JF-17/FC-1 Fighter Aircraft thread

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fishhead

Banned Idiot
Re: New JF-17/FC-1 thread

I think intake location is a bit favor of taste instead of good or bad thing. Overall said, intake under belly is better, since it makes the design simpler and the body has more space for equipments.

But smaller airplane doesn't have that luxury since its height clerance is low so they put intake to the sides. Note that all small airplanes have that design, including LCA.
 
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Scratch

Captain
Re: New JF-17/FC-1 thread

Why should just height clearance be a problem? You could just put the front gear under/into the intake, maintaining enough space. If the rear legs stay short, you might get an aircraft that has it's nose up on the ground, shouldn't be that bad either.
And the FC-1 is not really smaller than a F-16.
And I would argue that LCA does not have the intakes at the side of the belly like the FC-1 has, they are somewhat under the wings.
 

crobato

Colonel
VIP Professional
Re: New JF-17/FC-1 thread

A bit late now but some thoughts of mine I made up during that aerodynamics discussion several days ago.

Somehow I'm of the impression that aircraft inteded for high AoAs, at least in greater speed regimes, should have their intakes somewhere under the wing(root)s or the fuselage where the airflow can be forced into the induct.

This design you speak of, is actually pioneered by Jack Northrop. The idea is to use the LERX to create a boundary layer that flows into the engine intakes. The first planes to ever use this principle, was from Jack Northrop's company. Of course everyone copied it since then and the Russians have their own independent and parallel development.

Please note that the intake does not necessarily have to be under the LERX, an idea started by the YF-17 Cobra, but also on top. As a matter of fact, this is exactly the same principle on the F-5, the YF-17's direct ancestor, introduced first on the T-38 Talon trainers.

But this all moot for the JF-17, which uses a different principle in scooping air to the intakes, a process not unlike that of the Rafale and the F-35. Rather, the nose is V canted. That actually draws the air into the intakes at high AoA. The concept goes back to the original Grumman Super 7 design, which does have this V shaped walls along the side of the nose, and the concept is recentely resurrected on the JL-9.

Furthermore, the DSI intakes acts like Northrop's LERX by diverting and compressing the boundary air layer into the intake. It is also interesting to note that the edge of the intake at the bottom is forward of the edge on top, making it look like a "\", in contrast where in many planes, looking at the side of the intake, the edge looks like a "/". Clever, daring move, the idea again, harks back to the intakes Northrop designed for the Talon---moving the air upward, rather than downward.

For the F-16, the Typhoon and the J-10, it's different though, they use the underside of the nose to divert airflow into the engine.

Is it therefore correct to assume the FC-1's LERX are not primarily for vortex generation since the aircraft is not really meant to operate in high AoAs?

Since I have explained that the design is indeed suited for high AoA, then this is not true.

One should note however that the design of the LERX is closer to the F-18 Hornet than the F-16, despite the similarity of the plane's planform to the F-16. The F-16, like the MiG-29 and the Su-27, uses an inverted or concave LERX that forms the vortices close and over the fuselage. The JF-17 uses a convex shaped LERX which creates vortices in two areas, one directly at the root where it meets the intake. The intake itself is shaped like a dogtooth, meaning the outside sweeps forward and ahead of the root. That creates the vortice. Chances are the DSI intake may also be routing some of the air layer into this tooth, energizing this vortice layer further but I really cannot go further in understanding the vortice interaction between LERX and DSI.

The next vortice should appear where the LERX meets the wing, and that's fairly outward of the body. So the vortice generation is a bit more complex. But we know the benefits of creating a vortice or break outside and away from the fuselage, since that was one of the ideas behind the double delta. Also check the F-14 when the wings are swept forward. The break between glove and the swing wing happens to be away from the fuselage. Putting the vortice away from the fuselage turns out to improve maneuverbility, and this phenomenon puts the Tomcat ahead of other VG designs like the F-111 and MiG-23. It should be noted that the F-18 does the same thing too.

The curved shape of the new JF-17 LERX itself is intended to add more lift, moving the center of lift forward. Chances are the design of the aircraft now makes it more negatively unstable.

There is some reasonably complex aerodynamics involved, and shows you someone definitely doing their homework with vortice behavior.

