J-20 Radar Scattering Simulation

[S10]

So in conclusion - the J-20 is still worse off in RCS than the F-22 designed some 33 years ago and the F-35 designed some 20 years ago.

But, they do have some advantages in larger aperture options and in case of J-20 better transonic acceleration

J-XX utilized the 4S standard (Super maneuverability, supercruise, sensor fusion and stealth), but they were not on the same priority. Even the designer Yang Wei said stealth had to compromise for other 3S.

You also need to understand that J-20 was also designed nearly 20 years ago, not that far off from F-35. It's been almost 12 years since its first prototype.

 

[tphuang]

So in conclusion - the J-20 is still worse off in RCS than the F-22 designed some 33 years ago and the F-35 designed some 20 years ago.

But, they do have some advantages in larger aperture options and in case of J-20 better transonic acceleration

F-22 has all aspect stealth. F-35 is really only VLO in front sector. Both F-35A and J-20 joined service at around the same time (2016 vs 2018), so they are quite comparable. The current production rate is about the same. It's not China's fault that F-35A took this long to get developed.

In terms of stealth, keep in mind that US military uses an older F-35A in its aggressor squadron to simulate J-20 while using F-16 or super hornet to simulate Su-57. The reason is that they consider J-20 to be in the same level in frontal stealth to earlier F-35s. Maybe F-35s are notably more stealthy vs x-band radar from directly in front. But in the battlefield, you will be facing more S/L/UHF band radars from different directions. There are also considerations such as emission control. J-20 is more competitive from a broader view.

 

[maverick1977]

This happened today..

Airforce Worldwide on Instagram: "⚠️ F-35B CRASH TODAY 🇺🇸 • 🎥 Kitt Wilder via @theaviationist • TheAviationist: „The crazy video of the F-35B incident today at Forth Worth, filmed by Kitt Wilder, was posted by Fox 4 News and CBSDFW. It shows a bo

Airforce Worldwide shared a post on Instagram: "⚠️ F-35B CRASH TODAY 🇺🇸 • 🎥 Kitt Wilder via @theaviationist • TheAviationist: „The crazy video of the F-35B incident today at Forth Worth, filmed by Kitt Wilder, was posted by Fox 4 News and CBSDFW. It shows a bouncy landing after hover...

www.instagram.com

 

[SQ8]

I think the reason for that is when the Chinese designed this thing, they weren't sure of their engine tech's advancement. So they gave up some RCS / stealth on frontal due to canards to achieve agility. If I was to design it, I'd have used 2D TVC in achieving the agility. This option rarely is used, primarily in a dog fight for pointing the nose towards the opponent.

The design took inspiration from the JAST concepts - which abandoned canards for the very reason of RCS.

Hence it was a known trade off for high alpha and turn rate in the absence of powerful engines. Yet you will see Chinese members repeatedly bash the F-22 versus the J-20 even though the former had a lot less limitations even though being designed in the late 80s , 90s due to US superiority in aviation technology.

F-22 has all aspect stealth. F-35 is really only VLO in front sector. Both F-35A and J-20 joined service at around the same time (2016 vs 2018), so they are quite comparable. The current production rate is about the same. It's not China's fault that F-35A took this long to get developed.

In terms of stealth, keep in mind that US military uses an older F-35A in its aggressor squadron to simulate J-20 while using F-16 or super hornet to simulate Su-57. The reason is that they consider J-20 to be in the same level in frontal stealth to earlier F-35s. Maybe F-35s are notably more stealthy vs x-band radar from directly in front. But in the battlefield, you will be facing more S/L/UHF band radars from different directions. There are also considerations such as emission control. J-20 is more competitive from a broader view.

The F-35 also was built with limitations of being the stupid tri service platform(CTOL, STOVL) which it struggles to be - yet it achieves more.

The J-20 may be more competitive in terms of overall capabilities but that is speculation. The point is when bashing the F-35 Chinese members have no qualms going all out on what it can do but forget their own limitations in the designs they use.

As far as the battlefield is concerned, the F-35s will be aware of the radars and essentially planning their moves accordingly. Today’s pilot is probably less of a driver and more of a strategist.

Back in 2011 the PAF was shown the alternative stealth design by Chengdu(you can go back to my posts from 2012 since I refer to 3 designs) and concepts of having a twin seater with an advanced situational display where the backseater is playing “chess” with unmanned weapons and so on.

That is your J-20 twin seater - the US is moving on that concept with a single pilot on the F-35 and F-15EX/superhornet.
So all these elements will be aware of emissions and planning it all accordingly

 

[SQ8]

J-XX utilized the 4S standard (Super maneuverability, supercruise, sensor fusion and stealth), but they were not on the same priority. Even the designer Yang Wei said stealth had to compromise for other 3S.

You also need to understand that J-20 was also designed nearly 20 years ago, not that far off from F-35. It's been almost 12 years since its first prototype.

I think the compromise had to be made due to lack of decent engines. The Russian engines were known to be deficient in many aspects and the local engines were floundering at that stage.

