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JF-17 Thunder Multirole Fighter [Thread 6]

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The 'fly-by-wire' flight control system continues to confuse people. But it is understandable...:enjoy:

When the F-16 was under design, the philosophy was to create an exceptionally maneuverable fighter, one that would stress the human pilot more than the aircraft itself could be designed. When we finally admitted that the best the human pilot could withstand is 9g, that became the benchmark for maneuverability. The F-16 was designed with certain g-limit but it was based on the human limit. If General Dynamics wanted to, they could have designed the F-16 to withstand 20g, but what would be the point in that when the human pilot can handle only 9g ? So they designed the F-16 to be 10-ish g-limited. I was on the F-16 for five yrs. I know what 9g felt like on my body and to my vision.

Anyway...How to make such a maneuverable fighter ?

Traditional aircraft designs have always been about stability. The problem is that the higher the airspeed, the greater that stability to the point where the aircraft could not maneuver at all. It may sound somewhat odd but a certain degree of instability is needed to make maneuvers possible. What GD did was designed the F-16 to be unstable, not 'stable with some degrees of instability'. Do not confuse aerodynamics with stability. They are two separate things. Related -- but distinct. It soon became clear that the more unstable the design, the less the human pilot will be able to keep the aircraft under control.

Now there are three distinct items...

- Aerodynamics
- Stability
- Controllability

Item one -- easily done.

Items two and three -- serious problems.

General Dynamics resorted to using computers to replace the flight control system from cockpit to hydraulic actuators. Basically, there are only three truly mechanical components in the FLCS: stick, rudder, hydraulic actuators Everything in between are electrical wires. Some people might nitpick and consider the gyros and accelerometers as also mechanical components but that would be missing the larger point.

The system is a closed loop. At a high level explanation, when the pilot initiate a command thru the stick, the computer respond by moving the hydraulic actuator, which changes the aircraft's attitude such as pitch up/down or wings roll left/right. As the aicraft changes its attitude, the gyros and accelerometers senses the changes and feed that back to the computer, who then compares the result against the pilot's command. The entire loop works fast enough that stability and controllability are achieved and maintained throughout the maneuver, whether it is pitch up/down or wings roll left/right.

So to answer your question: There is no such thing as limited or full FBW FLCS.

What I explained above is either you have a FBW in an FLCS axis or a traditional mechanical FLCS in that axis.

I maybe wrong, but I think you misunderstood the design philosophy of the JF-17. The JF-17 was designed to have pitch instability but roll and yaw are primarily stable, so the pitch axis have FBW-FLCS but roll and yaw are traditional mechanical FLCS. Some people called this as 'limited' but it is incorrect. Does this mean the JF-17 design philosophy is the same as the F-16 ? No. The F-16 have all three axes as unstable.

Some people might say that if an aircraft have FBW-FLCS, that mean the design is unstable. That is incorrect. Airbus and Boeing moved to full FBW-FLCS in all three axes in their highly stable airliners. Weight is a penalty in flight. Airbus and Boeing literally saved thousands of kilos in weight by using FBW-FLCS. The FBW-FLCS actually made maneuvers even more stable and controlled in these large body aircrafts. Take-offs and landings in high and/or cross wind situations are safer because the computers can respond faster to attitude changes, large and small, created by the wind.

Hope that helped.
Thank you :D You did a very good job of explaining
 
:lol: Avionics has nothing to do with digital FBW. Are you sure we are in the same note? Hello?

FBW need to be done at plane design development phase. Software input and source codes. What does avionics do with FBW?
Actually, that is incorrect.

With the current technology, we can install complete three axes FBW-FLCS in any aircraft we want, even WW I era biplane designs. The point is still about weight minimalization in flight. If we design an aircraft with FBW-FLCS from conception, we already eliminated a substantial amount of weight. Volume is a different issue. We can keep the same volume as if we designed the aircraft with traditional mechanical FLCS, but without the bulk of those mechanical components, we can use that volume for other types of cargo.
 
By biggest complaint with this plane is the 7G limit. The biggest priority of PAF should be to improve the airframe to be able to withstand 9g.
 
By biggest complaint with this plane is the 7G limit. The biggest priority of PAF should be to improve the airframe to be able to withstand 9g.
do you even how much load is 7gs for human body
 
Amazing discussion is going on today. Thanks everybody for putting such a mindful content.

A question from @gambit and other informed members, is there anyway we could experience how does 7G or 9G feels like? I understand physically it is not possible outside a simulator or an actual jet but are there any videos which may give us a feel of it?

EDIT: I have actually found a video on it.
 
It so sad there are so many imposter trying to bad mouth JF-17, talking rot of elevator problem without FBW that causes crashed and even more ridiculous comment that we need France assist for FBW in this project.

I can't say any thing to those who bad mouth because they give what they have but regarding France avionics deal it's now an old and dead offer IMO. Even if India didn't go for Rafale I believe we may not go for that deal again because our machine is maturing day by day and the gap between technology and sophistication is narrowed day by day. That is a remote possibility that earlier when we asked France for Avionics so at that particular time we had asked for the FBW as well because China J-10 was not flown till that time and a it's been disclosed later in 2000. Now we have an option of Chinese FBW which is cheaper and reliable as it is in J-10 and have a thousands or may be hundred of thousands of hours logged while flying flawlessly.
 
I can't say any thing to those who bad mouth because they give what they have but regarding France avionics deal it's now an old and dead offer IMO. Even if India didn't go for Rafale I believe we may not go for that deal again because our machine is maturing day by day and the gap between technology and sophistication is narrowed day by day. That is a remote possibility that earlier when we asked France for Avionics so at that particular time we had asked for the FBW as well because China J-10 was not flown till that time and a it's been disclosed later in 2000. Now we have an option of Chinese FBW which is cheaper and reliable as it is in J-10 and have a thousands or may be hundred of thousands of hours logged while flying flawlessly.

Are you serious? J-10 project is started in the 80s and first Pt took to skies in 1998. JF-17 first pt took to skies in 2003. If we do not have FBW technology why would we bother to start JF-17 project? JF-17 is a project mostly undertake by Chengdu CAC, from wind tunnel, manufacturing and design is all done at Chengdu. I do not know how France getting into the picture of FBW as if we Chinese do not know FBW. Then how do J-10 being operational declared in 2003?
 
:lol: Avionics has nothing to do with digital FBW. Are you sure we are in the same note? Hello?

FBW need to be done at plane design development phase. Software input and source codes. What does avionics do with FBW?

I hope we are at the same note.
If we design a conventional aircraft it has to remain in control of pilots hence one can not exceed its performance beyond the performance of a pilot. Where as if we design an aircraft to be flown by computers then we can increase its performance beyond what pilot might be able to handle. The requirement varies with the capabilities of the computers the higher specifications the more unstable the aircraft can be.

Fly by wire basically controls the controlling surfaces electronically through wires which were conventionally controlled by pulleys, cables and strings. FBW system allows reduction in weight.
 
By biggest complaint with this plane is the 7G limit. The biggest priority of PAF should be to improve the airframe to be able to withstand 9g.

what are you posting .... where have you read 7g limitation for JF-17 .... ????
 
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