LCA Tejas vs JF-17 Thunder

[Rahul Singh]

why should energy bleeds matter. With one better ITR turn , it point it's nose with least effort ,

and it gets a high offbore sight WVR missile firing solution with HMDS. So where is the bleeding and yo yo loop?

The tight STR turns in JF-17 too are most fuel consuming and ultimately of no use against the HMDS high off bore sight shots.Sure the fighter won't out turn a missile in a continuous STR turn.it is an established fact.

That Yo-Yo and high energy bleed thing are only to tell, LCA can also shoot down its foe with cannon or gun (apart from with WVRAAM targeted by HMDS for which whole world can vouch now) ...which it certainly can.

 

[A chauhan]

...
But what is the most challenging effort is to use this fly by wire tech with full digital FCS along with complicated control laws to control the flight behavior of a DYNAMICALLY UNSTABLE FLIGHT PROFILE PLATFORM LIKE TEJAS...

With that Tajas must be giving an experience like taking a test ride of a sport bike ! i.e. highly responsive and maneuverable ! :thumb:

 

[farhan_9909]

there are many versions of fly by wire. Fly by wire simply means the pilot pulls the stick and his effort is converted into electrical or digital signals and the hydraulics of control surfaces obey the signal.That's all.

the british tried fly by wire in jaguar . the french tried it on old Mirage-IIIs.

So there is nothing wrong in china trying the same tech in J8II ACT ---the replacement of J8ACT and retired in early 2000s and mastering it. And this tech is bolted on to JF-17 from prototype -2 or 3 stage is completely agreeable.

But what is the most challenging effort is to use this fly by wire tech with full digital FCS along with complicated control laws to control the flight behavior of a DYNAMICALLY UNSTABLE FLIGHT PROFILE PLATFORM LIKE TEJAS.

IMHO the prototypes mentioned above are stable flight profile fighters meaning that they oppose the pilot's effort to maneuver the fighter and naturally return to the level flight once the pilot eases the stick. IMHO JF-17 belongs to this clause.if you have any evidence to the contrary do post.



So FCS and Fly by wire based on control laws for those stable flight profile is not demanding.IMHO Jf-17 belongs to this clause.
you just cannot add a dynamically unstable flight profile to a fighter as stable flight profile one like JF-17, may be you can add a bit more of maneuverability by relaxing stability to some extent in some axes.

But you cannot fundamentally change the fighter flight profile after prototype stage.IMHO if you want that you have to go for complete redesign. If you have any links to support such complete redesign please post.

It will add some residual performance of course. But it can never make a stable flight profile fighter to equal the unstable flight profile fighters.

But dynamically unstable flight profile deltas which tend to veer off in all directions if the control surfaces are not maneuvered many times in a single second is another cup of tea.

Control laws and fully digital FCS for these fly by wire system takes years to develop and validate. if you have any doubts just refer to the fligth test period of RAFALE with how many prototypes.

Tejas belongs in this clause designed as dynamically unstable flight profile delta from scratch while JF-17 is not is IMHO.

well i have already posted enough about quadruplex digital FBW of JFT

can you tell me how can you term JFT a complete Stable design?
while LCA dead compound tailess delta design is unstable?

LCA doesnt feature anything worth mentioning

Be it Lerx,(Levcons in JFT III),neither it has the DSI,has a single ventral fin?and most importand both F-16 and JFT feature similar cropped delta design while LCA is a compound delta similar to Mig 21

F-16 and JF-17 cropped delta design

JFT

Has Lerx similar to F-18

Lerx of F-18 and JF-17

*Has DSI similar to J-10B,J-20,F-35

LCA is a dead compound delta design..with no future upgrade potential..i doubt there is something worth mentioning in LCA design.this is the major reason for its least agility in the category of the rest of all 4th gen fighters
i really doubt it would be agile even with the 100kn thrust engine..since the design is very limied..unless they bring something new in mk2

Cropped delta usually such as JFT or F-16 are very much agile as evident from the F-16 agility or even JFT with lesser twr.

and as claimed above of how JFT evolved into a full digital FBW within prototypes stage. is very much possible since we all know how F-16 a/b turned into a quadruplex fbw over the time period.

 

[ersakthivel]

well i have already posted enough about quadruplex digital FBW of JFT

can you tell me how can you term JFT a complete Stable design?
while LCA dead compound tailess delta design is unstable?

