LCA News and Discussions

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Re: LCA News and Discussions

Postby Vashishtha » 03 Jul 2010 02:39

usually CG of an aircraft lies at 1/3rd of the chord length. Its standard practice while making aircraft.
U can even place a wing right behind the cg but this is an exception to the above rule and works on only certain designs.

Any of u over here who is an RC plane hobbyist?? This is as far as my knowledge goes.

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Re: LCA News and Discussions

Postby Indranil » 03 Jul 2010 03:46

Vashishtha wrote:usually CG of an aircraft lies at 1/3rd of the chord length. Its standard practice while making aircraft.
U can even place a wing right behind the cg but this is an exception to the above rule and works on only certain designs.

Any of u over here who is an RC plane hobbyist?? This is as far as my knowledge goes.


You are right. Actually, it should lie within limits. For stability the 1/3rd rules were applied. However in modern FBW planes many planes have a displaced CG. In fact the CG shifts with payload and fired missiles. As you say for stabilitymany other things are taken into account like centre of lift and deflection of control surfaces.

I was asking the question to understand the effects of the LCA wing more. We were trying to understand the effects/adv/dis-adv of the wing join not being parallel to the longitudinal axis. In fact, I see more to that join than just the wash out. In a wing twist, the chord at all cross sections still remains straight, right? On the Tejas, the chord of the airfoil at the wing join, doesn't look straight to me. Just a mere wing twist would have ended up with the leading edge of the wing join to have maximum AoA. But it doesn't seem to be the case, the leading edge seems like on a higher plane (but parallel to the longitudinal axis), then there is a curve which take the wing to a lower plane (but again parallel to the longitudinal axis). Please feel free to correct me. I am only too eager to learn. But if my observation seems right to you, what do you think would be the motive of such a design. I think the leading edge of the inner compound delta actually works like a canard and collects air flow above the rest of the wing and thus delays stall. However the reasons might actually be much more simpler than that, the designers just wanted to have the leading edge above the engine intakes. May be both!

P.S. and OT
I do fly RC planes. I am building (not assembling) my first one now.

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Re: LCA News and Discussions

Postby Sid » 03 Jul 2010 10:48

marimuthu wrote:
K Mehta wrote:Eagerly awaiting tomorrow's roll-out of NLCA!


I thought it was on July 6


yeah me too. http://tarmak007.blogspot.com says A.K. Anthony might be there for roll out.

but sooner the better :mrgreen:

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Re: LCA News and Discussions

Postby vina » 05 Jul 2010 09:14

Hmm. Our pal, Diyar Karnail Shook-Law seems to have taken up writing "thrillers" these days. I open today's Business Standard and I see a teaser titled "Testing Times for HAL " and my first thoughts flew to, ohhh.. financial trouble, production problems etc, but what Shook-Law meant was "aircraft flight testing".

Look at it hiyar Testing Times for HAL

And when I read these opening lines.

The Russian designers stared transfixed at the monitor as the model of India’s Sitara Intermediate Jet Trainer (IJT) went into a spin, rotating like a fan uncontrollably. Despite every attempt to straighten it out with the aircraft controls, the Sitara kept spinning. If this had been a real flight, rather than just a “spin tunnel” test in Russia, both pilots in the Sitara would have died as the uncontrollable trainer smashed into the ground.


I nearly fell off my chair laughing. Who would have thought that the act of dropping scaled wooden models by hand into a rising column of air in a tunnel would require such melodrama and at the end of it all, it "Crashes" into a net safely in the bottom. :lol: :lol: :lol:

While the "literary license" in presenting to a general audience is probably understandable, this part of it is harking back to the days of yore , a good "Shuklaseque Harrumph" if you will going back to the days of "Arjun is a Dabba" days. Sounds like this is straight from his beer buddies.

The Tejas has currently tested an Alpha of just 22-24 degrees, and will go up gradually to 28 degrees. But flying a higher Alpha risks stalling the fighter; its engine could go off (or flame out, as pilots call it) leaving the Tejas, without propulsion power, or electrical and hydraulic power for its fly-by-wire controls, to fall out of the sky like a stone.

