LCA News and Discussions, 22-Oct-2013

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Indranil
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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 30 Jan 2015 12:19

Yeah, I am increasingly getting sanguine that there is no APU on Tejas. When the engine flames-off, there is enough juice in the hydraulic pumps to go for about a minute. During this time EPU is comes up (either on pilot input or through the FCS sensing the fall in the engine RPM) and supports the hydrulic pumps for a few more minutes. During this time the JFS attempts to relight the engine.

The scoop is there to provide cool fresh air for one of the 3 cases I had speculated on the last page.

Case 1: This air is used along with the engine bleed air to cool the afterburner duct. This may be true because this air combines with the bleed air from the engine, then travels through the AB duct and leaves through the gap (in skirting at the base of engine nozzle along the upper semicircle) that I have pointed to before. This will also aid in IR signature suppression. The problem with this theory is that Tejas TDs did not have this scoop, but had two other scoops on each side of the dorsal spine. These scoops have been retained even now and are called "engine bay venting scoops". If air intake through these scoops was not sufficient, then they could have simply enlarged them. Why add a third bigger one, unless it provides more uniform cooling?
Case 2: The Environment Control System (ECS) in Tejas also uses the bleed air from the engine by cooling it through a series of heat exchangers and a Cold Air Unit. The air from the dorsal air intake is used to provide fresh air to this mixture.
Case 3: Both of the above. The air from the 3 scoops mixes with the bleed air of the engine. The ECS sucks in the air it needs and rest is passed through the AB duct.

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Re: LCA News and Discussions, 22-Oct-2013

Postby member_28932 » 30 Jan 2015 14:19

Yogi_G wrote:Is that a dorsal scoop a la F-16 Vista modification to bring in additional maneuvarability? The Americans had to scramble to get their fighters as nimble as the mig-29 and the sukhois and needed a series of modifications (physical and fly by wire) to be able to execute such maneuvers as the Pugachev.


This remind me a quotation of a Russian technologist who had said that If we are awarded the MMRCA contract, we shall transfer a technology to make plane highly maneuverable to India. I do not know what he was talking about but we should look into that. If we can improve the performance of our plane with consultancy such as this Russian technology or some come consultency in engine integration and air intake redesign, we should not mind in hiring these consultency. The contract should be performance based. i.e payment shall be in proportion to performance improvement.
Last edited by Indranil on 30 Jan 2015 20:23, edited 1 time in total.
Reason: This thread is on a tight lease. As I said earlier, if you speculate too wildly without knowledge, you will earn a warning. Well, now you have. If you wan't to speculate, take it to the newbie thread.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Thakur_B » 30 Jan 2015 21:07

Raman wrote:That one is probably the exhaust and, the grilled inlet between the MLG doors is probably the inlet, if this F-15 schematic is anything to go by.

Image


Similar openings can be seen at the port side behind cockpit on Tejas. Which is why I believe the intake at tail fin is for APU and not for jet fuel starter.
Image

indranilroy wrote:The scoop is there to provide cool fresh air for one of the 3 cases I had speculated on the last page.

Case 1: This air is used along with the engine bleed air to cool the afterburner duct. This may be true because this air combines with the bleed air from the engine, then travels through the AB duct and leaves through the gap (in skirting at the base of engine nozzle along the upper semicircle) that I have pointed to before. This will also aid in IR signature suppression. The problem with this theory is that Tejas TDs did not have this scoop, but had two other scoops on each side of the dorsal spine. These scoops have been retained even now and are called "engine bay venting scoops". If air intake through these scoops was not sufficient, then they could have simply enlarged them. Why add a third bigger one, unless it provides more uniform cooling?
Case 2: The Environment Control System (ECS) in Tejas also uses the bleed air from the engine by cooling it through a series of heat exchangers and a Cold Air Unit. The air from the dorsal air intake is used to provide fresh air to this mixture.
Case 3: Both of the above. The air from the 3 scoops mixes with the bleed air of the engine. The ECS sucks in the air it needs and rest is passed through the AB duct.


A cooling air outlet would not require be required to be made out of metal. A hot APU or EPU exhaust might warrant that.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 30 Jan 2015 21:59

Thakur_B wrote:Similar openings can be seen at the port side behind cockpit on Tejas. Which is why I believe the intake at tail fin is for APU and not for jet fuel starter.
Image

This is a little silly post by you. Why would the JFS be behind the cockpit?

Those openings are actually present on both sides, not just the port side. They are heat exchangers for the ECS. As I have said earlier, the ECS uses the bleed air from the 7th stage of the engine. One can see the pipe emanating from the side of the engine, travelling through the spine to the ECS equipment bay which is housed just behind the cockpit. There this air (at about 600 C) passes through 6 heat exchangers and a air cooling unit to bring down the temperature and pressure. The cooled air is then used for cockpit pressurization, deicing, cooling of avionics, demistifying the canopy etc. etc.
Image

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Re: LCA News and Discussions, 22-Oct-2013

Postby srai » 31 Jan 2015 01:09

On page 14 of Tejas: IOC Brochure:
Heat Exchangers
Successfully designed, developed by BHEL-HPVP (Formerly BHPV) and flight qualified 10 types of compact plate-fin heat exchangers for LCA-TEJAS aircraft.


Dr.G.J.Guru Raja
This blog describes the experiences as head of R&D of a public sector undertaking(Bharat Heavy Plate & vessels Ltd).

Details of heat exchangers brazed
17 numbers of heat exchangers were to be brazed, some of aluminium and some of stainless steel.

