Tejas: thoughts on an unusual wing
Tejas
The pictures shown earlier reveal that in making its recent arrested landing, Tejas was using an upward deflected LEVCON. This innovation makes a lot of sense for Tejas, because, as a pure delta with no balancing tail or canard surface, a conventional slat-and-flap high lift system cannot be used.
Moreover, the large upward deflection of the LEVCON will force the development of the leading-edge vortices, and the associated increase in lift, to occur at low incidence, allowing the view over the nose of the aircraft to be maintained for the approach to landing. Because the additional lift is developed over the whole length of the wing, it is likely that the pitching moment generated is less than would have been seen with a conventional system, and, on the approach, might even require a small droop of the trailing edge surfaces, which would also increase lift.
The only photographs I have seen of Tejas with LEVCON deployed are for the naval variant. The ski jump trials were conducted with the LEVCON more or less in line with the wing, increasing lift slightly, but with little effect on drag, whereas the recent arrested landing with upward deployed LEVCON would have generated significant lift and drag.
Subsequent development of the aircraft may see LEVCON integrated into the control system to improve manoeuvre capability for both variants, but whether this will be implemented remains to be seen.
Tejas is indeed an interesting little aircraft, and, in my view, is the first carrier aircraft to use a pure delta planform. I recognise that some might disagree with this, pointing to the Douglas F4D Skyray as having this distinction. In the Skyray, however, the landing approach speed problem was resolved using slats on the outboard wing, and large triangular trimming tail surfaces, forming the junction between the wing trailing edge and the fuselage, to cope with the slat-induced pitching moment. The Skyray was aerodynamically, in effect, a tailed-delta rather than pure delta.