To guard against that, the ARDC is fitting a test Tejas with a fast-response power pack that US company, Honeywell, manufactures for such flight-testing. Within milliseconds of the Tejas main engine going off, the hydrogen-operated power pack starts up, providing power to the fighter’s hydraulic and electrical systems, and re-lighting the main engine.

“In flying a single-engine aircraft, there is no bigger emergency than a flame-out”, says a former Tejas test pilot. “But no fighter engine should flame out at just 28 degrees Alpha. However, the Tejas air intakes have not been well designed and, as the Alpha increases, the intakes constrict the airflow, and the engine dies for want of air.

In contrast to the Tejas’ maximum Alpha of 28 degrees, India’s Sukhoi-30MKI can comfortably handle an Alpha of over 50 degrees. The US Navy F/A-18 Super Hornet can manage an Alpha of 58 degrees.


Someone please knock the Diyar Karnail on the head and tell him that nothing changes with the intakes and they "constrict" the airflow just as in normal flight, it is just that the airflow is now distorted and for any plane, there are strict flight limits within which the intakes are designed. Even something like a Mig29 which has very high tolerance to distorted air flows in the intakes will flame out if those are exceeded.

Also, I do think that 28deg alpha that he has quoted, is a misunderstanding. The designed alpha will be higher (around 32 to 35 deg I would guess), but in actual operating conditions, it would be limited by the FCS to 28deg. The 58deg alpha in a F-18 is the max possible alpha, but kind of alpha would be done in only a specially instrumented prototype test vehicle like NASA' F-18 High Angle test vehicle and not be done with an in service F/18 A/B/C/E with any Navy/Air force in the world. The alpha limits will be much less,closer to the 28 to 30deg in real life.

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Re: LCA News and Discussions

Postby Austin » 05 Jul 2010 12:22

The MKI is not restricted practically to any alpha isnt it ? Due to aerodynamics and integrated TVC with FCS

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Re: LCA News and Discussions

Postby Telang » 05 Jul 2010 12:28

What could have been Ajay Shukla's motive in writing that article is mysterious. Was he informing the Gurus of aviation and warning them? I dont think so, even a minion in HAL would have known all of that. Any one who knows how to google would know all of that. While the wisdom and knowledge doled out by our colonel sahib is common knowledge to the developers, it is scary to the uninformed. Why is he trying to infuse lack of confidence into common man's mind about the capabilities of our aviation industry?

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Re: LCA News and Discussions

Postby vina » 05 Jul 2010 12:46

What could have been Ajay Shukla's motive in writing that article is mysterious


To be honest, I really don't see any ulterior "motive" in the good Karnail's writings. He was just trying to be a good reporter in an area of reporting that requires deep insight, which unfortunately in this particular part he doesn't possess.

So we see "real flights of fancy" in the spin tunnel tests , heck, I can get any kid off the street to toss balsa wood model planes into a vertical column of air. And as for his depictions of stall and all the rest of it , including alpha etc, the less said the better.

For eg, in his blog in the photo of the IJT, he points to the strakes on the nose and the ventral strakes under the tail as "anti spin devices".. All I can do when I see such stuff is :roll: . I really dont know whether to be surprised or shocked. Maybe I am better off :cry:

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Re: LCA News and Discussions

Postby Suppiah » 05 Jul 2010 14:59

Telang wrote:What could have been Ajay Shukla's motive in writing that article is mysterious. Was he informing the Gurus of aviation and warning them? I dont think so, even a minion in HAL would have known all of that. Any one who knows how to google would know all of that. While the wisdom and knowledge doled out by our colonel sahib is common knowledge to the developers, it is scary to the uninformed. Why is he trying to infuse lack of confidence into common man's mind about the capabilities of our aviation industry?


These are just fillers. He has a quota to fill and it is not easy to come with original or new pieces all the time. So the next option is to recycle some 'knowledge' and come out with such articles until something newsworthy or interesting comes along...

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Re: LCA News and Discussions

Postby aditya.agd » 05 Jul 2010 16:23

LCA even in it's current form is better in all respects than JF-17 thunder. Pakistan will be inducting around 200 JF17 over the coming years. Since LCA is comparable to F16 and JF17, LCA itself should be capable of taking care of Pakistan's airforce. Our other air asset can effectively utilized to counter China threat.

