New JF-17/FC-1 Fighter Aircraft thread

[Indianfighter]

Originally Posted by crobato

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 this page >>

"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 here).

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.

Originally Posted by crobato

"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.

Originally Posted by crobato

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 F-15 Part II Directional control, which entirely deals with trimming. See also F-15 Part III- Lateral Control.

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.

Originally Posted by crobato

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.

Originally Posted by crobato

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.

Originally Posted by crobato

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.

http://www.ausairpower.net/TE-Flankers-Aug03.pdf

"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.

Originally Posted by crobato

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).

Originally Posted by crobato

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.

[crobato]

LOL. I did not say that the F-15 is unstable. I am saying it struck you that it has combined electronic and mechanical controls.

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.

Read the text again. That is incorrect.

What's being done here is quite similar to what airliners use for their FBW which is a feedback and response system running according to control rules.

Based on your definition, analog FBW would not be "intelligent" at all either because that's not much different from analog FBW.

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.

LOL. Can you define what partial FBW means eh?

You're playing desperately with words. What does partial FBW means? It would have meant fractional control between manual and electronic controls. How is that much different from control and stability augmentation/intervention? There is no such things as "partial" FBW because that is a contradiction in meaning, hence you won't see any industry usage of that term.

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.

.

Except that the industry does not use the term "partial" FBW because suchv a term is self contradictory on its own meaning. The F-20 tried to use it because of "marketing", but it really is hybrid.

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.

Nonsense logic, to use certification times as "proof" that the plane cannot be unstable.

I've already destroyed that logic with real examples, such as how quickly the YF-16, YF-17, X-32, and X-35 are doing aerobatics right off from their earliest prototypes. And along with the F-CK-1 fighter which went from prototype to certification in only three years. Furthermore, certification has a whole lot to do with a lots of other factors other than flight stability. Avionics testing. Reliability testing. Stress testing.

Another clue to the flight testing is that there has been more prototypes built of the FC-1 faster and in any given time than the history of the other "Asian" fighter, which enables the plane to log more flight hours faster.


This is not to mention that certification involved far more factors other than flight stability testing, such as reliability testing, stress testing, avionics integration, specification changes. That's common sense to everyone reading this. It should be noted that the FC-1 did not set very high only reasonable goals on these, and is there is very little specification changes.

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.

It is CAC and AVIC that continues to support the FC-1 and continues to do all all ther tests and validations. So it is CHINA that continues to support the plane, period. They know they have a winner that can make serious money on, and the government sees the diplomatic opportunities provided by the arms sales. Ironically its the PLAAF that may have a tendency to slow things down due to specification changes.

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.

Relaxed stability is just another term used interchangeably with static instability. Again you're playing with words. Do you think that by playing with language you can change reality. And what the heck gradually introduced instability with "increasing" FBW. Note the final product---pitch axis only FBW with relaxed stability (aka negative static stability).

Standard accepted definition of Relaxed Stability.

http://en.wikipedia.org/wiki/Relaxed_stability

In aviation, relaxed stability is the tendency of an aircraft to change its attitude and angle of bank on its own accord. An aircraft with relaxed stability will oscillate in simple harmonic motion around a particular attitude at an increasing amplitude.

This can be contrasted with the tendency of an aircraft with positive stability, which, when trimmed to fly at a certain attitude, will continue to do so in the absence of control input, and will oscillate in simple harmonic motion on a decreasing scale around the trimmed attitude, eventually returning to its trimmed attitude. A positively stable aircraft will also resist any bank movement. A Cessna 152 is an example of a stable aircraft. Similarly, an aircraft with "neutral stability" will not return to its trimmed setting without control input, but will oscillate in simple harmonic motion around the trimmed setting continuously and be susceptible to bank influences.

That's practically sounds like static instability, does it not?

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.

What you described happens in all planes. Instability always enters the system once the aircraft is in flight. That would be "dynamic" instability, and frankly FBW is also meant to reduce that.



