LCA news and discussion

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Craig Alpert
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Re: LCA news and discussion

Postby Craig Alpert » 17 Nov 2009 21:21

karan_mc wrote:Going supersonic and doing Supercruise are two completely different things all together

To put this in layman's term.. Supercruise is simlar to Cruise control in your car... If you want to cruise at a set speed in a car, you hit the cruise control and you'r car will drive at that set speed say (62mph/100kmp).. The higher the speed, the more fuel it conusmes, and likewise the steeper the terrain, the more fuel is burns as well.. With that same format all aircraft can currently CRUISE say at 500 kmph or 500mph, when the aircraft crosses the sound barrier at mach 1 or higher it increases it speed. IF and ONLY IF an aircraft is capable of flying itself at that set speed of say Mach 1.2 for a set amount of period/distance/altitude/with or without load can it be called "Super Cruise" Crossing a mach 1.2 speed and maintaing it for 30 secs to a 1min does not qualify it as "supercursing" It needs to be able to do it for over 5 mins or more however, the faster it goes and depending on the load it carries, it will use up it's fuel a lot sooner, and hence it will affect the total range of the aircraft as well.

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Re: LCA news and discussion

Postby KrishG » 17 Nov 2009 21:25

shiv wrote:I do accept that but unless you have a figure for drag you cannot relate t/w ratio to final velocity. The only "example" I can give is the theoretical ion rockets in a vacuum which are supposed to give a very low acceleration for weeks to reach tremendous velocities.


Vacuum has no drag. Ion thrusters have very high specific impulse but very very very low thrust. They can only be used in vacuum or similar conditions not from ground.

shiv wrote:
Rahul M wrote:well considering that the dry TWR for LCA with the IN20 engine (for full loaded weight) comes to 0.52 it is a bit hard to see how that happens.


Rahul the TW ratio as far as I know has more to do with climb rate and loss of thrust while turning than the ability to accelerate in level flight. If you keep accelerating the thing forward it go as fast as is possible until air resistance stops it from going any faster I guess. I am no expert though.


I would like to state this in a different way.

An aircraft is designed for certain max speed and operating speed. Once an aircraft reaches this speed the T/W ratio doesn't matter as long as the a/c is in level flight, assuming there is no major air drag difference b/w 2 same a/c with same speed but diff T/W ratios.

But about acceleration in level flight, greater T/W ratio necessarily means faster acceleration.

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Re: LCA news and discussion

Postby SaiK » 17 Nov 2009 21:39

would the chromium coatings [the other news from IISc we heard under the missile thread] help in reducing drag for a/cs?

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Re: LCA news and discussion

Postby KrishG » 17 Nov 2009 22:11

SaiK wrote:would the chromium coatings [the other news from IISc we heard under the missile thread] help in reducing drag for a/cs?


Nope! the a/c's nose coated with chromium willn't be hot enough for the reaction to take b/w air and chromium.

Anyway, if we coat the a/c's nose with chromium it will end up having high IR signature due Chromium being a good heat conductor and heating up. That's one of the reasons metals are never used on the nose of a/c especially supersonic ones.

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Re: LCA news and discussion

Postby Daedalus » 17 Nov 2009 22:15

SaiK wrote:would the chromium coatings [the other news from IISc we heard under the missile thread] help in reducing drag for a/cs?

I think this is a one time deal. Once the coating evaporates the effect is gone, then the a/c will have to be re-coated. More over the coating process may be real expensive like using vapor deposition method.

On the other hand chrome coated LCA will be hot sell :D .

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Re: LCA news and discussion

Postby SaiK » 17 Nov 2009 22:41

http://www.iisc.ernet.in/researchhigh/p ... ds2008.pdf

sorry.. this answers it!~ not for the low machs.

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Re: LCA news and discussion

Postby Kartik » 17 Nov 2009 23:55

Craig Alpert wrote:
karan_mc wrote:Going supersonic and doing Supercruise are two completely different things all together

To put this in layman's term.. Supercruise is simlar to Cruise control in your car... If you want to cruise at a set speed in a car, you hit the cruise control and you'r car will drive at that set speed say (62mph/100kmp).. The higher the speed, the more fuel it conusmes, and likewise the steeper the terrain, the more fuel is burns as well.. With that same format all aircraft can currently CRUISE say at 500 kmph or 500mph, when the aircraft crosses the sound barrier at mach 1 or higher it increases it speed. IF and ONLY IF an aircraft is capable of flying itself at that set speed of say Mach 1.2 for a set amount of period/distance/altitude/with or without load can it be called "Super Cruise" Crossing a mach 1.2 speed and maintaing it for 30 secs to a 1min does not qualify it as "supercursing" It needs to be able to do it for over 5 mins or more however, the faster it goes and depending on the load it carries, it will use up it's fuel a lot sooner, and hence it will affect the total range of the aircraft as well.


wow !! this is a new definition of super-cruise..please let me know which dictionary or book gave you this definition of super-cruise. the fact is that it has nothing to do with what the cruise in a car does or what its purpose is, so using that as an example is wrong. nor does any Lockheed Martin, Saab or EADS brochure say that it has to be done for a min. of 5 minutes..where on earth did you get this figure ?! and the best part is that you missed out on what is considered the absolute minimum requirement for super-cruise-> that the afterburner should not have been engaged in crossing Mach 1.

supersonic cruise, also called super-cruise was a term coined as one of the super-duper advantages of the F-22, where its pilot could cross the Mach barrier (with its associated huge drag peak right at the Mach barrier) WITHOUT using afterburner. many aircraft in a lightly loaded condition will be able to get close to the Mach 1 limit, but will not be able to cross it because there is a huge drag increase right at that point. till the area rule was discovered, most aircraft couldn't even cross that barrier. now of course all aircraft are designed with that rule in mind, and if the airframe is designed well, with low drag, and the T/W ratio of the aircraft is good, it will be able to cross that barrier without using AB, which really guzzles fuel. the pilot will still be using max. dry thrust, but that is nothing compared to the amount of fuel an AB consumes. most aircraft carry enough fuel only for a few minutes of AB during an entire mission.

