LCA: News & Discussions: 15 August 2017

[shiv]

BTW does Tejas have supersonic drop tanks? The Tejas in webpage tejas.gov.in has 2 different drop tanks on either wing with one stremlined more than the other. Is the light bluw drop tank a supersonic drop tank?

I do not know the answer to this question but I have not understood the purpose of supersonic drop tanks.(!read next sentence before replying!)

I request people not to tell me that it will allow Tejas to fly supersonic with drop tanks. The question I am asking is - under what situation would the Tejas be expected to fly supersonic with drop tanks?

If the Tejas is escaping from a tricky combat situation, flying supersonic or heading towards supersonic would be needed - but the drop tanks would be dropped first.

On an attack mission those drop tanks would be needed for range and supersonic flight would simply burn massive amounts of fuel and make the tanks redundant.

At the start of air air to combat, if it happens, drops tanks would be dropped

If the idea is to fly towards and intercept target as quickly as possible - then drop tanks would hinder acceleration and climb. The plane would be loaded with maybe 2 AAMs and flying clean otherwise to climb to altitude while accelerating to close in to the target.

So someone please explain to me why those supersonic drop tanks are needed.

[srai]

BTW does Tejas have supersonic drop tanks? The Tejas in webpage tejas.gov.in has 2 different drop tanks on either wing with one stremlined more than the other. Is the light bluw drop tank a supersonic drop tank?

Under development.

[JTull]

BTW does Tejas have supersonic drop tanks? The Tejas in webpage tejas.gov.in has 2 different drop tanks on either wing with one stremlined more than the other. Is the light bluw drop tank a supersonic drop tank?

I do not know the answer to this question but I have not understood the purpose of supersonic drop tanks.(!read next sentence before replying!)

I request people not to tell me that it will allow Tejas to fly supersonic with drop tanks. The question I am asking is - under what situation would the Tejas be expected to fly supersonic with drop tanks?

If the Tejas is escaping from a tricky combat situation, flying supersonic or heading towards supersonic would be needed - but the drop tanks would be dropped first.

On an attack mission those drop tanks would be needed for range and supersonic flight would simply burn massive amounts of fuel and make the tanks redundant.

At the start of air air to combat, if it happens, drops tanks would be dropped

If the idea is to fly towards and intercept target as quickly as possible - then drop tanks would hinder acceleration and climb. The plane would be loaded with maybe 2 AAMs and flying clean otherwise to climb to altitude while accelerating to close in to the target.

So someone please explain to me why those supersonic drop tanks are needed.

Are you questioning the need for any drop tanks or just the new ones? In any case, how long can LCA fly supersonic at full afterburners on level flight? I doubt it'll be longer than a few minutes.

I don't know if India ever designed/built droptanks in the past. There's no harm in us mastering this piece of kit.

Also, why should a drop tank suitable for another aircraft, say Mig-21, will be suitable for LCA? What's the harm in developing customised drop tanks that are more aerodynamic and suitable to the mission profiles of LCA? Who's is to say that a 'supersonic' drop tank won't help in sub-Mach/transonic flight.

[nam]

So someone please explain to me why those supersonic drop tanks are needed.

This is purely a guess. May be useful while flying on low level mission.

You would need extra fuel, hence the drop tanks. Need to be optimized for high drag, hence supersonic.

[shiv]

Also, why should a drop tank suitable for another aircraft, say Mig-21, will be suitable for LCA? What's the harm in developing customised drop tanks that are more aerodynamic and suitable to the mission profiles of LCA? Who's is to say that a 'supersonic' drop tank won't help in sub-Mach/transonic flight.

Sir you are asking me a question in response to my questions. But do you have an answer. This is a non answer

[shiv]

So someone please explain to me why those supersonic drop tanks are needed.

This is purely a guess. May be useful while flying on low level mission.

You would need extra fuel, hence the drop tanks. Need to be optimized for high drag, hence supersonic.

Thanks for attempting an answer and not using rhetoric as a reply.

You are saying that transonic drag may be handled better by supersonic drop tanks. Maybe. I wonder if anyone knows. But the reason I asked is that trying to go supersonic even with supersonic tanks especially at low altitude will burn up fuel at a horrendous rate.