My complaint about the JF-17 isn't located in the same area, but at the tail. Why use an F-16 like configuration where the end of the tail elevator neatly aligns with the end of the engine exhaust? Is it because it looks neat? But this is not optimal. I would have swept and extended the elevator well past the tip of the nozzle, much like the MiG-21 or the MiG-29. This tends to give better control authority on the elevator, and helps you maintain control at high AoA. The F-18, F-22 and F-35 have all gone to sweeping the elevator surface as far back as possible beyond the tip of the engine nozzle. As a matter of fact, one of the planform drawings of the JF-17, shortly revealed after the DSI version was first shown as a model, had exactly extended the elevators. I think I may find the picture somewher but I'm sure many of you would recall this drawing.
 
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maglomanic

Junior Member
Re: New JF-17/FC-1 thread

Crobato Said:
But this all moot for the JF-17, which uses a different principle in scooping air to the intakes, a process not unlike that of the Rafale and the F-35. Rather, the nose is V canted.

Crobato,
to me it appears that the slant V like flat surface in the fore of intakes(Pt-03) was replaced with a more curved surface flush with rest of curved body around that area (Pt-04) (not standing out like the V surface).

Here are two pictures, one of PT-03 and PT-04.

0304intakeox7.jpg
 

crobato

Colonel
VIP Professional
Re: New JF-17/FC-1 thread

Perhaps to move the air smoother from the bottom of the nose to over the intakes and the wings.

Note the interesting "\" slant on the intake which goes against conventional knowledge. They're not afraid to risk a few ideas here.
 

Zahid

Junior Member
Re: New JF-17/FC-1 thread

We had the BVR discussion with FC-1 having a rather small RCS and the neccessary avonics. But I would argue that in BVR fights, kinematic energy (speed) is an essential part, wich the FC-1 simply does not offer (aerodynamics, engine).

I seem to have missed the BVR discussion with FC-1 to which you allude. But is Mach 1.8 (that JF-17 is supposed to attain with WS13) slow enough that Kinematic energy assumes over-riding significance? Having advantages such as low RCS must still have relevance.

Also, I think that when JF-17 assumes the position of workhorse for PAF, there are bound to be variations favoring particular roles.
 

beijingcar

New Member
Re: New JF-17/FC-1 thread

"My complaint about the JF-17 isn't located in the same area, but at the tail. Why use an F-16 like configuration where the end of the tail elevator neatly aligns with the end of the engine exhaust? Is it because it looks neat? But this is not optimal. I would have swept and extended the elevator well past the tip of the nozzle, much like the MiG-21 or the MiG-29. This tends to give better control authority on the elevator, and helps you maintain control at high AoA. The F-18, F-22 and F-35 have all gone to sweeping the elevator surface as far back as possible beyond the tip of the engine nozzle. As a matter of fact, one of the planform drawings of the JF-17, shortly revealed after the DSI version was first shown as a model, had exactly extended the elevators. I think I may find the picture somewher but I'm sure many of you would recall this drawing."

I don't know anything so forgive me if i am way off base. I agree with you that the tail can and should be moved back a lot more. But I think the reason they did not move it is that 1. Higher the AOA, the higher powered engine is needed, because the true value of high AOA in combat is only achieved with enough power for the jet to recover the energy that have bleed off in high AOA flights, as we all know the RD93 and the future WS13 are both a little under powered for the FC-1, and with no other more powerfull engine in their place in the near future, I think they decided that move the tail back will not benefit much. 2. If the tail is moved back, I think it will add more empty weight for the jet and for the engine to work harder than need to be. I think it could add at least 100 KG for the jet if the tail is moved back. 3. In supersonic flights, the center of the jet moves to the back of the airplane, and the nose of the jet wants to go up. if they move the tail back and plus the result of this increased weight, the center point of the jet will have moved further back in supersonic flights, that will result for the need to rewrite the FBW software and to retesting, but time and $ are the issues here as well.
what do you guys think?
 

Scratch

Captain
Re: New JF-17/FC-1 thread

I seem to have missed the BVR discussion with FC-1 to which you allude. But is Mach 1.8 (that JF-17 is supposed to attain with WS13) slow enough that Kinematic energy assumes over-riding significance? Having advantages such as low RCS must still have relevance.