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Re: LCA News and Discussions

Postby Gaur » 05 Jul 2010 17:15

Austin wrote:The MKI is not restricted practically to any alpha isnt it ? Due to aerodynamics and integrated TVC with FCS

That is not possible for any aircraft. Every a/c is has a restricted alpha. It is simple physics and no a/c can escape that. When the airflow pressure both above and below the wing becomes the same, the a/c "will" stall. Even the 120 degree alpha that we see during cobra maneuver can only be achieved momentarily. The usual alpha, as it is pointed out in some posts is around 30 ( IIRC, MKI has amx alpha of 35. But I may be wrong here. So please feel free to correct me).

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Re: LCA News and Discussions

Postby vina » 05 Jul 2010 18:01

That is not possible for any aircraft. Every a/c is has a restricted alpha. It is simple physics and no a/c can escape that. When the airflow pressure both above and below the wing becomes the same, the a/c "will" stall. Even the 120 degree alpha that we see during cobra maneuver can only be achieved momentarily


That is exactly true. Beyond an alpha of 35deg or so, it is nearly impossible to sustain such maneuvers with any degree of stability with normal control surfaces. You need thrust vectoring in all probability.

The SU-30 MKI and other planes are not "flying" really (as flying with wings and controlled by aerodynamic surfaces), but really held aloft by just pure engine power and control. I think those guys call it as "post stall" maneuvering. The plane is well below it's stall speed.

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Re: LCA News and Discussions

Postby NRao » 05 Jul 2010 18:20

Gaur wrote:
Austin wrote:The MKI is not restricted practically to any alpha isnt it ? Due to aerodynamics and integrated TVC with FCS

That is not possible for any aircraft. Every a/c is has a restricted alpha. It is simple physics and no a/c can escape that. When the airflow pressure both above and below the wing becomes the same, the a/c "will" stall. Even the 120 degree alpha that we see during cobra maneuver can only be achieved momentarily. The usual alpha, as it is pointed out in some posts is around 30 ( IIRC, MKI has amx alpha of 35. But I may be wrong here. So please feel free to correct me).


IIRC (and I would like to lean on GJMan here - if he is lurking) the MKI has a "button" to "override" - to perform most, if not all, of the un-natural tricks.

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Re: LCA News and Discussions

Postby Gagan » 05 Jul 2010 19:14

The FA-18 has an interesting jet exhaust on the nose to push the nose down should it stall during high AoA. Planes usually have trouble recovering once they reach very high AoA it seems. If you look at pics of the FA 18 you will notice two small exhaust holes just behind the radome nose in front of the cockpit.

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Re: LCA News and Discussions

Postby vkashyap » 05 Jul 2010 19:55

Gagan wrote:The FA-18 has an interesting jet exhaust on the nose to push the nose down should it stall during high AoA. Planes usually have trouble recovering once they reach very high AoA it seems. If you look at pics of the FA 18 you will notice two small exhaust holes just behind the radome nose in front of the cockpit.


Gagan,
IIRC, the holes on the nose of the F/A-18 are for venting gun gases, as the F/A-18 has it's gun on top of the nose. You can find plenty of the videos on the net demostrating this.

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Re: LCA News and Discussions

Postby Gaur » 05 Jul 2010 20:08

NRao wrote:IIRC (and I would like to lean on GJMan here - if he is lurking) the MKI has a "button" to "override" - to perform most, if not all, of the un-natural tricks.

That maybe true and actually makes sense. The button may be to override the FCS to allow the pilot to perform post stall maneuvers like Pugachev's Cobra,J-Turn etc. But note that in all these post stall maneuvers, the aoa goes to extreme angles for a very short period of time. Such high alpha cannot be maintained continuously.

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Re: LCA News and Discussions

Postby Kanson » 05 Jul 2010 20:54

>>Such high alpha cannot be maintained continuously.

Could you explain more if you have time on what you mean by continously..