Let me ask another question that may be easier to answer. Are HAL/ADA trying to make supersonic drop tanks for LCA or is it BRF wishlist? I sometimes cannot tell for sure?

[Viv S]

I request people not to tell me that it will allow Tejas to fly supersonic with drop tanks. The question I am asking is - under what situation would the Tejas be expected to fly supersonic with drop tanks?

Interception.

Pair of aircraft are on ground, fuelled up. Scramble call comes, they launch. They need to get supersonic to intercept a enemy flight before it can get to X, jettisoning the tanks before hard maneuvering stage, while retaining internal fuel reserves for the fight & recovery.

You can launch without tanks but that'll limit your combat radius. Or you can launch with subsonic tanks which will increase the time taken to reach the combat area and may result in pilot jettisoning half empty tanks on arrival.

[shiv]

Interception missions.

Pair of aircraft are on ground, fuelled up. Scramble call comes, they launch. They need to get supersonic to intercept a enemy flight before it can get to X, jettisoning the tanks before maneuver, retaining internal fuel reserves for the fight & recovery.

You can launch without tanks but that'll limit your range. Or you can launch with subsonic tanks which will increase the time taken to reach the combat area and may result in pilot jettisoned partially filled tanks on arrival.

I accept this as a valid possibility but as I said in my first post a high speed dash would require a rapid climb to altitude where supersonic would help get closer to target. But those tanks would reduce both climb rate and acceleration.

There may be a "sweet spot" where a single drop tank and 2 missiles would usefully extend radius from say 150 km to 200, with missile range adding some to that

[NRao]

As a FYI, a drop tank design takes into account the additional drag introduced by the drop tank itself. So, some amount of fuel - in the drop tank - is actually allocated to overcome this additional drag. Remainder of the fuel is allocated for any other activity/task.

[shiv]

But if the purpose is urgency anything hanging off the aircraft is a liability. Most pictures I have seen of CAP by western fighters feature drop tanks. But none are doing CAP at supersonic speeds. They probably empty those tanks first and if at all a supersonic dash is needed they would jettison them. So there is no need for supersonic tanks in such a situation.

Ultimately "supersonic tanks" are merely.tanks that will fly past Mach 1 without misbehaving or ripping off the wing or crashing the plane if jettisoned.

Does anyone have any information that LCA drop tanks are NOT supersonic-safe?

[Indranil]

Hakeem,

The current tanks on LCA are subsonic tanks. I heard that the manufacturing of the supersonic tank has been completed. Most likely, they are undergoing ground tests now. There manufacturing technique is completely different from the subsonic tanks.

Supersonic tanks are not a priority for the same reason that you identified: their use case is very very limited. It can only be for A2A purposes where a slightly longer supersonic dash is required.

It is not an FOC requirement.

[Viv S]

I accept this as a valid possibility but as I said in my first post a high speed dash would require a rapid climb to altitude where supersonic would help get closer to target. But those tanks would reduce both climb rate and acceleration.

There may be a "sweet spot" where a single drop tank and 2 missiles would usefully extend radius from say 150 km to 200, with missile range adding some to that

Lets say average rate of climb is 300 m/s on internal fuel and 200 m/s with drop tanks. That's 33 secs to reach 35,000 ft in the first case, and 50 secs in the second case. A difference of about 15 secs +/-.

On the other hand, the speed difference with subsonic tanks, say Mach 1.2 (25 km/min) to Mach 0.9 (18.5 km/min) will mean a difference of almost 5 mins over 300 km (12 min to 16.5 min).

For launching without tanks you'd have see what kind of combat radius you can get but my guess is that the supersonic tanks will increase it by at least 50% - its an additional 2000-2500L over an internal fuel capacity of 3000L. So perhaps 300 km instead of 200 km.

[Viv S]

But if the purpose is urgency anything hanging off the aircraft is a liability. Most pictures I have seen of CAP by western fighters feature drop tanks. But none are doing CAP at supersonic speeds. They probably empty those tanks first and if at all a supersonic dash is needed they would jettison them. So there is no need for supersonic tanks in such a situation.

