ADA Tejas (LCA) News and Discussions

[Decklander]

@ersakthivel, I waited for you to answer my questions and since you did not reply, so I am replying to them.
Turn radius R is given by equation, R=V^2/g Tan theta,
rate of turn is given by, ROT=g Tan theta/V
now interpolating these two equations together we find that ROT=TAS/R.
which means that ROT is directly proportional to speed and inversely proportional to radius of turn i.e
1. higher the speed and lower the radius, higher will be ROT.
2. At constant TAS, increasing the bank angle will result in decreased R and increased ROT.
3. to maintain constant ROT, increasing speed requires, increased bank angle.
4. at constant bank angle, increasing the speed, increases R and reduces ROT.
we know that when an ac turns, we need centripetal force to maintain the turn and the lift must be increased to balance out the weight & the this centripetal force. L sin theta=centripetal force=WV^2/Rg. and L cos theta=W
So we realise that for a given bank angle, there will be a corresponding G reqd, so if you increase G, you will need to increase bank to maintain level turn, and if you increase bank, you will need to increase G till you reach your structure limit.
We also know that stall is dependent on weight and increase in load factor increases this stall speed. We also know that increase in bank angle and load factor will result in increase of drag and thrust must be adequate to overcome this drag to maintain level flight and speed otherwise the ac will start decelerating when it hits its max bank angle corresponding to the max structural limit load factor.
So we the minimum R and max ROT occurs at VA speed also called Maneuvering speed and also called Air Combat Manouevering speed (ACM).
VA speed is the speed up to which you can make control deflection and take the ac to its load limits, beyond that speed, you will end up damaging the ac if you pull to the limits.

I request you to pls remember the relationship between R & ROT & G and also the meaning of ACM. I will return after sometime to complete the second part of this tutorial to tell you how it affects the combat perf of LCA.

 

[Decklander]

From the equations of R & ROT it is very clear that we must have the ability to apply max load factor at lowest possible speed to have least R and max ROT. And we need max L to maintain level turn otherwise we will start losing height.
L=Clx1/2densityxV^2xS where S is surface area. so we can increase the lift by either increasing the Cl which means increasing AOA or by keeping high speeds which will be counter productive as we want to maintain low speeds to maintain high ROT and very low R, or by increasing the S.
S is a fixed value for any aircraft.
LCA has large S and veryhigh sweepback, which means that it achieves its peak Cl at very high AOA, and even though it has high S yet it has high stall speeds due to very high sweepback. We all know that highly swept wings have lower Clmax compared to unswept or less swept wings when compared apple to apple i.e clean or with leading edge and trailing edge lift augmentation devices deployed/extended. However we also know that sweepback increases the S for a given span. LCA is a small ac and it needed a large S so a very highly swept design was chosen to satisfy the need for speed and lift. LCA inspite of being optimised for its role suffers the typical problem of delta designs though partly overcome by its compound delta design.
high AOA to achieve high Cl results in veryhigh drag requiring high trust to overcome it. So we need more powerfull engines.
The use of words like wingloading to describe the turning perf of an ac is done to explain it to a layman and not to seasoned fighter pilots. wingloading does not effect the turning perf of an ac as much as the Clmax does. As explained above, inspite of high S and low weight, you may have lower overall lift available to pull 9g as your stall speed will be high. to make it more clear, let us assume two ac with equal weight, equal S, equal max loadfactor limits but one is LCA with 53* sweepback and another with 0* sweep. Which of the two will have higher ROT and why? Which will have lower reqts of thrust and why?
The ac with 0* sweep will have higher ROT as it will have a higher Clmax compared to LCA while their wing area is same, their loadfactors are same but the stall speeds for max loadfactor are lower for 0*sweep design. Lower V means lower R and higher ROT as explained by the equations.
The ac with 0* sweep will need lower thrust as it will reach its Clmax AOA at lower values compared to LCA with 53* sweepback and so will have lesser drag. But straight wing means poor speed potential. It will be like making a hurricane fight an LCA.
While comparing the ROT of two ac, pls do not get fooled by wingloading and instead go for max lift vs weight graph of an ac as an ac with smaller S with higher Clmax can still generate same amount of lift as an ac with large S and smaller Clmax.
F-22 is today credited by USAF to have the best ITR & STR of all fighters in the world and that ac has 42* sweepback and trapezoidal design with unstable aerodynamics.
I hope in future you will stop using the arguments about low wingloading to describe ROT.
........iti siddham

 

[p2prada]

Regarding LCA MK2, You have hit the nail on the head. IAF has tried its level best to kill this project and now we are in s ituation where the entry into service timelines of Mk2 & Rafale are matching.