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Re: LCA News and Discussions

Postby Gaur » 05 Jul 2010 21:31

^^
My understanding of this issue is very basic. Aircraft flies because of lift generated by the control surfaces. This lift is generated because the airflow speed is higher on top surface than the lower surface. This is because air has to travel more distance in the same time when covering upper surface (due to curvature). This creates pressure difference which creates lift. At least this was what was taught to us in class XI (though this is not a totally correct explanation but it will do for basic understanding). So, you can naturally expect that when the wing will be at a high certain angle to the ariflow, the distance needed by the air to travel will become same for both upper and lower surfaces. So, at that angle, no lift will be created.
Also, the intakes are designed to decrease the speed and smoothen out the airflow but they are hardpressed to do so at high alphas because of high turbulance in the airflow.
So, you can see that an aircraft cannot fly continuously at extreme angles continuously as each a/c has to obey the laws of physics. But a/cs like MKI and F-22 are able to go to extreme angles to attack for a short period of time because of their very high thrust and 3D TVC. When I say short period, I mean that while MKI or F-22 can maintain its natural aoa (lets say 35 degrees) for as long as it wants, that is not possible for these extreme angles such as 120 degrees achieved during cobra maneuver. But even so, achieving these super extreme alphas is an amazing achievement as it was evident when Western fighter pilots gaped open mouthed when Su-27 first demonstrated Pugachev's Cobra (at Paris airshow?).

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Re: LCA News and Discussions

Postby Juggi G » 05 Jul 2010 22:54

Image
Image

India's Own Naval Fighter Emerges Tomorrow, Team Readies Full-Fledged Test Centre At Goa
After the LCA Navy conducts its first few flights starting December this year (if all goes well, i.e.), the platform will begin formal testing at the Shore-based Test Facility (STBF) under construction by Goa Shipyard Ltd at the INS Hansa naval air station in Goa which will be the centrepoint for the entire schedule of testing for the platform. The Aeronautical Development Agency (ADA) is making preparations at INS Hansa with a mobile telemetry station, a full-fledged monitoring facility, a data storage and retrieval facility for all flight data generated, an optical and satellite link for transferring data between Goa and Bangalore, a calibration room, a data processing room and briefing conference rooms, offices for project director, engineers, flight-test crew, chief of flight test and supporting staff.

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Re: LCA News and Discussions

Postby Prem Kumar » 05 Jul 2010 22:58

Vina-ji: the question I have is the following: Ajai Shukla claims that the ASR for LCA specifies an AoA of 28 degrees but it will be achieved only in Mark 2 (in his response to comments). Is this true?

Apologies if this has been answered before in this thread

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Re: LCA News and Discussions

Postby Kanson » 05 Jul 2010 23:05

Gaur wrote:^^
My understanding of this issue is very basic. Aircraft flies because of lift generated by the control surfaces. This lift is generated because the airflow speed is higher on top surface than the lower surface. This is because air has to travel more distance in the same time when covering upper surface (due to curvature). This creates pressure difference which creates lift. At least this was what was taught to us in class XI (though this is not a totally correct explanation but it will do for basic understanding). So, you can naturally expect that when the wing will be at a high certain angle to the ariflow, the distance needed by the air to travel will become same for both upper and lower surfaces. So, at that angle, no lift will be created.
Also, the intakes are designed to decrease the speed and smoothen out the airflow but they are hardpressed to do so at high alphas because of high turbulance in the airflow.
So, you can see that an aircraft cannot fly continuously at extreme angles continuously as each a/c has to obey the laws of physics. But a/cs like MKI and F-22 are able to go to extreme angles to attack for a short period of time because of their very high thrust and 3D TVC. When I say short period, I mean that while MKI or F-22 can maintain its natural aoa (lets say 35 degrees) for as long as it wants, that is not possible for these extreme angles such as 120 degrees achieved during cobra maneuver. But even so, achieving these super extreme alphas is an amazing achievement as it was evident when Western fighter pilots gaped open mouthed when Su-27 first demonstrated Pugachev's Cobra (at Paris airshow?).

Thanks for the response...with my little understanding i was thinking whether stability or unstability of the aircraft have anything to do with that..

