JF-17/FC-1 Fighter Aircraft thread

[crobato]

Re: New JF-17/FC-1 Fighter Aircraft thread

No it is not true that all the 3 axes are made FBW-capable out of convenience. As I said previously, even if aircraft are just pitch unstable, they have FBW in 3 axes precisely because all the 3 axes do not work in isolation (contrary to your view) but they work together by supporting each other. In this very aspect, the tests of another Asian fighter jet under high AoA conditions were done keeping in mind directional stability, rolling moments, spin recovery and checking the quantum of rudder authority at high angles of attack.

Thus if JF-17 is indeed pitch unstable, it should have most probably have had FBW in other axes too, like all other combat aircraft in service presently.

That is incorrect. The F-20 is also unstable and yet it has a composite FBW system.

If an aircraft is pitch unstable, the main stability augmentation would be in the pitch axis. It is theoritically possible to be pitch axis unstable and have augmentation only in that area. Of course it won't be as controllable under very high axis of attack, but then again, the system on the JF-17 is composite. As mentioned in the web article, the roll and yaw axis is still stability augmented. This does not mean that roll and yaw axis are basically statically unstable, but what it does mean is that these are still being used to augment stability for any loss of stability in those axii during maneuvers which includes high AoA maneuvers. All this completely covers what you are saying.

Once again the presence of instability implies FBW, but the converse is not true. Examples of the converse are civilian aircraft like the Cessna examples that you gave now. Being civilian, they do not have the need to perform military maneuvers with passengers on board, and so do not have any need for instability.

And somehow you forgot the F-20 Tigershark example?

It's true that JF-17 does have leading edge flaps like the F-16, which are likely to be controlled intelligently by the flight-control computer, without the pilot's knowledge. This is done to enhance maneuverability.

Of course, but somehow you conveniently forgot to mention that leading edge flaps are also used for stability augmentation. There is no reason why it is not done so on the JF-17.

It's FBW also has the restrictive property in not allowing the pilot to exceed certain limits. But all this still does not imply instability. As I pointed out in PDF forum, the JF-17's testing period is even lesser than an Indian trainer, IJT Sitara, which took a little more than 3 years from debut flight to certification. Instable aircraft that too with FBW usually have been tested for at least a decade.

That's nonsense. Don't compare your country's development times with the rest of the world as proof of general example. Development times often include too many factors like obtaining funding and bureaucratic hurdles. You know how quickly the F-16 prototypes rolled out and were quickly doing aerobatics in test competitions against the YF-17, which also rolled out quickly. The X-35 was doing aerobatics within a week after the plane first rolled out.

Certification has nothing to do with it. Certification covers a whole lot of other specifications and requirements in the plane that has nothing to do with flight behavior.

The JF-17 managed to roll out quickly and get certified quickly because the aircraft has a conventional tailed design whose aerodynamic behavior is well understood. No tricks like canards or levcons on deltas whose properties are far less understood and studied.

By hybrid controls I meant the kind of controls JF-17 has like FBW in one axis and hydraulic in the other two. I'm not talking of manual backups like in the Cessna aircraft, which are present only for passenger safety. In fighters with full-FBW, manual back-ups are replaced by triple or quadruple redundant flight-control (so that if one line fails another can take over). In the other Asian fighter, there are provisions so that the safety control restrictions of the FBW are actually overridden in case of emergency situations.

Besides in case of the F-2, there was some dispute over the US providing the full source-code of the F-16's FBW to Mitsubishi. So maybe it's more due to politics rather than aerodynamics.

You really didn't read the articles didn't you? The Cessna article does not portray the manual system just simply as a backup, but the fact that manual control authority and FBW control authority are combined. The manual system and FBW are still working together and simultaneously in regular flight.

Read the lines in the KAMRA page and the image I get is that the roll and pitch axis are manual controls with stability augmentation.

The articles point out that the control authority is a sum of between a a percentage manual with hydraulic and the balance by the FBW. Don't you get it? X% Manual + Y% FBW. That means the FBW still has partial control of the roll and yaw axis controls.

The thing why aircraft with full FBW has three to four channels of redundancy is because by nature, FBW itself is not as reliable or as fail safe as any manual system. The use of a composite system on the F-20, the Cessna and the JF-17 share one common thing, they can reduce cost, complexity, space and weight through a composite system that combines the best of two worlds into one.

On the case of the F-2, legal disputes over the code has no bearing on the design decision on the aircraft to have a 3 channel FBW redundancy with a manual backup.

 

[Indianfighter]

Re: New JF-17/FC-1 Fighter Aircraft thread

That is incorrect. The F-20 is also unstable and yet it has a composite FBW system.

I think that you are confusing Cessna's so-called composite/mixed controls with hybrid controls. Terminology apart, the former (in Cessna and not in F-20 Tigershark) are a mixture of mechanical and FBW in each of the axes, in which actuators are divided into the authorities of mechanical and FBW controls; the latter is what JF-17 employs which is full FBW in an axis and none at all in the others. We are discussing the latter type.

Your main contention is that the JF-17's "stability augmentation" systems in the roll and yaw axes are like Cessna > part of the surface is actuated by direct mechanical input of the pilot and part of it is actuated by FBW. However, the F-20 system is different and it is corroborated by Cessna's representative who claimed that this system is a world-first and merits a patent, which otherwise would have gone to Northrop 27 years ago. The F-20 does not have split actuation of it's control surfaces unlike Cessna, but instead it has bifurcated control authority on the same surface actuators. This is best explained

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in the post by a poster named 'seahorse' (I tried but couldn't find aircraft examples).

This roughly explains the partial FBW of the F-20 in all the 3 axes, with varying percentages of mechanical authority and FBW authority for the same actuators of a surface. In a

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, it further said that >

Should the highly reliable FCES have failed for any reason, the mechanical system had sufficient authority under all loading conditions to control and land the aircraft safely. . .

In the event of multiple failures of the FCES, control reverted to the active mechanical control system, with handling qualities sufficient to allow the pilot to return to base and land safely.

Today, this outdated mechanism in combat jets is replaced by multiple redundancy in the control system so that if one line fails, another line can immediately and seamlessly take over the controls (like idle reins of a horse-carriage).

Cessna has done all this simply to maximize passenger safety by splitting it's eggs in 2 baskets :- it clearly states that should the mechanical cables fail, the FBW is there, and should the FBW fail the reliable cables are there.
Entirely different from Cessna, in 1971 the YF-17 preceded the principle as the F-20 a decade later, for the reason of reducing pilot workload, in turn by reducing the force that he had to exert on his joystick. The article details that

Excellent handling qualities were provided throughout the flight envelope by a combination of aerodynamic characteristics and a flight control system optimized to allow precise control with reduced pilot workload. Above 350 KCAS, a constant maneuvering stick force gradient of approximately 4 pounds per g was provided. Below 350 KCAS, where the aircraft could maneuver to maximum lift conditions at high angles of attack, the gradient increased with decreasing airspeed to yield a constant stick force as a function of pitch rate.

In the 70s and 80s, companies hesitated to relegate all handling to the FBW which was still new and untested . Today, this outmoded system is replaced by FBW having multiple redundancies in combat aircraft.

It is improbable that JF-17 is using Cessna's system.

And somehow you forgot the F-20 Tigershark example?

