LCA News and Discussions

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pralay
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Re: LCA News and Discussions

Post by pralay »

Shankaraa wrote: if GE414 engine was an impeding factor then how come we are buying 100 GE414 engines for Tejas?
well I am clearly not a guru but,
we are buying GE414 for LCA directly from the OEM.
but in case of Gripen, the OEM(SAAB) will have to procure from US.

But, I don't think the "third party engine and components" were only reasons for Gripen's elimination, there must be technical parameters as well.
btw, I never felt like Gripen had a chance to win MMRCA. :D:
member_20617
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Re: LCA News and Discussions

Post by member_20617 »

^^ we are surprised that you are surprised on this info.

Sid -Who are 'we'?

I am also surprised that 'we' (whoever they are!) have a lot more faith in me than myself! :lol:

Sameer - I was only curious about GE engines; I did not imply anywhere that Gripen should win the contest

I know that GE engines are more powerful than Kaveri but I thought we have reservations about US sanctions and/or the limits USA would put on us.
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Re: LCA News and Discussions

Post by shiv »

Cain Marko wrote:
That translates to 66 meters per sec in 15 sec, acceleration of 4.4 mpsec squared for a take off run of 500 meters.
My guesstimate is just about 750-800 mts based on the runway markings and google earth.
The calculation is simple

v=at where v=nose up velocity (240 kmph) and t=15 seconds to get nose up as per the video gives the acceleration as 4.4 meters per sec squared

Using a=4.4 and the formula s=(distance)=(a x t x t)/2 = (4.4 x 15 x 15)/2 = 495 meters for nose up.

One second later it's in the air - so about 560 meters. Assuming no headwind/tailwind.
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Re: LCA News and Discussions

Post by pralay »

Shankaraa wrote:I was only curious about GE engines; I did not imply anywhere that Gripen should win the contest
I know that GE engines are more powerful than Kaveri but I thought we have reservations about US sanctions and/or the limits USA would put on us.
At some point, I was thinking that EJ200 would be better choice in terms of TOT.
But i think it would have compromised the project goals.
we have screwed(delayed) up the LCA MK1, by building it around in-development/non-existing Kaveri Engine(it did not exist when the designed ). and it would not be wise to do the same mistake again with LCA MK2.
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Re: LCA News and Discussions

Post by nachiket »

Engine gurus, a question. This 2007 news from the GE website says that
The F404-IN-20 engine has generated more than 19,000 pounds (85 kN) uninstalled thrust and has completed 330 hours of Accelerated Mission testing, which is the equivalent of 1,000 hours of flight operation.
That value is more than the 78kN max thrust mentioned on the wiki page for the GE-F404 vanilla variant. But they are careful to mention "uninstalled thrust". How much would the thrust be lowered when the engine is actually inside an LCA? Is it only affected by the amount of airflow available or are there other factors involved in determining how much thrust an engine can produce when it is actually fitted inside an aircraft?
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Re: LCA News and Discussions

Post by Vashishtha »

v=at where v=nose up velocity (240 kmph) and t=15 seconds to get nose up as per the video gives the acceleration as 4.4 meters per sec squared

Using a=4.4 and the formula s=(distance)=(a x t x t)/2 = (4.4 x 15 x 15)/2 = 495 meters for nose up.

One second later it's in the air - so about 560 meters. Assuming no headwind/tailwind.
I'm afraid your estimate is a bit far off...

You do realize that equation is meant only for constant acceleration... Aircraft during takeoff roll DON'T have constant acceleration... Its indeed pretty complicated to calculate liftoff distance.
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Re: LCA News and Discussions

Post by nachiket »

Where is the 4.4m/s^2 value mentioned?
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Re: LCA News and Discussions

Post by SaiK »

assuming a ∆ less for tail/head wind, then it would be the take-off (560m approx) less ∆. So an average of 500 meters to take off is not a bad guess.

nLCA needs to achieve this in less than 1000ft or less. right?
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Re: LCA News and Discussions

Post by Indranil »