What is "fully" instable means? "Fully instable" means that not even the FBW can handle it. So even with a plane that has FBW, it can only be instable to a certain degree, and that degree or static margins is rather small. A plane is either statically stable or not. Even if the plane can still be managed by manual controls (the Japanese F-2 as based on the F-16 can) it can be considered statically unstable.

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.

LOL. How often you make feed back corrections has nothing to do with manual flyability. You can be doing trim corrections to optimize speed and cruising efficiency. If you are making small, very fast corrections, then the control surface deflections should be very small and minor.

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.

And READ AGAIN MY LIPS. It is not CAUSE and EFFECT. Otherwise, based on historical examples, a tyrannical autocracy would be the precondition for a democracy.

The Su-27 by every other account is considered a statically unstable aircraft and it only has a pitch axis FBW.

The objective of introducing instability is to coincide the CG with the Center of Lift.

No. It is to move the center of lift ahead of the CG. If the CL coincides with CG, it would be stable.

Basic encyclopedia reference and terminolory.

http://en.wikipedia.org/wiki/Static_margin

Relationship to aircraft and missile stability and control

* If the center of gravity (CG) of an aircraft is forward of the neutral point, or the CG of a missile is forward of the center of pressure, the vehicle will respond to a disturbance by producing an aerodynamic moment that returns the angle of attack of the vehicle towards the angle that existed prior to the disturbance.
* If the CG of an aircraft is behind the neutral point, or the CG of a missile is behind the center of pressure, the vehicle will respond to a disturbance by producing an aerodynamic moment that continues to drive the angle of attack of the vehicle further away from the starting position.

The first condition above is positive static stability. In missile analysis this is described as positive static margin. (In aircraft analysis it may be described as negative static margin.)
The second condition above is negative static stability. In missile analysis this is defined as negative static margin. (In aircraft analysis it may be described as positive static margin.)

It is only in the supersonic regimes that CG shifts backward which is a phenomenon observed in all aircraft.

That would be dynamic and only does so in acceleration. Static instability means instable at rest (static = rest) as in no control input and stable speed.

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).

You don't seem to get it do you? The LERX by increasing lift area moves the center of lift further forward, and considering they're bigger than the previous LERX, means it simultaneously increases the lifting forces while moving the CL forward. Then add the weight decrease of the DSI to that.

[Indianfighter]

Originally Posted by crobato

LOL. I did not say that the F-15 is unstable. I am saying it struck you that it has combined electronic and mechanical controls.

That's exactly what I've described since post #670, which on the F-15 is an electronic system that is between the hydromechanical linkages between the joystick and the control surfaces. It is not biomechanical. It is electronic, we know. So I can't understand the "shock" that you are attributing when there is none.

Originally Posted by crobato

Read the text again. That is incorrect.

What's being done here is quite similar to what airliners use for their FBW which is a feedback and response system running according to control rules.

Based on your definition, analog FBW would not be "intelligent" at all either because that's not much different from analog FBW.

No. The CAS on the F-15 is indeed a feedback control system that autonomously takes corrective action by sending electrical pulses to exercise it's X% of control authority on the surface. There is no computerized decision-making involved or invoked in this process.

In the F-20, the CAS also sends electrical pulses to exert it's control over the X% of control authority that it has been granted; but with the important difference that there is programmed decision making involved to decide on the electrical pulsing by considering flight conditions, stability maintenance, besides of course, the usual countering of unwanted oscillations (SAS).

Analog FBW in the Avro Vulcan was without any computer in the loop, but in the YF-16, there was a computerized analog FBW.

Originally Posted by crobato

LOL. Can you define what partial FBW means eh?

You're playing desperately with words. What does partial FBW means? It would have meant fractional control between manual and electronic controls. How is that much different from control and stability augmentation/intervention? There is no such things as "partial" FBW because that is a contradiction in meaning, hence you won't see any industry usage of that term.

Ok. But you can definitely find the terms "Partial authority FBW" and "Full authority FBW", which is a common industry term. The FC-1 has full authority FBW in the pitch axis and none at all in the remaining ones. If the FC-1 would have indeed had "Partial authority FBW" in the other two axes, there would have been a mention (no matter how brief).

