade. But it seems clear that India should invest some money to allow the LCA designers a research budget to investigate not only enlarging the LCA but also to create different variants of the LCA design, for example the naval version will already be different than the land based LCA. Any money for investigating how to add canards to the LCA is money well spent because the LCA has to slowly become larger to handle bigger tasks as needed by the Air Force.

How the LCA is Different