Interesting. If IAF killed LCA, then what about the Navy? They presented requirements years ago and ADA is not even concerned about the Naval prototypes today. They are focussing on IAF version instead when it was the Navy which came out with the Mk2 requirement first.

NP-1 has only finished four test flights and has been grounded for more than a year now. Wouldn't that mean it is the Navy which is putting things on hold. In fact, IN RFI for MRCA and RFP for LCA match timelines.

If we look at the dates, IN will end up inducting only 8 Mk1s, probably no Mk2s and mostly foreign MRCA looking at how things are progressing.

Maybe it is the IN which killed the LCA project by changing LCA design parameters and coercing IAF to change Mk2 requirements midway out of keeping the aircraft relevant. That enabled IN to buy time so they can match IAF's MRCA and LCA timelines which would in turn delay the N-LCA even more. This way IN can directly jump on to the Rafale/F-35 bandwagon citing LCA's obsolescence by the time the Naval version is ready. All the while it is the IAF which is trying to maintain power equations across the border while facing a depleting squadron strength. With the onus to induct more capable aircraft more quickly, LCA may end up being sidelined, but this will strengthen IN's position to induct better aircraft as well while completely sidelining N-LCAMk2, a requirement that probably never existed in the first place.

Anybody can make up conspiracy theories. All of LCA's flaws are technical which have no bearing on IAF. @Twinblade made that point clear in a recent post of his in another thread.

It looks like N-LCA Mk2 design parameters will change once again with the requirement to change the engine to a 1120KN F-414EPE instead of the current INS6. That adds some more years to the delay while ADA begins negotiations for the new engine instead of the INS6 that was negotiated for.

 

[rvjpheonix]

So @Decklander sir we have two options? Either go for a high thrust engine or reduce the sweepback of the aircraft. But wont it cause a lot of change to the way the aircraft behaves, changing oits margin of stability which means complete rewriting of FBW system. Presently is it possible to do so.within yhe stipulated time limit.and how does the present lca's lift to weight ratio compare with other crafts? Also what determines the max AOA an aircraft can achieve?

 

[Decklander]

Interesting. If IAF killed LCA, then what about the Navy? They presented requirements years ago and ADA is not even concerned about the Naval prototypes today. They are focussing on IAF version instead when it was the Navy which came out with the Mk2 requirement first.

NP-1 has only finished four test flights and has been grounded for more than a year now. Wouldn't that mean it is the Navy which is putting things on hold. In fact, IN RFI for MRCA and RFP for LCA match timelines.

If we look at the dates, IN will end up inducting only 8 Mk1s, probably no Mk2s and mostly foreign MRCA looking at how things are progressing.

Maybe it is the IN which killed the LCA project by changing LCA design parameters and coercing IAF to change Mk2 requirements midway out of keeping the aircraft relevant. That enabled IN to buy time so they can match IAF's MRCA and LCA timelines which would in turn delay the N-LCA even more. This way IN can directly jump on to the Rafale/F-35 bandwagon citing LCA's obsolescence by the time the Naval version is ready. All the while it is the IAF which is trying to maintain power equations across the border while facing a depleting squadron strength. With the onus to induct more capable aircraft more quickly, LCA may end up being sidelined, but this will strengthen IN's position to induct better aircraft as well while completely sidelining N-LCAMk2, a requirement that probably never existed in the first place.

Anybody can make up conspiracy theories. All of LCA's flaws are technical which have no bearing on IAF. @Twinblade made that point clear in a recent post of his in another thread.

It looks like N-LCA Mk2 design parameters will change once again with the requirement to change the engine to a 1120KN F-414EPE instead of the current INS6. That adds some more years to the delay while ADA begins negotiations for the new engine instead of the INS6 that was negotiated for.

Firstly LCA was never about IN. IN jumped in after seeing its potential and is also the first service to have put its own money into the project. had it not been for IN, Mk1 itself wud have been history and there wud have been no MK2. Pls remember IN never wrote the ASQR for this ac. IN was never a part of it and whatever we have asked for, we are paying for it upfront unlike IAF which is all about crying only.