the advantage that the F-22 gained due to this capability, was that it would allow an F-22 to get to the scene of action supersonically, over a long distance and over a longer period of time, without needing to use its AB. That meant that it had enough reserves of fuel left for it to be able to stay on station for a meaningful period of time. Japan's Air Chief had stated that it was the most attractive feature of the F-22 as far as they were concerned, because it would allow fighters based far away from the islands that they need to defend against China, to reach the battle quickly. If they buy F-35s, they need to build a new base closer to the disputed islands and sea lines, because getting there in time itself would take up most of the F-35's fuel (even though it carries a lot of internal fuel).

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Re: LCA news and discussion

Postby Picklu » 18 Nov 2009 00:21

shiv wrote:
Rahul M wrote:shiv ji, those are all related parameters related to the aircraft's energy. it can trade speed for height and vice versa and all of that comes from the engine thrust.

in level flight with no acceleration, the thrust has to negate the drag in order for the a/c to move.


I do accept that but unless you have a figure for drag you cannot relate t/w ratio to final velocity. The only "example" I can give is the theoretical ion rockets in a vacuum which are supposed to give a very low acceleration for weeks to reach tremendous velocities.


Someone told me that the thrust to drag ratio is what determines the max velocity but the ratio varies with the altitude and the speed of the aircraft and hence it is not a single figure but a curve. Such curves are to be computed for each store configuration to program flight simulators. However I am not sure how much trustworthy this source is so take it FWIW.

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Re: LCA news and discussion

Postby Picklu » 18 Nov 2009 00:38

KrishG wrote:Vacuum has no drag. Ion thrusters have very high specific impulse but very very very low thrust. They can only be used in vacuum or similar conditions not from ground.

I think Shiv used the above just as an analogy. The main point is thrust to wight ratio is used to determine the acceleration or climbrate but not for level flight. As long as the dry thrust counters the drag generated at the speed, the aircraft should be able to sustain that speed(Mach 0.5 ... Mach 1.2) using dry thrust only provided the engine can handle the airflow. Now, we do not know what is the drag generated by a clean LCA at various speed and altitude regime and hence all the speculation.

Again, most of us understand that this "capability" is not very useful in real world scenario as far as LCA is concerned. Fortunately, us joe public do not have to concern ourselves very much about the real world combat schenario due to good old Indian military and we can afford to create sotrm in a tea cup over such semantics of "supah cruize"

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 00:46

shiv wrote:I do accept that but unless you have a figure for drag you cannot relate t/w ratio to final velocity.

actually that's not very difficult.

in level flight w/o acceleration, thrust = drag and lift generated = weight of aircraft.

since drag is a function of the square of the velocity, it is the thrust that ultimately determines what speed it can sustain. (IOW, mathematically speaking, what amount of drag it can equalise)

--------------
Someone told me that the thrust to drag ratio is what determines the max velocity but the ratio varies with the altitude and the speed of the aircraft and hence it is not a single figure but a curve. Such curves are to be computed for each store configuration to program flight simulators. However I am not sure how much trustworthy this source is so take it FWIW.

from my limited understanding that is correct (*) since drag is also a function of air density, which changes with altitude. it is also proportional to square of velocity as I wrote above.

(*) except that it should probably read either "thrust to weight ratio" or "lift to drag ratio" ? AFAIK, for level flight at constant speed, thrust to drag ratio is always 1.

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Re: LCA news and discussion

Postby Craig Alpert » 18 Nov 2009 01:04

Kartik wrote:wow !! this is a new definition of super-cruise..please let me know which dictionary or book gave you this definition of super-cruise. the fact is that it has nothing to do with what the cruise in a car does or what its purpose is, so using that as an example is wrong. nor does any Lockheed Martin, Saab or EADS brochure say that it has to be done for a min. of 5 minutes..where on earth did you get this figure ?! and the best part is that you missed out on what is considered the absolute minimum requirement for super-cruise-> that the afterburner should not have been engaged in crossing Mach 1.

supersonic cruise, also called super-cruise was a term coined as one of the super-duper advantages of the F-22, where its pilot could cross the Mach barrier (with its associated huge drag peak right at the Mach barrier) WITHOUT using afterburner. many aircraft in a lightly loaded condition will be able to get close to the Mach 1 limit, but will not be able to cross it because there is a huge drag increase right at that point. till the area rule was discovered, most aircraft couldn't even cross that barrier. now of course all aircraft are designed with that rule in mind, and if the airframe is designed well, with low drag, and the T/W ratio of the aircraft is good, it will be able to cross that barrier without using AB, which really guzzles fuel. the pilot will still be using max. dry thrust, but that is nothing compared to the amount of fuel an AB consumes. most aircraft carry enough fuel only for a few minutes of AB during an entire mission.

the advantage that the F-22 gained due to this capability, was that it would allow an F-22 to get to the scene of action supersonically, over a long distance and over a longer period of time, without needing to use its AB. That meant that it had enough reserves of fuel left for it to be able to stay on station for a meaningful period of time. Japan's Air Chief had stated that it was the most attractive feature of the F-22 as far as they were concerned, because it would allow fighters based far away from the islands that they need to defend against China, to reach the battle quickly. If they buy F-35s, they need to build a new base closer to the disputed islands and sea lines, because getting there in time itself would take up most of the F-35's fuel (even though it carries a lot of internal fuel).