The minimum core weight of the aluminium heat exchanger(Liquid-Air HE) was o.28 Kg and the finished weight of the same heat exchanger was 0.85 Kg. The maximum core weight of the aluminium heat exchanger(Secondary HE) was 8.78 Kg the finished weight was 12.0 Kg. The aluminium fins are as thin as 0,0762 mm.

There were a number of stainless steel heat exchangers. The minimum core weight of the heat exchanger(Precooler) was 8.8 Kg and the finished weight was 12.0 Kg. The maximum core weight(Primary HE} was 15.6 Kg and the maximum finished weight was 23.0 Kg. The fin thickness was 0.0762 mm.


If you look at the thickness of the fins the difficulty in brazing can be gauged. CLOSE CONTROL OF THE BRAZING TEMPERATURE WAS ESSENTIAL FOR THE SUCCESS OF THE BRAZING OF THESE HEAT EXCHANGERS.

All these heat exchangers are performing successfully in the Supersonic air craft developed by Aeronautical Development Agency ,LCA TEJAS, and have clocked hundreds of flight hours. India is one of the few countries which have such a sophisticated technology.

My association with this project was in the initial brazing trials as I left BHPV in 1995.
Credit should go to R&D team led by Mr. Panigrahi DGM(R&D) who completed the project. Recently ADA has placed an order worth Rs.20 crores for a few sets of these heat exchangers.


vacuum brazed aluminium heat exhangers for aero space applications
Aeronautical Development Agency gave R&D of BHPV a development contract for the design of compact heat exchangers for the supersonic air craft which they were designing.The heat exchangers were to be fitted in an envelope volume specified by ADA. The smallest aluminium heat exchanger had dimensions of 130mm x 30mm x 55mm and the largest heat exchanger had dimensions of 250mm x 140mm x 370mm.

The smallest stainless steel heat exchanger had dimensions of 175mm x 118mm x 200mm and the largest heat exchanger had dimensions of 250mm x 140m x 282 mm.


The challenge was to optimise the design with in the space provided so that the heat exchangers meet the heat dissipating requirements. Our design engineers developed computer programmes to optimise the heat exchangers. It took us over an year to fit all the heat exchangers in the given envelope. Our work was finished.

Brazing of the heat exchangers was the responsibility of another metallurgical laboratory in the defence sector. ADA financed procuring a vacuum furnace for aluminum brazing. Even after several trials over a period of one year they were no where near achieving the brazing. The scientists in the laboratory were so secretive that they did not want us to see the brazing furnace. After much pursuation we were allowed to visit the laboratory where brazing was being carried out. Our visit convinced us that the brazing furnace is defective which was the cause for their failure in brazing. Even after several attempts the laboratory was not successful in brazing. At that time we made a proposal to ADA. We proposed that the brazing also should be a part of our design contract. ADA's scope was to import the components for brazing and supply to us.Once we acheved brazing the technology was the property of BHPV. ADA agreed to our proposal. Imported vacuum brazing furnaces are very expensive and hence we decided to manufacture a brazing furnace designed by us. The next blog describes how we went about the design of the vacuum brazing furnace.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Karan M » 31 Jan 2015 02:52

An Israeli view on Tejas. Defense Update is fairly well recognized and widely cited. The "took so long" stuff is prosaic & widely rehashed, the 60% indigenous part doesn't for instance bring in how "indigenous" the Gripen or similar platforms are. However the site acknowledges:

http://defense-update.com/20150118_teja ... MwAky7g_Ko

Among the causes for the lengthy development cycle was the Indian insistence on the local development of technology and manufacturing capabilities. As opposed to the Chinese developers which relied on spying and the reverse engineering of foreign designs, the Indian scientists and engineers did it all by themselves. As the program dragged along, and certain foreign technologies nevertheless still had to be used, the Indians obtained them with permission and through dialogue. They should be commended for their persistence and dedication in achieving their goals without the dubious Chinese methods.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Karan M » 31 Jan 2015 02:54

CAS Arup Raha on the Tejas. As surmised, declining squadron numbers have made the IAF refocus on the program.
http://www.thehindubusinessline.com/com ... 799380.ece

The CAS outlined that LCA is the need of the hour, given the operational needs of IAF. “We are happy to receive the documents of the first series production of LCA,” he said. He complimented HAL for handing over this aircraft, which would allow its induction and subsequent formation of the first Tejas squadron.
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Re: LCA News and Discussions, 22-Oct-2013

Postby Karan M » 31 Jan 2015 02:57

Naval view.
http://www.oneindia.com/feature/all-war ... 18037.html

All warships, submarines being built in India: Navy Chief

Bengaluru, Jan 10: The Chief of Naval Staff Admiral R K Dhowan said on Saturday that the Indian Navy has become a Builders' Navy from a Buyers' Navy. "Not a single ship or a submarine is on order any more abroad. Future warships will be built in India," he said during the Second Admiral R L Pereira Memorial Lecture in city.


Navy Chief pats NLCA team Admiral Dhowan met with the Naval LCA team from Aeronautical Development Agency (ADA) and congratulated them for the recent successful NP-1 trials in Goa. The NLCA had its maiden flight from the Shore-Based Test Facility (SBTF) in Goa, thereby crossing a critical milestone.