 

[Decklander]

So @Decklander sir we have two options? Either go for a high thrust engine or reduce the sweepback of the aircraft. But wont it cause a lot of change to the way the aircraft behaves, changing oits margin of stability which means complete rewriting of FBW system. Presently is it possible to do so.within yhe stipulated time limit.and how does the present lca's lift to weight ratio compare with other crafts? Also what determines the max AOA an aircraft can achieve?

Making major changes to LCA design will mean a completely new aircraft.

 

[ersakthivel]

From the equations of R & ROT it is very clear that we must have the ability to apply max load factor at lowest possible speed to have least R and max ROT. And we need max L to maintain level turn otherwise we will start losing height.
L=Clx1/2densityxV^2xS where S is surface area. so we can increase the lift by either increasing the Cl which means increasing AOA or by keeping high speeds which will be counter productive as we want to maintain low speeds to maintain high ROT and very low R, or by increasing the S.
S is a fixed value for any aircraft.
LCA has large S and veryhigh sweepback, which means that it achieves its peak Cl at very high AOA, and even though it has high S yet it has high stall speeds due to very high sweepback. We all know that highly swept wings have lower Clmax compared to unswept or less swept wings when compared apple to apple i.e clean or with leading edge and trailing edge lift augmentation devices deployed/extended. However we also know that sweepback increases the S for a given span. LCA is a small ac and it needed a large S so a very highly swept design was chosen to satisfy the need for speed and lift. LCA inspite of being optimised for its role suffers the typical problem of delta designs though partly overcome by its compound delta design.
high AOA to achieve high Cl results in veryhigh drag requiring high trust to overcome it. So we need more powerfull engines.
The use of words like wingloading to describe the turning perf of an ac is done to explain it to a layman and not to seasoned fighter pilots. wingloading does not effect the turning perf of an ac as much as the Clmax does. As explained above, inspite of high S and low weight, you may have lower overall lift available to pull 9g as your stall speed will be high. to make it more clear, let us assume two ac with equal weight, equal S, equal max loadfactor limits but one is LCA with 53* sweepback and another with 0* sweep. Which of the two will have higher ROT and why? Which will have lower reqts of thrust and why?
The ac with 0* sweep will have higher ROT as it will have a higher Clmax compared to LCA while their wing area is same, their loadfactors are same but the stall speeds for max loadfactor are lower for 0*sweep design. Lower V means lower R and higher ROT as explained by the equations.
The ac with 0* sweep will need lower thrust as it will reach its Clmax AOA at lower values compared to LCA with 53* sweepback and so will have lesser drag. But straight wing means poor speed potential. It will be like making a hurricane fight an LCA.
While comparing the ROT of two ac, pls do not get fooled by wingloading and instead go for max lift vs weight graph of an ac as an ac with smaller S with higher Clmax can still generate same amount of lift as an ac with large S and smaller Clmax.
F-22 is today credited by USAF to have the best ITR & STR of all fighters in the world and that ac has 42* sweepback and trapezoidal design with unstable aerodynamics.
I hope in future you will stop using the arguments about low wingloading to describe ROT.
........iti siddham

Well, all your explanations will fit for plain deltas like Mirage-2000,

But the one small detail you failed to consider is the role of the twist at wing root and the lesser swept angle at front which will generate huge vortice based energizing lift force , to calculate which you don't have any equation, I suppose.

The role of the compound or cranked delta wing form on Tejas is there precisely to over come this problem.

It has been studied in wind tunnel and ADA has also released a PDF on the role of the leading edge crank with lower swept back angle generating huge vortices that improve lift and delay stall.

I have posted that PDF in this thread as well as the closed thread- ADA Tejas-III.

So ADA did take into consideration all these factors in designing it.

The reason for the inability to reach 9G is higher empty weight of around a ton or so which makes the present GE-404-IN engine on Tejas a bit under powered.

Once this is rectified in tejas mk-2 with a higher power engine Tejas will reach the same 9Gs and a top speed around mach 2 as most of the modern delta canards with high thrust to weight ratio fighters like RAFALE and TYPHOON.

 

[ersakthivel]

Interesting. If IAF killed LCA, then what about the Navy? They presented requirements years ago and ADA is not even concerned about the Naval prototypes today. They are focussing on IAF version instead when it was the Navy which came out with the Mk2 requirement first.