Glad you like it! Unfortunately the book/dictionary is not for sale!
I said to put it in LAYMAN’S term SIMILAR being the key word.. I never mentioned the LITERAL CRUISE CONTROL OF A CAR and that in a FIGHTER JET chief!!! You didn’t get the analogy and since you took the literal meaning let me help you out with that.. A Bugatti veyron can travel around 90 miles on 26 gallons of fuel at HIGHWAY speeds, however it travels ONLY 20 odd MILES when it reaches it max speed of 254MPH with 26 gallons of GAS all emptied in just 12 MINUTES.. I never mentioned LM, EADS, SAAB or whoever you might think off for the 5 min grace period.. I said 5 or MORE in general terms because it has to be done over a CERTAIN PERIOD/ALTITUDE/RANGE/PAYLOAD. Since you want facts, let’s give them to you.
1) AF monthly carried an article where Col Boyd of the USAF set requirements for the F-16 phalcon to cruise supersonically over enemy territory for a minimum of twenty minutes (don't have the scans on hand).. However this was never implemented as the amount of fuel it requires to perform this is 40% over what it currently carries and with further decrease in ECM and Electronic pods carrying capacity. Nonetheless this was employed in F-22 as the design requirements were made with keeping this in mind so that it can carry adequate amount of fuel for it to supercruise for the allocated time mentioned.
2)Data for the F-22 is classified and hence cannot be discussed, however the F-22 has demonstrated supercruise speeds of at least Mach 1 – 1.7, at 40,000 ft (12,000 m) to 50,000ft. Supercruise is meant to imply a significant increase in effective combat speed with a full weapons load. Virtually all current and past jet fighters, prior to the F-22, cruise at approximately Mach 0.8~0.9 with a militarily significant weapons load. And to best support my arguments with open source information here’s a quote from Wiki “The F-22 represents a significant advance in cruise speed over previous types (for performance of current USAF types, see Air Force Magazine, May 2006, "Gallery of USAF Weapons," pp. 147–155 - [5]). Nonetheless, it can maintain this speed, even in supercruise, for only about five minutes, falling far short of the original performance requirement.”
You pointed out that I did not mention the MAIN POINT of supercruise which was the need to FLY WITHOUT THE AFTERBURNERS. This has been mentioned plenty of time just above our posts hence I did not mention that (no point in restating what is obvious, but I guess I had that one coming) I wasn't planning on giving a history lesson here, just a quick overview of what differs supercruise and supersonic, but you are correct I should have mentioned the point of not using afterburners, but I set myself up for that one. In a civilian jet Concord has demonstrated this capability time and again as it flies supersonic, WITHOUT the use of afterburners over a long distance with certain altitude.. Other obvious use of supercruise is that it increases the aircraft's stealth, as an afterburner plume reflects radar signals and creates a significant infra-red signature.

where on earth did you get this figure ?! and the best part is that you missed out on what is considered

I stated FACTS not FICTION! So the next time you decide to bring me down a notch, Keep in mind I'm NOT Prasun k. SEN-GUPTA.

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 01:55

The main point is thrust to wight ratio is used to determine the acceleration or climbrate but not for level flight. As long as the dry thrust counters the drag generated at the speed, the aircraft should be able to sustain that speed

I'm not sure that is the correct interpretation. TWR determines all of the above.
and if we want to find out if an a/c is capable of SC or not the TWR at max dry will be a determining factor.

as a matter of fact, at level flight/constant velocity, T/W=D/L.
where T/W is the TWR, D is the drag and L is the corresponding lift. hence the TWR is a function of the drag (since lift=weight can be taken to be a constant or a linearly varying factor) and hence a function of velocity.

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Re: LCA news and discussion

Postby Picklu » 18 Nov 2009 02:18

Rahul M wrote:from my limited understanding that is correct (*) since drag is also a function of air density, which changes with altitude. it is also proportional to square of velocity as I wrote above.

(*) except that it should probably read either "thrust to weight ratio" or "lift to drag ratio" ? AFAIK, for level flight at constant speed, thrust to drag ratio is always 1.


My layman understanding is that the ratio is calculated using max trust (dry/wet) just like the thrust to weight ratio. When in level flight the thrust setting is not max. The thrust can be increase further and hence speed can be increased. The AoA here plays a role to balance the weight with the lift.

Simply put, the speed at which the drag reaches the max dry/wet thrust is the corresponding max speed at that altitude for that particular configuration of the AC. Now if that speed is beyond M1 for max dry thrust then the AC can supercruise. The weight does not influence this calculation directly and hence the thrust to weight ratio is not that useful.

Again, all my layman understanding. I distinctly remember hereing the term thrust to drag ratio and I was also a bit surprised because till then, I only heard the term thrust to weight ratio.

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Re: LCA news and discussion

Postby shiv » 18 Nov 2009 07:57

Rahul M wrote:
shiv wrote:I do accept that but unless you have a figure for drag you cannot relate t/w ratio to final velocity.

actually that's not very difficult.

in level flight w/o acceleration, thrust = drag and lift generated = weight of aircraft.

since drag is a function of the square of the velocity, it is the thrust that ultimately determines what speed it can sustain. (IOW, mathematically speaking, what amount of drag it can equalise)



Yes, but without the math - this is what I am asking/thinking about. Two scenarios:

1) Imagine an aircraft accelerating on full power without afterburner. As it accelerates, it climbs and as it climbs the air becomes less dense. Assuming that the engines have enough air and power to keep on accelerating even at altitude a point will be reached when the aircraft just cannot climb any more but is flying at maximum speed maximum thrust (w/o afterburner). Can anyone, just by looking at T/W ratio decide that the maximum speed will be less than Mach 1?

2) The aircraft initially climbs at maximum thrust minus afterburner. At some point, before the aircraft has reached the point of maximum thrust maximum altitude the pilot adjusts the controls to arrest the climb. At this spot the power plant is still generating enough power to climb (accelerate), but the pilot introduces some drag to arrest the climb. How is it possible to say just by T/W ratio that the drag induced to convert to level flight at any altitude will exactly stop the acceleration and prevent the speed from climbing over Mach 1 at some point?

