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DISCUSSION: THUNDER AND TEJAS

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Any member who would like to answer the questions in my earlier post is welcome to do so. I am not bashing any member or fighter rather want new members to find out why the designers of the jft and lca went with their respective designs.

@ghazi768 @Bilal Khan 777

I am not an aerospace engineer, but the turn performance and of TEJAS and all Mirage derived aircraft is extremely poor. As a design, TEJAS is already obsolete. Some of our boys examined it in Bahrian and they couldn't hold back their laughter. Sigh of relief for Indians to be scrapping the Rafale and going for TEJAS.
 
The strengths of Tejas that we know so far

1.Low wing loading, Rapid Rate of Climb ; Good ITR

2. Good Thrust to weight ratio ;Relaxed Static Stability

3.Elta 2032 Radar + Derby BVR missile

4. DRFM based ASPJ ; RWR,

5.Lower frontal RCS ;Composite Materials

6. All digital 4 channel fly by wire

7. HMDS enabled close combat high off bore sight R 73 E
Python V combination which is deadly and allows no escape in close combat

Need to add

Integration with Litening Pod (Recon/Targeting)
 
My request to you sir, pls keep your eye on this thread and keep away the Troller and Trailer out of this thread.
Will try to do so (but you have to admit it was quite embarrassing :P) :lol:
OK serious now.
Please carry on with the discussion.
 
I am not an aerospace engineer, but the turn performance and of TEJAS and all Mirage derived aircraft is extremely poor. As a design, TEJAS is already obsolete. Some of our boys examined it in Bahrian and they couldn't hold back their laughter. Sigh of relief for Indians to be scrapping the Rafale and going for TEJAS.
Sir any idea regarding composite usage and the resultant decrease in frontal rcs of a loaded mission ready fighter?
 
The strengths of Tejas that we know so far

1.Low wing loading, Rapid Rate of Climb ; Good ITR

2. Good Thrust to weight ratio ;Relaxed Static Stability

3.Elta 2032 Radar + Derby BVR missile

4. DRFM based ASPJ ; RWR,

5.Lower frontal RCS ;Composite Materials

6. All digital 4 channel fly by wire

7. HMDS enabled close combat high off bore sight R 73 E
Python V combination which is deadly and allows no escape in close combat
Dear most of them is "work in progress" while JF17 already have comparable options operational in most of the cases. You may cite them as "strenghts of LCA" as you did but not as "Advantages over JF-17" like the thread is about. There have been discussion spreading not over pages but threads about the comparable equipment on board. Also the fact about what future holds for JF17.
I wont go into the same details again and will like Mishra here to continue with his technical details and information he is sharing. Hope to get back to sub systems sometime later in this thread.
 
For everyone else.. Gentleman, for note; please do not be intimated by such "rigorous mathematics" .
No sir, it is not a rigorous mathematics...It is just simple algebraic expressions derived from a very simple free body diagram force balance and use of some simple trigonometry...this is the first thing you do in any flight mechanics course...For people who are new to this subject I can simplify it,

In a steady (unaccelerating) and levelled flight, an airplane is in a total balance i.e. four major forces cancel each other
L=W means levelled flight ( balance in vertical direction)
, T=D means no acceleration or deceleration i.e. uniform speed (balance of forces in horizontal direction)
where L is the lift force generated by lifting devices i.e. wings mainly, and/or canards and/or fore-wing and also the tail but that is normally aimed to counter or provide the moment for pitching motion. The lift force balances the weight
W = m*g

L=CL* q *Sref, Lift is an aerodynamic force i.e. force due to the flow of air

q= 0.5*rho*U^2 dynamic pressure

CL is coefficient of the lift CL= CL0+CLa*a
CLa basically the slope of the cl curve and CL0 is the intercept... and for flate plate CLa =2*pi and it is dCL/da as i said it is just the slope.

Now the question comes to mind is how does the wing produces lift, so the simple explanation is considering a 2-D sections of the airplane wing (it is a 3D object/surface) called airfoil as shown in the figure blow ( taken fron internet) So when the air flows past an airfoil it divides into two paths, above and below the airfoil. If there is angle between the chord of the airfoil and incoming wind, the lengths of paths are different and that causes pressure difference between the lower and upper surfaces of the airfoil. The upper surface normally has lower pressure and thus known as suction side while the lower surface has a higher pressure or positive pressure. This pressure difference generates the lift

Screen Shot 2016-07-04 at 17.24.50.png

In figure below you can see the chord, leading edge and trailing of an airfoil.
Screen Shot 2016-07-04 at 17.25.08.png