I suggest you to read

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Instability in aircraft was introduced only much after FBW technology, after it's benefits in maneuvering were realized. The F-4 was first converted to 3 axes FBW and only then were instability causers like canards and slats were added in the PACT version. F-20 also had partial FBW so that it's instable design could be exploited.

Your argument is also that because JF-17 has got "stability augmentation" in the other two axes, so it must have a partial FBW system like F-20. I think you are attaching too much importance to that phrase, which could also simply mean trim tabs, and does not imply that JF-17 has partial FBW.

If an aircraft is pitch unstable, the main stability augmentation would be in the pitch axis. It is theoritically possible to be pitch axis unstable and have augmentation only in that area.

Pitch instability requires harmony with all the 3 axes and not just pitch axis alone. Please read the e-book I gave above and

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to see a contemporary example why all aircraft that are pitch unstable have FBW in all the 3 axes. The YF-17 had partial FBW in the 3 axes because according to wikipedia, in those early days of FBW, the designers did not want to commit all the controls to FBW for concerns of pilot safety.

The maneuvering flaps of JF-17 would be similar to F-20 which are automatically adjusted taking into account the instant speed, altitude and other conditions in order to achieve optimum maneuverability.

Of course it won't be as controllable under very high axis of attack, but then again, the system on the JF-17 is composite. As mentioned in the web article, the roll and yaw axis is still stability augmented. This does not mean that roll and yaw axis are basically statically unstable, but what it does mean is that these are still being used to augment stability for any loss of stability in those axii during maneuvers which includes high AoA maneuvers. All this completely covers what you are saying.

I don't think that it means JF-17 has got a partial FBW in the roll and yaw axes that acts according to given flight conditions on it's own. It probably means presetting trimming tabs so that the pilot does not have to continually maintain the stick in that position. This reduces pilot workload.

If it would have indeed been partial FBW, then I think the article would have explicitly mentioned it so, just like the mention on pitch FBW.

That's nonsense. Don't compare your country's development times with the rest of the world as proof of general example. Development times often include too many factors like obtaining funding and bureaucratic hurdles. You know how quickly the F-16 prototypes rolled out and were quickly doing aerobatics in test competitions against the YF-17, which also rolled out quickly. The X-35 was doing aerobatics within a week after the plane first rolled out.

I think you are ignoring facts. I compared the JF-17's development time with the trainer IJT's development time as well as similar development times across the world also. The development times of IJT & the other Indian fighter are in sync with the rest of the world, but the JF-17 is not. You would probably know that Gripen, Rafale, Eurofighter have all taken a decade each from debut flight to the end of all flight-testing. The earliest F-16A also took 5 years, which was because it's earliest versions used analog FBW.

In FBW systems, along with the the aircraft's design the validity of the flight-control software is also extensively tested. That's why such aircraft take much greater time to develop.

The JF-17 managed to roll out quickly and get certified quickly because the aircraft has a conventional tailed design whose aerodynamic behavior is well understood.

That is not correct. If you read the article which I posted, not only the aircraft's design has to be validated during testing, but also the Flight-control software that is meant to control the machine every 10 ms. This is a painstaking process and by examples across other countries, has never been completed in just under 3 years. The IJT Sitara took more time, even though it is a subsonic, fully hydraulic trainer. It needed only flight testing since it did not have to undergo weapons testing, radar testing &c.

Hence I think tphuang is probably right that PLAAF may be interested in the FC-1 only because there is some delay in the production of a locally made trainer. It may also act as a combat aircraft during war time. Only PAF will be relying on it as a main combat jet in it's fleet.

No tricks like canards or levcons on deltas whose properties are far less understood and studied.

Levcons on the naval-variant are scheduled a few years from now. The current variant is more conventional and is in it's eighth year of test-flights.

Read the lines in the KAMRA page and the image I get is that the roll and pitch axis are manual controls with stability augmentation.

I think that website should not be taken as seriously, even though it may be official because it has too many mathematical, factual and self-contradictory errors to be considered a credible source. I think you are according too much importance on that single sentence.

About Sitara... Well, it would certainly a bit faster if mr Singh closes and locks his canopy next time. It was very detailed mentionned on AFM magazine so please do believe that it is true.

That incident was during an Air show and not during flight test, which was well reported in the

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. The issues of engine changes came only last year for which testing has still to be done.

 

[crobato]

Re: New JF-17/FC-1 Fighter Aircraft thread

I think that you are confusing Cessna's so-called composite/mixed controls with hybrid controls. Terminology apart, the former (in Cessna and not in F-20 Tigershark) are a mixture of mechanical and FBW in each of the axes, in which actuators are divided into the authorities of mechanical and FBW controls; the latter is what JF-17 employs which is full FBW in an axis and none at all in the others. We are discussing the latter type.

Read what the KARMA page says again. Obviously it has stability augmentation at the roll and yaw axis.

Get an English dictionary and tell me what the word Augmentation means.

If that isn't stability assisted, what is the mechanisms that do this augmentation?

Get some logic and you will realize that the roll and yaw axis is being assisted. Cause and effect. Who is doing and determining that assistance?

That means, the pitch axis is fully FBW, but roll and yaw axis are manual with stability augmentation. Who is doing that augmentation? No other candidate there but the FBW.

Your main contention is that the JF-17's "stability augmentation" systems in the roll and yaw axes are like Cessna > part of the surface is actuated by direct mechanical input of the pilot and part of it is actuated by FBW. However, the F-20 system is different and it is corroborated by Cessna's representative who claimed that this system is a world-first and merits a patent, which otherwise would have gone to Northrop 27 years ago. The F-20 does not have split actuation of it's control surfaces unlike Cessna, but instead it has split control authority on the same surface. This is best explained

Claim does not make it so. Maybe the Cessna engineer wasn't familiar with the Northrop system after all. Saying that it "merits" the patent, does not mean it actually got the patent.

It may seem unique to Cessna for civilian aircraft where you won't find any other example.

F-20 had partial FBW authority in all the 3 axes with varying percentages of mechanical authority and FBW authority for the same actuators of a surface. In other words, actuation control was not spilt like in Cessna. In a

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, it is explained like this >

Your grammar twisting does not change that both planes have percentage manual and FBW control.

Today, this outdated mechanism in combat jets is replaced by multiple redundancy in the control system so that if one line fails, another line can immediately and seamlessly take over the controls (like idle reins of a horse-carriage).

How is hybrid mechanisms outdated? Because you declared it so?

Cessna has done all this simply to maximize passenger safety by splitting it's eggs in 2 baskets :- it clearly states that should the mechanical cables fail, the FBW is there, and should the FBW fail the reliable cables are there.
Entirely different from Cessna, in 1971 the YF-17 preceded the principle as the F-20 a decade later, for the reason of reducing pilot workload, in turn by reducing the force that he had to exert on his joystick. The article details that
In the 70s and 80s, companies hesitated to relegate all handling to the FBW which was still new and untested . Today, this outmoded system is replaced by FBW having multiple redundancies in combat aircraft.

Sigh. You apparently never did understand that the mechanical system is the ultimate fail safe which is why Cessna voted it.

It is improbable that JF-17 is using Cessna's system.

Sorry to say but it sounds like JF-17 does have a hybrid system.

I suggest you to read

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Instability in aircraft was introduced only much after FBW technology, after it's benefits in maneuvering were realized. The F-4 was first converted to 3 axes FBW and only then were instability causers like canards and slats were added in the PACT version. F-20 also had partial FBW so that it's instable design could be exploited.