In other words is there a known cut-off TW ratio that will guarantee that the aircraft cannot cross Mach 1 under any atmospheric conditions/altitude assuming that the aircraft is otherwise capable of supersonic flight?

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 08:46

Can anyone, just by looking at T/W ratio decide that the maximum speed will be less than Mach 1?

no, it has to be seen in conjunction with parameters like wing loading and L/D ratio, IOW parameters determined solely by the geometry of the aircraft.

now, since all modern fighters are optimised for the best values of the geometry parameters for similar performance requirements, (supersonic max speed, high climb speed, superior turning performance etc) these parameters occur in a comparatively narrow band of values, which makes TWR one of the determining parameters.


How is it possible to say just by T/W ratio that the drag induced to convert to level flight at any altitude will exactly stop the acceleration and prevent the speed from climbing over Mach 1 at some point?

the drag would be estimated from the geometry of the aircraft.

In other words is there a known cut-off TW ratio that will guarantee that the aircraft cannot cross Mach 1 under any atmospheric conditions/altitude assuming that the aircraft is otherwise capable of supersonic flight?

the figures do suggest something like that.
http://en.wikipedia.org/wiki/Supercruis ... upercruise

calculating TWR for loaded weight with max dry thrust for the fighters.

EE lightning : 0.752 (assumed loaded weight to be 16 t since exact figure is not given)
EF typhoon : 0.787
Gripen NG: 0.72 (probably more. I had to estimate F414G dry thrust figures)
F-22 : 0.703 (assuming max dry thrust to be a conservative 63% of max thrust)
YF-23 : 0.874

so dry thrust TWR of 0.7 for loaded weight seems to be cut-off for achieving SC.

I'll post some snippets later from an aircraft design book that should clarify this issue.

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Re: LCA news and discussion

Postby Cain Marko » 18 Nov 2009 08:54

In line with all the layman thinking, here are my two np:

Super cruise is as much a result of wing design/layout as thrust. Deltas and high swept wings are most likely to SC; straightish wings will find it most difficult.

Case in point, even the Gripen with the RM12 were able to SC (though not with meaningful loads) despite low power engines.

THe high swept design of the flanker and fulcrum and the f-16/f-15 are unable to do this despite more power. However, with even greater power, the fulcrum/flanker should be able to SC.
As far as a straightish wing goes as in the case of the Hornet/Shornet, I wonder if it'll SC even with the latest EPE GE-414 12.5 ton engines. Possibly, but these engines will make the shornet have the highest TWR in 4.5 gen a/c.

JMT

CM.

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 09:03

Super cruise is as much a result of wing design/layout as thrust. Deltas and high swept wings are most likely to SC; straightish wings will find it most difficult.

since we are talking jet fighters this is a given ! when was the last time a straight winged fighter was in service ? :D

Case in point, even the Gripen with the RM12 were able to SC (though not with meaningful loads) despite low power engines.

nope.
it was the NG model with the F-414 engines. F-414 has a 24% higher wet thrust than the F404. the dry thrust should also be significantly higher.
the NG model has only a 200 kg weight increase over the baseline gripen resulting in a significantly higher TWR.

http://en.wikipedia.org/wiki/JAS_39_Gripen#Gripen_NG
A two-seat "New Technology Demonstrator" has been built,[14] and was presented on 23 April 2008. It has increased fuel capacity, a more powerful powerplant, increased payload capacity, upgraded avionics and other improvements. The new aircraft is also referred to as the "Gripen Demo".[15][16]

http://www.gripen.com/en/MediaRelations ... ruises.htm
1/21/2009
During a test flight today the Gripen Demo aircraft proved its ability to “Supercruise”, the ability to fly supersonic without the use of afterburner which results in fuel savings and an increase in range.

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Re: LCA news and discussion

Postby Cain Marko » 18 Nov 2009 09:16

Rahul M wrote:since we are talking jet fighters this is a given ! when was the last time a straight winged fighter was in service ? :D

Dare I say the Shornet comes dangerously close :D

nope. it was the NG model with the F-414 engines. F-414 has a 24% higher wet thrust than the F404. the dry thrust should also be significantly higher.
the NG model has only a 200 kg weight increase over the baseline gripen resulting in a significantly higher TWR.


No, no saar, I assure you the reg'lar gripen did it too; there was a report by some tall swede pilot to that effect. I'll try to dig it up. In fact, iirc - the gripen a (or was it C) managed to carry a couple of AAMs to boot at just over mach speed. I think the gripen does that by a combination of wing design + extremely low drag design. If you compare it with the even the Tejas for example (head on), it presents a smaller profile.

CM.

Added l8r (via google/keypubs, the article was put up on Keypubs by one of the gripen fans -signatory i think): http://forum.keypublishing.co.uk/showth ... 432&page=3
"There was one interesting problem," Colonel Eldh concludes with a smile. Gripen is supersonic at all altitudes and can cruise supersonically with an external load including fuel tank, four AMRAAM and two Sidewinder missles without the need to engage the afterburner. "In the early days of operations, we found some pilots were inadvertantly flying supersonic over populated areas. The problem was one of habit, as these pilots had their throttle settings as high as on the older generation fighters that the Gripen replaced. it is fair to say that there were a few startled people on the ground, as their day-to-day work, or perhaps sleep, was disturbed by unexpected sonic booms! It was, of course, a simple task to solve the problem - the throttles were re-set and everyone was happy."

