LCA news and discussion

Hitesh
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Re: LCA news and discussion

Postby Hitesh » 11 May 2009 17:24

Kartik wrote:
Hitesh wrote:Looks like this above report corroborate some of what the non-Indian aerospace engineer told me.


such as what ? be specific. whatever you had written earlier about what some "non-Indian aerospace engineer" was just a lifted from a 2005 Hindu article and passed off as someone's own insights, which was patently untrue.


From the article posted above,

IAF sources said fitting the heavier engines would require design changes in the airframe, which could take up to three to four years.


It does seem to corroborate what the engineer told me. If you want higher thrust, you need to re-engineer the frame to withstand the stresses of the higher thrust, otherwise the frame will break apart. The article is dated May 9, 2009. Please post the 2005 Hindu article so I may compare this article with the 2005 Hindu article that you are referring to.

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Re: LCA news and discussion

Postby SaiK » 11 May 2009 18:12

yes.. there was this discussion to satisfy IAF's upthrusted requirements. and for this, hopefully, ADA is working hard to get the 100kN engines ported.

As Singhaji pointed, these will only delay.. delay.. and every one knows how politics and various clouts work., to push things around. I hope, the new engines are completely validated for the existing airframe and enough opportunity given.. that means another set of 1500/2000 hours with the new engine. It could be speeded up, like putting about a squadron of 20 LCAs with uprated engines, then make up the hours. But, is that math enough? it just beats the logic, for the requirement of stress testing for MTBF.

The faster they freeze the engine requirements, and get on!.. the better is the revival [political mantra :eek: ]... but, IAF should have looked at tranche blanche methods to upgrades.

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Re: LCA news and discussion

Postby vipins » 11 May 2009 18:34

If the article says that
The first LCA squadron, however, will come with the underpowered American GE-404 engines that deliver a thrust of only 80-85 Kilo Newton.

then why
"Initial operational clearance for the LCA is now expected in 2010. :?: "

as nothing is changed for the first squadron and new engines are for later squadrons??

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Re: LCA news and discussion

Postby Kartik » 11 May 2009 20:44

Hitesh wrote:From the article posted above,

It does seem to corroborate what the engineer told me. If you want higher thrust, you need to re-engineer the frame to withstand the stresses of the higher thrust, otherwise the frame will break apart. The article is dated May 9, 2009. Please post the 2005 Hindu article so I may compare this article with the 2005 Hindu article that you are referring to.

believe me Hitesh, that guy who's claiming to be an engineer is taking you for a ride. and you're happily riding along and coming and whining here.

you don't need to re-engineer the airframe to withstand the stresses due to the higher thrust (because even with higher thrust, the maximum dynamic load remains the same- i.e. 9Gs). You need to re-engineer the airframe because the exact dimensions of the F-404 and F-414 DO NOT MATCH. nor do they match for the F-404 and the EJ-200.

just so you know, the LCA was designed to be able to withstand dynamic G loads of 9Gs/-3Gs. that was RIGHT FROM THE BEGINNING, before the LCA ever flew and all load cases/envelope loads for doing the design were taken with that envelope in mind.

adding a higher thrust engine will NOT increase the maximum dynamic loading of 9Gs (which in turn causes stresses on the airframe), but because a higher thrust engine will also be heavier in itself (check out the weight difference between a F-404 and F-414), there will have to be localised strengthening. the engine bay will need to be modified for the new engine's dimensions, the engine intake will need to be widened, because the current channel is sufficient for airflow requirements of a 85 kN thrust engine, not a +90kN thrust engine.

all these other changes (modifying the intake, customising the engine bay) for the new engine will take redesign effort. but, just so you know, PV1 was initially meant to take the Kaveri, and so its engine bay was designed keeping in mind the Kaveri, but later had to be changed back to accomodate the F-404.

I suggest you educate yourself on the changes made to the Gripen NG Demo (from the Gripen D version) to get some idea of what an engine change requires.

it is because the EJ200 is a lighter than the F-414, that it seems like a more suitable engine for the LCA. no additional LOCALISED strengthening of the engine bay to carry the new engine is required, and no major CG shifts will occur, which would need ballast to counter (all in all, added weight).

as for the 2005 Hindu article's link, its there in my previous post. check it out.