Actually most aircraft are integrated with a set of supersonic as well as subsonic tanks. Eg. -

[srai]

... The question I am asking is - under what situation would the Tejas be expected to fly supersonic with drop tanks?
...
Are HAL/ADA trying to make supersonic drop tanks for LCA or is it BRF wishlist? I sometimes cannot tell for sure?

Your answers are in this presentation.

17th Annual CFD symposium, August 11-12, 2015, Bangalore
CFD studies of a Supersonic drop tank for a generic fighter aircraft (LCA)

...
I. Introduction
The shape optimization of a Fighter Aircraft’s external fuel tank plays a critical role in its mission performance. Specific Air-superiority missions need the use of a supersonic fuel tank to reach a far-off location as fast as possible and patrol the target zone. A large tank will cause a large drag but can carry significantly more fuel to comfortably achieve a particular mission. The main objective of this study is to arrive at a supersonic external fuel tank with the best compromise between maximum fuel capacity and minimum drag.
...

The final external fuel tank with 0.231 as L1 and 0.402 as L2 arrived at from this study gave a total volume of around 710LT with only 2 counts more than that of the existing 450LT fuel tank as shown in Fig.7. ...



The mission performance of the aircraft with its integrated under fuselage fuel tank is estimated from an In-House Point Mass model, YAPP [Ref.1]. Intentionally the details of the actual mission performance are not disclosed in this paper. Typically air superiority missions have a takeoff, climb and cruise to a specific target zone followed by loiter and combat segment. The higher the fuel capacity of the external tank, the greater is loiter time. The mission program YAPP takes input as the aerodynamic and engine characteristics of the aircraft with which the delta aerodynamics, delta weight and the delta fuel of the external fuel tank is added. The fuel and the drag values of the design samples are input along with their estimated structural weight for YAPP which estimates their corresponding mission performance. The final shape arrived at from this optimisation process with 0.231 L1 and 0.402 L2 gives approximately 11% increase in flight mission time due to the increase in fuel capacity of more than 260liters as compared to the existing 450LT. However its 2 counts drag penalty on the supersonic drag of the fighter aircraft is compensated by its increased fuel capacity for its mission.
...

[shiv]

17th Annual CFD symposium, August 11-12, 2015, Bangalore
CFD studies of a Supersonic drop tank for a generic fighter aircraft (LCA)

Very informative.

If this is about the LCA, the paper says that the existing 450 L tank is already a supersonic tank. This study was to increase the capacity of the fuel tank. So all this talk about "Should they make a supersonic fuel tank" and "Why not make a supersonic fuel tank" should be put to rest. There already is one -if this paper is to be believed.

Preliminary computations along with a grid independence study was carried out in PARAS and CFD++ for the existing circular supersonic 450LT (fuel volume is 450liters) tank in under-fuselage station of the Fighter Aircraft as a part of validation studies. The grid convergence study carried out in PARAS is with grid sizes ranging from 4million to60million and the delta drag of the external tank was found to be consistent with an acceptable error band.

Existing 450LT tank was circular with the length of the nose and trailing region being approximately 40% and25% of the total length of the tank. Present study, to arrive at a larger capacity fuel tank is based on this existing450LT tank which was elongated by about 400mm and widened around the major axis by about 170mm.

But..uh oh...

The paper is entitled:
"CFD studies of a Supersonic drop tank for a generic fighter aircraft "

Generic. Not LCA

[Abhibhushan]

Subject - supersonic interception

The discussion reminds me of a training profile during ops training on a MiG-21FL.

Scramble - climb subsonic with full after burner while turning to initial vector - at altitude 16km level out and accellarate to M2 - acquire target and launch K13. Return to base subsonic

(In actual combat drop tank to be carried and jettisoned in climb when empty )

The whole sortie lasted less than 10 minutes. Max intercept distance was about 120 km.

Please note: The last time that I practiced this profile was more than 49 years ago! My numbers (quoted from memory) may not be accurate.