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 09:40

Dare I say the Shornet comes dangerously close :D

:lol:
well, aircraft optimised for superior hi-speed performance will always have an advantage in that respect which is where airframes designed for low speed performance loses out.

btw, the mki TWR for constraints mentioned is 0.61 and it's 0.59 for the F/A-18, well less than the figures for other SC aircraft.

even for the baseline gripen the value is 0.65, higher than both the mig-29 and the mki (say). there's a catch apparently.
"The JAS-39 C/D today could reach the speed of Mach 1.05 without A/B, but only during the cold season of Sweden. We anticipate that after replacing RM12 with F414G, the Gripen NG shall be able to supercruise with the speed of Mach 1.1 in standard aircombat configuration (Meteor BVR AAMs*4 + IRIS-T WVR AAMs*2) during the normal weather."

mach 1.05 is what I believe is called transonic regime, not supersonic.

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Re: LCA news and discussion

Postby shiv » 18 Nov 2009 10:07

Rahul M wrote:even for the baseline gripen the value is 0.65, higher than both the mig-29 and the mki (say). there's a catch apparently.
"The JAS-39 C/D today could reach the speed of Mach 1.05 without A/B, but only during the cold season of Sweden. We anticipate that after replacing RM12 with F414G, the Gripen NG shall be able to supercruise with the speed of Mach 1.1 in standard aircombat configuration (Meteor BVR AAMs*4 + IRIS-T WVR AAMs*2) during the normal weather."

mach 1.05 is what I believe is called transonic regime, not supersonic.



More than one catch

"during the normal weather"

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Re: LCA news and discussion

Postby shiv » 18 Nov 2009 10:10

Rahul M wrote:fighters.

EE lightning : 0.752 (assumed loaded weight to be 16 t since exact figure is not given)
EF typhoon : 0.787
Gripen NG: 0.72 (probably more. I had to estimate F414G dry thrust figures)
F-22 : 0.703 (assuming max dry thrust to be a conservative 63% of max thrust)
YF-23 : 0.874

so dry thrust TWR of 0.7 for loaded weight seems to be cut-off for achieving SC.


That figure is true for that list

You have left out LCA and HF 24 from this list :(( Both are said to have achieved supersonic speeds in level non afterburning flight. OK it may not be an ability to cruise for long periods at those speeds but..

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Re: LCA news and discussion

Postby Cain Marko » 18 Nov 2009 10:57

Rahul M wrote:btw, the mki TWR for constraints mentioned is 0.61 and it's 0.59 for the F/A-18, well less than the figures for other SC aircraft.even for the baseline gripen the value is 0.65, higher than both the mig-29 and the mki (say).

Marginal difference don't you think bet. the gripen and fulcrum/flanker? Btw, that 0.65 figure should be for the lighter Gripen A. The C would have a figure of about 0.60 with internal fuel (empty ~ 6.8 tons, milpower ~ 5600kgf, loaded weight ~ 9200kg). AFAIK, the M2K cannot SC despite being in a similar TWR situation (loaded @ 10800kg: Mil Thurst @ 6600kgf ), surprising really. The gripen must have an exceptional drag:weight ratio.

But, yes to supercruise meaningfully, you'd need much more power on dry thrust. Also, iirc the EF-2000 carries its AAMs conformally thereby reducing drag.

FWIW, interestingly enough, the EJ-200, despite lower AB thrust (20000lbf) has higher Milpower thrust (13500lbf) compared to the GE-414-400 (22000lbf:12500)!

there's a catch apparently.

"The JAS-39 C/D today could reach the speed of Mach 1.05 without A/B, but only during the cold season of Sweden. We anticipate that after replacing RM12 with F414G, the Gripen NG shall be able to supercruise with the speed of Mach 1.1 in standard aircombat configuration (Meteor BVR AAMs*4 + IRIS-T WVR AAMs*2) during the normal weather."
mach 1.05 is what I believe is called transonic regime, not supersonic.


Still, not too bad considering the TWR. Also, do consider Eldh's words, he clearly states supersonic. My guess is that Eldh is talking about a Gripen A, which was a lighter than the C since the pdf is dated for 2001.

Anyway, the difference between a cruising flanker/fulcrum and a barely supersonic gripen/rafale is not that much. IIRC, the cruise speed for a flanker is v.close to M1. No idea about the Shornet though.

CM.
Last edited by Cain Marko on 18 Nov 2009 11:28, edited 1 time in total.

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Re: LCA news and discussion

Postby Cain Marko » 18 Nov 2009 11:15

Re. the Gripen C/NG. At the risk of going OT, the mil thrust of the 414 and the RM12 are not that different 5100kgf VS. 5600kgf. However, I believe that the Gripen lights up AB to get past the transonic bump and then is able to sustain SC without AB. I think the 414s with much higher AB thrust comes in handy here.

Don't see why the Tejas can't manage something similar with either the EJ-200 or the GE-414. I'd think it would sustain SC better with the EJ-200s. Esp. considering that the current 404s F2J3s are almost equivalent to the F-414-400s - 5500-600kgf at milpower! The EJ-200 can pump out 6000kgf on milpower.

FWIW, http://jet-engine.net/miltfspec.html

CM.

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 12:10

shiv wrote:You have left out LCA and HF 24 from this list :(( Both are said to have achieved supersonic speeds in level non afterburning flight. OK it may not be an ability to cruise for long periods at those speeds but..

I did give the LCA figures last page. :)

HF-24 : 0.49 assuming 9 t weight. funny thing is I'm not aware of any source for the supercruise of production maruts other than Wg Cmdr Bakshi. most sources say marut was supersonic only in dive. the supercruise ability also does not tally with recurrent refrains about the marut's low powered engines.
but then, there's this :
A promising design that could cruise supersonic at 40,000 feet, the Marut finally met a disappointing end thanks to un-kept promises and international politics that embroiled HAL and several successive engine vendors.


LCA : 0.578 assuming 9.5 t loaded weight (which the LCA is yet to achieve till latest reports)

----------------------------
of course, it is entirely possible that an almost empty aircraft can reach the magic TWR zone of > 0.7 and hence go supersonic on full mil power.
especially true for a light aircraft like LCA. for a weight of 7.5 t for example, the TWR would be 0.733.