EDIT: Repeated post. Sorry!
Last edited by Indranil on 17 Mar 2012 03:33, edited 1 time in total.
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Re: LCA News and Discussions

Post by Indranil »

EDIT: Repeated post. Sorry!
Last edited by Indranil on 17 Mar 2012 03:33, edited 1 time in total.
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Re: LCA News and Discussions

Post by tejas »

Shankaraa wrote:
if GE414 engine was an impeding factor then how come we are buying 100 GE414 engines for Tejas?
There was a ton of sanctionable items with the Gripen but also th e aircraft was (excluding price considerations) clearly inferior to the Rafale and Typhoon. The F1414-IN purchase is only a temporizing measure for the Tejas Mk1 powerplant. The mk2 will hopefully be powered by a SNECMA-GTRE revamped "Kaveri" engine with a french core and GTRE cold parts.
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Re: LCA News and Discussions

Post by Indranil »

I don't see much fault in Shivji's calculations (Assuming uniform acceleration). He is just using the basic mechanical equations and back of the envelop calculations which are not way off.

But we have an easier way to calculate this. Please notice the 1000 ft distance markers. The nose-wheel is up at (roughly) 2000 ft marker and the plane takes off. The think the MLG becomes airborne is 200 more feet.

So that translates to 610 mtrs for nose-wheel up and 670 mtrs for MLG up.
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Re: LCA News and Discussions

Post by SaiK »

indranil, if you agree/disagree once is enough.
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Re: LCA News and Discussions

Post by Indranil »

SaiK wrote:indranil, if you agree/disagree once is enough.
This was my first post and only post on the LSP 7 takeoff run ... anyways, point taken ... will follow henceforth.
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Re: LCA News and Discussions

Post by PratikDas »

Indranil, your post appeared 3 times, that's all. :)
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Re: LCA News and Discussions

Post by Indranil »

PratikDas wrote:Indranil, your post appeared 3 times, that's all. :)
SaiK sahab and Pratik sahab,

Ijust noticed it what had happened ... I don't know how that happened ... anyways I extend my apologies ... I have my posts ... thank you for pointing them out
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Re: LCA News and Discussions

Post by SaiK »

it must be the evil microsoft background process, that sent your three clicks. ;)
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Re: LCA News and Discussions

Post by Cain Marko »

indranilroy wrote:I don't see much fault in Shivji's calculations (Assuming uniform acceleration). He is just using the basic mechanical equations and back of the envelop calculations which are not way off.

But we have an easier way to calculate this. Please notice the 1000 ft distance markers. The nose-wheel is up at (roughly) 2000 ft marker and the plane takes off. The think the MLG becomes airborne is 200 more feet.

So that translates to 610 mtrs for nose-wheel up and 670 mtrs for MLG up.
Indranil, where do you see the 1000ft distance markers? I am no math guru (in fact quite handicapped in math by the standards on BR) so can't really comment on Shivji's numbers. However, what I did do was simply looked at the closest runway marker (denoted by white stripes) that the LCA takes off at, and then verified that length via google maps - what i found was that the LCA took off just before the 6th marker on the strip (starting from a standstill at HAL runway, direction didn't matter), and that was how I came to the conservative 750 meter distance.

But YES, I redid the same thing again, and I would agree that wheel-up happened around 600 meters just BEFORE the 5th marker lines.

I know it is not the most sophisticated or even accurate method, but is my best guesstimate :)

CM.
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Re: LCA News and Discussions

Post by Indranil »

CM sahab,

the 1000 feet markers are the black rectangular things sticking out by the side of the runway. they are visual cues used to mark how many 1000 feet to go to the end of the runway.
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Re: LCA News and Discussions

Post by Cain Marko »

Yeah, I thought of using those as markers as well but didn't know what distance exactly they were marking, even worse, they seemed non equidistant on google maps, so just went with runway stripes.
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Re: LCA News and Discussions

Post by shiv »

Vashishtha wrote: Aircraft during takeoff roll DON'T have constant acceleration..
No. For acceleration to change forces must change.