Originally Posted by crobato

I've already destroyed that logic with real examples, such as how quickly the YF-16, YF-17, X-32, and X-35 are doing aerobatics right off from their earliest prototypes. And along with the F-CK-1 fighter which went from prototype to certification in only three years. Furthermore, certification has a whole lot to do with a lots of other factors other than flight stability. Avionics testing. Reliability testing. Stress testing.

The YF-16 was an analog FBW system which also took 5 years before it could be cleared and begin serial manufacture. Acrobatics at Air-shows can be performed by any fighter aircraft even at the early stages of flight-testing (we have an example in India). This is for aircraft that have been developed for the first time, which was not the scenario for Ching Kuo and F-2. These were essentially duplicative efforts of past successful projects.

Originally Posted by crobato

Another clue to the flight testing is that there has been more prototypes built of the FC-1 faster and in any given time than the history of the other "Asian" fighter, which enables the plane to log more flight hours faster.

The former began testing 2 1/2 years earlier and by the time FC-1 debuted, it had 3 prototypes flying already, having logged over 200 flights. As of 2006, the number of prototypes of both were the same.

The FC-1 is actually continuing the remaining tests under the PAF, after the PLAAF discontinued further testing. The production facility was inaugurated in Kamra 3 years ago but little else happened during this span of time.

Originally Posted by crobato

And what the heck gradually introduced instability with "increasing" FBW. Note the final product---pitch axis only FBW with relaxed stability (aka negative static stability).

I think you haven't read the statement carefully. It says, "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."

There is some relaxed static stability, which obviously is upto a limit that the pilot can handle. "Various combinations of controls" was probably an experimentation, or gradual increase in the control system to match the decrease in relaxed static stability.

Originally Posted by crobato

What is "fully" instable means? "Fully instable" means that not even the FBW can handle it. So even with a plane that has FBW, it can only be instable to a certain degree, and that degree or static margins is rather small. A plane is either statically stable or not.

As I said earlier, stability is quantitative measure unlike true-false. But fully instable would mean the point where the pilot can no longer control the aircraft unlike the Su-27 SDU-10 in which instability was introduced gradually in such a way that it would still be controllable by the limited FBW capabity given to the pilot.

Originally Posted by crobato

Even if the plane can still be managed by manual controls (the Japanese F-2 as based on the F-16 can) it can be considered statically unstable.

F-2 has a partial control authority FBW like F-20.

Originally Posted by crobato

LOL. How often you make feed back corrections has nothing to do with manual flyability. You can be doing trim corrections to optimize speed and cruising efficiency. If you are making small, very fast corrections, then the control surface deflections should be very small and minor.

The FBW takes corrective actions depending on the instantaneous flight conditions to not only maintain a state of stability but also to maintain ideal optimum control surface deflections.

Originally Posted by crobato

And READ AGAIN MY LIPS. It is not CAUSE and EFFECT. Otherwise, based on historical examples, a tyrannical autocracy would be the precondition for a democracy.

You please read my posts. It is not explicitly mentioned, but it is obvious that full FBW was introduced only so as to facilitate the smooth transition to instability. It was only after that the precondition or prerequisite of full FBW was fulfilled, that the aircraft was made instable. To take your example, despotic regimes are supplanted by civil societies instead of assisting them. Full FBW assists the control of instable aircraft and is not an independent addition on an aircraft.

A highly instable aircraft implies full FBW in all the three axes, but the converse does not hold true.

Originally Posted by crobato

The Su-27 by every other account is considered a statically unstable aircraft and it only has a pitch axis FBW.

It has very limited relaxed static stability only enough for the pilot to handle with whatever controls he is provided. If at all the JF-17 has any static instability, it would be only be severely limited to what can be handled by the pilot. It wouldn't be too deviant from a stable aircraft.

Originally Posted by crobato

No. It is to move the center of lift ahead of the CG. If the CL coincides with CG, it would be stable.