Here is the airfoil with forces

IMG_2191.JPG



Now, in D=T, is an aerod. force in horizontal direction ( or parallel to the wind speed while the lift is at right-angles as shown in the figure above) for a levelled flight and is known as drag that simply means air resistenace and T is the thrust...which provided by the engine or specifically by the jet
D =Cd* q *Sref
D = T holds only when the airplane is flying with uniform or constant speed but if thrust goes up, it will accelerate and vice versa. So you can see drag as a negative effect/force and normally the designers try to minimize it or they try to optimise the lift to drag ratio.
As we discussed before, the angle between the direction of airflow i.e wind speed and the chord is called angle of attack (denoted by greek letter alpha or briefly AoA)...so the aerodyn. forces in the wind coordinates are life and drag while in body fixed (airfoil) coordinates are axial and normal forces with cofficients Cx and Cz as showin the figure above and these can be transformed into each other by simple vector or trigonometric analysis i.e. drawing the components of the forces one coordinate and equating them with the forces in the other coordinate and vice-versa and the AoA is only angle needed in this simplified case. A resultant force R is just obtained by the vector addition of axial and normal forces.
Now as soon as the aircraft will depart from this levelled and steady flight the balance will be disturbed and net force won't zero and components of the forces will appear and that's where trigonometric ratios come into play.
However a wing is a 3D object so the flow over it is 3D...which is not necessarily a good thing as it results in the 3D effect and can reduce the flight efficiency of an airplane. What happens is that the streamlines on the suctions side of the wings get contracted while the on pressure side reverse happens and this differential resultsi n vortex shedding and vortex is rotating flow structure in the wake and effect anything that it interacts. We will see it in more detail when we discuss the wing, canard, wing-tip devices (i.e. wing lets and wing tip mounted weapons). Now lets move on to more flight mechanics. So look at the picture below most probably inspired by our favorite F-16 :) . Here it is necessary to understand that how the body forces and the aerodynamic act on the body of the airplane...Due to a complex configuration of an airplane the pressure distribution around it changes however the resultant of the aerodynamic forces seems to act through a point called center of pressure while weight of the airplane acts through center of the gravity (cg)

FullSizeRender.jpg
 
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Two different birds. With two different philosophines. Very different dynamics of development and deployment. Comparison? How?
 
I am not an aerospace engineer, but the turn performance and of TEJAS and all Mirage derived aircraft is extremely poor. As a design, TEJAS is already obsolete. Some of our boys examined it in Bahrian and they couldn't hold back their laughter. Sigh of relief for Indians to be scrapping the Rafale and going for TEJAS.

I would like to RESPECTFULLY Disagree with You

We in INDIA believe that Tejas is superior in Air to Air combat against JF 17

That will be its primary role

And BTW we will buy 126 Rafales ; Tejas is just a supplementary plane replacing the Mig 21
 
I would like to RESPECTFULLY Disagree with You

We in INDIA believe that Tejas is superior in Air to Air combat against JF 17

That will be its primary role

And BTW we will buy 126 Rafales ; Tejas is just a supplementary plane replacing the Mig 21

I don't know why Indian members don't realize the importance of time.
India WILL buy this .. India WILL buy that .. LCA WILL have this .. LCA WILL have that ..
but you compare all this with what Pakistan has NOW .. By the time a full squadron (12-18 planes) of LCA Mk1 or whatever iteration is inducted in 2020 (or God know's when) .. PAF would obviously have moved on to Block 3 or who knows even Block 4.
 
Hi dear @Quwa
I must confess that your article is well written and very balanced-very rare to find such piece written by pakistani authors. But I would like to add couple of things that i felt you missed in your article.Kindly bear with me,as i will be a little rigorous mathematically.
Firstly,keeping everything aside,Tejas as a platform is superior to JF-17 thanks to two factors that I will explain mathematically-
1)Wing Loading:
Wing Loading is a very important factor in a lot of aircraft performance parameters. This is nothing but mass of the aircraft divided by itz wing surface area.A lower wing loading is prefered over higher wing loading as it vastly improves a lot of things ranging from min stall velocity,turning radius,take off distance to name a few.And i will prove all my points based on hard mathematics,i will try to not use advanced mathematics so that most can follow-pre requisite: Free body diagram analysis
View attachment 315602
(a) Effect of wing loading on turning radius: (kindly refer to my page above right side)
A lower wing loading(represented by Wl) will have lower turning radius vis-a-vis an aircraft higher wing loading- keeping everything constant
(b)Effect of wing loading on velocity required for take off: (on the left hand side of my page above)
Velocity is directly proportional to the square root of the wing loading,hence a lower wing loading will result into lower velocity with which an aircraft can take off- or land.This is specifically evident if we compare the take off and landing runs of both LCA and thunder-former's take off run is shorter by at least 200m!
I would like to point out that I have taken Thrust to be along V and L to be perpendicular to it,where "gamma" as usual denote flight path angle .Dotted line indicated local horizontal and vertical.

