QUORA DIARIES: LCA Tejas, A WORTHY SUCCESSOR?

The LCA-Tejas is the replacement for the soviet origin Mig-21 fighter aircrafts, which have been in air for around 70 years with various air-forces across the globe, Indian Air Force being a major customer with considerable numbers still in service. The LCA has hit the production lines and 123 are on order.

But it is still a question if LCA is a worthy successor to the Mig-21? and if the country has gained anything from this or is it just another piece of junk?

This answer shall dig into the above questions.

Content:

1.Role

2.Aerodynamics

3.Stealth

4.Safety

5.How it has helped the country?

ROLE

Mig-21: It was primarily designed and inducted as an Interceptor, Later it was modified as CAS and a airsuperiority fighter.

LCA: Point defense, multi-role fighter.

Inference: The primary job of an interceptor is to gain speed and height quickly and to intercept incoming threats. They are not primarily designed to undertake CAS and Air-superiority fighter roles whereas LCA from the first day was supposed to be a multirole fighter. The design of Mig allows it to travel at very high speeds with degraded performance at low speed where as LCA has a balanced performance in all speed regimes.

  • Little knowledge before going further:
    • Aspect Ratio(AR): Ratio of total lenth of wing(wing span) to Chord
    • Wing loading(WL): It is ratio of gross weight to be carried by wing to area of wing
    • Leading edge/Trailing edge :

  • Anhedral/Dihedral:

  • Chord: Line joining Leading edge to trailing edge
    • AOA: Angle between chord and Wind.

    • Critical AOA: AOA for which lift is maximum or angle after which lift starts decreasing rapidly.

  • Relation of AR with lift:
    • Lift Vs AOA for various AR:
  • Inference :
    • Higher AR will have higher Lift
    • More the AR less will be the Critical AOA.
    • Higher the AR, higher the induced drag

Aerodynamics of Delta Wings:

  • Lift generated by delta wing has two components: Vortex lift+Potential Flow lift (read Lift on a flat plate)

  • At lower angle of attack the lift is only the Potential flow component.(AOA=0*-5*)
  • At higher angle of attacks Vortex are generated by the leading edge, which flow over wing and creates a low pressure region over wing and hence lift is generated.(AOA=5*-20*)

  • At higher AOA the vortex starts getting disturbed and lift is decreased but can be controlled by certain measures.(AOA=20*-30*)

Delta wing shows low lift at low A.O.A because of following reasons:

  • More surface area for given amount of lift causes more viscous drag which decreases Lift/Drag ratio. More the ratio is better the lift.
  • At low AOA the formation of vortex is not uniform or flow separation or due to vortex burst(I oversimplified way too much).
  • Relation of WL with Maneuverability: The less the WL the better and faster will be the roll maneuver.

AERODYNAMICS

  • Wing Type:
    • Mig-21: Pure Cropped Delta with tail.

  • LCA: Cropped Compound tailless delta.
    • Inference: Mig had an extra control surface that added to the drag at high speed regime. Being pure cropped delta has it’s fair share of disadvantages as i mentioned above. Also due to the design the take off speed and distance is more for Mig-21 than Tejas.
  • AR:
    • Mig-21: 2.2
    • LCA: ~1.75(Wing span^2 / wing area)
    • Inference: Mig-21 focuses on more lift whereas LCA for less drag, no one wins in this department all matter of priorities. Trade-offs can’t be avoided.
  • WL:
    • Mig-21: 452
    • LCA: 247
    • Inference: LCA is a clear winner, this makes LCA more maneuverable in combat.
  • Thrust to Weight Ratio:

  • Mig-21: 0.7
    • LCA: 1.07
    • Inference: LCA wins, this gives LCA a better climb rate than Mig-21.
  • Wing Position:
    • Mig-21: -2* dihedral

Its 2 deg annhedral sir

  • LCA: Anhedral:

  • Inference: Anhedral position of delta wings generates extra lift. LCA wins.
  • AOA: This part is tricky.
    • Mig-21:30*
    • LCA:28*
    • Inference: Despite using dihedral swept back cranks LCA has AOA 2* less than Mig-21, but at the same time it is good in terms of existing 4.5 gen aircrafts. The reason for the following can be the pure delta of Mig-21 which are best suited in for high AOA but poor lift at low AOA where as LCA tries to keep the lift enact even at low AOA and low speed, so the reduction of 2* AOA in LCA is a trade-off for a wider flight envelope.

STEALTH

  • Inlet:
    • Mig-21: Inlet cone with Inlet at front of the plane.

  • LCA: Supersonic, Y-duct below and behind the wing.
  • Inference: Mig doesnot gives stealth due to the protruding cone and compressor RCS just visible at the front whre as LCA has two advantage:

    • Stealth by covering the Compressor RCS.
      • Continious suppply of air at high AOA.

  • Material Used:
    • Mig-21: Mostly metal or alluminium alloy
    • LCA: 44% is Carbon composite.
  • Inference: LCA is more lighter, stronger and stealthier.
  • Wing Blending: The Blending of wing with fuselage in LCA does two things:
    • Lower down the RCS.
  • Make fuselage a Lift generating object. This feature is not present in Mig-21.
  • RAM: Extensive use of RAM(Radar Absorbing Materials) decrease the RCS both of body and the Cockpit through canopy.

