Where Tejas falls behind
The purpose of this article is to evaluate the wing structure of IAF Tejas LCA, compare it with current 4th generation and beyond aircrafts.
With what information we have in regards with Tejas LCA's airframe diagrams, dimensions of the wings, aerodynamics.
We would keep the subject matter to manoeuvrability as this is one of the most important aspects of any fighter aircraft.
The purpose is not to ridicule but try to understand the reasons behind design decisions taken and to explore the short comings noticed/assumed.
We would compare the wing structure of Tejas with proven top of the line aircrafts.
Please note We are not discussing BVR detection/missiles BrahMos, Atomic bombs etc. so please refrain from off topic posts.
AoA and its importance.
Angle of Attack (AoA α) is the angle between the Vector representing the motion of the body and the aerofoil - represented by Alpha α. In aerodynamics the AoA would be the angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the air/atmosphere. Simply put AoA is an angle at which a wing meets air flow.
Turn:
Turn of an aircraft dictates how manoeuvrable an aircraft is. Turn is achieved by a combination of roll and lift. The faster the roll and better the lift the better turn/turn rate an aircraft achieves.
Generating lift force wing plays the primary role; there are specific ways of creating Lift Force. Air Foil Sections (the shape of a wing or blade) + increase of AoA.. Airfoil section and increased angle of attack. α determines the turn of an aircraft
The prominent feature of all top of the line proven combat – Air superiority and Light Combat Aircrafts is a Leading Edge Extension / Wing Root Glove.
Prominent in F-16, F-15, F-18 Hornet, SU-27, MiG-29, MiG-35, SU-27, SU-30 ..... etc. etc. etc.
Leading Edge Root Extension, Root Glove Extensions
In regards with SU-27 development, the wing root extension in SU-27 and all above mentioned aircrafts played a large part in achieving additional lift, airfoil sections were used in additional parts of the aircraft. A
'Wing Root Glove' / 'Leading Edge Extension' played a large part in creating lift force.
During SU-27 development the designers initially could not see the advantages of the wing root extension and such technical innovation.
The idea with the wing root extensions was to increase aircraft stability at supersonic speeds.
After a number of wind tunnel tests, the true potential of Root Leading edge extension / Wing Root Glove was realized.
Below quoting Georgiy Byushgens - one of the giants of Russian aeronautical engineering.
Georgiy Byushgens
Deputy Director of the Central Hydro-Aerodynamic Institute 1961-1991
Academician of the Russian Academy of Sciences
Hero of Socialist Labour
Lenin Prize Laureate
Laureate of the USSR State Prize.
'If The Wing Root Glove is made pointed – which means if the tip is sharp – a very powerful vortex was induced with this sharp tip. This effect made it possible to increase lift force by at least 50%.'
Pointed Leading edge extension in the root of the wing merging with the fuselage transforms the airflow into a powerful air vortex, this vortex creates a stable vacuum zone above the wing – resulting in deferential pleasure increase and casing additional lift.
With AoA increase the intensity of the vortex above the wings grows – this allows the aircraft to fly at high Angle of Attack without losing stability of stalling into a spin. Thus Directly proportional to
High Manoeuvrability. A combat turn can be performed more vigorously and aggressively – The intensity of the vortex is so great that the vortices can be seen with a naked eye.
On a modern fighter aircraft root glove extension provides important airflow over the wing at high angles of attack, this greatly delays the stall and improves lift. At high angles of attack, as often encountered in a dog fight, the vortex generated by Leading edge root extension/ root glove extension becomes a must for any competent manoeuvrable Dogfighter
IAF Tejas LCA.
So lets have a look at the wing structure of Tejas.
Note that on Tejas the line of the wing from the edge to the root of the wing at fuselage is not straight.
There is no leading edge root extension, rather to compensate the low angle of the overall leading edge of the wing with the fuselage it cuts short and joins the fuselage at a steeper angle.
In modern day design Pure Delta wing is not considered a great design for manoeuvrability.
Looking at modern day Delta wings (cropped deltas) such as the JAS Gripen, the Eurofighter Typhoon and the Dassault Rafale use a combination of canards and a delta wing to counter this specific phenomenon.
So Canards help generate vortex lift over the main wings.
Pure delta-wings fell out of favour somewhat due to their undesirable characteristics, notably flow separation at high angles of attack (swept wings have similar problems), and high drag at low altitudes. This limited them primarily to high-speed, high-altitude interceptor roles.
This fact is further strengthened by the fact that Pure Delta Wing Fighter aircrafts were primarily used as high speed interceptors not light combat manoeuvrable aircrafts. Example being Mirage III Family lightweight, all-weather interceptor capable of climbing fast.
ICAS 2004 study in delta wing and LEX configuration to achieve better AoA.
DELTA WING WITH LEADING EDGE EXTENSION AND PROPELLER PROPULSION FOR FIXED WING MAV
High α on Delta wing with leading edge extension. Better Alpha results.
First Contact:
A very import aspect of aerodynamic design in the wing and leading edge design is construction of first contact surface.
Further up the wing – modifications to the leading edge of the wing would have relatively lesser impact on the lift.
In a canard design the air flow will pass through forward canards first, in case of leading edge root extension the air flow would pass the root extensions of wing first.
Not having a sharper/pointed first contact surface at the leading edge of the wing root combined with Delta wing would cause additional Drag on Tejas.
The wing configuration of Tejas looks more like Reverse Compound Delta
Compound Delta.
The inner part of the wing has a very high sweepback, while the outer part has less sweepback, to create the high-lift vortex in a more controlled fashion, reduce the drag and thereby allow for landing the delta at acceptably slow speed
The wing Design of Tejas is reverse of above where first contact surface of the wing has bigger angle with fuselage than the rest of the wing's leading edge.
This would result in additional drag.
Naval Version:
As per news pieces the only Naval version of Tejas would have leading edge vortex controller to reduce the fighter's required speed on approach to the vessel. This is to compensate for the delta wing limitation in low speed manoeuvrability approaching an aircraft carrier.
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From the above it would appear that Tejas would be subpar when in terms of achieving high AoA.
The choice of wing configuration is different to any of the current top of the line fighter aircrafts, and some aerodynamic features suggest that Tejas might not be best suited for roles where manoeuvrability and agility is paramount.