NP-1 has only finished four test flights and has been grounded for more than a year now. Wouldn't that mean it is the Navy which is putting things on hold. In fact, IN RFI for MRCA and RFP for LCA match timelines.

If we look at the dates, IN will end up inducting only 8 Mk1s, probably no Mk2s and mostly foreign MRCA looking at how things are progressing.

Maybe it is the IN which killed the LCA project by changing LCA design parameters and coercing IAF to change Mk2 requirements midway out of keeping the aircraft relevant. That enabled IN to buy time so they can match IAF's MRCA and LCA timelines which would in turn delay the N-LCA even more. This way IN can directly jump on to the Rafale/F-35 bandwagon citing LCA's obsolescence by the time the Naval version is ready. All the while it is the IAF which is trying to maintain power equations across the border while facing a depleting squadron strength. With the onus to induct more capable aircraft more quickly, LCA may end up being sidelined, but this will strengthen IN's position to induct better aircraft as well while completely sidelining N-LCAMk2, a requirement that probably never existed in the first place.

Anybody can make up conspiracy theories. All of LCA's flaws are technical which have no bearing on IAF. @Twinblade made that point clear in a recent post of his in another thread.

It looks like N-LCA Mk2 design parameters will change once again with the requirement to change the engine to a 1120KN F-414EPE instead of the current INS6. That adds some more years to the delay while ADA begins negotiations for the new engine instead of the INS6 that was negotiated for.

IN the least funded service arm ,which set aside close to 1000 crores for Tejas project is killing it t!!!!

But IAF which refused to set aside a single crore for the past two decades is encouraging the project!!!!!!!1

Good joke,

ADA knows that IAF won't accept a tejas mk-2 e\which will have lesser perf than RAFALE when it comes to close combat since the IAF had it's hands on RAFALE.

Thats why IN and ADA are working for Tejas mk-2, IAF can give 20 more tejas mk-1 orders considering the 3560 obsolete MIGs and JAGs serving time in their fleet. It would have resulted in 16 per year capacity production line for Tejas , and it would have quickened the pace of TEJAS MK-2 itself , since higher capacity assembly line is there to produce PVs quickly.

But while lying that there is no alternative or back up plan for MMRCA tender(More number of Super SUKHOIs and Tejas mk-2 will certainly fill the void as there is no 5th gen tech on RAFALE, the french are even refusing to transfer their 4th gen tech on RAFALE saying HAL is unfit!!!!!!!!)IAF is busy blacklisting HAL from AVRO replacement tender for 56 planes worth close to 12000 crores , while inviting bids from foreign majors!

 

[CuriousBen]

Decklander Sir,
1. how do you think the LCA mk-1 fares ( or would ) against the competition.
Lets say how will it fare in dogfight against a F-16 coming from Pakistan .
And how do you think it will far when pitted against the chines adversary - lets say J-20.
Most of the chinese are clones of migs and su ?
So against which adversary aircraft will it be vulnerable .
I presume the main aim is to be a interceptor.

2. Another question is EW : electronic warfare. How do you think it will save the aircraft.
Do the EW have any mehanism to fool the incoming BVR and WVR missiles.
Also the USA and other leading countries are making power based weapons. Some on these weapons can fry the electronics.
Assume that the electronic are fried , can the ac still fly or will it fall out of the sky ?

 

[Decklander]

Well, all your explanations will fit for plain deltas like Mirage-2000,

But the one small detail you failed to consider is the role of the twist at wing root and the lesser swept angle at front which will generate huge vortice based energizing lift force , to calculate which you don't have any equation, I suppose.

The role of the compound or cranked delta wing form on Tejas is there precisely to over come this problem.

It has been studied in wind tunnel and ADA has also released a PDF on the role of the leading edge crank with lower swept back angle generating huge vortices that improve lift and delay stall.

I have posted that PDF in this thread as well as the closed thread- ADA Tejas-III.

So ADA did take into consideration all these factors in designing it.

The reason for the inability to reach 9G is higher empty weight of around a ton or so which makes the present GE-404-IN engine on Tejas a bit under powered.

Once this is rectified in tejas mk-2 with a higher power engine Tejas will reach the same 9Gs and a top speed around mach 2 as most of the modern delta canards with high thrust to weight ratio fighters like RAFALE and TYPHOON.