[Aditya_V]

Thanks.So LCA supersonic drop tanks are in development and are required for required to give better range in interception missions. 49 years ago inbetween the65 and 71 wars. Sir can I ask what was your role in 71?

[shiv]

The whole sortie lasted less than 10 minutes.

Wow. Slambam thankye maam!

[Kartik]

I sure hope so but i've seen reports that suggest otherwise too. Keeping fingers crossed although am sure that that mk1a will have the Derby I so that the radar range can be better exploited.

There is no new integration needed as such. The connectors remain the same. The weight will be different and will need some new CFD analysis and new flight testing, but all airplanes integrated with the Derby BVRAAM can carry the I-Derby ER as well. Anyway, Rafael has closed production of the older Derby model, so now its only I-Derby ER.

[Kartik]

Let me ask another question that may be easier to answer. Are HAL/ADA trying to make supersonic drop tanks for LCA or is it BRF wishlist? I sometimes cannot tell for sure?

It has been under development for a long time now. These figures of the supersonic drop tank and the paper describing its optimization were posted on the LCA thread many months ago.

The operational reason I can think of a supersonic drop tank is to allow for a near supersonic dash to a target or area of action. Not for every mission or every situation, but in cases where the Tejas will be needed to reach its area of action quickly, it should be able to without having to drop its fuel tanks. Escorting fast aircraft is another task that may require supersonic drop tanks. As an escort, you might need to dash ahead of a group of strikers to screen for enemy fighters.

I don't know what people think, but drop tanks are actually complex pieces of equipment and are not very cheap. Tejas' drop tanks are built of composites and dropping them in order to greatly reduce drag or the weight vs G limits imposed by the FBW is an act of desperation and not a SOP. Supersonic drop tank's will also allow for greater maneuverability and higher G restrictions in the FBW code. So the jet carrying it may not need to drop them under most circumstances.

[ramana]

Prasad, excellent article. Hope you get to write more and improve the quality of defense reporting.

So write a series of articles say one every two months.
Next one could be on the KA226T and the LUH.

One taboo word for me is "home grown"!

[Kartik]

But..uh oh...

The paper is entitled:
"CFD studies of a Supersonic drop tank for a generic fighter aircraft "

Generic. Not LCA

All LCA related studies are presented as 'generic fighter aircraft' but the figures and details give it away.

[ramana]

Thanks.So LCA supersonic drop tanks are in development and are required for required to give better range in interception missions. 49 years ago inbetween the65 and 71 wars. Sir can I ask what was your role in 71?

You don't know who the poster is!!!!

That's an Air Cdre who headed the Jaguar DARIN upgrade among other things.
And shiv that is saar not maam.

[Karan M]

But..uh oh...

The paper is entitled:
"CFD studies of a Supersonic drop tank for a generic fighter aircraft "

Generic. Not LCA

All LCA related studies are presented as 'generic fighter aircraft' but the figures and details give it away.

Just like CAGs "study of fighter A purchased from Britain with two engines and used as a strike aircraft by IAF".

[Indranil]

Actually most aircraft are integrated with a set of supersonic as well as subsonic tanks. Eg. -

The Mirage on the right cannot go supersonic without losing the two subsonic tanks.

Are these supersonic tanks? I don't think so.

The eminence of supersonic tanks for single-engined fighters and twin engine fighters are different. Light single engined fighters are almost always power limited. Even with relatively small internal fuel tanks, their aerodynamic shape and size is very close to what the engine can push through at supersonic speeds. That's why there is barely enough room to add one supersonic centerline tank. Conversely, if a single engined fighter could take multiple external supersonic tanks, a question could be asked as to why the designer did not increase internal fuel space instead?

Twin engined medium or heavy fighters, are less power and space limited. Designers have headroom to size the internal tank optimally where the fighter has sufficient endurance and retain good PWR for extreme agility. There is sufficient margin to add multiple supersonic fuel tanks if required.

Fifth gen medium fighters like F-35 and others make an aerodynamic compromise for stealth. They have oversized internal fuel tank for longer endurance and stealth. However, there is no option of overcoming form drag or induced drag if such a fighter is challenged to an aerial battle.