Your argument is also that because JF-17 has got "stability augmentation" in the other two axes, so it must have a partial FBW system like F-20. I think you are attaching too much importance to that phrase, which could also simply mean trim tabs, and does not imply that JF-17 has partial FBW.
Pitch instability requires harmony with all the 3 axes and not just pitch axis alone. Please read the e-book I gave above and

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to see a contemporary example why all aircraft that are pitch unstable have FBW in all the 3 axes. The YF-17 had partial FBW in the 3 axes because according to wikipedia, in those early days of FBW, the designers did not want to commit all the controls to FBW for concerns of pilot safety.

If the JF-17 isn't pitch unstable, why bother putting an FBW? It seems you are contradicting yourself here.

The maneuvering flaps of JF-17 would be similar to F-20 which are automatically adjusted taking into account the instant speed, altitude and other conditions in order to achieve optimum maneuverability.

Oh I see, and that would be done by the FBW, right?

Somehow you come up with an artificial argument that the trim controls can be automated to improve maneuverability but somehow cannot be used for stability at the edge of the flight envelope? Who would be stupid enough to design that?

You want to find examples of aircraft that actually do just that?

Or maybe you have not realized that both goals can be one and the same.

I don't think that it means JF-17 has got a partial FBW in the roll and yaw axes that acts according to given flight conditions on it's own. It probably means presetting trimming tabs so that the pilot does not have to continually maintain the stick in that position. This reduces pilot workload.

And you don't seem to understand that the constant trimming by pilots is actually the result of an aircraft that is inherently unstable. Yes, even before there was FBW, there were already unstable aircraft. You seem to confuse the notion of manageability that somehow unstable means uncontrollable.

If it would have indeed been partial FBW, then I think the article would have explicitly mentioned it so, just like the mention on pitch FBW.

Frankly many Chinese articles have already explained that the JF-17 is indeed pitch unstable.

I think you are ignoring facts.

You have been the one ignoring the facts, and doing fault finding in language, as if you can arrive to some holy truth here. Wrong. This is not a Bible or Koran class. Grammatic structure and expression are what they are, and they can be subjected to human vagueness.

I compared the JF-17's development time with the trainer IJT's development time as well as similar development times across the world also. The development times of IJT & the other Indian fighter are in sync with the rest of the world, but the JF-17 is not.

Oh, and how is that? Do you realize that the YF-16, YF-17 and X-35 had prototypes doing aerobatics fairly quick off the bat? I'm sorry to say the development times of the IJT is not in sync with the rest of the world. The Everyone has their own case.

You would probably know that Gripen, Rafale, Eurofighter have all taken a decade each from debut flight to the end of all flight-testing. The earliest F-16A also took 5 years, which was because it's earliest versions used analog FBW.

That's operational certification, which has nothing to do with the FBW's ability to fly.

The Gripen, Rafale and Eurofighter are testing new waters in canard-delta flight.

In FBW systems, along with the the aircraft's design the validity of the flight-control software is also extensively tested. That's why such aircraft take much greater time to develop.

Sigh. In all those examples you mentioned, flight control isn't the only thing that is occupying all those years of development.

You didn't know that the YF-16 and the YF-17 were doing serious aerobatics in their fly off against each other.

That is not correct. If you read the article which I posted, not only the aircraft's design has to be validated during testing, but also the Flight-control software that is meant to control the machine every 10 ms. This is a painstaking process and by examples across other countries, has never been completed in just under 3 years. The IJT Sitara took more time, even though it is a subsonic, fully hydraulic trainer. It needed only flight testing since it did not have to undergo weapons testing, radar testing &c.

Sigh. Read again the developmental history of planes like the YF-16/YF-17 and the X-32/X-35 competition, and these planes were doing aerobatics early on.

Frankly I don't think you have concrete and specific data that can isolate how much of the given development time were on the FBW alone. Furthermore, some of these planes have specification changes like the Typhoon that added 1000kg in weight to beef up the structure to increase air frame life. While other planes like the Rafale have to deal with different variants, which means you have to make changes in the FBW for each of these variants.

Any change of specification means you have to go back to the drawing board, like the Typhoon weight increase, because that changes the flight behavior, which cascades to changes in the FBW coding.

Note we have not seen major specs changes on the JF-17, and the main change we observed from the second to the third prototype never even changed its weight. We don't see innumerable variants of the JF-17 either. We don't see a lot of stuff that is rewriting the spec sheets or calling forth different variants, including a naval one. Also the JF-17 is quite conservative, and you can see from the planform it takes from the F-16. A conventionally tailed plane is a flight model that is far far better studied and understood, than some models like delta-canards.

Hence I think tphuang is probably right that PLAAF may be interested in the FC-1 only because there is some delay in the production of a locally made trainer. It may also act as a combat aircraft during war time. Only PAF will be relying on it as a main combat jet in it's fleet.

I don't see the JF-17 being a trainer not unless you have a two seater variant, which is non existent for the moment.

I think that website should not be taken as seriously, even though it may be official because it has too many mathematical, factual and self-contradictory errors to be considered a credible source. I think you are according too much importance on that single sentence.

You mean it should not be taken seriously just because it contradicts some myths you wish to believe about the JF-17. Even if that is the case, Chinese articles still and maintain the point that the plane is statically unstable.

Read what I said again about over analyzing text. Looking for grammatical and phrasing errors does not negate the message. Frankly I think such attempts to disprove evidence by technicalities seems like a desperate act to me. Further more, sites like this are purposedly vague because they do not want to reveal classified information, and often the writer himself or herself, are not the engineers, and are only typing in what they are told to. I see similar vague language with many of Raytheon's own brochures for example.

You won't find a fighter application where the plane has digital FBW, even on just the pitch axis alone, and yet this aircraft is somehow statically pitch stable? Your own comments contradict yourself. Then why would you have FBW if the plane is stable? To save costs, it could have gone completely manual even on pitch. FBW alone does not confer increased maneuverability unless the plane is made statically unstable. FBW as systems are stability augmentation devices. What they do is keep the aircraft within control.

For roll and yaw axis stability augmentation, it may be with the FBW controlling secondary control surfaces like the leading edge flaps, or assist in the control of the main control surfaces. It can be both. The language at least points to some additional stability control.

Let me get to you another example of another fighter that went from prototype to certification in about three years. That would be the F-CK-1 Ching Kuo. If they had tried to do a canard-delta, which is actually among the concept proposals, development might be delayed. Instead, they went with a conservative design similar to an F-16, conservative meaning, an air design that is already well known and tested. That example is quite relevant since the JF-17 seems intentionally having a similar aerodynamic model as the F-16 if you look at the planform.

 

[Infra_Man99]

Re: New JF-17/FC-1 Fighter Aircraft thread

It would be good to figure out if the JF-17 has a fly-by-wire system or not.

In regards to maneuverability, I don't think we can be sure about the JF-17's agility even if we know the JF-17 has a FBW system or not. FBW usually indicates a jet fighter is agile, but this is not always the case. I read that the early models of the MiG-29 had manual controls and was naturally stable, yet, the MiG-29 is one of the most agile jets out there.

 

[Indianfighter]

Re: New JF-17/FC-1 Fighter Aircraft thread

Read what the KARMA page says again. Obviously it has stability augmentation at the roll and yaw axis.

Get an English dictionary and tell me what the word Augmentation means.

If that isn't stability assisted, what is the mechanisms that do this augmentation?