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Re: LCA news and discussion

Postby Vivek K » 11 May 2009 22:46

Kartik, great post and thanx for that info in one post. Couldn't have been put better.

Isn't the thrust to weight ratio of the LCA equal or greater than that of the M2k? Why then is it underpowered?

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Re: LCA news and discussion

Postby Gaur » 12 May 2009 00:13

^^ Power is a relative thing. Even with the thrust provided by F-4-4, tejas is a potent a/c. However, IAF wants an a/c with enough power to match any modern a/c. So tejas is not exactly underpowered, so much as IAF wants more.

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Re: LCA news and discussion

Postby Kartik » 12 May 2009 04:16

Vivek K wrote:Kartik, great post and thanx for that info in one post. Couldn't have been put better.

Isn't the thrust to weight ratio of the LCA equal or greater than that of the M2k? Why then is it underpowered?


it could be that the installed thrust on the aircraft may not be the same as the dry thrust on a testbed, or that the F-404 derates under the hot conditions at sea level. or it could be a problem with the intakes. I'm not quite sure about what the reason could be.

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Re: LCA news and discussion

Postby Hitesh » 12 May 2009 04:37

Kartiv,

Thank you for the facts and your analysis. However, your acerbic comments such as"whining" was totally uncalled for. All I asked was for facts, not some personal attacks. I need to rebut this engineer with facts, not personal attacks. So please no jingoism, ok?

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Re: LCA news and discussion

Postby Raveen » 12 May 2009 06:08

Kartik wrote:
Vivek K wrote:Kartik, great post and thanx for that info in one post. Couldn't have been put better.

Isn't the thrust to weight ratio of the LCA equal or greater than that of the M2k? Why then is it underpowered?


it could be that the installed thrust on the aircraft may not be the same as the dry thrust on a testbed, or that the F-404 derates under the hot conditions at sea level. or it could be a problem with the intakes. I'm not quite sure about what the reason could be.


Although the thrust to weight ratio might be better you have yet to take into account the aerodynamic efficiency of the actual aircraft. The F-404+Tejas combo might have more thrust per lb it doesnt mean that it has lower drag than the M2k, which would imply it would have lower airspeed for the same amount of thrust (or take more thrust for the same airspeed)and therefore would effectively be underpowered.
Just my $.02

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Re: LCA news and discussion

Postby shiv » 12 May 2009 08:11

Kartik wrote:
you don't need to re-engineer the airframe to withstand the stresses due to the higher thrust (because even with higher thrust, the maximum dynamic load remains the same- i.e. 9Gs). You need to re-engineer the airframe because the exact dimensions of the F-404 and F-414 DO NOT MATCH. nor do they match for the F-404 and the EJ-200.


True.

But there is an additional factor here. Because nobody in India has designed a fighter aircraft before - Indian engineers have over-designed the LCA in areas where they are not sure how much stress tolerance is required. This is an obvious thing to do - because the last thing anyone wants is to underestimate the stresses and make the aircraft lighter but prone to breaking up.

This was revealed to me at Aero India in a conversation with the Navy head of the Naval LCA project. While they wrestle with weights it appears that the exact stresses that the undercarriage of a carrier based aircraft are mostly secret and India engineers may well have overdesigned the undercarrriage to take stresses that it is unlikely to face. If a rough idea of the exact stresses can be gleaned, a lot of weight can be shaved off the undercarriage - the figure was in several hundred Kgs. This is because weight is not only taken off the undercarriage structure but also the aircraft structure that supports the undercarriage (and takes stresses from the undercarriage) can also have its weight reduced to cope with realistic stresses rather than heavier stresses it was made for as part of overdesign.

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Re: LCA news and discussion

Postby Hitesh » 12 May 2009 09:41

When they put in the heavy engine and shave off the undercarriage to take off the extra weight, how will they compensate for the altered center of gravity?

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Re: LCA news and discussion

Postby rakall » 12 May 2009 11:24

Hitesh wrote:When they put in the heavy engine and shave off the undercarriage to take off the extra weight, how will they compensate for the altered center of gravity?