The Navy Chief also interacted with Cmde C D Balaji (Retd) Project Director LCA (Navy) and Commodore Jaideep Maolankar, the pilot who undertook the historic ski-jump take-off from SBTF. Later speaking to OneIndia, Cmde Balaji (Retd) said that the second prototype of NLCA (NP-2) will soon have its maiden flight. "We are done with most of the tests barring a few. We are hopeful that the NP-2 will have its first flight within a weeks' time," Cmde Balaji (Retd) told OneIndia. DRDO adds more teeth to Tejas


Image
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Re: LCA News and Discussions, 22-Oct-2013

Postby JTull » 31 Jan 2015 05:04

srai, excellent post on brazing.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Shreeman » 31 Jan 2015 09:47

This here picture isnew, and big.
Image

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Re: LCA News and Discussions, 22-Oct-2013

Postby deejay » 31 Jan 2015 10:03

Further on the JFS, I was reading the DRDO pages and there was a news release on the cold temperature starts with some details on the JFS.

http://www.drdo.gov.in/drdo/English/dpi/press_release/lca29012015.pdf

PRESS INFORMATION BUREAU (DEFENCE WING)
GOVERNMENT OF INDIA
*********
LCA TEJAS ACHIEVED YET ANOTHER ACCOMPLISHMENT
New Delhi: Magha 08, 1936*
Wednesday, 28 January 2015

With three consecutive start-ups of its engine after overnight soak in extreme cold(around -15ºC) conditions of Laddakh winter, that too withoutany external assistance, Tejas, the Indian Light Combat Aircraft has achieved yet another and a rare distinction. Starting the fighter aircraft under suchextreme condition without any external assistance or heating is atechnology challenge. The requirements become further stringent when the starting is to be done three times consecutively with a partially charged battery. Team LCA led by AERD&C of HAL, and members from ADA, NFTC, IAF, CEMILAC and DGAQA have succeeded in achieving this. “The team LCA has achieved a technological breakthrough”, stated Dr. PS Subramanyam PGD (CA) & Director, ADA.

The engine starter is developed indigenously by HAL Aero Engine Research and Design Centre (AERDC), Bangalore. Prior to aircraft tests, the Jet Fuel Starter (JFS) was extensively tested on test rig to meet starting conditions across the operating altitudes including Leh (10,700 ft.) and Khardungla (18300 ft.). The control software of JFS was fine tuned to work at all operating altitudes with no adjustments from cockpit. GE-F404-IN20 engine start up control schedule was also varied with several control patches to establish reliable start.
DM/RAJ


* I found this dating system interesting and hence a separate mention.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 31 Jan 2015 11:06

Since you brought it up, I would add more detail from HAL MSM volume 5, Issue 103 from May 2013.

AERDC Design T eam's Idea Recognised The requirement of three consecutive starts for the LCA main engine has been a long felt need. The JFS (GTSU-110) was modified for improved lubrication to achieve three consecutive starts with a time gap of 75 seconds between two successive starts. However, the demonstration could not be done till now because the flywheel which is connected to the output shaft of the GTSU-110 takes six minutes to come to a stop. AERDC team members Shri K. H. V enkatesha, Manager and Shri S. EsakkiMuthu, Senior Managrr (Design) came up with an innovative method to brake the flywheel, with air impingement on the fir-tree section of the flywheel, stopping it within 70 seconds. The novel idea was executed in one week and three consecutive starts were demonstrated infront of the committee members from IAF , ADA, RCMA (E) and ORDAQA (E). HAL has recognised the work of the team members, and a Certificate of Commendation was given to them during the AERDC Culture of Continuous Learning function.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Victor » 01 Feb 2015 00:42

With three consecutive start-ups of its engine after overnight soak in extreme cold(around -15ºC) conditions of Laddakh winter, that too without any external assistance, Tejas, the Indian Light Combat Aircraft has achieved yet another and a rare distinction. Starting the fighter aircraft under such extreme condition without any external assistance or heating is a technology challenge. The requirements become further stringent when the starting is to be done three times consecutively with a partially charged battery.

Those reports above by DRDO and HAL give the impression that the F404 main engine is being started three times consecutively with 75 second intervals but this is obviously not true. They must be referring to three starts of the fuel starter itself, not the main engine. The main engine will need several minutes to spool up if started and then spool down before the starter button can be pressed again. Given the "overnight soak in extreme cold" it must be a language issue.

Even if battery is partially charged, it will have to have enough juice to kick the compressed air bottles that will turn the JFS over, otherwise no go. Finally, -15ºC is "exteme cold"? Maybe in Bangalore but it's normal winter temp in places like northern US/Russia/Europe. Must be a typo since Leh goes to -30ºC during winter. But of course good that we did it ourselves.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 01 Feb 2015 04:21

No sir, they are not fudging the description in any way. It is 3 attempts at starting the main engine. Also, -15 C is difficult to start a gas turbine engine, especially when the plane has been "soaked" in that temperature overnight. For example, on the teens this necessisates a "Start 2" seqeunce which uses twice the power, as "Start 1" employed on the plains. Also, You might remember that multiple MMRCA candidates failed this same test. IAF helped them with some 'fixes' which benefitted some but not all.

Anyways, the start sequence can be summarized as follows:

1. Start the JFS. In LCA, it is through a battery. In other planes it can be through an explosive catridge or hydraulically compressed air.
2. Engage the engine (its high-pressure compressor shaft) and bring it up to 'start' RPM (typically about 20%)
3. At this point, fuel is introduced and a "light off" is attempted
4. If the lightoff is successfull, the engines continues to spool up and JFS automatically disengages
5. If the lightoff fails, a few more attempts can be made. However, a kind of a reset is required. E.g. the core cannot be allowed to become fuel rich, etc. Also, there is a sequence of things which happen while coming up to the start RPM. These need to be repeated. These typically place a minimum cutoff time between successive attempts as well.