SAFETY

Needless to say from the day LCA was first flown it had never ever met with an accident, Mig-21 doesnot have a appreciable safety record which has earned it the name of “Flying Coffin”.

How it has helped the country?

  • TECHNOLOGIES DEVELOPED:
    • Airframe and Aerodynamics(including stealth): Completely Indigenous tech, due to this many flight testing wind tunnels from slow speed to supersonic were setup across the nation for which earlier we had to go to western nations or Russia.
  • ENGINE:

A little bit history about the kaveri engine:

  1. The GTRE GTX-35VS Kaveri is a turbofan project developed by the (GTRE), a lab under the DRDO
  2. The Kaveri was originally intended to power production models of the Tejas LCA fighter.
  3. This was approx 202 mn $ project.
  4. Later on the project was divided into two category: K9 and K 10
    1. K9: Will be completely indigenous with only foreign consultation and certification.
    2. K10: Will be a joint venture with a foreign partner.
  5. Problems that occured:
    • Kaveri engine in its present form uses directionally solidified blade technology which is rather an old tech and it couldn’t tolerate the high temperature in its combustion chamber called “Kabini”. The solution was “single crystal blades”
    • The thrust generated was nearly 65 to 70% of what was needed.
    • Performance decay at high altitude.
    • A peculiar noise when in after burning mode..

The MMRCA deal which many think was a bad decision by the current leadership as it just bought 36 rafales. But if we look closely to the offset, it was boon to us as under the offset:

  • Snecma which manufacture the Rafales M-88 core agreed to help and certify the engine in 18 months.
  • DRDO has been given a virtual carte blanche to channelise offsets from the Indian Rafale deal to resurrect the Kaveri.Snecma, a partner in the Rafale programme, builds the Rafale’s twin M88 turbofan engines. Under the terms of the partnership , Snecma is working to modify, certify and integrate the Kaveri on a Light Combat Aircraft airframe before 2020.
  • A later phase in the partnership will involve modifications on the Kaveri for a twin configuration on India’s AMCA fifth generation fighter concept and an altered non-reheat version for the Ghatak UCAV.
  • According to DRDO chief the kaveri engine will be ready by next aero india.
  • Another good news is that altitude test and flying test bed trials have been completed. Official statement of MoD in Parliament” In a written reply to the Lok Sabha in December 2016, Minister of State for Defence Subhash Bhamre had called the effort of the GTRE in developing the engine as “an attempt to mastering one of the most complex technologies”. The minister said the altitude test and flying test bed trials for the engine had been completed and other developmental problems were being addressed to make the engine flight-worthy through in-house efforts as well with assistance from abroad”.
  • The engine will be first used on Tejas PV-1.Other uses will be
    • Ghatak UCAV(Dry variant or w/o afterburner)
  • AMCA
  • Tejas Mk2
  • Also, Rolls royce has collaborated with DRDO on developing the K10 engine. This engine’s first prototype is to be expected in 12 month. The news was broken out in Aero-india 2017 in february.
  • http://www.thehindu.com/news/national/india-uk-to-collaborate-on-engine-technology/article17993132.ece
  • UK’s Rolls Royce, India’s DRDO working together on engine for fighter jets

AVIONICS

  • Indigenous HUD.
  • EW suite for Tejas is under developement for LCA but since it is small it has to be compact other than that Tusker EW suite is the bigger derivative of the suite Mayavi EW for LCA and is used for Mig-29, jaguar and Su-30. Samyukta is also another EW suite that has used the experience from past developement of Mayavi and tusker EW.
  • Early version of tejas (PVs) had analog display now they fly on Digital display designed by DARE(DRDO).
  • Also DARE has developed the litening targetting pod for effective targetting of air version of brahmos.
  • It’s HMD is ELBIT designed, but its friend and foe detection is designed by DRDO.
  • UTTAM AESA (Further updates:Soikot Banerjee’s answer to Is India developing/working on AESA radars?)radar has given rise to many other forms of AESA radar such as that used on swordfish radar, AEW&C, recently successfully launched QRSAM.

CONTRIBUTION TO COUNTRY/INDUSTRY

  1. Private sector giants especially TATA SED and L&T have gained a lot of experience in electronics and manufacturing respectively.
  2. It has created a chain of MSMEs.
  3. Almost entire fuselage which includes wings, center of fuselage is made by private companies and HAL is only a integrator.

AMOUNT OF RESOURCE

  1. Tejas is the cheapest 4.5 gen aircraft programme ever with $1 bn spent on programme, whereas Gripen is 14 bn$ programme and F-16 even more.
  2. Tejas has never ever faced an accident whereas its competitor Grippen has faced Two accidents. So no wastage of resource.

CONCLUSION

Given the amount of experience by spending the least amount of money compared to any fighter jet programme as shown by above facts and two failed attempts to develop or continue to develop fighter jets, TEJAS LCA IS A SUCCESS AND A TRUE SUCCESSOR OF Mig-21. In terms of some performance parameters LCA may lack compared to it’s predecessor but that’s okay in terms of what useful extra stuff it has packed in it compared to the Mig-21.

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