Also, I think that when JF-17 assumes the position of workhorse for PAF, there are bound to be variations favoring particular roles.

Well, I should perhaps restate that. I would believe that in offensive BVR A-A missions the FC-1 has a disadvantage. The rather small radom can only hold a smaller radar ->reducing range -> offsetting the RCS advantage. Of course a small RCS has benefits, especially when guidance comes from a third party.
The range of the FC-1 is rather limited. Going to M1.8, or supersonic anyway for that matter, will of course need the afterburner, consuming that fuel rather fast.
You probably won't reach that M1.8 anyway, since accelarating to max speed takes rather long. You fly at cruise speed and once you come into firing position go to AB to accelerate somewhat before firing. Since I think the FC-1 starts from a rather slow cruising speed, I believe it to be in a disadvantage here.
In DCA mission were you have a reliable AEW controll it might rush on the attackers, shoot and evade.
 
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crobato

Colonel
VIP Professional
Re: New JF-17/FC-1 thread

"My complaint about the JF-17 isn't located in the same area, but at the tail. Why use an F-16 like configuration where the end of the tail elevator neatly aligns with the end of the engine exhaust? Is it because it looks neat? But this is not optimal. I would have swept and extended the elevator well past the tip of the nozzle, much like the MiG-21 or the MiG-29. This tends to give better control authority on the elevator, and helps you maintain control at high AoA. The F-18, F-22 and F-35 have all gone to sweeping the elevator surface as far back as possible beyond the tip of the engine nozzle. As a matter of fact, one of the planform drawings of the JF-17, shortly revealed after the DSI version was first shown as a model, had exactly extended the elevators. I think I may find the picture somewher but I'm sure many of you would recall this drawing."

I don't know anything so forgive me if i am way off base. I agree with you that the tail can and should be moved back a lot more. But I think the reason they did not move it is that 1. Higher the AOA, the higher powered engine is needed, because the true value of high AOA in combat is only achieved with enough power for the jet to recover the energy that have bleed off in high AOA flights, as we all know the RD93 and the future WS13 are both a little under powered for the FC-1, and with no other more powerfull engine in their place in the near future, I think they decided that move the tail back will not benefit much. 2. If the tail is moved back, I think it will add more empty weight for the jet and for the engine to work harder than need to be. I think it could add at least 100 KG for the jet if the tail is moved back. 3. In supersonic flights, the center of the jet moves to the back of the airplane, and the nose of the jet wants to go up. if they move the tail back and plus the result of this increased weight, the center point of the jet will have moved further back in supersonic flights, that will result for the need to rewrite the FBW software and to retesting, but time and $ are the issues here as well.
what do you guys think?

You got some pretty good explanations there.
 

crobato

Colonel
VIP Professional
Re: New JF-17/FC-1 thread

Well, I should perhaps restate that. I would believe that in offensive BVR A-A missions the FC-1 has a disadvantage. The rather small radom can only hold a smaller radar ->reducing range -> offsetting the RCS advantage. Of course a small RCS has benefits, especially when guidance comes from a third party.
The range of the FC-1 is rather limited. Going to M1.8, or supersonic anyway for that matter, will of course need the afterburner, consuming that fuel rather fast.
You probably won't reach that M1.8 anyway, since accelarating to max speed takes rather long. You fly at cruise speed and once you come into firing position go to AB to accelerate somewhat before firing. Since I think the FC-1 starts from a rather slow cruising speed, I believe it to be in a disadvantage here.
In DCA mission were you have a reliable AEW controll it might rush on the attackers, shoot and evade.

True, your engagement ranges would be limited, but such ranges are already limited by the NEZ ranges of your BVRAAM in the first place. It does not matter much if you detect 150km or 100km if you still need to come as close as 20 to 30km to get the high percentage kill range out of your BVRAAM.

Against an aircraft with a longer ranged radar, you would detect him just about the same time as he detects you, mainly because his radar would have set off your RWR.

What the FC-1 needs is a network to support it, target detection data for example, being fed by AEW aircraft, ground stations or even from fighters with more powerful radar. The FC-1 can stay in a silent mode as it tracks the target through the network, till it is in firing position.

It really isn't made as a all in one plane, but light fighters like these are intended and best used as support to larger fighters.
 
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