Additionally, ADA decided that the JFS on LCA should be able to provide at least three attempts. I don't know what the limiting criterion is, but this places an upperbound on the time as well. Obviously, each attempt includes the time required to bring the engine to start RPM, and if light off fails, reset everything back to a point where the next attempt can be initiated. The latter was to be limited to 75 seconds. They achieved it in 70.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Victor » 01 Feb 2015 07:05

I'm finding it difficult to understand what you wrote so bear with me.

The start-up/shut-down sequence as I understand it is:

JFS start
JFS spool-up
Main engine engage
Main engine spool-up/JFS shut off
Main engine ignition & light off
Main engine shut off
Main engine spool-down
Main engine turbine stop

Is this sequence completed in 70-75 seconds before the next JFS start or is next JFS start initiated before the sequence is complete? If so, at which point in the sequence do we fire up JFS again?

As I said, -15ºC (+5ºF) is not particularly cold for western countries where all current fighters are made. The bigger problem would be the rarefied air at altitude and maybe that was the problem the teens faced in Leh. Otherwise, these jets operate fine in US, Canada and Sweden where it gets much colder.

On starting the JFS, it seems a more judicious use of energy to use the battery to fire a compressed air cylinder than to actually turn the JFS turbine directly, although that can certainly be done. Start 1 & Start 2 refer to the number of Compressed air bottles used but these can be recharged manually if the engine doesn't start on the first try. How do we recharge a dead battery? This assumes no external help is available. Do we know why we chose this method instead of compressed air?

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Re: LCA News and Discussions, 22-Oct-2013

Postby Sid » 01 Feb 2015 07:15

Indranil,

If batteries are required to start JFS then how are they kept in optimal condition? Don't batteries loose charge in cold, specially if complete unit in soaked overnight in -15 or below?

Maybe thats the reason others use explosive cartriage/ compfessed air to negate any enviromental issues or maintenance issues?

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Re: LCA News and Discussions, 22-Oct-2013

Postby NRao » 01 Feb 2015 07:39

Batteries could degrade in cold (they degrade faster in hot conditions), but, if they have enough cracking power (amps) they should be fine.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Shreeman » 01 Feb 2015 08:14

Something is missing in the report. If the 404 was actually started, then the temperature along the whole chain rose well beyond -15 after engine start. So what test point did the second start achieve? Did they brake the engjne back to full stop or just relight? If its just a relighting attempt, the JFS probably doesnt play a (any, huge?) role. How precisely did the engine stop in 60secs? The JFS has a braking method, but does 404 have one too?

I have to admit, I dont understand the test. To me it read like the JFS was tested in cold weather and nothing more.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Sudip » 01 Feb 2015 08:37

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Re: LCA News and Discussions, 22-Oct-2013

Postby Shreeman » 01 Feb 2015 08:42

^^^ article is dated feb 4, 2013 but some images appear to be recent. Also notice scoops and antennae vary between craft. They are not refitting all of them to production std?

edit -- yes, the question is relevant. The tail antennae are subject of a recent upgrade and their shape/type/role assignment has not been performed here (or elsewhere), although it is not hard to do. As later LSPs were supposed to form part of the first team of four for sulur, it is natural to ask this question.
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Re: LCA News and Discussions, 22-Oct-2013

Postby Victor » 01 Feb 2015 09:16

Regarding APU, they are designed to produce electrical power when the main engine is not running to operate accessories like internal lights, air conditioning etc. For fighters, a dedicated starter to start the main engine and EPU for the cockpit are sufficient so LCA probably doesn't have one.

Regarding the intake at the base of the vertical stabilizer, maybe it is a ram air inlet for an EPU (the hump) that powers the ECS behind the cockpit. The dorsal spine has an "engine bleed air duct to environmental control system" per the cutaway posted earlier.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Khalsa » 01 Feb 2015 09:21

two questions regarding the big pic above.

Behind the cockpit, and to the left just above the wing... there is a rectangular hole of some sort... what is that ?
and is it present on the other side too

second question: why is paint missing in precise shapes all over the wing

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Re: LCA News and Discussions, 22-Oct-2013

Postby Gurneesh » 01 Feb 2015 10:19

Khalsa wrote:two questions regarding the big pic above.

Behind the cockpit, and to the left just above the wing... there is a rectangular hole of some sort... what is that ?
and is it present on the other side too

second question: why is paint missing in precise shapes all over the wing


The rectangular hole guides the boundry layer air, that is formed in the space between the intake and the fuselage, over the wing. This slow moving air stream is undesirable for engine performance; therefore, in the frontal image of the plane, you will see that the intake is slightly offset from the fuselage to keep this boundary layer out of the intake. And yes, it is the case on both sides.

Regarding paint missing in precise shapes, this has been seen in a lot in previous LCA's also. Maybe they are strain gauges, but the recent LSP's are not supposed to be instrumented. Perhaps, someone else can shed more light on this. Could also be a good question to ask during AI-15.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 01 Feb 2015 11:26

Victor wrote:I'm finding it difficult to understand what you wrote so bear with me.

The start-up/shut-down sequence as I understand it is:

JFS start
JFS spool-up
Main engine engage
Main engine spool-up/JFS shut off
Main engine ignition & light off
Main engine shut off
Main engine spool-down
Main engine turbine stop

Is this sequence completed in 70-75 seconds before the next JFS start or is next JFS start initiated before the sequence is complete? If so, at which point in the sequence do we fire up JFS again?

As I said, -15ºC (+5ºF) is not particularly cold for western countries where all current fighters are made. The bigger problem would be the rarefied air at altitude and maybe that was the problem the teens faced in Leh. Otherwise, these jets operate fine in US, Canada and Sweden where it gets much colder.