The brakes are released when the afterburner is lit. After that is done the thrust cannot increase any more. The after burner is not turned off until the aircraft is in the air - so no change in thrust.

Other variables are weight (no significant change in 20 seconds)

Headwind/tailwind I am ignoring.

acceleration = force/mass

if force and mass are constant the acceleration is constant.
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Re: LCA News and Discussions

Post by sanjaykumar »

Force subsumes mass. Change in direction changes acceleration.
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Re: LCA News and Discussions

Post by Abhibhushan »

shiv wrote:
Vashishtha wrote: Aircraft during takeoff roll DON'T have constant acceleration..
No. For acceleration to change forces must change.

The brakes are released when the afterburner is lit. After that is done the thrust cannot increase any more. The after burner is not turned off until the aircraft is in the air - so no change in thrust.

Other variables are weight (no significant change in 20 seconds)

Headwind/tailwind I am ignoring.

acceleration = force/mass
A small correction to the quoted statement is needed as static thrust is not equal to dynamic thrust.
if force and mass are constant the acceleration is constant.[/quote]
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Re: LCA News and Discussions

Post by Gurneesh »

As speed increases drag should also increase. So if engine thrust is held constant, increase in drag will cause a decrease in acceleration.

Which is why people using visual markers are reporting longer takeoff distances.
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Re: LCA News and Discussions

Post by shiv »

Gurneesh wrote:As speed increases drag should also increase. So if engine thrust is held constant, increase in drag will cause a decrease in acceleration.

Which is why people using visual markers are reporting longer takeoff distances.
I am sure you are right. But the data we have is that nose lift off is at 240 kmph. Nosewheel lift occurs in 15 seconds
You have the time taken. You have velocity and the point of time the nosewheel lifts. Calculating distance from that is trivial.
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Re: LCA News and Discussions

Post by Indranil »

shiv wrote:
Gurneesh wrote:As speed increases drag should also increase. So if engine thrust is held constant, increase in drag will cause a decrease in acceleration.

Which is why people using visual markers are reporting longer takeoff distances.
I am sure you are right. But the data we have is that nose lift off is at 240 kmph. Nosewheel lift occurs in 15 seconds
You have the time taken. You have velocity and the point of time the nosewheel lifts. Calculating distance from that is trivial.
Shivji, I agree with your back of the envelop calculations ... I would do the same simplifications (of uniform acceleration) for a quick estimate.

But I would not say the bold part in your response. The displacement is the area under the velocity time graph. In straight-line motion, this is the area under the speed-time curve. So, technically distance cannot be inferred by just knowing the time and the final speed :-) . for example the distance will be in increasing order with the came final speed and time taken if the speed curve is concave (double differentiation of speed > 0), than when speed curve is a straight line joining 0 to final speed (acceleration is constant), than when speed curve is convex (double differentiation of speed < 0).
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Re: LCA News and Discussions

Post by Gurneesh »

Just an illustration of the above

Image

If we take the area under the curve (which is the distance traveled), it will be different for the three cases even when the final velocity and the time taken is same for all three (and not to mention that the plane is always accelerating in all three cases).
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Re: LCA News and Discussions

Post by vic »

I think that apart from 40 Mark-1 LCA we should order another 20 Mark-1 for additional squadron and 20 twin seater Mark-1 to be used as AJT/CAS etc, which should give LCA Mark-1 a respectable run while giving time to Mark-2 to get going.

Further apart from AMCA we should plan for LCA Mark-3 (semi stealth like MAKO) with Kaveri-Snecma engine to cater for any delay in AMCA
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Re: LCA News and Discussions

Post by Will »

Just concentrate the MK-1 as a point defence fighter. The IAF has enough strike aircraft for the moment. The LCA can be turned into a true multirole if needed when the MK.II program matures. As it is, being a light fighter and a limited if not decent range it makes more sense as an A-2-A aircraft. It is imperative that the LCA suceeds if the IAF is going to reach its goal of 60 sqd with over 1000 fighters by 2030.
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Re: LCA News and Discussions

Post by koti »

Is there a possibility to modify LCA MkI into a MkII a/c later on?

