J-20 5th Gen Fighter Thread VI

[Air Force Brat]

Because it would otherwise defeat the purpose of having canards in the first place. To get meaningul benefits from canards they have to rearrange airflow so the canards are throwing the air over the wings. If their whole surface was at the same level as wings, they would not be able to fulfill their aerodynamic purpose.

The primary purpose of the canards on the J-20 is to increase "pitch authority" in order to allow the J-20 to be pitched above the stalling angle of attack into the post stall flight regime, and once post stall to allow the nose to be pushed right or left with rudder and aileron, and then to effect recovery by de-pitching the aircraft. The distant coupled canards increase the "moment arm", increasing canard pitch authority over "close coupled" canards, allowing the J-20 similar pitch authority to aircraft equipped with OVT...

They are tightly angled upward as you suggest in order to move the canards "tip vortices" above the leading edge of the main wing, energizing the flow, and further lowering the pressure over the top of the wing and creating additional lift over the main wing...

 

[Air Force Brat]

Sorry, I'm joking somewhat but I become triggered when the topic begins to veer towards the "eyeballing of aerodynamics".
In terms of J-20's canards, I don't want to claim to know enough about aerodynamics to suggest what exact benefit their positioning provides, but there must be a reason why it is not perfectly in plane with the wing.
All aircraft (as with all engineering projects) are a mix of deliberate compromises, as I'm sure you appreciate.


As for J-20's engine nozzles, I think they are somewhat treated; they don't look like standard Al-31 family nozzles after all.

I would suggest that you go back and read Siege's excellent translation of Dr. Song's aerodynamic paper explaining the aerodynamics of the J-20 and his reasoning for the distant coupled canards in the first place. I would also suggest you see the extensive video from Zhuhai, where the vapor clouds produced by heavy maneuvering makes Dr. Songs theories quite visible, once again illustrating his fresh and dynamic approach to a heavy fighter.

 

[ZeEa5KPul]

However the way you phrased your original suggestion really made it sound like you were wanting this aircraft to emerge before WS-15 came out.

Yeah, I definitely could have phrased it better. Let me put it in bullet points so there are no ambiguities:

• Work should begin on a new variant of the J-20, with improved stealth (both shaping and material), aerodynamics, avionics, sensors, etc. It should not radically depart from the original J-20.
• This new variant (called v2) should enter service in the mid-2020's.
• v2 should be designed to use the WS-15 or some variant thereof.
• Although the WS-15 is not in production, enough is known about its performance and characteristics to make the design of v2 tractable and "surprise-free".
• Work on v2 should in no way impede production and procurement of current J-20s, which remain the priority since fifth-generation fighters are proliferating in China's periphery.

It may well be impossible under the PLAAF's current budget constraints to undertake this project.

Sorry, I'm joking somewhat but I become triggered when the topic begins to veer towards the "eyeballing of aerodynamics".

No worries whatsoever, I sympathize completely. I get triggered when the topic veers towards "shortchanging China". Unfortunately for me, my trigger is a lot more prevalent.

In terms of J-20's canards, I don't want to claim to know enough about aerodynamics to suggest what exact benefit their positioning provides, but there must be a reason why it is not perfectly in plane with the wing.

If you'll allow me some "eyeball aerodynamics", a reason that comes to mind is getting good airflow along the LERX, which a co-planar canard might interrupt.

As for J-20's engine nozzles, I think they are somewhat treated; they don't look like standard Al-31 family nozzles after all.

That's interesting. Let's do a comparison, here's a Su-35 nozzle

a J-10C

and two J-20s

The J-20s definitely look "cleaner", but if there's some RCS-reducing treatment it begs the question of why the nozzles aren't serrated as well. We know 611 experimented with that in prototype 2021.

 

[ZeEa5KPul]

On the subject of Zhuhai, here's some very nice, high quality footage. Check out 4:25 in slow motion, what a sight:

I think I do see some coupling between the trailing edge of the canard and the main wing during the second burst.

 

[Blitzo]

Yeah, I definitely could have phrased it better. Let me put it in bullet points so there are no ambiguities:

• Work should begin on a new variant of the J-20, with improved stealth (both shaping and material), aerodynamics, avionics, sensors, etc. It should not radically depart from the original J-20.
• This new variant (called v2) should enter service in the mid-2020's.
• v2 should be designed to use the WS-15 or some variant thereof.
• Although the WS-15 is not in production, enough is known about its performance and characteristics to make the design of v2 tractable and "surprise-free".
• Work on v2 should in no way impede production and procurement of current J-20s, which remain the priority since fifth-generation fighters are proliferating in China's periphery.