I have very clearly mentioned that compound delta design of LCA has overcome part of the problems but not all. I also agree with your POV that when vortex generators or close couple canards are used they, increase the CL and that can't be calculated by normal equations. BUT, same can be done for non delta less swept wing also? That is why I used the term,"apple to apple". Rafale and Typhoon have 46* sweep if I am not wrong.

 

[Decklander]

Decklander Sir,
1. how do you think the LCA mk-1 fares ( or would ) against the competition.
Lets say how will it fare in dogfight against a F-16 coming from Pakistan .
And how do you think it will far when pitted against the chines adversary - lets say J-20.
Most of the chinese are clones of migs and su ?
So against which adversary aircraft will it be vulnerable .
I presume the main aim is to be a interceptor.

2. Another question is EW : electronic warfare. How do you think it will save the aircraft.
Do the EW have any mehanism to fool the incoming BVR and WVR missiles.
Also the USA and other leading countries are making power based weapons. Some on these weapons can fry the electronics.
Assume that the electronic are fried , can the ac still fly or will it fall out of the sky ?

I won't rate MK1 much against these ac but MK2 will be able to take on the best. J-20 is more of a bomber and not a fighter.
LCA due to its small size and low RCS will have a very low burn thru range giving it advantage in EW jamming envoirnment.
I can't say much about energy weapons and their effect on LCA electronics. But em hardenning of LCA electronics has been done afaik.

 

[ersakthivel]

I have very clearly mentioned that compound delta design of LCA has overcome part of the problems but not all. I also agree with your POV that when vortex generators or close couple canards are used they, increase the CL and that can't be calculated by normal equations. BUT, same can be done for non delta less swept wing also? That is why I used the term,"apple to apple". Rafale and Typhoon have 46* sweep if I am not wrong.

in Fig. 6 for angle of attack a = 13° and 18° . A fairly good comparison is observed. The vortical flow field captured in calculations is presented in Fig. 7. The particle traces illustrate the detailed structure of the rolled-up vortices.It is seen that the leading edge vortices are strengthened as the flow develops progressively away from the leading-edge of the win

The wind tunnel model of the contribution of the cranked delta design to better lift to drag ratio - at high AOA these vortice generation energizes air flow over the wing and contributes to better lift to drag ratio

 

[Decklander]

The wind tunnel model of the contribution of the cranked delta design to better lift to drag ratio - at high AOA these vortice generation energizes air flow over the wing and contributes to better lift to drag ratio

I hope you can interpret what you have just posted. It seems to prove your statements wrong.

 

[dealwithit]

2. Another question is EW : electronic warfare. How do you think it will save the aircraft.
Do the EW have any mehanism to fool the incoming BVR and WVR missiles.
Also the USA and other leading countries are making power based weapons. Some on these weapons can fry the electronics.
Assume that the electronic are fried , can the ac still fly or will it fall out of the sky ?

LCA tejas has been Tested with KALI 5000..

The microwave-producing version of Kali has also been used by the DRDO scientists for testing the vulnerability of the electronic systems of the Light Combat Aircraft (LCA), which was then under development.

It has also helped in designing electrostatic shields to "harden" the LCA and missiles from microwave attack by the enemy as well as protecting satellites against deadly Electromagnetic Impulses (EMI) generated by nuclear weapons and other cosmic disturbances, which "fry" and destroy electronic circuits. Electronic components currently used in missiles can withstand fields of approx. 300 V/cm, while the fields in case of EMI attack reach thousands of V/cm.

 

[dvdiyen]

LCA tejas has been Tested with KALI 5000..

Not sure about the LCA testing with KALI 5000 (I seriously have my own doubts. KALI 5000 beam weapon is too bulky - it weighs26 tons - including tanks containing 12000 litres of oil. ). But KALI 10000 is under development for quite sometime for IL-76 platform.

 

[ersakthivel]

I hope you can interpret what you have just posted. It seems to prove your statements wrong.

Nothing proved wrong , since I don't make a claim I can not support,

From the equations of R & ROT it is very clear that we must have the ability to apply max load factor at lowest possible speed to have least R and max ROT. And we need max L to maintain level turn otherwise we will start losing height.

L=Clx1/2densityxV^2x S where S is surface area. so we can increase the lift by either increasing the Cl which means increasing AOA or by keeping high speeds which will be counter productive as we want to maintain low speeds to maintain high ROT and very low R, or by increasing the S.

Since it has high S value higher total lift can be had even with bit lesser Cl with a bit lesser AOA.