So I retract my earlier statement, it is entirely possible for the LCA to go supersonic on mil power alone, just not with any real military significance.

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 12:29

picklu dada, for you. :)

Image

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Re: LCA news and discussion

Postby Kailash » 18 Nov 2009 12:45

We pioneered composites a decade ago. We have been testing on the the LCA for quite some time now. There should be better and lighter composites that would be availabe now than what was available 10 years ago right?

Being the conservatives we are, and considering LCA is one test program with no major setbacks, we should have definitely over designed many parts. Is there still any efforts to shave off weight or replace older materials/alloys etc with new ones? how useful has the EADS consultancy been?

Everytime we are going to the "T" part of the T/W ratio. Is the "W" so difficult to change?

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Re: LCA news and discussion

Postby ArmenT » 18 Nov 2009 13:43

Kailash wrote:Everytime we are going to the "T" part of the T/W ratio. Is the "W" so difficult to change?

If history is any indicator, for almost all the aircraft manufactured in the world since the 50s, the W part of the equation has been going up as newer variants of the aircraft are produced. This is because people keep adding better computers, radar, avionics, engines etc. as part of the upgrades, and all the weight savings of using newer composites is offset by all the new stuff they add to it. For instance, the prototype of F-16 was ~ 13,500 lbs empty weight, F-16A was ~16,300 lbs, F-16C was ~19,000 lbs and by the time the F-16E rolled around, it had ballooned to ~22,000 lbs empty weight. This is not just unique to the F-16 alone, it is true for F-18, MiG 29, Mirage III and just about any aircraft that has had multiple variants.

So if we take past history to be an indicator of the future, people upgrade the "T" part of the equation as well to maintain the T/W ratio.

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Re: LCA news and discussion

Postby Rishirishi » 18 Nov 2009 19:09

Craig Alpert wrote:
Kartik wrote:wow !! this is a new definition of super-cruise..please let me know which dictionary or book gave you this definition of super-cruise. the fact is that it has nothing to do with what the cruise in a car does or what its purpose is, so using that as an example is wrong. nor does any Lockheed Martin, Saab or EADS brochure say that it has to be done for a min. of 5 minutes..where on earth did you get this figure ?! and the best part is that you missed out on what is considered the absolute minimum requirement for super-cruise-> that the afterburner should not have been engaged in crossing Mach 1.

supersonic cruise, also called super-cruise was a term coined as one of the super-duper advantages of the F-22, where its pilot could cross the Mach barrier (with its associated huge drag peak right at the Mach barrier) WITHOUT using afterburner. many aircraft in a lightly loaded condition will be able to get close to the Mach 1 limit, but will not be able to cross it because there is a huge drag increase right at that point. till the area rule was discovered, most aircraft couldn't even cross that barrier. now of course all aircraft are designed with that rule in mind, and if the airframe is designed well, with low drag, and the T/W ratio of the aircraft is good, it will be able to cross that barrier without using AB, which really guzzles fuel. the pilot will still be using max. dry thrust, but that is nothing compared to the amount of fuel an AB consumes. most aircraft carry enough fuel only for a few minutes of AB during an entire mission.

the advantage that the F-22 gained due to this capability, was that it would allow an F-22 to get to the scene of action supersonically, over a long distance and over a longer period of time, without needing to use its AB. That meant that it had enough reserves of fuel left for it to be able to stay on station for a meaningful period of time. Japan's Air Chief had stated that it was the most attractive feature of the F-22 as far as they were concerned, because it would allow fighters based far away from the islands that they need to defend against China, to reach the battle quickly. If they buy F-35s, they need to build a new base closer to the disputed islands and sea lines, because getting there in time itself would take up most of the F-35's fuel (even though it carries a lot of internal fuel).

Glad you like it! Unfortunately the book/dictionary is not for sale!
I said to put it in LAYMAN’S term SIMILAR being the key word.. I never mentioned the LITERAL CRUISE CONTROL OF A CAR and that in a FIGHTER JET chief!!! You didn’t get the analogy and since you took the literal meaning let me help you out with that.. A Bugatti veyron can travel around 90 miles on 26 gallons of fuel at HIGHWAY speeds, however it travels ONLY 20 odd MILES when it reaches it max speed of 254MPH with 26 gallons of GAS all emptied in just 12 MINUTES.. I never mentioned LM, EADS, SAAB or whoever you might think off for the 5 min grace period.. I said 5 or MORE in general terms because it has to be done over a CERTAIN PERIOD/ALTITUDE/RANGE/PAYLOAD. Since you want facts, let’s give them to you.
1) AF monthly carried an article where Col Boyd of the USAF set requirements for the F-16 phalcon to cruise supersonically over enemy territory for a minimum of twenty minutes (don't have the scans on hand).. However this was never implemented as the amount of fuel it requires to perform this is 40% over what it currently carries and with further decrease in ECM and Electronic pods carrying capacity. Nonetheless this was employed in F-22 as the design requirements were made with keeping this in mind so that it can carry adequate amount of fuel for it to supercruise for the allocated time mentioned.
2)Data for the F-22 is classified and hence cannot be discussed, however the F-22 has demonstrated supercruise speeds of at least Mach 1 – 1.7, at 40,000 ft (12,000 m) to 50,000ft. Supercruise is meant to imply a significant increase in effective combat speed with a full weapons load. Virtually all current and past jet fighters, prior to the F-22, cruise at approximately Mach 0.8~0.9 with a militarily significant weapons load. And to best support my arguments with open source information here’s a quote from Wiki “The F-22 represents a significant advance in cruise speed over previous types (for performance of current USAF types, see Air Force Magazine, May 2006, "Gallery of USAF Weapons," pp. 147–155 - [5]). Nonetheless, it can maintain this speed, even in supercruise, for only about five minutes, falling far short of the original performance requirement.”
You pointed out that I did not mention the MAIN POINT of supercruise which was the need to FLY WITHOUT THE AFTERBURNERS. This has been mentioned plenty of time just above our posts hence I did not mention that (no point in restating what is obvious, but I guess I had that one coming) I wasn't planning on giving a history lesson here, just a quick overview of what differs supercruise and supersonic, but you are correct I should have mentioned the point of not using afterburners, but I set myself up for that one. In a civilian jet Concord has demonstrated this capability time and again as it flies supersonic, WITHOUT the use of afterburners over a long distance with certain altitude.. Other obvious use of supercruise is that it increases the aircraft's stealth, as an afterburner plume reflects radar signals and creates a significant infra-red signature.