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Re: LCA News and Discussions

Postby karthik » 06 Jul 2010 00:36

The navy version sure looks awesome, may be they can drop the nose in the AF version to if its only for making it sexy! :D

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Re: LCA News and Discussions

Postby Indranil » 06 Jul 2010 01:15

Gaur wrote:^^
My understanding of this issue is very basic. Aircraft flies because of lift generated by the control surfaces. This lift is generated because the airflow speed is higher on top surface than the lower surface. This is because air has to travel more distance in the same time when covering upper surface (due to curvature). This creates pressure difference which creates lift. At least this was what was taught to us in class XI (though this is not a totally correct explanation but it will do for basic understanding). So, you can naturally expect that when the wing will be at a high certain angle to the ariflow, the distance needed by the air to travel will become same for both upper and lower surfaces. So, at that angle, no lift will be created.
Also, the intakes are designed to decrease the speed and smoothen out the airflow but they are hardpressed to do so at high alphas because of high turbulance in the airflow.
So, you can see that an aircraft cannot fly continuously at extreme angles continuously as each a/c has to obey the laws of physics. But a/cs like MKI and F-22 are able to go to extreme angles to attack for a short period of time because of their very high thrust and 3D TVC. When I say short period, I mean that while MKI or F-22 can maintain its natural aoa (lets say 35 degrees) for as long as it wants, that is not possible for these extreme angles such as 120 degrees achieved during cobra maneuver. But even so, achieving these super extreme alphas is an amazing achievement as it was evident when Western fighter pilots gaped open mouthed when Su-27 first demonstrated Pugachev's Cobra (at Paris airshow?).


The explanations are not exactly correct but the inferences are!!! I think the term that Gaurji is looking for is sustained rate of turn!

To write down the explanations would require writing down the basics of aerodynamics, so I will abstain from it! But the basic correction that I would like to write down is that the speed of air flowing above and below the plane doesn't change. (how can it, when the wing surfaces won't change shape). But the air flowing above the wing becomes turbulent and finally stops flowing over the top surface all together. you can understand this by simply taking a cardboard and gliding it horizontally, now hold the cardboard tilted and again glide it horizontally. You will feel a bigger "drag". That is because the top surface (now facing backwards) now deprived of airflow and the airflow has become more turbulent above it. The higher the tilt angle the more deprived it becomes!

Also while turning the inside wing tip also has a lower speed. so there are many factors.

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Re: LCA News and Discussions

Postby Luxtor » 06 Jul 2010 03:03

indranilroy wrote:
Gaur wrote:^^
My understanding of this issue is very basic. Aircraft flies because of lift generated by the control surfaces. This lift is generated because the airflow speed is higher on top surface than the lower surface. This is because air has to travel more distance in the same time when covering upper surface (due to curvature). This creates pressure difference which creates lift. At least this was what was taught to us in class XI (though this is not a totally correct explanation but it will do for basic understanding). So, you can naturally expect that when the wing will be at a high certain angle to the ariflow, the distance needed by the air to travel will become same for both upper and lower surfaces. So, at that angle, no lift will be created.
Also, the intakes are designed to decrease the speed and smoothen out the airflow but they are hardpressed to do so at high alphas because of high turbulance in the airflow.
So, you can see that an aircraft cannot fly continuously at extreme angles continuously as each a/c has to obey the laws of physics. But a/cs like MKI and F-22 are able to go to extreme angles to attack for a short period of time because of their very high thrust and 3D TVC. When I say short period, I mean that while MKI or F-22 can maintain its natural aoa (lets say 35 degrees) for as long as it wants, that is not possible for these extreme angles such as 120 degrees achieved during cobra maneuver. But even so, achieving these super extreme alphas is an amazing achievement as it was evident when Western fighter pilots gaped open mouthed when Su-27 first demonstrated Pugachev's Cobra (at Paris airshow?).


The explanations are not exactly correct but the inferences are!!! I think the term that Gaurji is looking for is sustained rate of turn!

To write down the explanations would require writing down the basics of aerodynamics, so I will abstain from it! But the basic correction that I would like to write down is that the speed of air flowing above and below the plane doesn't change. (how can it, when the wing surfaces won't change shape). But the air flowing above the wing becomes turbulent and finally stops flowing over the top surface all together. you can understand this by simply taking a cardboard and gliding it horizontally, now hold the cardboard tilted and again glide it horizontally. You will feel a bigger "drag". That is because the top surface (now facing backwards) now deprived of airflow and the airflow has become more turbulent above it. The higher the tilt angle the more deprived it becomes!

Also while turning the inside wing tip also has a lower speed. so there are many factors.