[Indranil]

Subject - supersonic interception

The discussion reminds me of a training profile during ops training on a MiG-21FL.

Scramble - climb subsonic with full after burner while turning to initial vector - at altitude 16km level out and accellarate to M2 - acquire target and launch K13. Return to base subsonic

(In actual combat drop tank to be carried and jettisoned in climb when empty )

The whole sortie lasted less than 10 minutes. Max intercept distance was about 120 km.

Please note: The last time that I practiced this profile was more than 49 years ago! My numbers (quoted from memory) may not be accurate.

That sounds very right in every aspect.

[Philip]

Indy, I was thinking the same reg.LCA weight saving with a lighter AESA radar, dumping ballast for an enlarged fuel tank.

[Viv S]

Actually most aircraft are integrated with a set of supersonic as well as subsonic tanks. Eg. -

The Mirage on the right cannot go supersonic without losing the two subsonic tanks.

Are these supersonic tanks? I don't think so.

That's kind of the point.

I posted pics of two aircraft types. One example of each type with subsonic tanks and another example of the same type with supersonic tanks - to illustrate the fact that the two distinct types of drop tanks can be and are integrated on the same aircraft. Not merely wishful thinking on BRF.

The eminence of supersonic tanks for single-engined fighters and twin engine fighters are different. Light single engined fighters are almost always power limited. Even with relatively small internal fuel tanks, their aerodynamic shape and size is very close to what the engine can push through at supersonic speeds. That's why there is barely enough room to add one supersonic centerline tank. Conversely, if a single engined fighter could take multiple external supersonic tanks, a question could be asked as to why the designer did not increase internal fuel space instead?

Three would be a stretch, but two ought to be quite doable.

Fifth gen medium fighters like F-35 and others make an aerodynamic compromise for stealth. They have oversized internal fuel tank for longer endurance and stealth. However, there is no option of overcoming form drag or induced drag if such a fighter is challenged to an aerial battle.

The F-35 can more than hold its own in any aerial battle, and once its pilots got to grips with it, the majority preferred it over the F-15C & F-16. The real problem with the wider fuselage is transonic drag where a lightly loaded Viper-C or a Rafale/EF with a medium load clear the hump significantly faster.

[Indranil]

Yes, the Mig-21 could do it. But it could also reach Mach 2 without them. LCA/Gripen don't have that level of margin.

Sorry, I seemed to have touched a nerve with the F-35. You can tell me about what some say. I can tell you what some others say. That is not the question. Beating the F-15/F-16 with a plane designed 30-40 years later is also not the question.

What the LM engineers did was a well thought out compromise. For the same amount of fuel, the F-35 pays less form drag than say the Rafale with external fuel tanks. But it does not have the liberty to change that drag. The Rafale does. I don't understand the need to be so protective about it. It is all physics only. Su-27 family also pays that price. It is okay.

[Indranil]

Indy, I was thinking the same reg.LCA weight saving with a lighter AESA radar, dumping ballast for an enlarged fuel tank.

AESA radar will be heavier. There is no space for the LCA to increase internal fuel. I think they should really try to lighten the plane, smooth out the edges(literally) and add CFTs.

[Eric Leiderman]

I also thought AESA would be lighter, The RAVen ASEA of the gripen ng specs below.

TECHNICAL SPECIFICATION
Frequency X Band
Scan coverage +/- 100°
Scan velocity Instant beam switching
Cooling Liquid and air
Weight 215kg
Key interfaces Ethernet, 1553B

I am not sure what the weight of our current Yahoodi radar is.

[shiv]

And shiv that is saar not maam.

ramana you have obviously not heard the original joke about Speedy Gonzalves saying "Slambaamthankyoumaam"

That apart I know Abhibushan personally. In fact when I was forum admin he had requested me to give him the forum handle "Ahibhushan". I misread the message and gave him the handle "Abhibhushan". He was a personal friend and mentor of late Wingco Suresh and the story of how he was involved with Suresh's marriage is there on his blog -TKS tales

[Viv S]

Yes, the Mig-21 could do it. But it could also reach Mach 2 without them. LCA/Gripen don't have that level of margin.