where on earth did you get this figure ?! and the best part is that you missed out on what is considered

I stated FACTS not FICTION! So the next time you decide to bring me down a notch, Keep in mind I'm NOT Prasun k. SEN-GUPTA.


In all fairness you are right, but should have mentioned the AB factor.
Put is simply. Supercruise = Engines that enable the aircraft to fly at supersonic speeds, without using the afterburner. You save a lot of fuel as AB are very fuel consuming. The range is reduced by using AB.

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Re: LCA news and discussion

Postby Jagan » 18 Nov 2009 21:22

Rahul M wrote:[

HF-24 : 0.49 assuming 9 t weight. funny thing is I'm not aware of any source for the supercruise of production maruts other than Wg Cmdr Bakshi. most sources say marut was supersonic only in dive. the supercruise ability also does not tally with recurrent refrains about the marut's low powered engines. .


"Supercruise" for the Marut gives a false impession of it being a smooth and effortless operation. I am sure it would be a struggle for it to reach that and maintain it even for a sustainable time, and it was probably not a regular event. It is somewhat like the Mach3 number for MiG-25. We know it can go there, but I doubt if aircraft were routinely pushed to that limit as the engines get ruined after such a flight. That probably applies to the Marut. to push it to level flight may require max power for a sustianed period of time. All for what - a supersonic boom that you can easily get it in a gentle dive?

That said the Marut's figures are as below (given by Pushpindar Singh in his article on the Marut)

Max Level speed attainable at 40,000 feet M=1.02 or 673mph
(helped by the low density air, lighter wt of ac due to fuel burn during climb etc - no chance of it happening at lower levels).

Clean take off weight is given as 8951 kg.

Edit: Speed given as 620 kts at low level but because speed of sound at low level is much higher its not supersonic speed yet

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Re: LCA news and discussion

Postby Rahul M » 18 Nov 2009 21:49

thanks jagan. mach 1.02 is transonic regime where the drag spikes, so it definitely would have been a struggle. transonic regime extends to 1.2 mach I gather, so smooth supersonic flight can only take place beyond that.

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Re: LCA news and discussion

Postby Picklu » 18 Nov 2009 21:52

Rahul M wrote:picklu dada, for you. :)

Being the all knowing expert from nano technology to tata nano(mexican type), I ignore the above disdainfully :P
Instead latch onto a different statement quoted below, declare myself "Victorious Magnificus" and crow from rooftop with an energetic lungi dance. :twisted:
Rahul M wrote:So I retract my earlier statement, it is entirely possible for the LCA to go supersonic on mil power alone


But seriously, thanks for the info, it does appear that gurus give importance to weight for determining the max speed.
Hummmm, now I understand why i used to come last in the annual school sports events.
:idea:

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Re: LCA news and discussion

Postby Picklu » 18 Nov 2009 22:00

From now onward, I shall be known as Area Commander, Supah Cruize Brigade, LCA dhaga

Shameless attempt to increase post-count

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Re: LCA news and discussion

Postby Kartik » 19 Nov 2009 00:01

[
Kailash wrote:We pioneered composites a decade ago. We have been testing on the the LCA for quite some time now. There should be better and lighter composites that would be availabe now than what was available 10 years ago right?

Being the conservatives we are, and considering LCA is one test program with no major setbacks, we should have definitely over designed many parts. Is there still any efforts to shave off weight or replace older materials/alloys etc with new ones? how useful has the EADS consultancy been?

Everytime we are going to the "T" part of the T/W ratio. Is the "W" so difficult to change?


Lighter ? they're already using carbon fiber composites for the most part. with more R&D and new manufacturing processes, its entirely possible that there are newer and better epoxy resins or carbon fibers which may be lighter but with equivalent strength, but the bigger problem will be sourcing it for large scale production. for the current carbon fiber composites available in India itself, there has been a major investment made for it to be built in India. Its not quite so easy to move to newer materials every 5-6 years. besides, any gains would be marginal at best compared to the effort required for re-design, re-analysis and re-testing.

What will be happening is that with flight-test data on flight loads, temperatures, etc. they may find that having been conservative initially, the loads may be lower than intially derived or the temperatures may be lower than what they figured based on their CFD analysis prior to detailed design. When that happens, some parts, panels, etc. could be made lighter. However, its also possible that the reverse happened and that flight loads went up (in most western civilian designs this is what happens)- in which case, weight shedding would be out of the question, and on the contrary, another round of detailed design and drawing release to suppliers and manufacturing would be required.

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Re: LCA news and discussion

Postby Rahul M » 19 Nov 2009 00:16

kailash, there is always scope creep throughout a fighter aircraft's life. I don't think there's even one fighter that has emerged lighter in its subsequent versions.

even if better materials are used/ desingners shave off some flab as kartik says, newer equipment will pull back weight to old levels or even higher requiring higher power engines. IOW, they need to be running to stay in the same place.