LCA doesnt feature anything worth mentioning

Be it Lerx,(Levcons in JFT III),neither it has the DSI,has a single ventral fin?and most importand both F-16 and JFT feature similar cropped delta design while LCA is a compound delta similar to Mig 21

F-16 and JF-17 cropped delta design

JFT

Has Lerx similar to F-18

Lerx of F-18 and JF-17

*Has DSI similar to J-10B,J-20,F-35

LCA is a dead compound delta design..with no future upgrade potential..i doubt there is something worth mentioning in LCA design.this is the major reason for its least agility in the category of the rest of all 4th gen fighters
i really doubt it would be agile even with the 100kn thrust engine..since the design is very limied..unless they bring something new in mk2

Cropped delta usually such as JFT or F-16 are very much agile as evident from the F-16 agility or even JFT with lesser twr.

and as claimed above of how JFT evolved into a full digital FBW within prototypes stage. is very much possible since we all know how F-16 a/b turned into a quadruplex fbw over the time period.

So any fighter with LREX and DSI are unstable flight profile as per your claim!!!!

lrex and DSI has nothing to do with unstable flight profile.

FBW alone doesnot make a fighter unstable. british tested the FBW on Jaguar, SO will that make jaguar an unstable flight profile super agility fighter like Mirage-2000?

if cropped delta is so good and the large compound delta of tejas is obsolete, why did the RAFLE and TYPHOON choose the big delta like tejas. Sure they could have chose cropped delta wing form of the JF-17, why they didn't?

Why didn't the chinese choose the same high wing loading cropped delta for their J-20?

Why they chose a large low wing loading delta wing like Tejas?

 

[farhan_9909]

So any fighter with LREX and DSI are unstable flight profile as per your claim!!!!

lrex and DSI has nothing to do with unstable flight profile.

FBW alone doesnot make a fighter unstable. british tested the FBW on Jaguar, SO will that make jaguar an unstable flight profile super agility fighter like Mirage-2000?

if cropped delta is so good and the large compound delta of tejas is obsolete, why did the RAFLE and TYPHOON choose the big delta like tejas. Sure they could have chose cropped delta wing form of the JF-17, why they didn't?

Why didn't the chinese choose the same high wing loading cropped delta for their J-20?

Why they chose a large low wing loading delta wing like Tejas?

Compound does has its own advantage?

JFT being more complex design with alot of new technology be it levcons in the close future and lerx for the time being,DSI,twin ventral fins is a stable design but LCA with a raw level designed is claimed to be completely unstable

do you have any official certificate claiming JFT not to be a unstable,,while if i remember even cobrato has once claimed it to be more better than J-10 in design category..what it lack is range and higher payload and a limited combat radius..which makes it not as good as j-10 for a very big country like china.

 

[farhan_9909]

@ersakthivel

a very good book about JFT written by najam

you can also browse each chapter in more detail but read the summary of all the chapters in the chapter 8

- PAFwallpapers Blog

if you want you can read each chapter as well..it cover almost everything about JF-17

 

[ersakthivel]

Compound does has its own advantage?

JFT being more complex design with alot of new technology be it levcons in the close future and lerx for the time being,DSI,twin ventral fins is a stable design but LCA with a raw level designed is claimed to be completely unstable

do you have any official certificate claiming JFT not to be a unstable,,while if i remember even cobrato has once claimed it to be more better than J-10 in design category..what it lack is range and higher payload and a limited combat radius..which makes it not as good as j-10 for a very big country like china.

Jf-17 is a not a radical new design like the lca Tejas or F-16. it is an improved version(super 7) of an already operated soviet fighter in PLAF under the name F-7 which was a copy of Mig-21.So noway you can claim it to be dynamically unstable.

The lrex and DSI were implemented to solve the handling problems, not to make it dynamically unstable ,


SO it is very much a dated design with Lrex, DSI thrown into it. So noway you can say JF-17 is a fully unstable in all axis flight profile plat from.

The old J-7 or F-7 which was an inferior copy of Mig-21,

The Jf-17 with LREX and DSI over the same wing design of F-7 above.

 

[ersakthivel]

@ersakthivel

a very good book about JFT written by najam

you can also browse each chapter in more detail but read the summary of all the chapters in the chapter 8

- PAFwallpapers Blog

if you want you can read each chapter as well..it cover almost everything about JF-17

In the days of J-7 or F-7 or mig-21 there was no concept of dynamically unstable flight profile.

opposed to this The LCA design was finalised in 1990 as a small tail-less delta winged machine with relaxed static stability (RSS) to enhance manoeuvrability performance. from the design stage itself.