There I agree you are right and I was wrong. But if CL coincides with CG it would be neutral, or in other words the zone between stability and instability. In such a case, it would continue in the direction of trim. It won't dampeningly oscillate to stability, nor increasingly oscillate out of control.

Originally Posted by crobato

You don't seem to get it do you? The LERX by increasing lift area moves the center of lift further forward, and considering they're bigger than the previous LERX, means it simultaneously increases the lifting forces while moving the CL forward. Then add the weight decrease of the DSI to that.

That's a matter of observation. Canards for example, increase weight in the front but also shift the CL to the front. But still it is claimed that canards are "natural instability devices". As I said before, LERXs also add weight to the front which could be offset by weight loss due to DSI, to an unknown extent. So you cannot definitely claim that this has led to sure instability.

[antimatter]

IndianFighter, are you involved in the works of Indian indegenous plane, LCA? what do you think of it?

[PrOeLiTeZ]

lol this thread is so off topic, but I'm enjoying reading the debate between Indianfighter and Crobato though...come on you two start leaning back towards the JF-17 area of engineering

[Indianfighter]

Originally Posted by antimatter

IndianFighter, are you involved in the works of Indian indegenous plane, LCA? what do you think of it?

No I'm not. Discussion about it is banned on this thread so it's off topic. It's not too different from the JF-17.

Originally Posted by PrOeLiTez

lol this thread is so off topic, but I'm enjoying reading the debate between Indianfighter and Crobato though...come on you two start leaning back towards the JF-17 area of engineering

It is not exactly offtopic because other examples like F-15 ,F-20 and Cessna were taken up to determine what kind of FCS the JF-17 has. I am not continuing the debate beyond this.

I think what the FC-1 needs now most is commitment, else an otherwise very decent 4th generation combat jet will not be used to it's full potential. For this PLAAF's support would be crucial. PAF has managed to clear the engine issue and further tests, integration of a European avionics package, and integrating weapons definitely can't be done by PAF on it's own.

[Munir]

I do not agree that is is comparable... I means that F16 is exactly the same as Mirage 2000... It means 24/7 ecocomy is same as 100% foreign input. It means a few hardly finished planes are same as more then a squadron on testing while first operational squadron is being built.


I do not say one plane is better or worser but I do say hese programs may have same ideology (light fighter) the results are not comparable. Not financially, not technology, not operaionally and a lot more.

I am amused that I have to go several pages of text where an Indian says that JF17 has no fully bvr and ou chinese friend says it does. We do know forums are there to do that but it is a waste of bandwith to repeat this. It isn't even comparble with the Mentos add. Atleast there they both produced the product. Here the Chinese produce it and and an Indian tells that it is not having certain specifications. Weird. Does it matter when it comes to agility? Probably not.

About experts and posters. Tphuang tells on AFM that he thinks that FC20 is not lot different with the basic J10. So the AFM and the Pakistani ACM are dumbo's? If the J10 is not much better then why would the ACM say so on several occasions? If the FC20 is not much better then why paying lots of time and cash to get almost the same?
I do not believe that FC20 is superb or matured but alteast I do believe people that know the details and publish the facts instead of opinions.


crobato, Good work. You do have lots of knowledge and logic.

[Gollevainen]

Murin, you could restain yourself by generalising JF-17 doupters as "Indians". If I spot you repeating it, I will issue you a warning based on racial discrimination.

Gollevainen
Super mod.

[Munir]

I was lazy to type Indianfighter... So assumed Indian would be easier to do and understandable for most. But if you ask me to type the next time Indianfighter then so be it, you do have a point about generalizing. That tends to be a bad habbit but the web is filled with those people. Point taken. Next time I will post names like those that are generally negative about the Chinese fc1 or those that adore...

I accept the warning now instead of being treated soft.

[crobato]

Originally Posted by Indianfighter

That's exactly what I've described since post #670, which on the F-15 is an electronic system that is between the hydromechanical linkages between the joystick and the control surfaces. It is not biomechanical. It is electronic, we know. So I can't understand the "shock" that you are attributing when there is none.