2)Second factor that makes LCA superior to JF-17 is "RELAXED STATIC STABILITY" in pitch plane. This helps LCA achieve higher pitch rates as compared to JF-17. Just for the benefit of readers I want to point out that a conventional flight must be simultaneously "balanced or trimmed at a particular alpha" and "stable".However due to requirement of higher maneuverability,modern fighter jets have inbuilt instability and that i achieved by placing CG aft of aerodynamic centre. This has a lot of advantages apart from providing excellent pitch rates and i will list them here-
(a) An unstable aircraft requires lesser hinge torque to displace the control surfaces.This in turns results in smaller actuators that can do our job.
(b)An unstable aircraft requires smaller net control surface area for producing moments.This in turns translates into smaller drag produced by control surfaces.
But this makes the design of control appreciably much more complex vis-a-vis an aircraft with stable design.Because now the aircraft wont return to itz equilibrium trim state when disturbed,so control surfaces must be "actively" used to constantly keep the aircraft in trim state. Thankfully RSS is almost always used by FBW system,because it is almost impossible to fly an unstable aircraft manually- which entails- balancing or trimming at a particular angle and stability.The pilot will just go mad! Hence a computer actively controls the stabilators to constantly trim the aircraft at a particular alpha as commanded by the pilot.This is also known as "artificial stability" in american literature because although the aircraft isnt stable,it "appears" stable thanks to behind the scene action of a computer- that makes it stable to fly for pilots!

The only area where JF-17 is ahead is operational deployment in force structure of PAF.This would have enabled them to frame their combat policies and deployment including thunder.This will take couple of years in IAF with LCA.We must also accept the fact that when thunder was inducted into forces,it could hardly fire BVR,a2a refueling,carry a designator pod,EW suite etc,However the IAF didnt give the IOC unless it could do all of it. SO,I tend to think that PAF inducted a fighter that couldnt perform any of these whereas IAF chose otherwise.

I would like @Oscar and @JamD to add their points to expand this discussion- ofcourse based on rigorous mathematics.

Dear friend, please don't take this the wrong way. I truly admire your patience and effort but I must agree with @Oscar here.

To quote Albert Einstein:
“If you can't explain it to a six year old, you don't understand it yourself.”

Firstly, the analysis you seem to have done is very rudimentary. We do this thing in our basic undergraduate courses but we are taught to appreciate the limitations of these analyses as well. Something you might not have an appreciation for. It is easy to fall into the trap of believing it will give some unique insight. The equations you have posted, those who will understand it don't need to go through them again, and those who don't will be utterly confused. (Frankly I was bored and did not bother going through them lol sorry). Try to summarize your points, be concise, it makes life easier for everyone.

Deriving basic expressions like these is just a waste of your time and talent. Don't worry about it.

Now to the wing loading. You seem to be under the false impression that wing loading is everything. It is just one thing. If there's anything I've learned in aerospace engineering is that there is no other engineering application where compromise is more dominant than in aircraft design. For every design parameter (like wing loading) you can list 10 virtues and 10 disadvantages. To claim anything of substance based on one parameter is ill-informed.

The rest of the pages of the discussion I haven't had time to read. I will if I get the time. Thanks again for your effort. Please try to be concise. Thanks.


Two different birds. With two different philosophines. Very different dynamics of development and deployment. Comparison? How?
Two different birds. With two different philosophies. Very different dynamics of development and deployment. Comparison? How?

Best thing I've read on this thread so far. @amardeep mishra is focusing on wing loading viz a viz turn rates. There are so many other things you could compare them on. In the end they are designed for a different kind of flying. Each pilot would try to use the advantages of each aircraft while trying to exploit the disadvantages of the other. The JF-17 would try to bait the LCA into sustained turns to bleed its energy and the LCA will try to point its nose at the JF-17 and get a lock.

What I think we are trying to compare then are dogfighting capabilities against each other in a one on one un-networked scenario. The best bet we have of figuring anything out is to use a half decent flight simulation model for both aircraft and get two people (preferably pilots) to go at each other over and over again and see if a pattern emerges. This topic is so complicated that I wouldn't touch it with a 100 foot pole, (let alone a wing loading analysis :p).
 