^^^
Good basic explanation of problems encountered with high AoA. As far engine choking under high AoA, the engine air intake design has significant influence on it. Tejas has air intakes opening that is perfectly symmetrical; that is all the edges of the opening are even with each other. If you look at air intakes of other high performance fighter aircraft like the SU-30 MKI, Mig-29, F-15, F/A 18 Super Hornet etc., what do you see? the bottom portion of the air intake is offset back in comparison with the top. This is so that at high angle of attacks air can still get into the engine intakes. With Rafale the shape of fuselage with it's pronounced dent like shape acts to scoop up air and deflect it into the air intake at high AoA. The Eurofighter Typhoon has a deflector extension at the top front of the air intakes that acts to deflect air into the air intakes at high AoA. So with Tejas the air intake openings may have to be redesigned to fix this engine choking problem in high AoA.

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Re: LCA News and Discussions

Postby Indranil » 06 Jul 2010 03:41

Luxtor wrote:So with Tejas the air intake openings may have to be redesigned to fix this engine choking problem in high AoA.


I am not sure about the same, though I understand what you are saying.

F-18 [b] had [\b] almost similar intakes as the LCA (though much bigger) which were changed to the rectangular beveled ones later. I had read about how it helps in reduction of RCS and a better implementation of the area rule. Don't know if it had anything to do with increasing the AoA. In fact the NASA High Alpha Research Vehicle [HARV] had the same "semicircular" intakes and yet demonstrated
research pilots Bill Dana and Ed Schneider completed the envelope expansion flights in February 1992. Demonstrated capabilities included stable flight at approximately 70 degrees angle of attack (previous maximum was 55 degrees) and rolling at high rates at 65 degrees angle of attack. Controlled rolling would have been nearly impossible above 35 degrees without vectoring

http://www.nasa.gov/centers/dryden/history/pastprojects/HARV/index.html

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Re: LCA News and Discussions

Postby Indranil » 06 Jul 2010 04:30

While we are here, I had an observation.

I remember reading a post by Kartik where he had explained about the bleed channels in the LCA wings. These channels are fed through the boundary layer air discharge slots and help in providing airflow over the wing at high AoA to delay stall.

The f-18 uses the exact same assembly. However, the objective for the F-18 is different. It is not for providing airflow over the wings but feeding air to the vertical stabilators. This assembly also mitigates the parasitic drag created by other solutions (other kinds of slots, vanes, etc). This is required because the LEXs on the F-18 extend quite a lot. This is essentially a similar problem with having a delta wing.

Is there any piece of literature which speaks about the bleed channels on the LCA. I just find the design problem and the solution very similar. So I believe that the LCA's bleed channels were also designed for a similar reason. I would like to learn more.

Kartik, did you read about the bleed channels on the Tejas somewhere? The reason I ask is because, the air flowing through the channel at high AoA would be pretty slow and low in volume to provide any significant change in the lift. Remember the air through this slot is already turbulent boundary air. This would help us understand the LCA's maneuverability better!

P.S.: The post was by Kartik and not Karthik. Thank you Rahul da!
Last edited by Indranil on 06 Jul 2010 04:40, edited 4 times in total.

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Re: LCA News and Discussions

Postby Rahul M » 06 Jul 2010 04:32

indranil, do not get confused between kartik and karthik ! ;) it's the former who is connected to aero industry, not the later.

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Re: LCA News and Discussions

Postby Indranil » 06 Jul 2010 04:50

DELETED: Meaningless!

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Re: LCA News and Discussions

Postby steve » 06 Jul 2010 07:30

Hurray!! To day the LCA Navy version will be unveiled :)

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Re: LCA News and Discussions

Postby Kartik » 06 Jul 2010 07:40

indranilroy wrote:While we are here, I had an observation.

I remember reading a post by Kartik where he had explained about the bleed channels in the LCA wings. These channels are fed through the boundary layer air discharge slots and help in providing airflow over the wing at high AoA to delay stall.

The f-18 uses the exact same assembly. However, the objective for the F-18 is different. It is not for providing airflow over the wings but feeding air to the vertical stabilators. This assembly also mitigates the parasitic drag created by other solutions (other kinds of slots, vanes, etc). This is required because the LEXs on the F-18 extend quite a lot. This is essentially a similar problem with having a delta wing.

Is there any piece of literature which speaks about the bleed channels on the LCA. I just find the design problem and the solution very similar. So I believe that the LCA's bleed channels were also designed for a similar reason. I would like to learn more.