Get some logic and you will realize that the roll and yaw axis is being assisted. Cause and effect. Who is doing and determining that assistance?

That means, the pitch axis is fully FBW, but roll and yaw axis are manual with stability augmentation. Who is doing that augmentation? No other candidate there but the FBW.

I think you overemphasizing that single phrase, "stability augmentation", which you are interpreting exaggeratingly. Firstly, I'm afraid you have not understood that there is a vast difference between what Cessna and F-20 employed. The former divides the actuators of a surface between FBW and pilot; the latter divides authority of the same actuator(s) of a surface between the pilot and FBW. You claim that JF-17 employs the latter kind of system.

Coming to semantics, the F-20 has control augmentation. This term precisely means that the pilot's control is augmented or assisted by FBW. Now in case of FC-1, the term "stability augmentation" means that stability is augmented, and not control. That's why I said previously, this term could just as well mean presetting trimming tabs on the FC-1. It does augment stability because the pilot does not have to continuously keep holding his stick, and still keep flying as though he does in normal conditions.

Your grammar twisting does not change that both planes have percentage manual and FBW control.

I changed that grammatically incorrect quote before your post, so probably you missed it.

Once again, suppose the vertical tail has 2 actuators. In Cessna, one actuator will be controlled by FBW and the other mechanically by the pilot. But in F-20, both of them will be partially controlled by the FBW and mechanical controls each. This is the main difference between the two, and neither of which the FC-1 reportedly has.

How is hybrid mechanisms outdated? Because you declared it so?

Please remember that full FBW was adopted as early as F-4 PACT program and YF-16. Since then, at least I have not heard of any military jet reverting back to the system of F-20.

Sorry to say but it sounds like JF-17 does have a hybrid system.

I think the term "control augmentation" (like C.A.S. in F-20) would have meant that. Stability augmentation is most likely to mean presetted trimmers, which freeze the control surface at a point.

If the JF-17 isn't pitch unstable, why bother putting an FBW? It seems you are contradicting yourself here.

All unstable aircraft till date have FULL FBW in the 3 axes. I repeat once again that FBW existed long before instability was introduced. In page 177 of the e-book, it is stated that F-4 PACT was made unstable only after full FBW was added to it. Earlier, when instability was not introduced, it flew with FBW only in the pitch axis - just like FC-1 does now.

Oh I see, and that would be done by the FBW, right?

That's correct. Forward maneuvering flaps in the F-16 are also controlled automatically : depending on the altitude, speed, conditons the flaps are adjusted accordingly.

And you don't seem to understand that the constant trimming by pilots is actually the result of an aircraft that is inherently unstable. Yes, even before there was FBW, there were already unstable aircraft. You seem to confuse the notion of manageability that somehow unstable means uncontrollable.

That is not necessary, just as it is not necessary that any FBW controlled aircraft must necessarily be unstable. In WW2, German aircraft had such trimmers more because it drastically reduces pilot workload, otherwise the pilot would have to be on edge every time.

Oh, and how is that? Do you realize that the YF-16, YF-17 and X-35 had prototypes doing aerobatics fairly quick off the bat? I'm sorry to say the development times of the IJT is not in sync with the rest of the world. The Everyone has their own case.

Subsonic light trainers take only about 3 years to develop across the world, unlike fighter aircraft that take far longer. IJT's development time is also in agreement with L-15 (scheduled to join next year).

That's operational certification, which has nothing to do with the FBW's ability to fly.

Sigh. In all those examples you mentioned, flight control isn't the only thing that is occupying all those years of development.

Weapon certification and radar worthiness only take 1 to 1 1/2 year at the most. The rest of the time is consumed by flight-testing. It is impossible that the FC-1 has supposedly completed flight-testing, weapons testing avionics testing in just less than 3 years. That may explain PLAAF's interest in it only as a possible trainer.

Sigh. Read again the developmental history of planes like the YF-16/YF-17 and the X-32/X-35 competition, and these planes were doing aerobatics early on.

The other Asian fighter has also performed spectacular acrobatics early in it's testing years at various air-shows and in front of visiting dignitaries. Though not of the level of competition, they were nonetheless very mature.

Frankly I don't think you have concrete and specific data that can isolate how much of the given development time were on the FBW alone. Furthermore, some of these planes have specification changes like the Typhoon that added 1000kg in weight to beef up the structure to increase air frame life. While other planes like the Rafale have to deal with different variants, which means you have to make changes in the FBW for each of these variants.

Any change of specification means you have to go back to the drawing board, like the Typhoon weight increase, because that changes the flight behavior, which cascades to changes in the FBW coding.

Note we have not seen major specs changes on the JF-17, and the main change we observed from the second to the third prototype never even changed its weight.

The FC-1 too had to undergo numerous drastic changes 1 year after it's development began when DSI and LERX had to be added. But even after this change, it was declared completed after just 2 years which is impossible unless the FBW has not been tested fully (and of course, as the complete course of instable flight-testing did not have to be done).

You mean it should not be taken seriously just because it contradicts some myths you wish to believe about the JF-17. Even if that is the case, Chinese articles still and maintain the point that the plane is statically unstable.

Read what I said again about over analyzing text. Looking for grammatical and phrasing errors does not negate the message. Frankly I think such attempts to disprove evidence by technicalities seems like a desperate act to me. Further more, sites like this are purposedly vague because they do not want to reveal classified information, and often the writer himself or herself, are not the engineers, and are only typing in what they are told to. I see similar vague language with many of Raytheon's own brochures for example.

For an aircraft that was to be the F-16 of poor countries, atleast a proper website that is not vague and obscure must have been maintained, as a marketing tool.

I think that PLAAF has abandoned the FC-1 to concentrate on the J-10, J-XX and other important projects. In PLAAF at least the FC-1 is unlikely to be inducted as anymore than a trainer. It will find acceptance only in PAF.

You won't find a fighter application where the plane has digital FBW, even on just the pitch axis alone, and yet this aircraft is somehow statically pitch stable?

I think that the JF-17 is exactly such an application : FBW in the pitch axis with pitch stability.

Then why would you have FBW if the plane is stable?

That is done to partly reduce pilot workload, to reduce weight due to mechanical cabling and systems. The earliest aircraft like F-4 which had only pitch FBW were not instable. I repeat, that they added instability only after the aircraft was made fully FBW in all the 3 axes (read page 177 of the e-book for details).

Let me get to you another example of another fighter that went from prototype to certification in about three years. That would be the F-CK-1 Ching Kuo. If they had tried to do a canard-delta, which is actually among the concept proposals, development might be delayed. Instead, they went with a conservative design similar to an F-16, conservative meaning, an air design that is already well known and tested. That example is quite relevant since the JF-17 seems intentionally having a similar aerodynamic model as the F-16 if you look at the planform.

The Ching-Kuo had such a low development time probably because it is an F-16 clone. The US contractor Lockheed Martin were not developing anything new so it took far lesser time. Chengdu on the other hand had no such assistance even though FC-1 borrowed the F-16's wing layout.

 

[crobato]

Re: New JF-17/FC-1 Fighter Aircraft thread

I think you overemphasizing that single phrase, "stability augmentation", which you are interpreting exaggeratingly. Firstly, I'm afraid you have not understood that there is a vast difference between what Cessna and F-20 employed. The former divides the actuators of a surface between FBW and pilot; the latter divides authority of the same actuator(s) of a surface between the pilot and FBW. You claim that JF-17 employs the latter kind of system.