Thats where the little secret of Yindoo engineers lies.. in ballast form..

Prasad - correct me if i am wrong.. but Cmdr. Balaji did mention this, right?

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Re: LCA news and discussion

Postby rakall » 12 May 2009 11:32

shiv wrote:
But there is an additional factor here. Because nobody in India has designed a fighter aircraft before - Indian engineers have over-designed the LCA in areas where they are not sure how much stress tolerance is required. This is an obvious thing to do - because the last thing anyone wants is to underestimate the stresses and make the aircraft lighter but prone to breaking up.

This was revealed to me at Aero India in a conversation with the Navy head of the Naval LCA project. While they wrestle with weights it appears that the exact stresses that the undercarriage of a carrier based aircraft are mostly secret and India engineers may well have overdesigned the undercarrriage to take stresses that it is unlikely to face. If a rough idea of the exact stresses can be gleaned, a lot of weight can be shaved off the undercarriage - the figure was in several hundred Kgs. This is because weight is not only taken off the undercarriage structure but also the aircraft structure that supports the undercarriage (and takes stresses from the undercarriage) can also have its weight reduced to cope with realistic stresses rather than heavier stresses it was made for as part of overdesign.



To add to Shiv's post...for example..

NLCA descent rate is 3-4m/sec. By Mil standards - you have to design the undercarriage to a certain sigma variation ( 1-sigma IIRC).. which means NLCA undercarriage has to be designed for a vertical descent rate of 7.5m/sec.

But when the LCA designers had a chance to have a discussion with Rafale TP's they came to know that carrier borne Rafale undercarriage is designed for only 6.9m/sec. How is Dassault confident that the design for 6.9m/sec is enough? EXPERIENCE !!!

Similarly.. some factors of safety have been assinged high margins in LCA and the proposed consultancy agreement with BAe is to simply leverage their experience to re-assign those margins etc stuff.. The intention is not to CtrlC+CtrlV BAe designs into LCA.

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Re: LCA news and discussion

Postby putnanja » 12 May 2009 11:35

In fact, one argument against F414 is that it alters the Center of Gravity significantly compared to EJ-200 ( compared to current F-404 engine). But EJ's thrust currently is around 90kN currently compared to 95-100kN of F-414. Then again, Ej-200 is supposed to have much more growth potential as compared to F-414.

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Re: LCA news and discussion

Postby Dileep » 12 May 2009 13:37

Hitesh, that guy is not an engineer for sure, so leave that part. The undercarriage being overweight by 3000 lbs? That is a dead giveaway that the 'engineer' is in fact a DCH puki kid.

Also, the 'real estate' problem was positively identified as one for the HACK aircraft used to test the MMR, not for the LCA. The HACK is a big AC, and they used long cables to connect the antenna, which was a problem.

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Re: LCA news and discussion

Postby vina » 12 May 2009 16:28

shiv wrote: If a rough idea of the exact stresses can be gleaned, a lot of weight can be shaved off the undercarriage - the figure was in several hundred Kgs. This is because weight is not only taken off the undercarriage structure but also the aircraft structure that supports the undercarriage (and takes stresses from the undercarriage) can also have its weight reduced to cope with realistic stresses rather than heavier stresses it was made for as part of overdesign.


Shivji, what you have described is called the "design spiral" . It is an iterative process, especially the weight estimate. You do it in multiple spiral loops until you get to the center (hence spiral).

Lemme explain. If you take 1 ton out of the undercarriage (say)

Loop 1 .If you take out weight out of undercarriage , coz you found that it was over designed, you take weight out of the fuselage and hence overall weight comes down (by say delta 1 , lets say 1 ton total)

Loop 2: Now for the reduced overall weight (from loop 1), you will see that the undercarriage is again "over designed" and you will lower weight in undercarriage and therefore fuselage and hence overall weight comes down again (by say delta 2, lets say 500 kg)

Loop3 :Now for the reduced overall weight (from loop 2), you will see that the undercarriage is again "over designed" and you will lower weight in undercarriage and therefore fuselage and hence overall weight comes down again (by say delta 3, lets say 100 kg)

Loop 4: Now for the reduced overall weight (from loop 3), you will see that the undercarriage is again "over designed" and you will lower weight in undercarriage and therefore fuselage and hence overall weight comes down again (by say delta 3, lets say 0.5 kg)

After loop 4, you have hit the law of diminishing returns and any excess weight loss is minuscule and you stop!.