The sequence is not completely correct. The JFS doesn't power the engine all the way till it spools up to idle rpm. Let me explain once again. The JFS only turns the High pressure shaft. The high pressure compressors attached to this shaft start turning as well starting the airflow in the engine. When the RPM reaches the 'start rpm' (typically about 20%), the flow fuel is started into the combustion chamber and an ignition is provided. If the combustion starts, then the exhaust gases power the HP turbine (which are connected to the HP compressors through the HP shaft) and also the LP turbine (which is connected to the LP compressor). At this point the combustion spins the turbines and the turbines spin the compressors, and the JFS can disconnect. The engine continues to spool up, i.e. the rpm of both the LP and HP stages continue to rise till they reach 'idle' rpm.

Now, starting up the engine can fail at various stages.
1. The fuel flow is started before the start RPM is reached (called a hot start), ignition will fail (not enough air).
2. Even after the flow of the fuel is started and the ignition provided, combustion may not start (due to various environmental conditions, temperature of fuel).

In either case, you have to stop the process and go back to the point where you can restart (does not always need the engine RPM be 0). This generally puts a minimum time required, typically about 20 secs. I do not know what makes ADA put an upper limit of 75 seconds on this. But if they can keep this interval down to 75 seconds, they can make three relight attempts.

Victor wrote:On starting the JFS, it seems a more judicious use of energy to use the battery to fire a compressed air cylinder than to actually turn the JFS turbine directly, although that can certainly be done. Start 1 & Start 2 refer to the number of Compressed air bottles used but these can be recharged manually if the engine doesn't start on the first try. How do we recharge a dead battery? This assumes no external help is available. Do we know why we chose this method instead of compressed air?

Of course not. If you change from electrical energy to potential energy, then potential energy to kinetic energy you will always have more loses. No engineer will do this! The air cylinders in the teens are not filled up using batteries either. The are are filled up using hydraulic pumps powered by the engine, when it is running. Both the battery method and the compressed air cylinders can fail to start the JFS. For the teens, you have at most 2 chances. ADA designers have ensured that LCA has at least 3 chances. If the battery is dead, you can use an external battery in parallel, pretty much like jump starting your car. In the case of teens, if compressed air in both the cylinders are used up, one has to power the hydraulic pumps using an external source to build up pressure in the cylinders again.

Sid wrote:Indranil,

If batteries are required to start JFS then how are they kept in optimal condition? Don't batteries loose charge in cold, specially if complete unit in soaked overnight in -15 or below?

Maybe thats the reason others use explosive cartriage/ compfessed air to negate any enviromental issues or maintenance issues?


You are right the batteries under-perform when it is really cold. And that is what they were checking. Do the batteries have enough juice to start the JFS. The answer seems to be yes even after soaking the plane overnight at -15 C. That should be good.

Victor wrote:Regarding the intake at the base of the vertical stabilizer, maybe it is a ram air inlet for an EPU (the hump) that powers the ECS behind the cockpit. The dorsal spine has an "engine bleed air duct to environmental control system" per the cutaway posted earlier.

:eek: EPU and ECS have no connection whatsoever. :wink:
1. EPU stands for Emergency Power Unit, which is used only when the engine flames out in mid-flight. Since the engine drives the hydraulic pumps, the hydraulic pressure starts to fall. If it falls below a limit, the EPU kicks in, and turns the turbine which is connected to the hydraulic pump and the hydraulic pressure is maintained so that the flight control surfaces remain operable till engine relight occurs.
2. ECS is Environment Control System which is working all the time. It takes care of the cockpit environment, i.e. pressure, temperature, humidity etc. and also temperature of the environment around various avionics-bays.

The ECS gets its air from the engine bleed air, which is why the duct is called "engine bleed air duct". The duct carries the bleed air from the 6th stage of the engine to the ECS (housed behind the cockpit). There it goes through a series of heat exchangers and cooling unit to bring the air to the required temperature and pressure. I think I am pointing this out for the third time, once with pictures with the duct outlined. Here it is again!
Image

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Re: LCA News and Discussions, 22-Oct-2013

Postby Khalsa » 01 Feb 2015 12:29

Many thanks Gurneesh

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Re: LCA News and Discussions, 22-Oct-2013

Postby Karan M » 01 Feb 2015 13:15

Indranil, there should be some way to catalog/document all the above posts, like the ones on JFS/ECS etc which are factual, so they dont get lost amongst the noise, discussions. Otherwise these efforts are going to go waste.

Since you have mod powers, can you create a sticky post which you can keep adding to? Thats a start to a FAQ right there.

I suggest breaking it into subsections or starting a new thread which you have some dozen posts each with a heading which you can keep adding to:

History
Program challenges
General Tech - xyz being developed for LCA
Avionics
Aeronautics
Airframe (composites)
Airframe subsystems (eg JFS, ECS etc go right there)
Propulsion (can link to Maitya/Kaveri)
Performance (all the stuff about STR/ITR relevance vs tactics)
Quotes/Pilot/Developer statements
Weapons (Astra, LGB etc tests)

etc etc
Each time you make a post, add it back to the original post/s in the relevant section.
Last edited by Indranil on 02 Feb 2015 02:36, edited 1 time in total.
Reason: Good suggestion. Will come up with a way in consultation with other mods.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Akshay Kapoor » 01 Feb 2015 13:35

^

and Tactics. We know the LCA MK1's ranges, aerodynamics , turn rates. We should definitely have some FAQs on tactics and roles. Sorry to repeat this again and again.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Thakur_B » 01 Feb 2015 14:03

Why not simply update BR wikia and make it a sticky post ?