I am claiming that we don't exactly know what the system the JF-17 is employing, it can be something of the either or both.

Coming to semantics, the F-20 has control augmentation. This term precisely means that the pilot's control is augmented or assisted by FBW.

Did you suddenly just invent that because all FBW does that.

Now in case of FC-1, the term "stability augmentation" means that stability is augmented, and not control. That's why I said previously, this term could just as well mean presetting trimming tabs on the FC-1. It does augment stability because the pilot does not have to continuously keep holding his stick, and still keep flying as though he does in normal conditions.

When you're pulling the stick and the rudders, you are controlling the main control surfaces. The main control surfaces are as part of the stability equation.

Should the secondary control surfaces be sufficient to provide stability, that argument alone can show stability augmentation through secondary control surfaces would be sufficient to control instability in all three axis, wouldn't it?

Again, contradicting yourself.

I changed that grammatically incorrect quote before your post, so probably you missed it.

Grammatically incorrect, based on your opinion, is not proof to disprove evidence.

Once again, suppose the vertical tail has 2 actuators. In Cessna, one actuator will be controlled by FBW and the other mechanically by the pilot. But in F-20, both of them will be partially controlled by the FBW and mechanical controls each. This is the main difference between the two, and neither of which the FC-1 reportedly has.

And how sure are you? How will stability augmentation work on the tail then?

Please remember that full FBW was adopted as early as F-4 PACT program and YF-16. Since then, at least I have not heard of any military jet reverting back to the system of F-20.

That does not necessarily invalidate the concept.

I think the term "control augmentation" (like C.A.S. in F-20) would have meant that. Stability augmentation is most likely to mean presetted trimmers, which freeze the control surface at a point.

Wrong.

Here is the old way of doing it---all the things being described here are now all being handled by modern electronic FCS.

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All unstable aircraft till date have FULL FBW in the 3 axes. I repeat once again that FBW existed long before instability was introduced. In page 177 of the e-book, it is stated that F-4 PACT was made unstable only after full FBW was added to it. Earlier, when instability was not introduced, it flew with FBW only in the pitch axis - just like FC-1 does now.

Nope. The F-4 PACT was made unstable with the addition of canards which changed the aerodynamic lift center, an event that took place only long after the FBW was fully implemented. That's a big difference from being "immediately after".

That is not necessary, just as it is not necessary that any FBW controlled aircraft must necessarily be unstable. In WW2, German aircraft had such trimmers more because it drastically reduces pilot workload, otherwise the pilot would have to be on edge every time.

Read the link again, to see what stability augmentation means. Its entirely in the context of flight control, not trimming.

Subsonic light trainers take only about 3 years to develop across the world, unlike fighter aircraft that take far longer. IJT's development time is also in agreement with L-15 (scheduled to join next year).

And how long has the JF-17 been in development? Are you counting the total time from paper to flying prototype? You're comparing apples to oranges here. The JF-17 has been in development through out the nineties, certainly much longer development behind the scenes than the L-15.

Weapon certification and radar worthiness only take 1 to 1 1/2 year at the most.

Nonsense. These processes takes years if you suddenly develop problems or have new specifications added midway. There were things in the MKI for example, that took three years before these weapons were completely certified. Does not matter if its ship or plane or sub; look how long the Kilos finally got the Klubs ready.

The rest of the time is consumed by flight-testing. It is impossible that the FC-1 has supposedly completed flight-testing, weapons testing avionics testing in just less than 3 years. That may explain PLAAF's interest in it only as a possible trainer.

That's completely wrong. Take for example the F-22. The Raptor got flight control right quite early, even the YF-22 was doing aerobatics. The long delinquent development time was focused on the avionics and electronics, which were beset by problems, complexity and changing specifications.

The other Asian fighter has also performed spectacular acrobatics early in it's testing years at various air-shows and in front of visiting dignitaries. Though not of the level of competition, they were nonetheless very mature.

You call that "spectacular"? I call it rather routine, if not playing safe. The videos were rather unimpressive.

The FC-1 too had to undergo numerous drastic changes 1 year after it's development began when DSI and LERX had to be added.

It already had a LERX to begin with. The new one is bigger though.

But even after this change, it was declared completed after just 2 years which is impossible unless the FBW has not been tested fully (and of course, as the complete course of instable flight-testing did not have to be done).

Oh please keep comparing it with other delayed projects. The delays on the "other" Asian fighter is due to bureaucracies, some ill thought off primary parameters, and ever changing specifications. None of that afflicted the JF-17 except for the DSI and LERX change.

For an aircraft that was to be the F-16 of poor countries, atleast a proper website that is not vague and obscure must have been maintained, as a marketing tool.

LOL. A website isn't the primary marketing tool. Why you think people would buy multibillion fighters by what they read in a website? Don't be ridiculous. The website is the least important. Prospective buyers would be handed documentation, and the people in the decisioning process would be interacted directly by staff.

I think that PLAAF has abandoned the FC-1 to concentrate on the J-10, J-XX and other important projects. In PLAAF at least the FC-1 is unlikely to be inducted as anymore than a trainer. It will find acceptance only in PAF.

Nonsense. The FC-1 came after the J-10. The speed of the FC-1's development is a result of the success of technologies and experienced executed and learned from the J-10. In effect, the JF-17 is the child of the J-10.

I think that the JF-17 is exactly such an application : FBW in the pitch axis with pitch stability.

I disagree with you. I ike everyone else in this board, thnk you have an agenda. You're not an expert or have better access to knowledge regarding the JF-17 than Chinese or Pakistani members, yet you claim or want to act like as if you know better than them? I remember the designers of the JF-17, also the designers for the J-10, comment that the JF-17 is unstable and therefore required FBW, through an interview years ago.


You won't find anywhere in the world where a fighter that features LERX---which tends to adjusts the center of lift forward---and has advertised FBW yet to be somehow statically stable in pitch.

That is done to partly reduce pilot workload, to reduce weight due to mechanical cabling and systems.

There is no current example of any fighter plane where FBW is implemented to do only just that.

The earliest aircraft like F-4 which had only pitch FBW were not instable. I repeat, that they added instability only after the aircraft was made fully FBW in all the 3 axes (read page 177 of the e-book for details).

Read this link and please note that this page belongs to an actual US Air Force base. (af.mil).

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"The Precision Aircraft Control Technology (PACT) program continued to use the F-4, now with a set of canard surfaces attached to fuselage. This configuration altered the aerodynamic balance, moving the center of pressure slight forward and reducing the inherent stability of the F-4."

So it became unstable only after the canards were added. And that took place well after the plane had full FBW, not immediately after it. So there was no cause and effect on this one. The F-4 PACT became unstable only after the program was extended, even long after the LFW competition had taken place.


So you apparently don't know what causes the aircraft to be unstable. It is by moving the center of lift ahead of the center of gravity. And when you have LERX, it tends to do just that.

Read the F-15 flight control system again.

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The plane has conventional mechanical-hydraulic controls. Yet a dual channel electronic control and stability augmentation and 3 axis dampening system is superimposed on it.

Regardless of anything, when you have control and stability augmentation, you have three axis damping. This is a job that is now done by modern digital FCS and FBW.