I don't know why Indian members don't realize the importance of time.
India WILL buy this .. India WILL buy that .. LCA WILL have this .. LCA WILL have that ..
but you compare all this with what Pakistan has NOW .. By the time a full squadron (12-18 planes) of LCA Mk1 or whatever iteration is inducted in 2020 (or God know's when) .. PAF would obviously have moved on to Block 3 or who knows even Block 4.
things is

1.HAL has made 16 exampels of Tejas as of NOW

2.Tejas has 4channel digtial FBW in all axis as of NOW

3.Tejas has HMDS-HOBS missile combo as of NOW

4.Tejas is tested and intigrated with digital and intgrated RWR & LWR as of NOW

5.Tejas has EL2032MMR with Derby & IDerby ER intigrated and tested as of NOW

7.Tejas is lighter but still has lower Wing Loading , Better T/W ratio and carries more fuel than JF17 as of NOW

8.Tejas is in testing with IFR and OBOGS under testing as of NOW

9.Tejas has highest ammount of composites in skin(95%) & total body weight (40%) in its class as of NOW

10.Tejas is tested under day & night and all kinds of weather with Litening G3 +paveway2 LGB as of NOW

these all things are with Tejas MK1 IOC2 standard as of NOW which JF-17 wants to HAVE in its BLK III

and till JF17BlkIII WILL come so WILL Tejas MK1A with EL2052 GaN based AESA Radar and AESA based combined & intigrated EW + ECM + internal Jammer suite & possibally and internal IRST

as for JF17 well still it cant drop LGBs or any bombs in night and dont have HOBS+HMDS or BVR cabality but still is induced in PAF and has 60+ numbers as its forntline fighter they do not have a choice but unlike IAF which both has money and choices and wants a fully tested and working/combat ready Fighter jet that too for Point defence/internal air policing job but what i dont get is when tejas carries more fuel has lower weight and better T/W ratio than JF 17 how come it has 1/3rd the combat radius as that of JF17 ?
 
things is

1.HAL has made 16 exampels of Tejas as of NOW

2.Tejas has 4channel digtial FBW in all axis as of NOW

3.Tejas has HMDS-HOBS missile combo as of NOW

4.Tejas is tested and intigrated with digital and intgrated RWR & LWR as of NOW

5.Tejas has EL2032MMR with Derby & IDerby ER intigrated and tested as of NOW

7.Tejas is lighter but still has lower Wing Loading , Better T/W ratio and carries more fuel than JF17 as of NOW

8.Tejas is in testing with IFR and OBOGS under testing as of NOW

9.Tejas has highest ammount of composites in skin(95%) & total body weight (40%) in its class as of NOW

10.Tejas is tested under day & night and all kinds of weather with Litening G3 +paveway2 LGB as of NOW

these all things are with Tejas MK1 IOC2 standard as of NOW which JF-17 wants to HAVE in its BLK III

and till JF17BlkIII WILL come so WILL Tejas MK1A with EL2052 GaN based AESA Radar and AESA based combined & intigrated EW + ECM + internal Jammer suite & possibally and internal IRST

as for JF17 well still it cant drop LGBs or any bombs in night and dont have HOBS+HMDS or BVR cabality but still is induced in PAF and has 60+ numbers as its forntline fighter they do not have a choice but unlike IAF which both has money and choices and wants a fully tested and working/combat ready Fighter jet that too for Point defence/internal air policing job but what i dont get is when tejas carries more fuel has lower weight and better T/W ratio than JF 17 how come it has 1/3rd the combat radius as that of JF17 ?
All this have been answered in the last three pages. Perhaps you would like to educate yourself about it there.
 
Firstly, the analysis you seem to have done is very rudimentary. We do this thing in our basic undergraduate courses but we are taught to appreciate the limitations of these analyses as well.

@JamD
The reason why I kept it very rudimentary is because in past I was accused of using mathematical construct very few could understand,hence I tried to be very rudimentary.and I never claimed it otherwise. Secondly, there is indeed no doubt in my mind that wing loading alone determines the superiority of one aircraft over the another.There are a lot of other parameters that needs to be investigated.but I'm sure if you've read my post, you'd agree that I've clearly stated that wing loading along with RSS are two areas where LCA is superior to JF17-which is infact a true proposition. I'd strongly urge you to go through my other posts as well on this thread.
 
All this have been answered in the last three pages. Perhaps you would like to educate yourself about it there.
yes i dint see all that sir but i will now thanks for reminding im not trolling only trying to increase my knwledge on this subject thank you
 
yes i dint see all that sir but i will now thanks for reminding im not trolling only trying to increase my knowledge on this subject thank you
Somehow i seriously doubt this.
But still, please do so by seeing "all that" in previous pages. Knowledge can be better acquired by observing an educated discussion and going through the posts as it have answers to all the questions NOT by asking the same questions over and over again until someone take the bait and comes up with an off-topic reply. So please keep in line or stay away!
 
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