It may well be impossible under the PLAAF's current budget constraints to undertake this project.

As I said, I have no problem with the idea of improved J-20 variants in future. However I believe such a variant, if it is intended to have aerodynamic/structural changes, should only be intended to enter service a few years after WS-15s have entered service.

I have my own ideas about the future of what J-20 production may look like going into the 2020s and beyond, and I can certainly envision at least one major improved variant emerging in the future during the mid to late 2020s and perhaps another even in the early 2030s.

The J-20s definitely look "cleaner", but if there's some RCS-reducing treatment it begs the question of why the nozzles aren't serrated as well. We know 611 experimented with that in prototype 2021.

Current J-20s use Al-31 variant engines. I do not think China would've had that much input into requesting any substantial design features like RCS reduced nozzles.
The design of those engines and whatever features may or may not exist cannot reasonably be attributed to Chengdu's oversight because they wouldn't have had much control over the way it was designed.

Prototype 2021 obviously uses WS-10 variant engines, meaning whatever RCS reduction features we saw on it could've reasonably been due to Chengdu or Shenyang-Liming or a combination of the two collaborating.

 

[Blitzo]

I would suggest that you go back and read Siege's excellent translation of Dr. Song's aerodynamic paper explaining the aerodynamics of the J-20 and his reasoning for the distant coupled canards in the first place. I would also suggest you see the extensive video from Zhuhai, where the vapor clouds produced by heavy maneuvering makes Dr. Songs theories quite visible, once again illustrating his fresh and dynamic approach to a heavy fighter.

I'm well aware of Dr Song's paper and I've read it multiple times before.

However I do not recall Dr Song's paper specifically mentioning canards which are dihedral. As totoro wrote, it may be like that to properly allow the canards to fulfill their aerodynamic purpose which cannot be done effectively if they are on the same plane as the main wings. However as I said, I did not want to eyeball that myself.

 

[PiSigma]

Yeah, I definitely could have phrased it better. Let me put it in bullet points so there are no ambiguities:

• Work should begin on a new variant of the J-20, with improved stealth (both shaping and material), aerodynamics, avionics, sensors, etc. It should not radically depart from the original J-20. Already started a couple of years ago.
• This new variant (called v2) should enter service in the mid-2020's. Just waiting for Ws15
• v2 should be designed to use the WS-15 or some variant thereof.
• Although the WS-15 is not in production, enough is known about its performance and characteristics to make the design of v2 tractable and "surprise-free".
• Work on v2 should in no way impede production and procurement of current J-20s, which remain the priority since fifth-generation fighters are proliferating in China's periphery.

It may well be impossible under the PLAAF's current budget constraints to undertake this project.


No worries whatsoever, I sympathize completely. I get triggered when the topic veers towards "shortchanging China". Unfortunately for me, my trigger is a lot more prevalent.


If you'll allow me some "eyeball aerodynamics", a reason that comes to mind is getting good airflow along the LERX, which a co-planar canard might interrupt.


That's interesting. Let's do a comparison, here's a Su-35 nozzle

a J-10C

and two J-20s

The J-20s definitely look "cleaner", but if there's some RCS-reducing treatment it begs the question of why the nozzles aren't serrated as well. We know 611 experimented with that in prototype 2021.

The Ws15 size is known. No major changes required structurally....
See other part in green. Can't say much more.

 

[gelgoog]

Other than the engines, I think the major modifications should be in terms of weapon systems support and link integration between platforms.
Possibly add the cannon back. Add some anti-radiation missiles.

 

[Blitzo]

Other than the engines, I think the major modifications should be in terms of weapon systems support and link integration between platforms.
Possibly add the cannon back. Add some anti-radiation missiles.

Those sort of modifications can be introduced with block upgrades or even production batch upgrades, as new software and weapons become developed and integrated into the fleet.

The last page has instead been talking about more major modifications that include some structural and aerodynamic changes beyond expanding the aircraft's weapons suite and software/networking. Basically, a wholly new "variant".

 

[TerraN_EmpirE]

Well the gun system may be a structural mod as we have never seen a clear show of where it is supposed to be.

Other than the engines, I think the major modifications should be in terms of weapon systems support and link integration between platforms.
Possibly add the cannon back. Add some anti-radiation missiles.

Add in a DIRCM.