Now so what is the weight savings you made to the airplane ?. If you say 1 ton, you are a clueless Paki !

The correct answer is 1000 + 500 + 100 + 0.5 ~ 1600 kg ..approx 1.6 ton!

Weight gain is the flip side of the design spiral !. Obviously, now if you have over designed, and still close to your original weight, it is far easier to reduce weight and hit weight targets by optimization, than if you are under designed and close to you weight target!.

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Re: LCA news and discussion

Postby k prasad » 12 May 2009 17:06

shiv wrote:This was revealed to me at Aero India in a conversation with the Navy head of the Naval LCA project. While they wrestle with weights it appears that the exact stresses that the undercarriage of a carrier based aircraft are mostly secret and India engineers may well have overdesigned the undercarrriage to take stresses that it is unlikely to face. If a rough idea of the exact stresses can be gleaned, a lot of weight can be shaved off the undercarriage - the figure was in several hundred Kgs. This is because weight is not only taken off the undercarriage structure but also the aircraft structure that supports the undercarriage (and takes stresses from the undercarriage) can also have its weight reduced to cope with realistic stresses rather than heavier stresses it was made for as part of overdesign.



rakall wrote:Prasad - correct me if i am wrong.. but Cmdr. Balaji did mention this, right?


Yup Rakall... Balaji did mention that we'd end up needing to add about 150 kg of weight in front to compensate.

Other scientists mentioned that this requirement may indeed be a small blessing, by allowing them to strengthen the cockpit (add some xtra armor), or add a bigger/more powerful radar. However, that weight will need to be added.

Just to mention at this point, the GTRE director also spoke about 150kg extra weight with an engine that is 100 kg over design weight. However, he said that given the margins built in, that wasn't of too much concern.

I worried about this statement of his till Tamilmani's talk, where he said that there is still a lot of extra weight and margin on the LCA, and that will go away with testing, once they see the limits. (Wiring isn't lightweight either btw :-D).

So I guess the overweight thing isn't too much of a problem with the LCA designers. And given the level of confidence that the IAF is showing in the project, I don't see why we should worry.

Just to nitpick, 3000lb ~ 1.3 ton, which is in fact the new empty weight of the LCA (6.5 tons). If ADA isn't calling that overweight, why worry. :D

rakall wrote:To add to Shiv's post...for example..

NLCA descent rate is 3-4m/sec. By Mil standards -


Precisely Rakall... excellent explanation. Not sure if you had written down the exact descent rates, but i remember Balaji saying that NLCA's was 7.5 (or was that 7.9 m/s?) m/s while Rafale's was 6.1 m/s. However, if you've got it written down, then thats the right one.

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Re: LCA news and discussion

Postby negi » 12 May 2009 18:15

LCA's landing gear might have been made for a higher descent rate as compared to Rafale or other fighter ,however what is important is what is its approach speed during landing when compared to Rafale (that difference will have to factored in) ?

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Re: LCA news and discussion

Postby vina » 12 May 2009 18:38

Landing gear will be designed for a specific sink rate (ie vertical speed of the plane in the vertical direction as it descends). The horizontal speed is not really important for structural design of landing gear (of course for a given airfoil , sink rate will be related to min landing speed, the plane needs to by flying after all and not stalling and falling!). The pilot has to keep both the sink rate and the horizontal speeds under watch while he is landing. Sink rate for landing gear limits and horizontal speed to make sure that you can brake and come safely to a halt before running out of runway!.

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Re: LCA news and discussion

Postby vina » 12 May 2009 18:49

k prasad wrote:Yup Rakall... Balaji did mention that we'd end up needing to add about 150 kg of weight in front to compensate.

Other scientists mentioned that this requirement may indeed be a small blessing, by allowing them to strengthen the cockpit (add some xtra armor), or add a bigger/more powerful radar. However, that weight will need to be added.