Reaching Mach 2 was more a function of the design rather than the thrust-to-weight ratio. Ultimately, what matters is adequate excess thrust to cover the drag added by the tanks (plus interference) in order to clear the transonic hump. How the aircraft behaves over Mach 1.5 doesn't really matter that much.

Sorry, I seemed to have touched a nerve with the F-35. You can tell me about what some say. I can tell you what some others say. That is not the question. Beating the F-15/F-16 with a plane designed 30-40 years later is also not the question.

What the LM engineers did was a well thought out compromise. For the same amount of fuel, the F-35 pays less form drag than say the Rafale with external fuel tanks. But it does not have the liberty to change that drag. The Rafale does. I don't understand the need to be so protective about it. It is all physics only. Su-27 family also pays that price. It is okay.

No no, no nerve touched. Just mentioning that the 'not-a-dogfighter' is a popular myth that's come up a lot in debates around the web and elsewhere, although its been losing traction since the aircraft's performance at the events like the Paris Air Show. So I was just relating what most of the pilots have been saying. Superb high AoA performance, (subsonic) acceleration and energy recovery but so-so STR, so your comparison to the Su-27 is quite apt.

[Cain Marko]

If the idea is to fly towards and intercept target as quickly as possible - then drop tanks would hinder acceleration and climb. The plane would be loaded with maybe 2 AAMs and flying clean otherwise to climb to altitude while accelerating to close in to the target.

So someone please explain to me why those supersonic drop tanks are needed.

The above reason seems most likely. Say target is at a distance that can be only reached via EFTs, and fighter needs to go there quickly - what other optiion is available better than supersonic EFTs? IFR perhaps, but i'm not sure how long this procedure normally takes. btw why would plane be restricted to only 2 AAMs? Wouldnt this be a function of its thrust ? I seem to recall seeing Rafale and M2k pics with supersonnic efts and bristling with AAMs...

Doh...I see said pics already put up by Viv, a bit slow and hasty on my part....

[shiv]

Folks here is a little titbit (a little item of information, NOT a part of a mammary gland)
http://www.airvectors.net/avvulcan_1.html

About the Vulcan

Once in the air, the Vulcan B.2 had excellent high-altitude performance, with its big wing allowing the bomber to maneuver with agility at heights where interceptors would be struggling to make a turn.

The Tejas should be great in the Himalayan region and over Tibet no?

[shiv]

Folks here is a little titbit (a little item of information, NOT part of a mammary gland)
http://www.airvectors.net/avvulcan_1.html

About the Vulcan

Once in the air, the Vulcan B.2 had excellent high-altitude performance, with its big wing allowing the bomber to maneuver with agility at heights where interceptors would be struggling to make a turn.

The Tejas should be great in the Himalayan region and over Tibet no?

[Cain Marko]

^ Thiss is the second time i've heard something of this nature. Previously it was from a knowledgeable fellow who said that above 30000 feet, the LCA will be absolutely dominant. FWIW.

[shiv]

. btw why would plane be restricted to only 2 AAMs? Wouldnt this be a function of its thrust ? I seem to recall seeing Rafale and M2k pics with supersonnic efts and bristling with AAMs...

Those Rafale pics show 4 BVR and 2 WVR - and vulgar looking aesthetics killing drop tankis but those planes are on AWACS controlled timepass CAP mission. Not even one AAM has ever been actually phyrred.

What I am talking about is actual conflict like scenario where Tejas is required to close in on a target that has just entered Indian airspace and intercept ASAP. In the Indian situation this has often meant visual identification. Hence WVR. And for acceleration and high climb rate - just 2 AAMs. If two Tejas take off - that gives 4 AAMs and the possibility of nailing the target from two different directions.

My guesstimate is a target 100-150 km away requiring contact within minutes

[Indranil]

It is exactly that. It is a supersonic dash from TO to intercept within 10 minutes, subsonic thereafter.

I expect LCA to be able to this with 4 AAMs each though.

[Indranil]

Meanwhile, I don't know why the subsonic centerline tank is circular in cross section? They can easily reach the 1200 ltr target with an oval tank!