I would find it difficult to conceive in a case where the plane already has a pitch axis FBW, and still have a separate two axis dampening system being acted on the roll and axis, considering the objective is to reduce complexity and keep it as simple as possible. The FBW has to be in charge of roll and yaw axis dampening, through superimposition over the manual controls. Otherwise this type of model is certainly nonsensical and nonexistent.

Equally nonsensical, would be a fighter plane that already has an onboard FBW that controls pitch, and yet must have manually and preset trims? This is considering that it won't be FBW if the system won't be able to control the trim.

The Ching-Kuo had such a low development time probably because it is an F-16 clone. The US contractor Lockheed Martin were not developing anything new so it took far lesser time. Chengdu on the other hand had no such assistance even though FC-1 borrowed the F-16's wing layout.

Nonsense. Chengdu is the developer of the J-10, isn't it? With alleged Israeli, Russian help on the J-10, and alleged Pakistani help on the JF-17, which would tap on the know how developed on the former. The Ching Kuo has the basic planform of the F-16, but there are too many differences in weight, size, etc,. to make it a clone.

You don't seem to remember the many pictures of Chinese wind tunnels, and among those pictures, the subject model is often an F-16. You would have figured out that the Chinese would try to model the performance of the F-16 by studying its aerodynamics, because the F-16 can be regarded as one of the aircraft the PLAAF is most likely to face. Yet at the same time, that knowledge can turn out to be useful when developing a new aircraft. Furthermore, the JF-17's FCS would have been derived from the J-10's, so Chengdu isn't developing these from scratch just for the JF-17. China first started experimenting with FBW as early as in the eighties, when they installed the first system on a J-6. Similar systems are incorporated on the JH-7 as a means to improve stability and flight ride on low altitude terrain following flight. And other implementations of the Chinese FBW system also includes the L-15 and the J-11B.

 

[crobato]

Re: New JF-17/FC-1 Fighter Aircraft thread

It would be good to figure out if the JF-17 has a fly-by-wire system or not.

In regards to maneuverability, I don't think we can be sure about the JF-17's agility even if we know the JF-17 has a FBW system or not. FBW usually indicates a jet fighter is agile, but this is not always the case. I read that the early models of the MiG-29 had manual controls and was naturally stable, yet, the MiG-29 is one of the most agile jets out there.

One has to remember that the F-15 is also quite agile, and the F-14 as well. All have manual controls. Naturally stable, the term better expressed is statically stable. That means the plane has a tendency to go in another direction other than straight if no control authority is applied. If you make a paper airplane via origami, throw it and it does not fly a straight flight, you've just made a statically unstable plane.

The idea that being unstable makes a plane more maneuverable comes only when you want to make the plane depart from straight line flight. But then, there are other means to make an aircraft depart from straight line flight, and by far what is most important is the control authority from the flight surfaces. Even if you have a statically pitch unstable aircraft, but if you have poor flight control authority, don't expect much.

Once you go beyond straight line flight, being "unstable" has no use at all. In fact, its stability that becomes more important. You want your aircraft to be stable right to the edge of the control envelope. Stability means controllability. If an aircraft is unstable at the edge, it would lose control and crash. So everything is being done to augment stability like pitch, roll and yaw dampening when the plane is at the edge of the envelope.

I don't have enough documentation on the MiG-29 but it should have some kind of system that acts as stability dampeners. Prior to the development of FBW, such a system would be needed, but today, they would be replaced by digital FCS/FBW.

 

[Indianfighter]

Re: New JF-17/FC-1 Fighter Aircraft thread

I am claiming that we don't exactly know what the system the JF-17 is employing, it can be something of the either or both.

I don't think it's either of the two. The first part of the reference that you provided is

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titled "The F-15 Hydro-Mechanical Control System". So it is not FBW at all at the outset. It explicitly states that the F-15 in question has a conventional hydro-mech control system and illustrated with diagrams to actually show push-pull cables that are connected between the pilot's stick to a channel assembly and the actuators of the surfaces. It has no FBW and states that just a sort of FBW "feel" is achieved only after mechanical system failure.

About the FBW "feel" that the pilot is given just after mechanical systems fail, here is what it states :

Should a linkage jam occur, mechanical control is no longer possible: however, pedal forces can be sent to the CAS electrically which will give "fly-by-wire" control of the rudders. ..

Added safety is also obtained should there be a linkage separation downstream of the PRCA. If a separation does occur, a "fly-by-wire" capability is provided by the electronics and the pilot will still have positive feel at the stick.

In the section on Stability Augmentation (which is just one part of the overall pitch CAS), the CAS is described as just a servo-gyro circuit assembly, that senses the frequency of any disturbance, and sends an electrical signal to a servo, which takes corrective action. There is no FBW and not even FBW computers are involved.

In pitch CAS, the pressure of the pilot's stick is sent to a servo amplifier --- and not a FBW computer --- that sends a signal to the actuator to deflect accordingly. The only element of "intelligence" here is that the amount of deflection is decided by a summer of pilot-input and gyro-accelerometer readings.

Although it describes only the pitch CAS, if FC-1 has such a system in the roll and yaw axes, it proves that it has a hydro-mechanical system in those axes, because the KAMRA page clearly states that it is a conventional system with stability augmentation; or in other words it is simply a servo-gyro assemblage to avoid oscillations and disturbances. There is no partial FBW or any remotest kind of built-in intelligence that is involved in the loop like F-20.

Should the secondary control surfaces be sufficient to provide stability, that argument alone can show stability augmentation through secondary control surfaces would be sufficient to control instability in all three axis, wouldn't it?

Regarding secondary control surfaces, the only one FC-1 has are maneuvering flaps (firstly, the CAS that we just saw controls primary surfaces; the horizontal stabilator in pitch CAS for example). These are automatically controlled to improve maneuverability according to KAMRA which I have not denied.

Nope. The F-4 PACT was made unstable with the addition of canards which changed the aerodynamic lift center, an event that took place only long after the FBW was fully implemented. That's a big difference from being "immediately after".

I doubt if you read what I wrote previously to the same effect. Here is my quote :- Instability in aircraft was introduced only much after FBW technology, after it's benefits in maneuvering were realized. The F-4 was first converted to 3 axes FBW and only then were instability causers like canards and slats were added in the PACT version. F-20 also had partial FBW so that it's instable design could be exploited.

By full FBW it is meant FBW in all the 3 axes, according to the e-book. Earlier with only pitch FBW, the F-4 was kept stable. Canards were added only after full FBW was provided. This was done under PACT.

Oh please keep comparing it with other delayed projects. The delays on the "other" Asian fighter is due to bureaucracies, some ill thought off primary parameters, and ever changing specifications. None of that afflicted the JF-17 except for the DSI and LERX change.

No. Procedural bureaucracies and sanctions affected it in the 90s. Since 2001 till 2008, testing of FBW has gone very smoothly.

I disagree with you. I ike everyone else in this board, thnk you have an agenda. You're not an expert or have better access to knowledge regarding the JF-17 than Chinese or Pakistani members, yet you claim or want to act like as if you know better than them? I remember the designers of the JF-17, also the designers for the J-10, comment that the JF-17 is unstable and therefore required FBW, through an interview years ago.

Can you post that interview or any possible link if it is still available ?

You won't find anywhere in the world where a fighter that features LERX---which tends to adjusts the center of lift forward---and has advertised FBW yet to be somehow statically stable in pitch.

That could have been offset by the loss of weight after DSI was designed. Conventional separators have much a heavier assembly.