Compared to all other modern 4.5 the gen and 5th gen fighters which have a far lower value for S compared to their weight.

And another factor that will add more total lift (L)to the LCA that is not in this equation is the role of the cranked delta in developing flow energizing vortices which substantially improve the total available lift.

Your equation does not take into account this crucial design detail inherited from the design of F-16 XL. So even at a lower AOA the total available lift for Tejas will be more because of the relatively higher value for S and the enhanced lift to drag ratio that can be had by the cranked delta generated vortices,

Simply these vortices beneficially increases the LIFT to Drag ratio which add significantly to higher lift.

S is a fixed value for any aircraft.

Fixed values , accepted. But what is important is it is always a higher value compared to empty weight for Tejas and if you add the role of the cranked delta generated vortices in significantly increasing LIFT to DRAG ratio then total L is far higer for Tejas even at lower AOA compared to any other 4.5 or 5th gen fighter in the world.

LCA has large S and very high sweep back, which means that it achieves its peak Cl at very high AOA, and even though it has high S yet it has high stall speeds due to very high sweep back.

Wrong . Due to large S and better lift to drag ratio enabled by cranked delta tejas can achieve comparable lift even at a lower AOA than other fighters, You have to factor in the role of cranked delta besides Cl

it is a very beneficial quality, achieving higher LIFT at lower AOA means you have far lower drag as well.

The reason for the wing form of tejas is clearly stated in the

http://www.airforcemag.com/MagazineArchive/Pages/1983/November 1983/1183f16xl.aspx

Importance of High Turn Rate

For a decade and a half, many fighter tacticians have stressed the paramount importance of being able to sustain a high turn rate at high Gs. The rationale was that with such a capability, enemy aircraft that cannot equal or better the sustained turn rate at high Gs could not get off a killing shot with guns or missiles.

With developments in missiles that can engage at all aspects, and as a result of having evaluated Israeli successes in combat, the tacticians are now leaning toward the driving need for quick, high-G turns to get a "first-shot, quick-kill" capability before the adversary is able to launch his missiles. This the F-16XL can do. Harry Hillaker says it can attain five Gs in 0.8 seconds, on the way to nine Gs in just a bit more time. That's half the time required for the F-16A, which in turn is less than half the time required for the F-4. The speed loss to achieve five Gs is likewise half that of the F-16A.

All of these apparent miracles seem to violate the laws of aerodynamics by achieving greater range, payload, maneuverability, and survivability. Instead, they are achieved by inspired design, much wind-tunnel testing of shapes, exploitation of advanced technologies, and freedom from the normal contract constraints.

The inspired design mates a "cranked-arrow" wing to a fifty-six inch longer fuselage. The cranked-arrow design retains the advantages of delta wings for high-speed flight, but overcomes all of the disadvantages by having its aft portion less highly swept than the forward section. It thus retains excellent low-speed characteristics and minimizes the trim drag penalties of a tailless delta.

Although the wing area is more than double that of the standard F-16 (633square feet vs. 300 square feet), the drag is actually reduced. THe skin friction drag that is a function of the increased wetted (skin surface) area is increased, but the other components of drag (wave, interference, and trim) that are a function of the configuration shape and arrangement are lower so that the "clean airplane" drag is slightly lower during level flight, and forty percent lower when bombs and missiles are added.

And although the thrust-to-weight (T/W) ratio is lower due to the increased weight, the excess thrust is greater because the drag is lower – and excess thrust is what counts..

[So even with lower TWR tejas can produce this crucial excess thrust enabled by low wing loading cranked delta is the reason behind the wing design, not because it was a small plane with with high swept back wings.

when the fighter turns at knife edge ,it is this crucial excess thrust enabled by wing design, ,that helps immensely in achieving higher ITR and better STR for Tejas compensating for the traditionally lower STR for plain deltas like Mirage-2000]

Next, we maneuvered at slow flight speeds and high angles of attack, demonstrating the F-16XL's agile handling in that corner of the performance envelope. With airspeed below 150 knots, Jim invited me to try a roll to the left. Pressure on the side-stick controller resulted in a fast roll, with no sensation of lagging because of the heavy payload. Release of pressure stopped the roll immediately. I tended to "ratchet," and tried to end the roll with opposite pressure. That's unnecessary with the F-16XL's system, as Jim demonstrated. I tried it again, more smoothly this time.