No. The CAS on the F-15 is indeed a feedback control system that autonomously takes corrective action by sending electrical pulses to exercise it's X% of control authority on the surface. There is no computerized decision-making involved or invoked in this process.

So sorry but it does. You are contradicting yourself and you are simply wrong. An FBW is a feedback control system nonetheless. A computerized application is nothing more than a feedback control system, and any system that does this must have control rules, which does not necessarily require a digital system to implement this.

Otherwise by your invented definition, analog FBW, which does not use digital computers per se, isn't FBW at all.

In the F-20, the CAS also sends electrical pulses to exert it's control over the X% of control authority that it has been granted; but with the important difference that there is programmed decision making involved to decide on the electrical pulsing by considering flight conditions, stability maintenance, besides of course, the usual countering of unwanted oscillations (SAS).

Analog FBW in the Avro Vulcan was without any computer in the loop, but in the YF-16, there was a computerized analog FBW.

And how is that different from the F-15's system? Oh please, don't think its that simple. The author only makes it seems readably "simply" for laymen education purposes, but don't assume that it would actually be that "simple" based on simple description. Systems like this would require multiple volumes of thick books to fully explain.

And what exactly is a "computerized analog"?

You keep inventing definitions as you go on. You don't understand the basic nature of electronics at all and at the same time applying double standards.

Analog FBW isn't much different from the system being described in the F-15. For that matter, all digital FBW does in civil airliners are nothing but control and stability augmentation, no different here.

Read the basic principle of cybernetics which covers flight control theory.

http://en.wikipedia.org/wiki/Cybernetics


"circular, causal chains that move from action to sensing to comparison with desired goal to action."

The F-15's system fits well within this category of cybernetic cyclical feedback and control system that essentially also governs FBW. The system in the Avro, F-16 and Su-27 isn't that much different here, all are cybernetic systems.

You also imply that the F-15's system does not have any programmed control laws. BS. The design itself is like any analog computer and it is an analog computer, where the design itself is an implementation of programmed control laws. Any self regulating system by its very definition---self regulation---has control laws that determines that regulation.

Ok. But you can definitely find the terms "Partial authority FBW" and "Full authority FBW", which is a common industry term. The FC-1 has full authority FBW in the pitch axis and none at all in the remaining ones. If the FC-1 would have indeed had "Partial authority FBW" in the other two axes, there would have been a mention (no matter how brief).

WRONG. Partial authority FBW is never a common industry term. You invented it. Show me an article that actually mentions this.

The fact that the FC-1 has stability augmentation at the other two axis shows you there is FBW intervention in those axis. There is no such thing in the industry where you have FBW and have separate SAS units in the other axis because such a plane by principle would have been unflyable, due to independent decision making at all three axis.

If you wish, show me an example how that is possible.

The YF-16 was an analog FBW system which also took 5 years before it could be cleared and begin serial manufacture. Acrobatics at Air-shows can be performed by any fighter aircraft even at the early stages of flight-testing (we have an example in India). This is for aircraft that have been developed for the first time, which was not the scenario for Ching Kuo and F-2. These were essentially duplicative efforts of past successful projects.

Wrong. You assumed that the F-16's entire development time is the FBW's development time.

CLEARLY WRONG.

Sorry but your example in India wasn't making aerobatics early in its flight testing. And even now, the recent videos is underwhelming as it does not show high angles of attack. The first flight video was in fact a plane taking off, cruising for a moment over an airfield, then landing. The JF-17 was literally diving, then doing zoom climbs and making loops in its first "official" (as in front of officials) flight a month after it first came out of the factor.

The former began testing 2 1/2 years earlier and by the time FC-1 debuted, it had 3 prototypes flying already, having logged over 200 flights. As of 2006, the number of prototypes of both were the same.

Why don't you show how many prototypes you have in the first year, eh? You didn't have second or third prototypes made in the first year, which the JF-17 has.