Read this link and please note that this page belongs to an actual US Air Force base. (af.mil).

Please, Log in or Register to view URLs content!

"The Precision Aircraft Control Technology (PACT) program continued to use the F-4, now with a set of canard surfaces attached to fuselage. This configuration altered the aerodynamic balance, moving the center of pressure slight forward and reducing the inherent stability of the F-4."

That is exactly what I've incessantly told you that when only pitch FBW was there, there was no instability in the F-4. Only when full FBW was added, did instability causers like canards and slats were added (only a year after full FBW was incorporated in 1972).

 

[crobato]

Re: New JF-17/FC-1 Fighter Aircraft thread

I don't think it's either of the two. The first part of the reference that you provided is

What is your point in posting things that I already know? It is you that seemed to be in complete

Of course its not a complete FBW. This is an FCS overlaid over a mechanical system. The point that I'm trying to make to you, of which apparently caught you in surprise that you can have both mechanical and electrical control systems that overlay each other.

Although it describes only the pitch CAS, if FC-1 has such a system in the roll and yaw axes, it proves that it has a hydro-mechanical system in those axes, because the KAMRA page clearly states that it is a conventional system with stability augmentation; or in other words it is simply a servo-gyro assemblage to avoid oscillations and disturbances. There is no partial FBW or any remotest kind of built-in intelligence that is involved in the loop like F-20.

I only showed you one page, there are more pages that also show control of roll and yaw axis? Are you actually reading the material?

Did you read the F-15 page closely? Eh?

"I'm going to assume that you've had some basic exposure to the F-15 flight control system and know that it uses conventional hydro-mechanical ailerons and differential stabilator for roll control, collective stabilator for pitch control, and a rudder on each vertical for yaw control. In addition, there is a dual-channel, high-authority, three-axis CAS (Control Augmentation System) superimposed on the hydro-mechanical system. The CAS is utilized to shape aircraft response to pilot inputs, as well as provide three-axis damping and autopilot functions. The CAS can also provide aircraft control in the event of a mechanical system failure.

With this in mind, I'd like to break the control system into two elements - the basic hydro-mechanical system and the electronic system (CAS) - then further subdivide each and perhaps give you some insight as to why things are as they are."

And more

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"Having taken a look at the mechanical aspects of the F-15 Flight Control System, let's turn our attention to the electronic portion, the Control Augmentation System. Possibly the most frequently asked questions are: "Just what is the Control Augmentation System?" "What does it do for me?" "How does it do it?"

" The Control Augmentation System (CAS) consists of two distinct functions. The first is our old friend, the Stability Augmentation System, otherwise known as Stab Aug or SAS. "

(Even though CAS and SAS are often described as in terminology, they're two different systems, more often than not, CAS and SAS implementations tend to be blended into a single system, since CAS and FAS both interact if not integral with each other. You cannot say that the JF-17 lacks CAS---on the roll and yaw axis---either, CAS in layman's terms, is "power steering" and is standard in modern aircraft.)

As for the KAMRA page it said that stability augmentation is involved, It did not exactly say what is being used on that. I'm pointing this out to you to REFUTE your invented definition of stability augmentation as something with manually preset limiters, that it is in fact, an electronic system. And by the way, FBW also happens to use gyroscopes too.

or in other words it is simply a servo-gyro assemblage to avoid oscillations and disturbances."

Which on the record happens to be an oversimplified description of earlier FCS and even analog FBW systems.

What the page says it is stability augmented. It did not describe how that was done. You seem to miss that what FBW does is stability augmentation. What they do on the roll and yaw axis is precisely just that. Furthermore, such a system is electronic in construction, and be reminded that FBW does use gyroscopes. The system being described on the F-15 can qualify as an FCS. The fundamental difference is that that FBW as we know it, is control by wire. In other words, its the pilot input turned into electrical signals. Fundamentally, the F-15's FCS works with the same principles and control laws as any early FBW.

Now you're starting to get the picture. FCS and FBW are not exactly the same. FCS or Flight Control System describes a system that control's the aircraft's flight. FBW or Fly By Wire only describes a system where the pilot input is turned into electrical signals. An FCS does not necessarily have to be FBW and not all FCS is FBW.

Frankly there is no such thing as having two independently working FCS. You only have one master FCS, although that FCS can have multiple computers and even more gyroscopes. So you're saying that the JF-17 operates with an FBW on one part and a completely separate FCS (stability augmentation system) on another part is nonsensical. There is no precedent for it. Its also complete nonsense, and you know the reason for that.

What is being described is here is that the JF-17's pitch control is completely by wire---no mechanical input involved. My examples of the Cessna, F-20 and F-15 shows that just because you have mechanical controls, does not mean you cannot have electronic control overlay. The point remains is this, that the JF-17's FCS still has control over the roll and yaw axis of the plane. Only because it does not have electrical pilot input, means it cannot be called FBW by definition on the roll and yaw axis. But by operation, the JF-17's roll and yaw axis can be and is still controlled by the FCS. It is not the electrical control of pilot input on the three axis that counts, but the fact that there is FCS control on all three axis acting as dampeners using an electronic feedback cycle based on control laws.

I doubt if you read what I wrote previously to the same effect. Here is my quote :- Instability in aircraft was introduced only much after FBW technology, after it's benefits in maneuvering were realized. The F-4 was first converted to 3 axes FBW and only then were instability causers like canards and slats were added in the PACT version. F-20 also had partial FBW so that it's instable design could be exploited.

By full FBW it is meant FBW in all the 3 axes, according to the e-book. Earlier with only pitch FBW, the F-4 was kept stable. Canards were added only after full FBW was provided. This was done under PACT.

Sigh. None of this shows that you need FBW on roll and yaw axis as proof that you need to have a pitch unstable plane. You are constantly overinterpretating.

The text needed to validate the FBW in all three axis for safety and reliability before moving on to unstable designs. Its a safety procedure, not "you need FBW in all three axis before using on unstable design".

In fact, if I remember from discussions in AFM and ACIG with people who are quite aware with the design of the Su-27 aircraft, the fighter only has a pitch only analog FBW combined with mechanical controls.

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"From the outset the design was to use various combinations
of mechanical hydraulic and fly-by-wire (FBW) controls
with some reduced static stability to achieve
exceptional manoeuvrability."

Oh I see. And there's more.

The all important Flight Control System (FCS) in the
Su-27 family evolved incrementally, with the first generation
hybrid analog system running in parallel with the conventional
hydro-mechanical design.

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The SDU-10 pitch-only fly-by-wire system controls the pitch of the aircraft to ensure stability and controllability for the pilot, increase aerodynamic performance, limit overload and angle of attack when needed and decrease the airframe aerodynamic load.

No. Procedural bureaucracies and sanctions affected it in the 90s. Since 2001 till 2008, testing of FBW has gone very smoothly.

That's not what I keep hearing about.

Can you post that interview or any possible link if it is still available ?

I can't retrieve stuff that has been posted at least five years ago, especially since Chinese sites update their material often and dispose of the old.

That could have been offset by the loss of weight after DSI was designed. Conventional separators have much a heavier assembly.

The DSI would have decreased weight in the front further, pushing the CG further back. So what are you talking about? It only makes the plane more statically unstable.

That is exactly what I've incessantly told you that when only pitch FBW was there, there was no instability in the F-4. Only when full FBW was added, did instability causers like canards and slats were added (only a year after full FBW was incorporated in 1972).