We accelerated back to more than 400 knots and I tried more 360° rolls. Once I was accustomed to the correct control stick pressures, the roll rate was fast and the controls crisp. The same feelings were apparent at 500 knots – quick, sure response, with no feeling of carrying the heavy bomb load.

Then we descended to low level for penetration at high speed. Jim set up the aircraft at 600 knots indicated airspeed at 100 feet above ground level. The ride quality on a very hot day was smooth. The G-indicator on the head-up display (HUD) showed excursions of less than 0.2 above the below 1.0, but they were undetectable in the body. On similar flights with an F-4 as the chase aircraft, its G excursions were as high as 2.0, making for an uncomfortable ride and heavy concentration on flight controls.

In the loaded configuration, the F-16XL can penetrate at low level at airspeeds fifty-to-ninety knots faster than the basic F-16 when similarly configured. In fact, at every corner of the performance envelope, the aircraft has power in reserve, according to members of the Combined Test Force at Edwards.

Next, we conducted simulated weapons passes on a ground target, using the continuously computed impact point system (CCIP) displayed on the HUD. With this system, even this novice pilot, who has difficulty with a non-computing gun-sight, achieved on-target results. Attack maneuvers resulted in G forces ranging to +7.0. With the heavy bomb load aboard, the F-16XL is cleared for maneuvers up to +7.2 Gs, compared with 5.58 Gs in the F-16A. This demonstrates how the designers were able to increase the aircraft weight while maintaining structural integrity and mission performance.

We all know that highly swept wings have lower Clmax compared to unswept or less swept wings when compared apple to apple i.e clean or with leading edge and trailing edge lift augmentation devices deployed/extended.

But unswept wings will always have a far lesser value for S , SO IT EVENS OUT.

It does not matter because the higher value for S and better LIFT to DRAG ratio enabled by cranked delta generated vortices more than make in arriving at higher value for L

However we also know that sweepback increases the S for a given span. LCA is a small ac and it needed a large S so a very highly swept design was chosen to satisfy the need for speed and lift.

Not just that . To take off from meaning full loads at high altitude future Himalayan forward air bases are also another important consideration in having a larger wing area S.It has nothing to do with LCA being a smaller fighter.

With later revision of ASRs it was made to compete and go a further than the Mirage-2000 which too had larger wing area S. You can read test pilots saying take offs are sharper than Mirage-2000 even with restricted flight envelope in Tejas LSps. And a senior official at testing establishment remarked that LCA mk-1, which is considered "underpowered " by IAF itself exceeds the Mirage-2000(which are being upgraded with 40 million dollar a fighter still with the same lesser TWR than Tejas mk-1, so their close combat specs won't increase at all.) in many parameters,

So a larger wings on LCA was a design intent from the start, nothing to with LCA being smaller or having high sweep back. Kota Harinarayana himself has said the cranked delta wing on Tejas was chosen based on the specs of the F-16 XL.

LCA inspite of being optimised for its role suffers the typical problem of delta designs though partly overcome by its compound delta design.
high AOA to achieve high Cl results in veryhigh drag requiring high trust to overcome it.

The statement is right only if LCA is a plain delta like Mirage-2000. It is not , it is a cranked delta ,and so it doesnot suffer from the problems associated with typical deltas.

in Fig. 6 for angle of attack a = 13° and 18° . A fairly good comparison is observed. The vortical flow field captured in calculations is presented in Fig. 7. The particle traces illustrate the detailed structure of the rolled-up vortices.It is seen that the leading edge vortices are strengthened as the flow develops progressively away from the leading-edge of the wing

It is to clarify these things I posted the vortex generation effect of the cranked delta released by NAL.

 

[Decklander]

Nothing proved wrong , since I don't make a claim I can not support,

It is to clarify these things I posted the vortex generation effect of the cranked delta released by NAL.

Vortex generators can be LERX and chins also. The compound delta wing of LCA also does that so nothing new about. But do you know that vortex add drag to the ac? The graph you posted was about movement of CP with AOA and not about Cl. That is what I wanted to inform you. the x/c means distance along x-axis of the chord of the airfoil. we also have y/c which means height along y-axis from wing centerline. The coordinates of airfoil are written in x/c & y/c form. The pix of airflow which you posted is typical of high sweepback airfoil where in the leading edge vortices combine to form one large vortex and result in spanwise airflow rather than along the length of the airfoil.
I wanted to just point that out.