Compare that to the J-10 project. Prototype 01 retired after having more than 3,500 flight hours. Note the plane flew for the first time in March 1997, and there has been over 15 prototypes ever since.

The FC-1 is actually continuing the remaining tests under the PAF, after the PLAAF discontinued further testing. The production facility was inaugurated in Kamra 3 years ago but little else happened during this span of time.

WRONG. What makes you think you will get away with this lie eh? You don't know anything about the JF-17 program and whatever happened to it. The PLAAF never tested it, all testing was under the auspices of CAC and AVIC corporation, and is still doing so.

I think you haven't read the statement carefully. It says, "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."

There is some relaxed static stability, which obviously is upto a limit that the pilot can handle. "Various combinations of controls" was probably an experimentation, or gradual increase in the control system to match the decrease in relaxed static stability.


As I said earlier, stability is quantitative measure unlike true-false. But fully instable would mean the point where the pilot can no longer control the aircraft unlike the Su-27 SDU-10 in which instability was introduced gradually in such a way that it would still be controllable by the limited FBW capabity given to the pilot.

WRONG again. You simply don't know anything about the topic.

A plane is either stable or unstable. There is a point where its black and white.

Read again what is the term of "relaxed stability"---which is the industry term for what you are saying "instability".

Either the plane returns to its original position even if no control authority is exerted (stable), or the plane continues to depart away further from its original direction if no control authority is exerted (unstable).

This is either or.

Even if the plane is unstable, it does not mean its not controllable.

You are once again inventing what the Su-27 does, all wrong and has nothing to do with reality.

First of all, you are hinging your argument on a totally made up concept that stability and instability has something to do with human controllability and manageability, which is clearly wrong. The concepts of both hinges on flight behavior, and whether its controllable by human is entirely a different matter.

There is no such thing as instability being introduced gradually (changes in stability in flight are all dynamic and does not necessarily come with a curve). Why don't you explain how that happens? By increasing speed? LOL, when you increase speed, stability tends to increase due to the wind flow around the plane that has to be countered by increased control authority. The Su-27, like all planes, is most maneuverable at low speeds. Otherwise all those airshow maneuvers won't be possible. Let me point out to you that while the SDU-10 has pitch only FBW, its FCS handles stability augmentation in all three axis, clearly implying intervention or overlay in the roll and yaw axis. All FCS are at the bare minimum, should handle all three axis.

F-2 has a partial control authority FBW like F-20.

WRONG.

The F-2 has three redundant FBW channels, and a complete mechanical backup.

The FBW takes corrective actions depending on the instantaneous flight conditions to not only maintain a state of stability but also to maintain ideal optimum control surface deflections.

No different from any CAS/SAS system.

You please read my posts. It is not explicitly mentioned, but it is obvious that full FBW was introduced only so as to facilitate the smooth transition to instability. It was only after that the precondition or prerequisite of full FBW was fulfilled, that the aircraft was made instable. To take your example, despotic regimes are supplanted by civil societies instead of assisting them. Full FBW assists the control of instable aircraft and is not an independent addition on an aircraft.

Oh please, reread the history given to you by Wright AB. The change to instability happened long after the YF-16 and quite some time after the initial PACT tests were made. The decision (not original) was made later to further test.

Again, what you are saying is not a technical proof of your made up condition that a plane that is pitch unstable requires FBW in all three axis. Clearly disproven by the Su-27 example.

A highly instable aircraft implies full FBW in all the three axes, but the converse does not hold true.

That's nonsense. From the first place there is no such thing as a very highly unstable aircraft. Try reading about basic aerodynamics for a while. A highly unstable plane is not a flyable plane at all. You are implying about a plane with high positive static margins, but so sorry even FBW, no matter how sophisticated, has its limits, and no aircraft---especially fighters---really has high positive static margins because there is a point not just of diminishing returns but where it becomes counterproductive. Furthermore, mechanically the most unflyable aircraft---those with good static margins---are not exactly the most maneuverable either. Look at the B-2 and F-117 as examples.