Kartik, did you read about the bleed channels on the Tejas somewhere? The reason I ask is because, the air flowing through the channel at high AoA would be pretty slow and low in volume to provide any significant change in the lift. Remember the air through this slot is already turbulent boundary air. This would help us understand the LCA's maneuverability better!

P.S.: The post was by Kartik and not Karthik. Thank you Rahul da!


Indranil, Super Hornets don't have such a channel. They use leading edge root extensions (LERXes) to generate these vortices at high AoA. Look at this picture to see what vortices at high AoA I'm talking about

The LCA has no LERXes, so it mimics this effect of high AoA vortices by the channel that diverts/bleeds air from the boundary layer between the fuselage and intake splitter plate. regarding where I first read about it, it was in B. Harry's excellent "The Radiance of the Tejas" article.

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Re: LCA News and Discussions

Postby Singha » 06 Jul 2010 08:32

TOI confirms NLCA rollout is today, chaired by Defmin. we can expect some photos by tonight mashallah...hope Simha sir is there.

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Re: LCA News and Discussions

Postby Indranil » 06 Jul 2010 09:01

Kartik wrote:
Indranil, Super Hornets don't have such a channel. They use leading edge root extensions (LERXes) to generate these vortices at high AoA. Look at this picture to see what vortices at high AoA I'm talking about
.


I am aware of the usage of the LERXs for the vortex generation. But you can see the slots that I am speaking of here.

on the hornets they had the slot parallel to the longitudinal axis.
here (just next to the dorsal spine and behind the registration, VFA-94),here, and here (next to where hornet is written on the spine).

On the Super Hornets, the slot was made along the wing span.
here, here and here.

Also from wiki.
the gap between the Leading edge extensions (LEX) and the fuselage mostly filled in. The gap, called the boundary layer air discharge (BLAD) slots, controlled the vortices generated by the LEX and presented clean air to the vertical stabilizers at high angles of attack. However, they also generated a great deal of parasitic drag, worsening the problem of the F/A-18's inadequate range. McDonnell filled in 80% of the gap, leaving a small slot to bleed air from the engine intake.


Obviously, the LCA has no LERXs or LEXs, but it does have relative big delta wing and at high AoA, even its vertical stabilator would be deprived of air flow! Hence I said that they were similar problems.

I would surely read the article that you have pointed me to!

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Re: LCA News and Discussions

Postby shiv » 06 Jul 2010 09:45

Here are two Mirage 2000s of the IAF - delta wing, symmetrical intakes doing sustained high AoA flight. Wait for the video to load and move the progress bar to 1:02 where the Mirages fly high AoA and slow to formate with an HPT 32

http://www.youtube.com/user/cybersurg?b ... tuY5LxN_18

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Re: LCA News and Discussions

Postby Indranil » 06 Jul 2010 10:48

Kartik wrote:regarding where I first read about it, it was in B. Harry's excellent "The Radiance of the Tejas" article.


What a wonderful read! Thank you for directing me towards it. Just goes to how big a loss his demise was. The kind of reporting we read today! :x

I read about the spill ducts over the wings of the Tejas. Harry writes
Two hollow spill ducts on the wing, next to the leading edge, connect with the intake splitter and acts as a suction system for boundary layer/vortice control and reducing skin friction drag.


I understand the boundary layer control and reduction of the skin drag. ( I had spoken about similar usage on the F-18 ). I can understand the vortex creation due to these ducts, but can't understand how it increases the control at high AoA.

I firmly believe that the LCA can pull quite high AoA. Harry says its design objective is 35 degrees. That should not be very difficult to comprehend given the fact that Mirage-2000 pulls 25-28 degrees and LCA is designed to be much more aerodynamically agile than the Mirage and overcome inherent demerits of the delta at low-speed, low-altitude regime.

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Re: LCA News and Discussions

Postby vina » 06 Jul 2010 11:23

I understand the boundary layer control and reduction of the skin drag. ( I had spoken about similar usage on the F-18 ). I can understand the vortex creation due to these ducts, but can't understand how it increases the control at high AoA.


Basic aero 101. The vortex sheet prevents the flow separation and the critical stall angle is "postponed" . That is what is basically done in the newer (teen series onwards) designs and that gives higher AoA /alpha than earlier possible.