Just to mention at this point, the GTRE director also spoke about 150kg extra weight with an engine that is 100 kg over design weight. However, he said that given the margins built in, that wasn't of too much concern.


But that is still 250Kg extra weight that you are carrying on an empty aircraft . Adding weight in the front is a sub optimal pipe wrench solution and is probably being done in the interest of time , effort and need to get aircraft in service at the earliest.

You wouldn't do it if it were a clean sheet design. With the extra 100 kgs (assuming that is the difference between the F404 IN 20 and the F414 /EJ 200/whatever), you would get new dynamic response data and the new control parameters of the aircraft and feed the new data into the flight control system and make it handle the extra instability due to the 100kgs or whatever.

Now that would need an entire flight test and validation regime starting from the wind tunnel to get data,confirm it in flight and validate the FCS. Now that is what I think they are looking to shortcut and save all the testing effort by having similar amount of static margin as the original design.

JMT , 2 centsand ramblings and all the rest of the usual disclaimers.

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Re: LCA news and discussion

Postby rakall » 12 May 2009 18:53

negi wrote:LCA's landing gear might have been made for a higher descent rate as compared to Rafale or other fighter ,however what is important is what is its approach speed during landing when compared to Rafale (that difference will have to factored in) ?



The vertical descent rate is nearly equal is what he said.. the design space on the LHS side or lower limit side of vertical descent is probably a big wall at 3-4m/sec... Everyone will try to make the vertical descent rate as small as possible... I think the design margin for that is really tight..

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Re: LCA news and discussion

Postby negi » 12 May 2009 20:05

vina wrote:Landing gear will be designed for a specific sink rate (ie vertical speed of the plane in the vertical direction as it descends). The horizontal speed is not really important for structural design of landing gear (of course for a given airfoil , sink rate will be related to min landing speed, the plane needs to by flying after all and not stalling and falling!). The pilot has to keep both the sink rate and the horizontal speeds under watch while he is landing. Sink rate for landing gear limits and horizontal speed to make sure that you can brake and come safely to a halt before running out of runway!.

Gurudev...how important ...I am unable to comment (but correct me if I am wrong there should be a significant amount of shearing forces induced on the Undercarriage due to the Horizontal component of Impulse during the touch down ) . And in case of carrier based ops using CATOBAR config Horizontal speed during the landing is critical .

Rakall thanks for the info.

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Re: LCA news and discussion

Postby SaiK » 12 May 2009 20:18

Wouldn't a slight roll due to directional winds while touch down cause additional stress to one of the wheels more than the other, when the whole weight of the aircraft (assuming this scenario) be on one stress point?

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Re: LCA news and discussion

Postby Kartik » 12 May 2009 21:05

k prasad wrote:Just to mention at this point, the GTRE director also spoke about 150kg extra weight with an engine that is 100 kg over design weight. However, he said that given the margins built in, that wasn't of too much concern.

I worried about this statement of his till Tamilmani's talk, where he said that there is still a lot of extra weight and margin on the LCA, and that will go away with testing, once they see the limits. (Wiring isn't lightweight either btw)


which is what I've been trying to say to a lot of people. inexperience, not having a huge database of the precise material properties, failure allowables, etc. built up over decades of experience with materials, analysis methods which are conservative and textbookish, all these tend to lead the Stress engineers to oversize parts.

however, as the LCA flight test brings in data on what is the precise aerodynamic load, and they compare it with the predicted loads over the envelope, if they find that the flight test loads are lower, then weight will come down. the other way is to bring in consultants like EADS and get them to take a look at Strength Check Notes and see if the methods are too conservative and margins too high.

BTW, the new 747-8F Boeing freighter is nearly 8000 lbs overweight (only a fraction compared to its empty weight), but this is quite common in the aero-industry. many manufacturing requirements also drive up weight.