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Re: LCA News and Discussions, 22-Oct-2013

Postby Lalmohan » 01 Feb 2015 18:03

Akshay Kapoor wrote:^

and Tactics. We know the LCA MK1's ranges, aerodynamics , turn rates. We should definitely have some FAQs on tactics and roles. Sorry to repeat this again and again.


there should be no serious discussion about tactics on an online forum

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Re: LCA News and Discussions, 22-Oct-2013

Postby Akshay Kapoor » 01 Feb 2015 21:19

Agreed Lalmohan, but using only easily accessible public info (and absolutely no insights from chai/paanwaala should be used) we can at least discuss things like, mission profile, staging airfields and targets. However security takes precedence of course...no point in giving info / doing analysis for the enemy.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Victor » 02 Feb 2015 04:07

indranilroy wrote:When the RPM reaches the 'start rpm' (typically about 20%), the flow fuel is started into the combustion chamber and an ignition is provided.

I was under the impression it's the other way around. Ignitors are activated first and only after a certain rpm is reached is the fuel injected for burn. The unburnt fuel spit out the back would make for dutty airfields otherwise.

In either case you have to stop the process and go back to the point where you can restart (does not always need the engine RPM to be 0).

This is what is confusing me. In order to do a 3 x start, the engine has to acually ignite and run for a while before the JFS shuts off. Do we at that point abort the spool-up and hit the start again? If so, what are we testing if the blades are still turning and not at 0 rpm?

Of course not. If you change from electrical energy to potential energy, then potential energy to kinetic energy you will always have more loses. No engineer will do this!

I guess the F-16 & F-18 engineers are not as good as us then, even though they have been doing this much longer than us.

For the teens, you have at most 2 chances. ADA designers have ensured that LCA has at least 3 chances.

Actually I saw it the other way around. It takes a lot more power to turn a JFS turbine than to fire a compressed air bottle. Since the latter is manually rechargeable, it will provide far more starts than the former given the same battery. Of course this only matters if we don't have electrical backup available on the tarmac.

:eek: EPU and ECS have no connection whatsoever. :wink:

Yes that is not a correct speculation on my part about the scoop. I was looking at both the Tornado and Kfir which had similar scoops. The Tornado uses it for a primary heat exchanger near the engine with exhaust ducts and shields which look similar to the LCA's. The Kfir uses its dorsal scoop to cool the afterburner and it also has the gap around the exhaust like the LCA. The LCA probably does one or both with its scoop. That would free up some space behind the cockpit.

Here is the Tornado's tail area:
Image
Last edited by Victor on 02 Feb 2015 04:13, edited 1 time in total.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Shreeman » 02 Feb 2015 04:12

http://aviation.stackexchange.com/quest ... es-started

This seems to be generally accepted.

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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 02 Feb 2015 05:10

Victor wrote:
indranilroy wrote:When the RPM reaches the 'start rpm' (typically about 20%), the flow fuel is started into the combustion chamber and an ignition is provided.

I was under the impression it's the other way around. Ignitors are activated first and only after a certain rpm is reached is the fuel injected for burn. The unburnt fuel spit out the back would make for dutty airfields otherwise.


I did not say anything about ignitors, or the sequence. I said the fuel is ignited.

Victor wrote:
In either case you have to stop the process and go back to the point where you can restart (does not always need the engine RPM to be 0).

This is what is confusing me. In order to do a 3 x start, the engine has to acually ignite and run for a while before the JFS shuts off. Do we at that point abort the spool-up and hit the start again? If so, what are we testing if the blades are still turning and not at 0 rpm?


I do not know how exactly the test was performed. May be fuel was never provided and it was checked if the JFS could spin up the engine to the required RPM. May be the fuel flow was introduced only momentarily to check if ignition starts. May be the fuel flow was allowed for just a few seconds to see if the spool up continues as expected and then cut-off. There are many ways of doing these tests. For example, testing if relighting of an engine is possible in mid flight does not require switching off the engine completely. My question is why are you doubting them only because they are from HAL/ADA/DRDO/CEMILAC? Also don't you think IAF will verify these claims?

Victor wrote:
Of course not. If you change from electrical energy to potential energy, then potential energy to kinetic energy you will always have more loses. No engineer will do this!

I guess the F-16 & F-18 engineers are not as good as us then, even though they have been doing this much longer than us.

I did make make fun of your suggestion. But, I showed no disrespect towards the engineers of the teens. This is what I had written.

Of course not. If you change from electrical energy to potential energy, then potential energy to kinetic energy you will always have more loses. No engineer will do this! The air cylinders in the teens are not filled up using batteries either. The are are filled up using hydraulic pumps powered by the engine, when it is running. Both the battery method and the compressed air cylinders can fail to start the JFS.


You on the other hand split my sentence (which changes its meaning and import) to suit your narrative. I will put the reason to an adamancy to prove your point.

Victor wrote:
For the teens, you have at most 2 chances. ADA designers have ensured that LCA has at least 3 chances.

Actually I saw it the other way around. It takes a lot more power to turn a JFS turbine than to fire a compressed air bottle. Since the latter is manually rechargeable, it will provide far more starts than the former given the same battery. Of course this only matters if we don't have electrical backup available on the tarmac.


Again, this is ridiculous. If only you remove your bias, you would see the obvious. Battery carts/generators are ubiquitous at every airport. It is as easy, if not much easier, than hydraulically charging a compressed air bottle to 3000 psi!

Victor wrote:
:eek: EPU and ECS have no connection whatsoever. :wink:

Yes that is not a correct speculation on my part about the scoop. I was looking at both the Tornado and Kfir which had similar scoops. The Tornado uses it for a primary heat exchanger near the engine with exhaust ducts and shields which look similar to the LCA's. The Kfir uses its dorsal scoop to cool the afterburner and it also has the gap around the exhaust like the LCA. The LCA probably does one or both with its scoop. That would free up some space behind the cockpit.