The engine is heavier AFAIK but will this cost be prohibitive to do the modification?
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Re: LCA News and Discussions

Post by Singha »

Mk2 is supposed to be longer fuselage (longer nose for aesa radar back end and a longer area behind cockpit for addl fuel and to fix wave drag or something...). this means a bigger wing also.

so no way Mk1 can change to Mk2...
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Re: LCA News and Discussions

Post by chiragAS »

koti wrote:Is there a possibility to modify LCA MkI into a MkII a/c later on?

The engine is heavier AFAIK but will this cost be prohibitive to do the modification?
kotiji Not sure but last i heard, they were planning to increase the length by a meter and some wing dimension reduction.
So i guess they would not modify considering all the trouble ($$$ considerations), engine weight, inlet design change, new wing dimensions, extra length.

oops just saw singhaji has already answered it.
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Re: LCA News and Discussions

Post by koti »

>>so no way Mk1 can change to Mk2

What about engine upgrade alone?

Chirag ji, The cost of upgrade can be offset(to some extent) by ordering more MkI now and later modifying them with the newer engine.
If the IAF may be ok with 40 f404, it may be ok with 80 f414'ed MkI too. I think we will be getting more birds rolling a lot quicker this way then waiting for MkII to order big at a later point.
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Re: LCA News and Discussions

Post by Singha »

that would totally waste the life of the 404IN20 engine.
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Re: LCA News and Discussions

Post by chiragAS »

koti wrote:>>so no way Mk1 can change to Mk2

What about engine upgrade alone?

Chirag ji, The cost of upgrade can be offset(to some extent) by ordering more MkI now and later modifying them with the newer engine.
If the IAF may be ok with 40 f404, it may be ok with 80 f414'ed MkI too. I think we will be getting more birds rolling a lot quicker this way then waiting for MkII to order big at a later point.
Yes only engine is possible. but in this case(414) inlet has to change for extra thrust. but I Agree numbers can offset the cost
and i wish they get MK1 in numbers than waiting for another FOC (for MK-II)which will only be done after xxx number of hours of testing.

PS please take out the ji from me :D

Singhaji has a point!
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Re: LCA News and Discussions

Post by koti »

Singha wrote:that would totally waste the life of the 404IN20 engine.
Ya.
Any exchange with OEM for more F414 or sell off to JAS/F-18 operators possible?
I read that around 4000 F404's are operational workdwide in Hornets alone.
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Re: LCA News and Discussions

Post by Rahul M »

no need to change Mk1 to Mk2 by a MLU. when IAF has enough Mk2's the Mk1's can be used for the roles OCU is used for.
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Re: LCA News and Discussions

Post by Singha »

the hornets (F-18C/D) use a older model of 404 engine. the superhornets use 414. the older hornet operators like canada/swiss/australia/spain will likely just retire them in the next decade.
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Re: LCA News and Discussions

Post by Yagnasri »

Have a production line with M1 going one with some 20 per year and when M2 arives have good no with that. Now that we have a decent M1 which is more than sufficient for most of the S**t of pakiland and old rubbsih from Panda we can have a good no of them also. Further these M1s can be used extensively for petrolling, training etc to get their life span hours compleated as early as possible so that they can be retired early to be replaced by M2s sat in a decade or so. Wasting the model which is suitable and avaliable for production is stupid and in fact criminal when we have such a low no of aircrafts at present.
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Re: LCA News and Discussions

Post by chackojoseph »

The conversion of Mk 1 to Mk 2 will be illogical. They will have to change the airframe, engine and the avionics. Then what is left? However, Mk 1 can have its own MLU, not necessarily as per Mk 2 standards, but, can have commonality. Sending it to ASTE is also not an option 'afterwards,' it has to be now.

As someone pointed out that it should be retained as pure a2a; for CAP and other peace time duties like OCU.
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