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Re: LCA news and discussion

Postby Kartik » 12 May 2009 21:39

vina wrote:Landing gear will be designed for a specific sink rate (ie vertical speed of the plane in the vertical direction as it descends). The horizontal speed is not really important for structural design of landing gear (of course for a given airfoil , sink rate will be related to min landing speed, the plane needs to by flying after all and not stalling and falling!).


the horizontal speed contributes to the shearing effect on the landing gear. its not a stone dropping from a height, which has no horizontal velocity component, but rather an object with quite substantial vertical and horizontal velocities.

add the weight of the arresting gear to the weight of the aircraft. the higher the horizontal velocity, the greater the load on the arrestor, which again requires a very strong connection to the aircraft. all of that adds weight. unless they reduce the approach speed significantly by adding high lift devices, its one more heavy component added to the NLCA.

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Re: LCA news and discussion

Postby shiv » 12 May 2009 21:47

Hitesh wrote:When they put in the heavy engine and shave off the undercarriage to take off the extra weight, how will they compensate for the altered center of gravity?


Depending on where the CG is, they will add a lead weight or piece of thermocole in place of the tail chute.

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Re: LCA news and discussion

Postby Cain Marko » 12 May 2009 21:53

k prasad wrote:
Yup Rakall... Balaji did mention that we'd end up needing to add about 150 kg of weight in front to compensate.

Other scientists mentioned that this requirement may indeed be a small blessing, by allowing them to strengthen the cockpit (add some xtra armor), or add a bigger/more powerful radar. However, that weight will need to be added.


But that is still 250Kg extra weight that you are carrying on an empty aircraft . Adding weight in the front is a sub optimal pipe wrench solution and is probably being done in the interest of time , effort and need to get aircraft in service at the earliest.


Couple of ammatur questions onlee:

1) Doesn't the EJ-200 weight less than/equal to the current f-404? why offset with extra weight in the nose?

2) IF they need to get more weight in the nose, won't an AESA/IRST combo take care of it?

Regards,
CM.

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Re: LCA news and discussion

Postby vina » 12 May 2009 21:58

Aircraft tail hooks are connected to the fuselage and not landing gear. The shock loads from the arresting gear gets transmitted to the fuselage structural members, which anyway are stressed enough to withstand high combat loads and can take the landing stress from the tail hooks without too much trouble with some amount of strengthening.

Shear forces and resultant moments while landing again are not taken by the landing gear per se , but by the aircraft fuselage/wing attachment points of the undercarriage, which too like the arresting hooks need to be strengthened.

The reason why undercarriages of carrier aircraft tend to be more heavy duty than land based aircraft is that the sink rates in carrier landings are much higher than land based aircraft. That is because, you cannot flare the aircraft in the final approach like you do on land on a carrier approach. You literally fly (or control crash ) the aircraft into the deck, unlike land where you gently drop down on the tarmac like a feather (as the plane still continues to fly) and then cut power once you touch down.

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Re: LCA news and discussion

Postby SaiK » 12 May 2009 22:21

can it be still composite materials handling the stress points where the fuselage and landing gear shear forces meets?

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Re: LCA news and discussion

Postby KrishG » 12 May 2009 22:23

We have also got to look into the fuel economy and air-flow requirements of both EJ200 and F414. The F414 in particular burns a lot of fuel and is termed to be 'in-efficient' to an extent whereas the even the uprated version of EJ200 at 96 kN would have better fuel economy then the F414. The fuselage modifications will not increase the volume of fuel that can be stored internally. So, putting an F414 on LCA will decrease it's range.

And also, what will be the bring back weight of NLCA ?

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Re: LCA news and discussion

Postby Jayram » 12 May 2009 22:45

So simple question only. Why is wieght removal a problem for the undercarriage for trhe regular LCA (Not the NLCA) ? The land based LCA is never going to land on an aircraft so why not release that in Version 1 after shaving whatever weight savings they need do by an iterative process or whatever and be done with it.
Why are we talking about the NLCA and the Landbased LCA in one breath? Some simple enlightment will be much appreciated.
-Jayram

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Re: LCA news and discussion

Postby negi » 13 May 2009 03:13

Vina ji not only the sink rates infact the approach speed during landing itself has to be higher so that aircraft can take off un-assisted in case the tail hook misses the arristor wire .Also the tyre pressure for carrier based aircraft is pretty low as compared to their land based counterparts .