Here is the Tornado's tail area:
http://i211.photobucket.com/albums/bb280/brjingo/tornadotaildetail_zps5ca50634.jpg

You have come back to what I have been saying for two pages now ;-)

Shreeman wrote:http://aviation.stackexchange.com/questions/1959/how-are-turbine-engines-started

This seems to be generally accepted.

Which is more or less what I have written.

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Re: LCA News and Discussions, 22-Oct-2013

Postby brar_w » 02 Feb 2015 05:12


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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 02 Feb 2015 05:21

Victor wrote:Here is the Tornado's tail area:
Image

But this picture is interesting. I wonder if Tejas also has some heat exchangers there. It will explain the metallic covers for exhaust just behind the dorsal intake. Will try to find out.

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Re: LCA News and Discussions, 22-Oct-2013

Postby SaiK » 02 Feb 2015 06:48

10 types of heat exchangers
http://tejas.gov.in/IOC-Brochure.pdf

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Re: LCA News and Discussions, 22-Oct-2013

Postby Indranil » 02 Feb 2015 07:26

Thank you Victor sahab, you set me on the right track. I think I have my answer (subject to somebody verifying it at AI-15).

The bleed air from the engine is first fed to a heat exchanger housed at the base of the fin marked in the following diagram.
Image

Since this air is hot (about 600 degrees), the exhaust duct is metallic along with the skin of the spin just aft of the exhaust.
Image

The cooled air continues to pass through the bleed air duct (placed in the dorsal spine) to a further set of heat exchangers marked as 47 in the following figure. The ram intake (marked as 41) for this heat exchanger is placed at the base of the boundary layer diverter duct .
Image

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Re: LCA News and Discussions, 22-Oct-2013

Postby srai » 02 Feb 2015 08:04

SaiK wrote:10 types of heat exchangers
http://tejas.gov.in/IOC-Brochure.pdf


DRDO Techfous (Oct 2004) - Mechanical & Propulsion Systems
Aircraft-Mounted Accessories Gearbox

An Aircraft-Mounted Accessories Gearbox (AMAGB) has been designed and developed for Tejas. It is a lightweight, single-input, multi-output gearbox, which takes its input drive from engine through a power take off shaft at a rated speed of 16810 rpm. AMAGB has a high power-to-weight ratio and a self-contained lubrication system. It carries four aircraft accessories on its output pads, viz., two hydraulic pumps (60 kW @ 6000 rpm each), one generator (40 kW @ 7950 rpm), and one starter unit. Together, these cater to a major part of hydraulic and electrical power requirements of the Tejas and hence forms a crucial part of its secondary power system.

Image

Salient Features
Power plant : GE-F404-F2J3/Kaveri
Power transmission : 185 kW (250 hp)
Speed : 16810 rpm
Weight : 34.4 kg
Overall dimension : 720 mm (L) x 450 mm (H) x 120 mm (W)


Jet Fuel Starter

A Jet Fuel Starter has been designed and developed by Engine Division of HAL, Bangalore, especially to start the engine of Tejas on ground and in the air. Design optimisation of rotating elements and shaft has been achieved by use of 3-D modelling, dynamic and stress analysis software to reduce weight of the JFS with the safe margin for shaft critical speed and element's resonance frequency as well as to reduce vibration and noise levels.
Also, dynamic balancing of entire rotating assembly to G2.5 as per the ISO 1940/1-1986 (E) has been carried out for reduction in unbalanced mass and vibration and noise level and to improve turbine volumetric efficiency through the controlled radial clearance between rotor and stator.

Image

Salient Features
Type : Free turbine type
Power output : 110 kW
Max. speed : 50500 rpm
Compressor PR : 3.5
Turbine inlet temp : 1150 K
Weight : 50 kg
Fuel : JET A-1/DERD 2494/F-35/IS 1571-85 or
JP-5


Cold Air Unit

Cold Air Unit (CAU) has been designed and developed by Lucknow Division of HAL for Tejas. Design optimisation of rotating elements and shaft has been done by use of 3-D modelling, dynamic and stress analysis software for reduction in weight with the safe margin for shaft critical speed and element�s resonance frequency as well as reduction in vibration and noise levels. Rotating assembly of CAU is dynamically balanced to G2.5 (ISO 1940) to incorporate reduction in unbalanced mass, reduction in vibration and noise levels, and reduction in loads on bearing.

Image

Salient Features
Type : Turbo compressor
Medium : Air
Speed : 69000 rpm
Flow rate : 34 kg/min
Turbine PR : 9
Compressor PR : 1.8
Min. Turbine outlet temp : - 30 oC
Weight : 6.5 kg


Reheater

Reheater Heat Exchanger is a cross-flow plate fin heat exchanger made of Al alloy. It performs the function of cooling the hot air before it enters the condenser and reheat the hot air before it enters the turbine of cold air unit. It cools charge air from 75 �C at a flow rate of 35 kg/min to less than 63 �C for cold air at 38 �C at a flow rate of 34.5 kg/min.

Image

Salient Features
Hot Air Side
Mass flow rate : 35 kg/min
Temperature drop : 20 �C
Pressure drop : 60 mbar
Cold Air Side
Mass flow rate : 34.5 kg/min
Pressure drop : 80 mbar


Regenerative Heat Exchanger

Regenerative Heat Exchanger is a cross-flow plate fin heat exchanger made of Al alloy. It performs the function of cooling charge air coming from secondary heat exchanger (SHE) by using a part of ram air tapped from SHE ram air inlet duct and water drained from the water separator. It includes a mixing chamber with water injected at ram air inlet end. It cools charge air at 102 �C and flow rate of 35 kg/min to less than 75 �C by using mixture of ram air at 91 �C and water with a mass flow rate of 5.2 kg/min.