Sigh. The historical order of development is not cause and effect. They wanted to verify the FBW in all three axis first for safety and reliability. They did not in fact, originally plan to make the F-4 PACT an unstable aircraft, nor preplanned full FBW as a requirement before making the aircraft unstable.

In a three axis FBW system, what the system does on the roll and yaw axis is axis dampening anyway, or stability augmentation. That's no different from what is being on the F-15 or in the F-20.

To sum it up, JF-17 has FCS + FBW control on the pitch axis, and FCS + manual on the roll and yaw axis. Add the LERX, strongly suggests that the plane is statically unstable in pitch.

 

[Indianfighter]

Re: New JF-17/FC-1 Fighter Aircraft thread

What is your point in posting things that I already know? It is you that seemed to be in complete

Of course its not a complete FBW. This is an FCS overlaid over a mechanical system. The point that I'm trying to make to you, of which apparently caught you in surprise that you can have both mechanical and electrical control systems that overlay each other.

Note that I described an electrical control system itself in my post before, which itself presupposes that the system in question is obviously an electrical-mechanical system. So I do not understand your point above.

The F-15 system is a fully hydro-mechanical system. But in between the direct linkages between the pilot's stick and the control surfaces, there is a CAS control system, which is essentially a servo-gyro control assembly.

The first part of CAS is stability augmentation and the other (and larger part) is CAS itself.
The first part or stab aug system within the CAS assembly, is an autonomous system that counters oscillatory movements in a knee-jerk reaction, principally in the same way that a home appliance UPS handles fluctuating voltages. There is no intelligent or programmed decision-making involved at any stage of this process.

The other part of CAS augments pilot controls to his direct mechanical ones : essentially similar to an F-20. It has an authority to deflect the pitch control surfaces only upto +/- 10 degrees. This it does by sending appropriate electrical pulses to the servos, which in turn deflect the actuators. The remainder authority is held by the pilot's direct mechanical input. Similarly, in the rudders, the CAS commands +/- 15 degrees of the total authority. But unlike the F-20, here the CAS gyro-accelerometer only senses the pitch rates and compares them with the pilot's stick force command. Using this summing info, it exerts it's portion of authority on the horizontal elevators in such a way that the pilot feels a constant stick force per g (as I also described in my post before).

Now this job of making the pilot feel a constant stick force was also done by the CAS computers of the F-20. But to exert their percentage of the total authority, the CAS computers calculated their electrical pulses by not just simply summing the pitch rates with pilot input (as in F-15), but also keeping in mind the aircraft's instability and the ideal response needed at that instant. In other words, programmed decision-making was involved in deciding how much of it's portion of authority should be augmented to the pilot's direct mechanical input.

This programmed decisioning was not needed in the CAS of the F-15 and instead only a knee-jerk servo-gyro CAS sufficed, because the F-15 so described was a stable aircraft according to Hoffman's statement on

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>>

"Well, we know that the F-15 airframe is basically stable, and that the manual flight controls are designed to give Level II handling without augmentation." (for level I, II and 3 qualities see

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).

Hence, the JF-17 is definitely a stable airframe, besides having an autonomous CAS in the roll and yaw axes. Had it indeed been like that of the F-20, pac.org would surely have explicitly mentioned that it has partial FBW in those axes. Merely stab aug would most probably only imply a simple autonomous CAS control system.

"Having taken a look at the mechanical aspects of the F-15 Flight Control System, let's turn our attention to the electronic portion, the Control Augmentation System. Possibly the most frequently asked questions are: "Just what is the Control Augmentation System?" "What does it do for me?" "How does it do it?"

I don't think we should be awed by mere terms like "electronic" and the earlier "stability augmentation" and so on. Both of us are not lay people. We know it's electronic and not something like 'chemical'. I suggest you try to read the Hoffman papers in detail that you posted, to atleast get a gist of how the autonomous CAS in the stable F-15 works.

As for the KAMRA page it said that stability augmentation is involved, It did not exactly say what is being used on that. I'm pointing this out to you to REFUTE your invented definition of stability augmentation as something with manually preset limiters, that it is in fact, an electronic system.

Please note that the Hoffman articles precisely mention that the stab augs in the roll and yaw axes are meant only for trimming and not much else. Please read

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, which entirely deals with trimming. See also

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.

The articles describe how the CAS in these two axes helps to freeze the trimmer settings of the pilot and establish new neutral positions of the joystick.

And by the way, FBW also happens to use gyroscopes too.

I think you are again getting exited merely by some terms. French gyroscopes are also used in the quad-FBW of the neighbouring Asian fighter too. It is a primary component of any digital FCS.

Frankly there is no such thing as having two independently working FCS. You only have one master FCS, although that FCS can have multiple computers and even more gyroscopes. So you're saying that the JF-17 operates with an FBW on one part and a completely separate FCS (stability augmentation system) on another part is nonsensical. There is no precedent for it.

That is exactly what it seems, because had it been one integrated CAS within one FCS then it would surely have been termed as partial FBW in the roll and yaw axes, instead of being called as just "stability augmentation". Besides, there is no reason to halt at partial FBW in those axes, because it would have been more prudent 'go all the way' and convert it into a full FBW.

This, coupled with the astonishingly low time in which the FC-1 was declared complete and ready for serial production from the date of it's debut flight, has left no doubt that it is not a system that you are claiming or interpreting it to be.
I think the PLAAF has ceased all support to the FC-1 and it is upto PAF to complete the remaining tests and validations, which is why even after 2 years since the production facility in Kamra was declared to begin production, prduction has not yet begun. Instead, PAF is still carrying out tests.

In fact, if I remember from discussions in AFM and ACIG with people who are quite aware with the design of the Su-27 aircraft, the fighter only has a pitch only analog FBW combined with mechanical controls.

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"From the outset the design was to use various combinations
of mechanical hydraulic and fly-by-wire (FBW) controls
with some reduced static stability to achieve
exceptional manoeuvrability."

This says that Su-27 gradually introduced instability with increasing FBW, obviously only so long as the pilot managed to keep the aircraft under control at all times and conditions. If at all the JF-17 would have any instability it would only be slight that can be manageable by the pilot with whatever controls he has been provided. It can't be fully instable (instability is a quantitative measure and not a yes/no aspect) because the pilot won't be able to handle it.

Note that the full-FBW in the other Asian combat jet sends out corrective signals every 10 or 12 milliseconds to keep the aircraft flying stably. This would be beyond the manual control of a pilot.

The DSI would have decreased weight in the front further, pushing the CG further back. So what are you talking about? It only makes the plane more statically unstable.

The objective of introducing instability is to coincide the CG with the Center of Lift. It is only in the supersonic regimes that CG shifts backward which is a phenomenon observed in all aircraft. You said earlier that LERXs would increase instability, but their weight addition was more or less neutralized by the
weight reduction by DSI (to what extent, I can't tell).

Sigh. The historical order of development is not cause and effect. They wanted to verify the FBW in all three axis first for safety and reliability. They did not in fact, originally plan to make the F-4 PACT an unstable aircraft, nor preplanned full FBW as a requirement before making the aircraft unstable.

Please read page 177 of that e-book. It clearly states that instability was mooted only after FBW was introduced and that the PACT-4 aircraft were built only after full FBW was incorporated into the F-4. It is implied that full FBW was the prerequisite for PCAT-4, though it is not mentioned explicitly.