RSS technology was introduced in 1974 on the General Dynamics YF-16, which was the world's first production aircraft to be slightly aerodynamically unstable by design.

Most aircraft are designed with "positive" static stability, which means they have a natural tendency to return to level and controlled flight in the absence of control inputs; however, this quality tends to oppose the pilot's efforts to maneuver.JF-17 belongs to this class.

An aircraft with "negative" static stability (i.e., RSS), on the other hand, will quickly depart from level and controlled flight unless the pilot constantly works to keep it in trim; while this enhances manoeuvrability, it is very wearing on a pilot relying on a mechanical flight control system.tejas belongs to this class .

Development of a FBW flight control system requires extensive knowledge of flight control laws and the expensive writing of a considerable amount of software code for the flight control computers, as well as its integration with the avionics and other electronic systems.

When the LCA programme was launched, FBW was a state-of-the-art technology and such a sensitive one that India could find no nation willing to export it. Therefore, in 1992 the LCA National Control Law (CLAW) team was set up by the National Aeronautics Laboratory to develop India's own version.The CLAW team's scientists and mathematicians were successful in developing their control laws

 

[farhan_9909]

Jf-17 is a not a radical new design like the Mirage or LAC Tejas or F-16. it is an improved version of an already operated soviet fighter in PLAF. SO it is very much a dated design with Lrex, DSI thrown into it. So noway you can say JF-17 is a fully unstable in all axis flight profile plat from.

Which fighter of soviet are you talking about?..can you show me a similar fighter aircraft to JFT other than F-16 and f-18?

Mig 21 is a compound delta like lca but with tail.

Mig 33 again like majority of soviet project was a complete unstable design.

leave aside everything..tell me why you think JFT with all those complex design feature is stable but LCA with raw compound delta design is unstable?

 

[farhan_9909]

credits GAMBIT

Gambits mentions that if this statement

JF-17 has quadruplex, digital, fly-by-wire flight control system and two hydraulic systems for backup.

is taken true(the above stetement is officially from JF-17.com) than JFT has digital fbw in all axis

der Multirole Fighter [Thread 4]
Looks like some clarifications are in order...

The reason why there MUST be quadruplex, meaning four channels, of signals per axis (pitch, roll, yaw) is because of the voting process. The flight control computer (FLCC) receives four signals from each accelerometer, gyro, and cockpit command. Three are used in the voting process with one as back up. If one signal is out of tolerance, the fourth is used. A missing signal count as out of tolerance. This design was started with the F-16 and proved to be most reliable so it was adopted pretty much worldwide, civilian and military.

Is it possible to have a fly-by-wire (FBW) system in one axis but not the other two? Yes. But that one FBW-ed axis must still have a quadruplex design. The other two are probably mechanical-hydraulics.

This statement...

JF-17 Avionics | JF-17 Thunder
JF-17 has quadruplex, digital, fly-by-wire flight control system and two hydraulic systems for backup.
...Should be taken to mean all three axes are FBW-ed. The 'two hydraulics systems' simply mean there are two hydraulics systems on the aircraft: Primary and Utility.

If the J-17 has only the pitch axis as FBW-ed, then that statement is quite misleading. The hydraulics are not for back up. They are used all the time. The Primary system is for major flight controls actuators. The Utility system is for landing gear doors, nose wheel steering, and similar less flight related sub-systems. Either system can power the aircraft by itself, but not for long and not as efficient.

Stability augmentation (stabaug) is in all three axes, FBW-ed or not.

For example...

STRIKE - RAAF STYLE
Due to the nature of its role, the F-111 has a rather complicated flight control system, using hydromechanical actuators controlled by electrical signals from a stability augmentation system (SAS),...
The -111 flight control system is mechanical-hydraulics. And it got stabaug.

Stabaug is a complex loop that involves signals from altitude, speed, accelerometers, gyros, cockpit commands, and positional feedbacks from the hydraulic actuators. Stabaug is constantly going on. If an F-16 on the ground has electrical power and hydraulics applied, anyone can grab the F-16's pitot tube shaft and shake up/down the aircraft and when the rear horizontal stabs moves, that is stabaug working. The FLCC is trying to compensate for the gyros' inputs.

This statement...

Russian provide a switch in the cockpit to shut down FBW, crazy.
...Probably mean to shut off stabaug and give full authority to the pilot. That mean he has to compensate for every bit of crosswind, every bit of overshoot on the stick, every little turbulence, etc. All he has is 3,000 lbs/psi of hydraulics to assist him moving those heavy metal flight control surfaces.

