PARIKRAMA
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Well MKI uses 3D thrust vectoring. 3D thrust vectoring allow to deflect the thrust in both pitch and yaw whereas 2D uses only two straight vanes above and below the jet exhaust, which will create only pitch movements (no yaw).
Of course 3D TVC helps the jet a lot but if its a stealthy airframe 2D TVC is preferred owing to the fact that when the aircraft starts making Yaw movement too, the probability of detection increases significantly owing to bouncing of waves from all angles.
It is also to be noted 3D TVC is not an absolute requirement .. if we use conventional control systems via on wings and tail, then aerodynamic control surfaces takes space and additional loads are induced on the airframe. Space in wings is already a constraint owing to installation of wing flaps. Tails planes is a factor of drag inducement and cost for maneuverability and stability.
TVC OTOH adds weight, cost and complexity to the aircraft maintenance and operations. The good news is there is no penalty of drag but then its usage is basically proportional to thrust of the engine and desired Maneuverability. But bad news is also there..
Here is a good explanation
Is 3D thrust vectoring, like that found on advanced MiG-29 and Su-27 variants, the threat some say it is when it comes to the within visual range fight?
First, a little thrust vectoring history. The USAF tested a 3D nozzle on the Multi-Axis Thrust Vectored F-16 in the early 1990s. It was found that thrust vectoring was really only useful at speeds below 250 knots (with the F-16; the speed will vary with other jets). Above that speed the jet had enough g available and was maneuverable enough that thrust vectoring didn't add anything. Also, at high speeds, if the nozzles start to swing the jet violently around you're apt to induce unacceptable loads on the airframe.
Thrust vectoring, whether 2D or 3D, is a two-edged sword. If you're going to use it, you'd better kill me now. Ever seen videos of the Super Flanker spinning around like a top and doing back flips at an airshow? First off, the jet is slow – not a place to be in a multi-bogey environment. Second, when thrust is steered off-axis the axial component of thrust is decreased. Axial thrust pushes the jet (and wing) through the air at a speed required to maintain lift. Take away forward thrust, take away speed and lift. Go back to the videos. What's happening? The Flanker is dropping like a rock at slow speed (no lift is being produced by the wing). If the Flanker pilot does not kill me now, the other edge of the sword is about to fall. He's automatically building in vertical turning room for me and it's going to take an unacceptable amount of time for him to get enough smash back to take it away due to his low airspeed. If I'm still alive I'm turning him into a strafe rag.
I flew enough BFM against the Raptor before I retired where the new Raptor pilots were discovering there's a time for thrust vectoring and there's a time to leave that club in the bag.
How To Win In A Dogfight: Stories From A Pilot Who Flew F-16s And MiGs
When we induce additional loads on the airframe and on top the TVC module is an added weight and maintenance issues, we are going to increase time in hanger between sorties for checks and also a cost part in maintenance. Also the schedule Time Between Overhauls TBOs has to be a much narrower window to ascertain the often load induced stress on the air frame and on the TVC part has not resulted into any structural deformity/defect.
If you see IAF MKI engines are rated for 4000h service life and yet the mean time between overhaul is reportedly 1,000 hours with a full-life span ; the titanium nozzle has a mean time between overhaul of 500 hours
According to wiki
In early 2015, Defence Minister Manohar Parrikar stated before Parliament that the Al-31FP had suffered numerous failures, between the end of 2012 and early 2015, a total of 69 Su-30MKI engine-related failures had occurred; commons causes were bearing failures due to metal fatigue and low oil pressure, in response several engine modifications were made to improve lubrication, as well as the use of higher quality oil and adjustments to the fitting of bearings.[51]
The Su-30MKI's Al-31FP powerplant built on the earlier Al-37FU, adding two-plane thrust vectoring nozzles are mounted 32 degrees outward to longitudinal engine axis (i.e. in the horizontal plane) and can be deflected ±15 degrees in one plane. The canting allows the aircraft to produce both roll and yaw by vectoring each engine nozzle differently; this allows the aircraft to create thrust vectoring moments about all three rotational axes, pitch, yaw and roll. Engine thrust is adjusted via a conventional engine throttle lever as opposed to a strain-gauge engine control stick. The aircraft is controlled by a standard control stick. The pilot can activate a switch for performing difficult maneuvers; while this is enabled, the computer automatically determines the deflection angles of the swiveling nozzles and aerodynamic surfaces
Sukhoi Su-30MKI - Wikipedia, the free encyclopedia
Notice the word usage - Metal fatigue
Metal fatigue is the weakening of a material caused by repeatedly applied loads. It is the progressive and localised structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values that cause such damage may be much less than the strength of the material typically quoted as the ultimate tensile stress limit, or the yield stress limit.
Fatigue occurs when a material is subjected to repeated loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands (PSBs), and grain interfaces.
Fatigue (material) - Wikipedia, the free encyclopedia
Thus wiki says something which adds to the load induce issues i said above.