 

[ersakthivel]

Vortex generators can be LERX and chins also. The compound delta wing of LCA also does that so nothing new about. But do you know that vortex add drag to the ac? The graph you posted was about movement of CP with AOA and not about Cl. That is what I wanted to inform you. the x/c means distance along x-axis of the chord of the airfoil. we also have y/c which means height along y-axis from wing centerline. The coordinates of airfoil are written in x/c & y/c form. The pix of airflow which you posted is typical of high sweepback airfoil where in the leading edge vortices combine to form one large vortex and result in spanwise airflow rather than along the length of the airfoil.
I wanted to just point that out.

the vortice flow is generally beneficial and contribute to BETTER LIFT TO DRAG ratio is commonly accepted .

LREX and canards also generate vortices in similar manner. But they impede pilot visibility in close combat. But the cranked delta is part and parcel of the wing so while providing beneficial LIFT to DRAG ratio , it does not affect the pilot visibility.

What I wanted to point out was the wing design of Tejas was not due to its size or high sweep back.

The chief Designer of Tejas , Dr Kota Harinarayana himself has stated that the Wings of Tejas was modeled on F-16 XL in an interview in ADA website.

Also Your formula for L (total lift ) calculations don't factor into them the better lift to drag ratio enabled by the cranked delta which was explained with clarity in the following site,

The Revolutionary Evolution of the F-16XL
from which I quoted a few passages in the post above.

The cranked-arrow design retains the advantages of delta wings for high-speed flight, but overcomes all of the disadvantages by having its aft portion less highly swept than the forward section. It thus retains excellent low-speed characteristics and minimizes the trim drag penalties of a tailless delta.

Although the wing area is more than double that of the standard F-16 (633square feet vs. 300 square feet), the drag is actually reduced.

The skin friction drag that is a function of the increased wetted (skin surface) area is increased, but the other components of drag (wave, interference, and trim) that are a function of the configuration shape and arrangement are lower so that the "clean airplane" drag is slightly lower during level flight, and forty percent lower when bombs and missiles are added.



And although the thrust-to-weight (T/W) ratio is lower due to the increased weight, the excess thrust is greater because the drag is lower – and excess thrust is what counts

This the F-16XL can do. Harry Hillaker says it can attain five Gs in 0.8 seconds, on the way to nine Gs in just a bit more time. That's half the time required for the F-16A, which in turn is less than half the time required for the F-4. The speed loss to achieve five Gs is likewise half that of the F-16A.
..

So how come the vortice impose drag penalty when it is clearly explained that the total drag is lesser than F-16 _A which had a much smaller wing area than the F-16 XL?

When the F-16 XL which has a double the wing area of F-16-A can pull five GS in less than half the time required for F-16 A ,

and achieve than half the speed loss of F-16 A,

how can you say the vortices generated by cranked delta impose more drag?

F-16 XL also has a very highly swept wing like with high sweep back angle like tejas as well.

If it is the case F-16 Xl should take twice the time required by F-16 A to pull 5Gs and loss double the speed lost by F-16-A in the process.

So if we add the extra lift from the vortices irrespective of the high sweep angle Tejas has better lift available even in lower AOA if you take the F-16 XL which had the similar low wing loading cranked delta for comparison.

The ones above is F-16 Xl,
Ones below is Tejas

take a look at the sweep back angle.

From the following pic it is clear that the F-16 Xl (which has a more highly swept back angle cranked arrow low wing loading delta exactly like Tejas ) than the F-16 A flying along with it, pulled more Gs faster with less loss of speed and lower clean airplane drag compared to F-16,

.

So the same principle applies to Tejas as well when you compare it with fighter that have lesser sweep back angle wing than Tejas.

 

[Decklander]

This is what I do not like, you keep repeating same stuff over and over again. I must say just the way you had no idea about ROT and wingloading, you are wrong about L/D ratio also. can you please explain to me how L/D ratio affects performance of a jet engined ac and what is the diff between min drag speed and max reserve of power speed of a jet ac. How do they effect the ability of a jet fighter?

And my humble request to you. Pls do not post anything regarding F-16XL. That crap is long forgotton with advancements in tech and aerodynamics. It may have been what you claim in 1986, but now it is as obsolete as piston engine fighters.

 

[ersakthivel]

F-16 XL above has almost identical highly swept back wing angle as well as cranked delta wing shape as that of tejas below,