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Re: LCA news and discussion

Postby Cain Marko » 19 Nov 2009 01:46

The use of composites is most effective in 4gen fighters that originally used few such materials. The flanker and fulcrum are prime egs. In case of the aircraft such as the F-18, which were already pretty high on composites, the advantages are not so visible in later avatars.

Also the weight increase is a result of massive increases in payload capacity - this requires structural strengthening and results in weight increase. The MiG-29A/F-16/F-18/F-15E/Su-30 are all examples of increased payload and therefore increased weight.

Still, the point remains that composite usage seems to offer stellar results in mostly metal alloy airframes. The original MiG-29K (1988) for instance had an empty weight of 12700kg; the current one that the IN is about to receive weighs 12400kg. A good 300kgs shaved off - its a bit of an anomaly though. Ditto with the latest Su-35. And that is despite a huge difference in the number of gizmos. Another factor is that the newer gizmos are lighter than their counterparts of 80s/90s vintage.

CM

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Re: LCA news and discussion

Postby Kailash » 20 Nov 2009 12:45

Thanks for all your replies.

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Re: LCA news and discussion

Postby SaiK » 20 Nov 2009 22:07

EF typhoon : 0.787

Per defence daily reports (Indradhanush ex link), EF supercruise is without weapons load. !!!.. oxymoronic!

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Re: LCA news and discussion

Postby Uttam » 23 Nov 2009 01:28

IAF orders more Tejas LCAs to replace MiG-21s
Ajai Shukla / Bangalore November 23, 2009, 0:45 IST
The Indian Air Force is taking a crucial step towards accepting the indigenous Tejas Light Combat Aircraft (LCA) as a replacement for its ageing MiG-21 fighters. Senior air force officers told Business Standard that IAF was ordering a second Tejas squadron (20 aircraft), in addition to the 20 fighters already on order.

Ashok Nayak, chairman of Hindustan Aeronautics Ltd, which will manufacture the Tejas, has confirmed this development. “The Ministry of Defence (MoD) tender for 20 additional Tejas fighters is on track,” he told Business Standard. “After it is issued, we will sit down with MoD and negotiate a price.”

The order for a second squadron is a vital expression of IAF’s confidence in the future of the long-running Tejas programme. So far, IAF had insisted on evaluating the performance of the first squadron before ordering a second, by 2015-2016. That would allow the Tejas to be upgraded to the Tejas Mark II, which would have a new, more powerful engine. But now, with its fighter fleet dwindling, as the old MiG-21s are retired, IAF is taking the Tejas as it is.

“The Tejas, even with its current GE-404 engine, is a better fighter than the MiG-21,” explained a senior IAF officer who is familiar with equipment policy. “By 2015, the first Tejas squadron will be ready for IAF. HAL’s assembly line will be free; while the Tejas Mark II finishes testing, HAL can build a second squadron with the GE-404 engine,” he added.

So far, the plan was to produce 12 twin-seater Tejas trainers after the first squadron was built. The new order will be for 18 single-seater and 2 twin-seater Tejas: exactly what equips a fighter squadron.


Here’s why IAF urgently needs that second squadron: Against a sanctioned requirement of 39.5 squadrons (each squadron has 21 fighters), IAF is now down to just 32 squadrons. By 2015, another six squadrons of MiG-21s and two squadrons of MiG-27s would have finished their service lives. Meanwhile, HAL is manufacturing Sukhoi-30MKIs, but the current production is just 14 per year. The mathematics is clear: By 2015, IAF will have just 29 squadrons of fighters.

Making this shortfall even more worrisome is the new requirement of five IAF squadrons for north-east India, as a result of an increased threat assessment from China. Senior IAF officers have recently declared that India actually needs 45 squadrons.

In this context, IAF cannot wait to induct the Tejas as the next light fighter, a role that the MiG-21 has long performed. Medium fighters are as urgently needed, and IAF is currently evaluating six aircraft for this role. But the new Medium Multi-Role Combat Aircraft (MMRCA), even if the contract is placed expeditiously, is unlikely to enter service before 2015-16. Only in the heavy fighter segment is IAF well placed, with the superlative Sukhoi-30MKI steadily joining the fleet.

The Tejas is currently undergoing weapon trials to obtain its Initial Operational Clearance, most likely by early 2011. Then starts the two-year process for obtaining Final Operational Clearance, after which it can enter service in early 2013. Then, if HAL can deliver 10 Tejas fighters per year, the first squadron will be ready by the end of 2014. And, if all of that goes smoothly, the second Tejas squadron will join IAF by the end of 2016.

IAF has decided that No 45 Squadron, which operated MiG-21M fighters until they were recently retired, will be the first Tejas squadron. It will be based in Sulur, near Coimbatore. It is still not clear where the second Tejas squadron will be based.

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Re: LCA news and discussion

Postby enqyoob » 23 Nov 2009 02:29

10 fighters a year is a terribly poor production rate for something which is probably needed in a couple of thousand units. However, the engine fiasco means that the rate cannot be hiked so easily. Given the rate of production, the IAF is really providing the "pull". Great, but now if something can be done about the engine....

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Re: LCA news and discussion

Postby jai » 23 Nov 2009 02:54

The MRCA competition needs to be completed asap...at least there would be some clarity for HAL in terms of which engine to go for.

In the meantime, considering that HAL already has 40 404 engines (and has 414's/RD 33's on offer) - can they not start the production parallely - are major changes expected between now and FOC ? Why is the production dependent on FOC ?

Also, how much change would be needed to the airframe / structural components to use 414's ? Considering that IAF needs more powerful engines, why not order 40 414's and use these for the first two squadrons till MRCA decision gets taken/ operationalized ?

Considering that we already have 4 - 5 operational prototypes, is it possible for HAL to try out EJ 200, RD 33, GE 414, Rafael's 88 etc on a prototype ? Would it make sense to ? Perhaps this data can feed into the MRCA decision ?

Can Guru's please enlighten. Thanks.


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