It sounds crazy, but sometimes necessary, such as battle damage and the gyros are giving the FLCC funny signals. Shut off that loop and struggle on the flight home. The Americans do not have that shut off feature. We trust our avionics sh1t.

 

[ersakthivel]

credits GAMBIT

Gambits mentions that if this statement


is taken true(the above stetement is officially from JF-17.com) than JFT has digital fbw in all axis

Again I never said that JF-17 did not have FBW, All i said was it was a stable flight profile fighter(positive static stability) and not a relaxed static stability design like Tejas(negative static stability).

So Positive static stability fighters always tend to oppose pilots efforts to maneuver and try to come to level fight,meaning lesser maneuverability,

relaxed or negative static stability fighters like tejas will go with the pilot's intent to maneuver and will not try to oppose his efforts by trying to come to level flight, thereby more maneuverable.

 

[farhan_9909]

Again I never said that JF-17 did not have FBW, All i said was it was a stable flight profile fighter(positive static stability) and not a relaxed static stability design like Tejas(negative static stability).

So Positive static stability fighters always tend to oppose pilots efforts to maneuver and try to come to level fight,meaning lesser maneuverability,

relaxed or negative static stability fighters like tejas will go with the pilot's intent to maneuver and will not try to oppose his efforts by trying to come to level flight, thereby more maneuverable.

Agreed..but what makes you think JFT is not a unstable fighter?what is the reason?

it has all the complex design structures such as lerx,dsi,twin ventral finds for better take off during high load..

JFT is like a mini F-16 but with different design intakes

 

[farhan_9909]

both are almost 95% similar..considering the wing design.while people still claim JFT is a stable aircraft

 

[sayareakd]

First Mig 33 was cancelled project.
Then China purchased the design and then cancelled its project FC-1.
Finally Pakistan jump in the project for its AF now called JF17.

Funny part is PAF is only air force in the world which makes and manage its own plane. BTW what so special about this 3rd generation aircraft ?

 

[farhan_9909]

First Mig 33 was cancelled project.
Then China purchased the design and then cancelled its project FC-1.
Finally Pakistan jump in the project for its AF now called JF17.

Funny part is PAF is only air force in the world which makes and manage its own plane. BTW what so special about this 3rd generation aircraft ?

BS post..dont derail this thread atleast

 

[sayareakd]

BS post..dont derail this thread atleast

its third generation fighter that is what is official.

 

[farhan_9909]

its third generation fighter that is what is official.

BS post once again..ooops as usuall

LCA is also termed as Bison by your ACM..should we consider LCA as 3rd or late 2nd generation as well?

 

[sayareakd]

BS post once again..ooops as usuall

LCA is also termed as Bison by your ACM..should we consider LCA as 3rd or late 2nd generation as well?

dont divert the attention to LCA i am talking about JF 17.

 

[ersakthivel]

Agreed..but what makes you think JFT is not a unstable fighter?what is the reason?

it has all the complex design structures such as lerx,dsi,twin ventral finds for better take off during high load..

JFT is like a mini F-16 but with different design intakes

This too looks like JF-17 wing arrangement, minus LREX and DSI. SO this Mig-21 copy also a 4th gen relaxed static stability fighter?

 

[sayareakd]

BS post..dont derail this thread atleast

its third generation fighter that is what is official.

BS post once again..ooops as usuall

since you dont accept what i am saying and continue to live in your make believe world, here this is from your own official source, dont forget to thank me.

Production

Pakistan Aeronautical Complex (PAC) holds the exclusive rights of 58% of JF-17 airframe co-production work. A comprehensive infrastructure comprising state of the art machines and required skilled human resource has very quickly been developed at the Complex.
The final assembly and flight testing of the aircraft was the first JF-17 co-production activity to start at PAC. The first PAC produced aircraft was handed over to Pakistan Air Force in November 2009. Since then, aircraft are being produced regularly to meet the required schedule. The co-production of sub assemblies and structural parts has also commenced and is sequentially attaining the sustained production status. Besides upgrading the production system, PAC has also upgraded its quality, technology and archive management systems to meet the production and management standards of a 3rd generation fighter aircraft.

Pakistan Aeronautical Complex

now dont give us the shit that it was Chinese third generation which means Pakistani 4th Generation and in your view it is 4.5 or 4+++++++++++ generation.

BTW PAC only got right of 58% but now they make only 40% of airframe and in few years they will make 58% airframe. :thumb: