JF-17 Thunder Multirole Fighter [Thread 7]

[siegecrossbow]

A couple of questions from the Jef experts here which I'm sure have been discussed before several times but are buried somewhere in 100s of threads.

Can someone please get me catch me up with:

1. Is jf 17 a relaxed static stability design or not? If not then is unstable design a key component of 4th gen fighters? What other 4th gen fighters come with a stable design?

2. Can Jef super cruise? The following link says it can: (some more claim the same too, just mentioning one)

Pakistan's JF-17 Aircraft 'Top Contender' For Malaysian Fighter Jet Contract -- Korean Media

JF-17 Thunder - In an interesting twist to the Malaysian Air Force’s hunt for a Light Combat Aircraft, the China-Pakistani JF-17 fighter ‘Thunder’ has now thrown its hat in the ring.

eurasiantimes.com

On wikipedia (which is a very unreliable source) it says jef's cruising speed is 1,359 km/h i.e. Mach 1.1? So can it supercruise? If yes then in what configuration?

@Bilal Khan (Quwa) sir can u help?

1. Block 3 will have relaxed stability in all three axis, which Blocks 1 and 2 don’t have.
2. No

 

[Big_bud]

1. Block 3 will have relaxed stability in all three axis, which Blocks 1 and 2 don’t have.
2. No

Block 3 will have fly by wire I know. But there seems to be no design change otherwise. Fly by wire helps more for jets that are unstable to fly otherwise. For stable designs FBW would not make too much difference is what I know. FBW is not equal to relaxed stability. However FBW is crucial for getting maximum performance out of relaxed stability/unstable design. This is what I have got so far from the googles.

 

[The Raven]

A couple of questions from the Jef experts here which I'm sure have been discussed before several times but are buried somewhere in 100s of threads.

Can someone please help me catch up with these:

1. Is jf 17 a relaxed static stability design or not? If not then is unstable design a key component of 4th gen fighters? What other 4th gen fighters come with a stable design?

2. Can Jef super cruise? The following link says it can: (some more claim the same too, just mentioning one)

Pakistan's JF-17 Aircraft 'Top Contender' For Malaysian Fighter Jet Contract -- Korean Media

JF-17 Thunder - In an interesting twist to the Malaysian Air Force’s hunt for a Light Combat Aircraft, the China-Pakistani JF-17 fighter ‘Thunder’ has now thrown its hat in the ring.

eurasiantimes.com

On wikipedia (which is a very unreliable source) it says jef's cruising speed is 1,359 km/h i.e. Mach 1.1? So can it supercruise? If yes then in what configuration?

@Bilal Khan (Quwa) sir can u help?

1. The JF-17 is not a relaxed stability design, it is statically neutral. A relaxed stability design is not a key attribute of all fourth gen aircraft, it is merely a method for improving manoeuvrability by shifting the centre of gravity aft of the centre of lift, thereby improving instantaneous pitch rate. To control the aircraft FBW is needed, the latest of which is digital redundant (e.g. triplex or quadruplex, although analogue can also be used), especially in the pitch axis, but this can be applied to all three axis. In some cases, a relaxed stability design is not needed, and in fact disadvantageous to the required performance, e.g. the F/A-18 Hornet is a statically neutral design as it was primarily designed with ground strike and attack in mind, requiring neutral stability for accurate weapon delivery, but with the addition of large LERX to augment turn rate performance at high AoA. The JF-17 follows a similar design objective, with neutral stability and large LERX, with very little difference vs a statically unstable design.

2. No, the JF-17 can't surpercruise, at least not in any meaningful weapon/fuel configuration. Perhaps in clean configuration with less than 50% fuel load.

1. Block 3 will have relaxed stability in all three axis, which Blocks 1 and 2 don’t have.
2. No

It doesn't quite work like that. Block III will have digital FBW in all three axis, as apposed to only in pitch for the Block I/II (analogue in roll and yaw), but that doesn't then automatically turn it into a relaxed stability design. As far as I know, all three versions are statically stable designs, with centre of gravity pretty much in line with centre of lift. The all digital FBW design has been adopted to reduce weight and ease of maintenance.

 

[JamD]

A couple of questions from the Jef experts here which I'm sure have been discussed before several times but are buried somewhere in 100s of threads.

Can someone please help me catch up with these:

1. Is jf 17 a relaxed static stability design or not? If not then is unstable design a key component of 4th gen fighters? What other 4th gen fighters come with a stable design?

2. Can Jef super cruise? The following link says it can: (some more claim the same too, just mentioning one)

Pakistan's JF-17 Aircraft 'Top Contender' For Malaysian Fighter Jet Contract -- Korean Media

JF-17 Thunder - In an interesting twist to the Malaysian Air Force’s hunt for a Light Combat Aircraft, the China-Pakistani JF-17 fighter ‘Thunder’ has now thrown its hat in the ring.

eurasiantimes.com

On wikipedia (which is a very unreliable source) it says jef's cruising speed is 1,359 km/h i.e. Mach 1.1? So can it supercruise? If yes then in what configuration?

@Bilal Khan (Quwa) sir can u help?

1. The JF-17 is not a relaxed stability design, it is statically neutral. A relaxed stability design is not a key attribute of all fourth gen aircraft, it is merely a method for improving manoeuvrability by shifting the centre of gravity aft of the centre of lift, thereby improving instantaneous pitch rate. To control the aircraft FBW is needed, the latest of which is digital redundant (e.g. triplex or quadruplex, although analogue can also be used), especially in the pitch axis, but this can be applied to all three axis. In some cases, a relaxed stability design is not needed, and in fact disadvantageous to the required performance, e.g. the F/A-18 Hornet is a statically neutral design as it was primarily designed with ground strike and attack in mind, requiring neutral stability for accurate weapon delivery, but with the addition of large LERX to augment turn rate performance at high AoA. The JF-17 follows a similar design objective, with neutral stability and large LERX, with very little difference vs a statically unstable design.

2. No, the JF-17 can't surpercruise, at least not in any meaningful weapon/fuel configuration. Perhaps in clean configuration with less than 50% fuel load.



It doesn't quite work like that. Block III will have digital FBW in all three axis, as apposed to only in pitch for the Block I/II (analogue in roll and yaw), but that doesn't then automatically turn it into a relaxed stability design. As far as I know, all three versions are statically stable designs, with centre of gravity pretty much in line with centre of lift. The all digital FBW design has been adopted to reduce weight and ease of maintenance.

Just to add some more (possibly unnecessary) detail to @The Raven's excellent post:
Things get even more complicated for fighter jets, which have to fly both subsonic and supersonic. Basically the center of lift shifts significantly (moves aft) as you transition to supersonic flight.

If you want to be stable throughout the envelope (as I suspect JF-17 is) you have to design the subsonic center of lift to be just behind CG but this means supersonically the center of lift moves quite a lot futher back. The moment generated by the lift (about the CG) must be balanced by a tail. Of course the tail must be designed for the worst case (supersonic). Notice tail generates downforce (not lift) so it's wasting energy in cruise.

As you can probably imagine, you can have the situation where your jet is stable supersonic but unstable subsonic.

Here your tail can be smaller and actually produces lift subsonically. BUT now you require active stabilization in subsonic flight.



Finally you can have

This is the kind of situation you have in aircraft like X-29 (nevermind that it has a canard instead of a horizontal tail). In this design you are always unstable but you never produce unecessary downforce so you are aerodynamically efficient.


So in addition to the advantage in turn rate, being unstable makes you cruise more efficiently (that is you can fly further on less fuel) because you don't produce downforce and your tail can be smaller sometimes.

So why aren't all jets unstable then?
1. You require active stabilization through FBW system - this can be expensive and/or heavy and/or out of your technological ability.
2. Being unstable imposes fundamental limitations on robustness to off-nominal behaviour. So an unstable design stabilized by a control system is more sensitive to changes in weight distribution etc than a stable design, and might be less versatile.

Sorry if this is too much detail lol.

 

[White and Green with M/S]

A couple of questions from the Jef experts here which I'm sure have been discussed before several times but are buried somewhere in 100s of threads.

Can someone please help me catch up with these:

1. Is jf 17 a relaxed static stability design or not? If not then is unstable design a key component of 4th gen fighters? What other 4th gen fighters come with a stable design?

2. Can Jef super cruise? The following link says it can: (some more claim the same too, just mentioning one)

Pakistan's JF-17 Aircraft 'Top Contender' For Malaysian Fighter Jet Contract -- Korean Media

JF-17 Thunder - In an interesting twist to the Malaysian Air Force’s hunt for a Light Combat Aircraft, the China-Pakistani JF-17 fighter ‘Thunder’ has now thrown its hat in the ring.

eurasiantimes.com

On wikipedia (which is a very unreliable source) it says jef's cruising speed is 1,359 km/h i.e. Mach 1.1? So can it supercruise? If yes then in what configuration?

@Bilal Khan (Quwa) sir can u help?

Yes , JFT is the relaxed stability design, its design inspired by F-16 design, if this design is not relaxed stability design than tell me why its using fly by wire system (first hybrid 1x fly by wire and 2x mechanical system) for JF-17 block-1 and 2, and now for block-3 this will have be 3x digital fly by wire system, that's means JF-17 is relax static stability design

may be J-17 can super cruise on clean configurations ( without any weapons) but with weapons it can't be super cruise i think, and not needed to have a super cruise capability

Block 3 will have fly by wire I know. But there seems to be no design change otherwise. Fly by wire helps more for jets that are unstable to fly otherwise. For stable designs FBW would not make too much difference is what I know. FBW is not equal to relaxed stability. However FBW is crucial for getting maximum performance out of relaxed stability/unstable design. This is what I have got so far from the googles.

Jf-17 is a unstable/relax stable design inspired by F-16

 

[The Raven]

Yes , JFT is the relaxed stability design, its design inspired by F-16 design, if this design is not relaxed stability design than tell me why its using fly by wire system (first hybrid 1x fly by wire and 2x mechanical system) for JF-17 block-1 and 2, and now for block-3 this will have be 3x digital fly by wire system, that's means JF-17 is relax static stability design

may be J-17 can super cruise on clean configurations ( without any weapons) but with weapons it can't be super cruise i think, and not needed to have a super cruise capability

Jf-17 is a unstable/relax stable design inspired by F-16

Just because an aircraft has a FBW FCS (whether digital or analogue) doesn't necessarily mean that it has relaxed stability, case in point; F/A-18 Hornet. Block I/II aircraft have quadruplex digital FBW in pitch axis and analogue FBW in roll and yaw, while Block III and the B model have quadruplex digital FBW in all three axis. The move to an all digital FBW was mainly to save weight and ease maintenance, it has nothing to do with whether the aircraft has relaxed stability or not.

 

[ghazi52]

 

[ProudPak]

PAF official website showing dual rail sd-10 on JF-17. Pic posted few hrs ago.

Anything coming up.

https://www.facebook.com/207826782931454/posts/1399558030424984

Where is the dual rail
That looks like individual hardpoints

 

[Pampa]

View attachment 753845

Real o CGI? Block 1 with IFR?
Regards

 

[White and Green with M/S]

Just because an aircraft has a FBW FCS (whether digital or analogue) doesn't necessarily mean that it has relaxed stability, case in point; F/A-18 Hornet. Block I/II aircraft have quadruplex digital FBW in pitch axis and analogue FBW in roll and yaw, while Block III and the B model have quadruplex digital FBW in all three axis. The move to an all digital FBW was mainly to save weight and ease maintenance, it has nothing to do with whether the aircraft has relaxed stability or not.

buddy its a design based Russian/Soviet rejected project 33 which was similar in design that of F-16 its center of gravity and pressure just like F-16 or Mig-29, so most probably its a relax stability design

 

[Thorough Pro]

That is a dual rail, look closely

Where is the dual rail
That looks like individual hardpoints

 

[m52k85]

Just to add some more (possibly unnecessary) detail to @The Raven's excellent post:
Things get even more complicated for fighter jets, which have to fly both subsonic and supersonic. Basically the center of lift shifts significantly (moves aft) as you transition to supersonic flight.
View attachment 753916
If you want to be stable throughout the envelope (as I suspect JF-17 is) you have to design the subsonic center of lift to be just behind CG but this means supersonically the center of lift moves quite a lot futher back. The moment generated by the lift (about the CG) must be balanced by a tail. Of course the tail must be designed for the worst case (supersonic). Notice tail generates downforce (not lift) so it's wasting energy in cruise.

As you can probably imagine, you can have the situation where your jet is stable supersonic but unstable subsonic.
View attachment 753917
Here your tail can be smaller and actually produces lift subsonically. BUT now you require active stabilization in subsonic flight.



Finally you can have
View attachment 753918
This is the kind of situation you have in aircraft like X-29 (nevermind that it has a canard instead of a horizontal tail). In this design you are always unstable but you never produce unecessary downforce so you are aerodynamically efficient.


So in addition to the advantage in turn rate, being unstable makes you cruise more efficiently (that is you can fly further on less fuel) because you don't produce downforce and your tail can be smaller sometimes.

So why aren't all jets unstable then?
1. You require active stabilization through FBW system - this can be expensive and/or heavy and/or out of your technological ability.
2. Being unstable imposes fundamental limitations on robustness to off-nominal behaviour. So an unstable design stabilized by a control system is more sensitive to changes in weight distribution etc than a stable design, and might be less versatile.

Sorry if this is too much detail lol.

So does this mean we can watch the tail closely in level sub-sonic flight, and if it is deflected, then that conclusively implies a stable design? Can such a thing be eye balled from HiRes videos/ pictures?

 

[JamD]

So does this mean we can watch the tail closely in level sub-sonic flight, and if it is deflected, then that conclusively implies a stable design? Can such a thing be eye balled from HiRes videos/ pictures?

Theoretically yes. Practically no. It would also depend on loads fuel altitude speed etc. What I have presented is a simplified picture for understanding things.

 

[m52k85]

Theoretically yes. Practically no. It would also depend on loads fuel altitude speed etc. What I have presented is a simplified picture for understanding things.

In case you havent already seen this, he does a lot of eye-balling on the control surfaces, but I realize it for less subtle things. In any case i thought you would enjoy it:

 

[Scorpiooo]

India has already committed by buying Rafale, what are they going to do if Pakistan gets the meteor? Will they not buy the planes or the missiles, after all they've already dumped a crap ton of money into it.

Do you really think French's will give meteor to Pakistan, why they want to make angry there milking cow (india)