I firmly believe that the LCA can pull quite high AoA. Harry says its design objective is 35 degrees. That should not be very difficult to comprehend given the fact that Mirage-2000 pulls 25-28 degrees and LCA is designed to be much more aerodynamically agile than the Mirage and overcome inherent demerits of the delta at low-speed, low-altitude regime.


Open any textbook and look. The delta wing has a low wave drag and in addition, has a higher critical angle than a normal wing. That is because,the sharp leading edge fore part of the deltas start generating vortex sheets that sweep over the wing when the alpha increases and the flow transitions to this regime for deltas. In fact there were CFD diagrams of the LCA with such vortex sheets under higher alpha floating around somewhere. BR had them, I know I have seen them, but cant remember where.

As a rule, deltas have HIGHER alpha limits than conventionally winged planes. The F-18 kind of planes compensate for that by having LERXs which generate those vortices and careful design of containing those alphas in the flight regimes over various alphas . Now you know why as a rule delta winged planes DON'T need LERXs while the conventional ones (F16, F18, Mig 29, Su 30 etc) have such LERX.

Now before some illiterate fan boy comes up with LCA bad because No LERX, while JF-17 Bandar and Su-30 are super duper because they have, you know the reason.

Also thanks for pointing out B.Harrys' brilliant work. Yes, his figure of design figure of 35deg AoA seems spot on for the Tejas with the Delta wing that it has.

Now compare the kind of work that B.Harry did on the LCA, Arun Vishwakarma did on the Missiles and JCage did on the Arjun etc, vs what we get from the Shook-Laws , Rajat Pandits and the rest of them.

A difference of earth and sky. The first one had strong scientific rigor, had good sound engineering and technical analysis behind them and any opinion was based on those facts and conclusions sound. In fact, JCage, B.Harry and Arun_S work was simply brilliant by any standard.

On the other hand, the "mainstream" reporters have a perfect vacuum in the "upper stories", don't have the scientific rigor and engineering skills to even comprehend anything as technical as this and at best are reduced to reproducing hand outs from DRDO /others , innuendos / unsubstantiated opinions from interested parties /onlookers /some participants who are simply not skilled and trained to make such comments, or worse be unwitting hatchet jobs for Natashas and rival arms makers and agents.

Consider Shook-Law's not on what he has written in his blog about the IJT's strake on the nose and the ventral fins in under the engine as "anti spin " devices. Obviously he didn't think of it himself , someone told him that those are what those things purportedly are and he faithfully reproduced them as "facts". Ajai can't recognize what those are , even if someone hit him on the face with with wet undie and told him what they are and ask him to locate them on a plane!.

After all I have written about LERX and vortex sheets and all that, someone should ask Ajai , what that strake on the nose is for ? And how is it "anti spin".. Similarly, what does the ventral strakes under the tail do. Are they "anti spin" as well ?


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Re: LCA News and Discussions

Postby Sagrawal » 06 Jul 2010 12:30

Just saw the NLCA rollout live on News X. Livefist images seems to be TV grab of same telecast. Was it on DoorDarshan too? I wonder why there is not enough publicity of these events like ISRO launches. News X seems to be keeping any eye on LCA and LCH programs. I remember seeing LCH display too on News X.

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Re: LCA News and Discussions

Postby Avinandan » 06 Jul 2010 12:31



Need good quality photos :x ....
If I am not wrong , this looks like the 2 seater LCA Trainer variant.
When is it the single seater NAVAL fighter going to roll out ?

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Re: LCA News and Discussions

Postby KrishG » 06 Jul 2010 12:54



Interestingly the naval variant has LCA written over it where as all the LSPs and PVs have it as Tejas.

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Re: LCA News and Discussions

Postby Manish_Sharma » 06 Jul 2010 14:07

KrishG wrote:
Interestingly the naval variant has LCA written over it where as all the LSPs and PVs have it as Tejas.



Perhaps due to its extraordinary beauty and curvyness they are going to name it Tejomayi beautiful sis of bad boy Tejas. 8)

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Re: LCA News and Discussions

Postby sunny y » 06 Jul 2010 14:13

Naval LCA roll out ceremony 8)

http://www.youtube.com/watch?v=lEZDT1bHgjY


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