Btw there was an interesting write up in dassault's proceedings for the Rafale explaining how the Canards not only were instrumental in improving the overall flight characteristics but also bringing down the approach speed during the landing when compared to Mirage-2000 .

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Re: LCA news and discussion

Postby Kartik » 13 May 2009 04:04

vina wrote:Aircraft tail hooks are connected to the fuselage and not landing gear. The shock loads from the arresting gear gets transmitted to the fuselage structural members, which anyway are stressed enough to withstand high combat loads and can take the landing stress from the tail hooks without too much trouble with some amount of strengthening.


Vina, I didn't say that the arrestor hook is attached to the landing gear. I said that it adds to the weight of the aircraft. The arrestor hook- aft fuselage joint will be subjected to very high loads applied during a very short duration. the hook, with the joint itself, will have to be very strong, to stop a fighter that weighs nearly 10-12,000 kgs (depending on the N-LCA's bring back load and on board fuel reserves) from a speed of nearly 140-150 knots down to zero.

Shear forces and resultant moments while landing again are not taken by the landing gear per se , but by the aircraft fuselage/wing attachment points of the undercarriage, which too like the arresting hooks need to be strengthened.


point is that its not a simple problem of dropping an object with no forward velocity from a height. the nose wheel gear will also be beefed up, again adding to the weight. all in all, unless a serious weight reduction occurs for the Tejas, the Tejas N will have far more serious weight/range/bring back load issues than the regular Tejas.

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Re: LCA news and discussion

Postby NRao » 13 May 2009 06:00

A new game?

Vick wrote:Boeing's Super Hornet seeks export sale to launch 20% thrust upgrade
The F414 enhanced performance engine (EPE) includes an all new core and forward fan to dramatically increase the fighter's takeoff performance, said Bob Gower, Boeing vice president for F/A-18E/F.

The improvements would increase the F414 thrust rating from 22,000lbs to 26,600lbs.


Commonality with LCA Mk-II?

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Re: LCA news and discussion

Postby Vick » 13 May 2009 07:04

N-LCA can use all the takeoff thrust it can get in order to have any significant load and/or endurance off a non-cat carrier. I believe the F-414 EPE offers the most thrust from any of the LCA compatible engine families (M-88, EJ200 and F414).

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Re: LCA news and discussion

Postby karan_mc » 13 May 2009 07:09

Did Boeing Offered this new 414 engines for Tejas program ,it has massive power

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Re: LCA news and discussion

Postby Vick » 13 May 2009 07:16

karan_mc wrote:Did Boeing Offered this new 414 engines for Tejas program ,it has massive power

Not explicitly, it's assumed that if the SH wins the MMRCA, then its engine would also be the front runner to power the Tejas. But you know when one assumes...

Also, GE makes the engine, so it's GE's to offer. Boeing is hoping that a large external customer would be willing to invest into mating the F414 EPE with the SH frame and all of its attendent costs.

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Re: LCA news and discussion

Postby vina » 13 May 2009 11:46

And in case of carrier based ops using CATOBAR config Horizontal speed during the landing is critical .

not only the sink rates infact the approach speed during landing itself has to be higher so that aircraft can take off un-assisted in case the tail hook misses the arrestor wire .Also the tyre pressure for carrier based aircraft is pretty low as compared to their land based counterparts .


Lets look at the basics here. You need less horizontal speed while landing because you need to be able to brake and stop before you run out of runway. For a given braking capacity, the momentum you carry when you are landing has to be less than what the brakes can stop!.

Now for carrier landings, you have a very very small runway aka deck , indeed :wink: :wink: . So to assist you in landing, the arrestor mechanisms will be rated for certain max loads (aka momentum , ie m*v) , which can bring a plane to halt within the specifed distance. There are limits everywhere , including the max deceleration the airplane can handle , the max the pilots can withstand, the optimum for long term life of the structure etc..

If you are landing a biggie like a EC2C hawker on a carrier, you need to come in really slow so that the total momentum carried is less than what the arrestors can handle. You will even dump excess weight if your momentum is higher than what the wires can handle at approach speed.