Image

Salient Features
Hot Air Side
Nominal mass flow : 35 kg/min
Temperature drop : 25 �C
Pressure drop : 150 mbar
Cold Air Side
Nominal mass flow : 5 kg/min
Pressure drop : 150 mbar


Liquid-to-Air Heat Exchanger

Liquid-to-Air Heat Exchanger is a cross-flow plate fin heat exchanger made of Al alloy. The outlet on air side has two connections, one for cabin cooling and other for avionics cooling. It performs the functions of cooling the coolanol R25 coming from radar by using cold air coming from the low pressure side of the condenser.

Image

Salient Features
Liquid
Nominal flow : 15 L/min
Heat removal capacity : 3 kW
Pressure drop : 500 mbar
Air
Nominal mass flow : 33 kg/min
Pressure drop : 200 mbar


Condenser Heat Exchanger

Condenser Heat Exchanger is a cross-flow plate fin heat exchanger made of Al alloy. It performs the function of cooling the hot air coming from reheater before entry to water separator using cold air from turbine inlet. It cools charge air from 63 �C at a flow rate of 35 kg/min to less than 38 �C for cold air at -31�C and mass flow rate of 33 kg/min.

Image

Salient Features
Hot Air Side
Mass flow rate : 35 kg/min
Temperature drop : 25 �C
Pressure drop : 130 mbar
Cold Air Side
Mass flow rate : 33 kg/min
Pressure drop : 100 mbar


Secondary Heat Exchanger

Secondary Heat Exchanger is a cross-counter flow plate fin heat exchanger made of Al alloy with a single pass for the cold stream (ram air) and a double pass for hot stream (charge air). A part of the heat exchanger is also used for cooling air supply for fuel tank and gearbox pressurisation. It cools charge air at 230 �C and mass flow rate of 34 kg/min to less than 102 �C for ram air at 91 �C and mass flow rate of 224 kg/min.

Image

Salient Features
Hot Air Side
Nominal mass flow : 34 kg/min
Temperature drop : 130 �C
Pressure drop : 350 mbar
Cold Air Side
Nominal mass flow : 285 kg/min
Pressure drop : 260 mbar


Secondary Power System Heat Exchanger (HE-1)

The hydraulic oil�IDG oil-fuel cooler is a part of secondary power system of Tejas. It is in fact a combination of two separate heat exchange sections in series. Section one is hydraulic oil-fuel section, while section two is IDG oil-fuel section. Fuel from the aircraft's fuel supply tank enters section one first, cooling the hydraulic oil. Heated fuel then enters section two, where it is further heated up by heat transfer from IDG oil.

Salient Features
Heat load
Hydraulic oil : 9 kW
IDG oil : 14 kW
Temperature (max.) : 135 oC
Pressure (max) : 35 bar

Secondary Power System Heat Exchanger (HE-2)

The gearbox oil�hydraulic oil-fuel cooler is a part of secondary power system of Tejas. It is also a combination of two separate heat exchange sections in series. Section one is gearbox oil-fuel section, while section two is hydraulic oil-fuel section. Fuel from the aircraft's fuel supply tank enters section one first cooling the gearbox oil. Heated fuel then enters section two, where it is further heated up by heat transfer from hydraulic oil.

Image

Salient Features
Heat load
Hydraulic oil : 11 kW
Gearbox oil : 6.5 kW
Temperature (max.) : 135 oC
Pressure (max.) : 35 bar


Gimbal Joints

Gimbal Joints are used to provide angular movement of + 6o (cone angle 12o) through 360o caused due to engine manoeuvring or thermal expansion of ECS bleed pipes. The components of these parts are fabricated with high temperature resistant INCONEL 625/718 material. ADA has designed and developed f63, f50, and f32 mm Gimbal Joints for Tejas. The technology has been transferred to M/s Metallic Bellows, Chennai.

Image

Salient Features
Gimbal Joint Ф63 mm Ф32 mm Ф50 mm
Operating pressure (bar) 7 7 37
Operating temperature (�C) 650 650 650
Angle of deflection (degree) �6 �6 �6
Life (cycles) 100000 100000 100000

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Re: LCA News and Discussions, 22-Oct-2013

Postby shiv » 02 Feb 2015 08:23


Victor
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Re: LCA News and Discussions, 22-Oct-2013

Postby Victor » 02 Feb 2015 08:39

indranilroy wrote:
The bleed air from the engine is first fed to a heat exchanger housed at the base of the fin marked in the following diagram.

Since this air is hot (about 600 degrees), the exhaust duct is metallic along with the skin of the spin just aft of the exhaust.

The cooled air continues to pass through the bleed air duct (placed in the dorsal spine) to a further set of heat exchangers marked as 47 in the following figure. The ram intake (marked as 41) for this heat exchanger is placed at the base of the boundary layer diverter duct .

Yes, that makes the most sense. Also, the gap around the exhaust could mean that the scoop does double duty in cooling the afterburner exhaust also.

BTW, I'm not doubting anyone just because they are DRDO/HAL/ADA whatever. In my first post on this, I registered my doubts about this test involving the main engine partly because of language (ie. soaking in cold) but mostly because it didn't make sense to me (75 sec between starts). Unless more convincing facts become known, I still think the test was only of the JFS.


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