It has very limited relaxed static stability only enough for the pilot to handle with whatever controls he is provided. If at all the JF-17 has any static instability, it would be only be severely limited to what can be handled by the pilot. It wouldn't be too deviant from a stable aircraft.

Complete nonsense. The Su-27 clearly has relaxed stability and that's all what it takes. You don't know the actual % of static margin the Su-27 has until you show some documentation.

There I agree you are right and I was wrong. But if CL coincides with CG it would be neutral, or in other words the zone between stability and instability.

This is the only thing correct you said so far.

In such a case, it would continue in the direction of trim. It won't dampeningly oscillate to stability, nor increasingly oscillate out of control.


That's a matter of observation. Canards for example, increase weight in the front but also shift the CL to the front. But still it is claimed that canards are "natural instability devices". As I said before, LERXs also add weight to the front which could be offset by weight loss due to DSI, to an unknown extent. So you cannot definitely claim that this has led to sure instability.

Canards add lift far more than its weight. Let me point out to you that the main weight added by canards comes from its control mechanisms, and not the wing itself.

Which brings the point of the DSI in the JF-17. How did it save weight? By removing the control mechanisms used by the variable intake. Did the new LERX add control mechanisms? No

The weight loss is by the removal of mechanisms. Increasing the LERX would not have matched the weight caused by such mechanisms. So its impossible for the LERX itself to offset the weight loss caused the removable of the control mechanisms in the intake.

[Nomi929]

Pakistan Air Force looking towards western engine for their JF-17 Thunders.

[Deino]

Originally Posted by Nomi929

Pakistan Air Force looking towards western engine for their JF-17 Thunders.

Is that just Your personal opinion or only a statement ??? If not please tell us the source !!

In my opinion that's completely ridiculous as it would waste additional time and –again IMO – there’s no Western engine available that fits just in place ! It would take much too long to redesign the rear-fuselage, no Western aero-engine-manufacture would be allowed to deliver any of its high-end turbofans to Chengdu to assist the integration and for the PAF such an aircraft would come much too late.

IMO they will probably wait for the WS-13.

Deino

[Nomi929]

Originally Posted by Deino

Is that just Your personal opinion or only a statement ??? If not please tell us the source !!

In my opinion that's completely ridiculous as it would waste additional time and –again IMO – there’s no Western engine available that fits just in place ! It would take much too long to redesign the rear-fuselage, no Western aero-engine-manufacture would be allowed to deliver any of its high-end turbofans to Chengdu to assist the integration and for the PAF such an aircraft would come much too late.

IMO they will probably wait for the WS-13.

Deino

Its not my Personal opinion or wish!

PAF Air Chief today in an TV interview said that they are also looking for Western Engine for JF-17.

Reasons he gave are

1) PAF not fully satisfied with Performence of RD-93.
2) Life span of Russian/Chinese engine is 1/4th of western engine.

He also said that, current batch of 50 aircrafts will be of this Russian engine and Chinese Radar + missies.

For the next Batch of 50, they will consider French offer for Thales RC-400 + MBDA MICA along with other western options, and compare it with what Chinese has to offer at that time.

Regarding Western Engines , PAF has been using and maintaing SNECMA engines for last three deacdes.

So there might some solution from the french on the table. Some existing engine (like of SNECMA used in Mirage 2005) can be modified to fit into JF-17.

Best Regards.

[Totoro]

They're trying to get the best deal possible out of chinese, once the second contract for the second batch becomes a reality. It's called healthy competition. It's certainly possible but there's many things to be taken into account, especially considering it's a decision to be made in a few years and not now. Too many to say if it is probable.

[Nomi929]

Originally Posted by Totoro

They're trying to get the best deal possible out of chinese, once the second contract for the second batch becomes a reality. It's called healthy competition. It's certainly possible but there's many things to be taken into account, especially considering it's a decision to be made in a few years and not now. Too many to say if it is probable.

NO!

PAF chief said that decision about second batch of jf-17 (Avionics+Engine) will be finalized within next 12 months.