Now for a fighter, which is lighter than the EC2C , you can come in faster because you can carry more momentum , and anyway, the fighters have a higher stall speed than the EC2C and will stall if they come in as slow as the Hawkeye.So theoretically, yes, as long as you are within the arrestor's capacity, you can come in fast, but your deceleration will be violent!

From what I know, the arrestor gear brake capacity is adjust for each plane. You dont apply full potential to every plane, but is tailored so that max deceleration is not exceeded and the plane comes to a relatively gentle stop.

All the same, you cannot come below a minimum because the plane still needs to be flying when it hits the deck and not stalled and maybe take off again if it misses a wire!. So yes, the lesser your flying approach speed, the better it is (given the deceleration limits, the max capacity of the arrestor etc). Notice, the basics is not very different from landing on an airfield. You fly in faster, you need to apply more brakes, decelerate more to stop within runway length, than you would if you came in slower!. The wire is just a massive booster assisted power brake. That is all.

Lower tyre pressures have higher rolling resistance. But that again is not really important here for this reason (lower pressure tyres have better springing and shock absorbing capabilities than high pressure ones, so load on struts and undercarriage will be less). The plane is above stall speed when it hits the deck and with the engines on at full power, there will be no problem in taking off again.

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Re: LCA news and discussion

Postby vivtho » 13 May 2009 12:22

negi wrote:Vina ji not only the sink rates infact the approach speed during landing itself has to be higher so that aircraft can take off un-assisted in case the tail hook misses the arristor wire .Also the tyre pressure for carrier based aircraft is pretty low as compared to their land based counterparts .

Btw there was an interesting write up in dassault's proceedings for the Rafale explaining how the Canards not only were instrumental in improving the overall flight characteristics but also bringing down the approach speed during the landing when compared to Mirage-2000 .


WRT the high landing speed of the Mirage 2000, all delta wing aircraft have a high landing speed. It is a major disadvantage of that configuration, which is one of the reasons (the other main reason is their comparatively poor maneuverability) why they went out of fashion after the early 60s. On a canard-delta configuration. during high AoA maneuvers, the canard not only provides a turning moment, but also increases the airflow over the main wing. This is somewhat similar to the effect that the F/A-18s LERXs have on the type's great low-speed maneuverability.

vina wrote:From what I know, the arrestor gear brake capacity is adjust for each plane. You dont apply full potential to every plane, but is tailored so that max deceleration is not exceeded and the plane comes to a relatively gentle stop.

All the same, you cannot come below a minimum because the plane still needs to be flying when it hits the deck and not stalled and maybe take off again if it misses a wire!. So yes, the lesser your flying approach speed, the better it is (given the deceleration limits, the max capacity of the arrestor etc). Notice, the basics is not very different from landing on an airfield. You fly in faster, you need to apply more brakes, decelerate more to stop within runway length, than you would if you came in slower!. The wire is just a massive booster assisted power brake. That is all.

Vina, that is indeed correct. Before landing, a carrier pilot will calculate the estimated weight of his aircraft by subtracting the fuel burnt and weapons expended from his take off weight (of course, any in-flight refueling would complicate this calculation a bit more). He then radios this to the carrier, on the basis of which the hydraulics for the arrestor gear are adjusted for that particular weight. Failure to do this can lead to spectacular accidents. I once saw a video clip where an F/A-18 made a landing on a carrier where the arrestor gear was configured for an E-2 (IIRC the E-2 was waved off and the Hornet did not have fuel to hold any longer). The tailhook on the Hornet was ripped off the aircraft and the pilot was forced to eject just as he left the angled portion of the deck.

I'd also like to add a little more information here. A carrier landing approach on a jet is flown at around 70-80% N1 RPM depending on the configuration. This is because jet engines take several loooong seconds to spool up from idle to a usable amount of thrust and the thrust does not increase in a linear manner with the RPM. (for example, on a Boeing 737-700, it takes around 63% N1 RPM to get enough thrust to even start taxiing. Beyond 63% N1 RPM, thrust per RPM increases rapidly). So unlike a regular runway landing, the pilot will keep his engine running at a higher RPM and use speedbrakes and/or spoilers to maintain his speed.


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