The J-20 isn’t a dogfighter , its an interceptor and capable of sustained supercruise to take out high value targets. But that is less and less relevant as time goes on in terms of super maneuverability. The Su-30MKI today is carrying dead weight with its TVC for 80% of the scenarios it has to face.

Be glad the PLAAF rejected TVC when Russia offered it for the Su-30Mk2 follow on and instead would rather have that saved weight for more weapons. With the J-16 that is all moot now.

 

[siegecrossbow]

The design took inspiration from the JAST concepts - which abandoned canards for the very reason of RCS.

That’s not true. They abandoned it since it complicated the STVOL configuration with the fan, which was a requirement.

 

[SQ8]

That’s not true. They abandoned it since it complicated the STVOL configuration with the fan, which was a requirement.

Trade studies were conducted to refine the design in late 1993. Configuration 140 emerged as a baseline used to build a 92 percent scale powered model. The requirements for testing the model in the NASA Ames 80- by 120-foot wind tunnel called for a safety factor of five times the normal design loads. To meet these requirements, the model was fabricated from sheets of 1/4-inch steel plate. The result, which weighed almost 50,000 pounds, incorporated an F100 engine and a lift fan built from the first stage of an F119 engine. The model was used to test the interaction of the airflow from lift fan and the aft nozzle. The data gathered from this these tests helped Lockheed win the Concept Development phase of the X-35 program. [Lockheed photo]

 

[siegecrossbow]

Trade studies were conducted to refine the design in late 1993. Configuration 140 emerged as a baseline used to build a 92 percent scale powered model. The requirements for testing the model in the NASA Ames 80- by 120-foot wind tunnel called for a safety factor of five times the normal design loads. To meet these requirements, the model was fabricated from sheets of 1/4-inch steel plate. The result, which weighed almost 50,000 pounds, incorporated an F100 engine and a lift fan built from the first stage of an F119 engine. The model was used to test the interaction of the airflow from lift fan and the aft nozzle. The data gathered from this these tests helped Lockheed win the Concept Development phase of the X-35 program. [Lockheed photo]
View attachment 906234

I don't see how this contradicts what I've said. They built the full scale model for testing and it didn't work out.

 

[SQ8]

I don't see how this contradicts what I've said. They built the full scale model for testing and it didn't work out.

It isn’t because of the fan

“The LockMart design went from canard to quad-tail shortly before the CDA RFP deadline (which was in 1996). The main reason was that the carrier version was going to need a larger wing than the span-restricted (LH-class parking) CV/STOVL aircraft, and larger control surfaces. Scaling up a delta wing, while keeping its sweep angles constant (LO constraint) is difficult configuration-wise because the increase in root chord - in feet and inches - gets very large... so where do you put the (also larger) canard? A wing with less sweep and taper, and an aft tail likewise, made it easier to accommodate two wing designs on the same body shape.”

Also
“besides carrier suitability, one driving consideration for switching to a conventional configuration from the original canard was a question of weapons bay placement. the bays ended up "too far aft" (i'm assuming because they have to straddle the cg; this could have all sorts of implications in aerodynamics and structures ). The other reason, was that the canards could, under some conditions, mask the field of view of air launched weapons.”

So for whatever reason the J-20 is in high alpha and with deflecting canards and it needs to shoot at a target +\- off axis, the PL-10 seeker from the side bays would have trouble looking through them. With helmet cueing through the IRST and LOAL capabilities that is moot but it does make sense from a 90s design perspective.

@gambit , any thoughts?

 

[Pogical Thinking]

(you can go back to my posts from 2012 since I refer to 3 designs)

Restricted profile sir...

 

[siegecrossbow]

It isn’t because of the fan

“The LockMart design went from canard to quad-tail shortly before the CDA RFP deadline (which was in 1996). The main reason was that the carrier version was going to need a larger wing than the span-restricted (LH-class parking) CV/STOVL aircraft, and larger control surfaces. Scaling up a delta wing, while keeping its sweep angles constant (LO constraint) is difficult configuration-wise because the increase in root chord - in feet and inches - gets very large... so where do you put the (also larger) canard? A wing with less sweep and taper, and an aft tail likewise, made it easier to accommodate two wing designs on the same body shape.”

Also
“besides carrier suitability, one driving consideration for switching to a conventional configuration from the original canard was a question of weapons bay placement. the bays ended up "too far aft" (i'm assuming because they have to straddle the cg; this could have all sorts of implications in aerodynamics and structures ). The other reason, was that the canards could, under some conditions, mask the field of view of air launched weapons.”

So for whatever reason the J-20 is in high alpha and with deflecting canards and it needs to shoot at a target +\- off axis, the PL-10 seeker from the side bays would have trouble looking through them. With helmet cueing through the IRST and LOAL capabilities that is moot but it does make sense from a 90s design perspective.

@gambit , any thoughts?

Seems I have misremembered. Thanks for the detailed information.

 

[gambit]

It isn’t because of the fan

“The LockMart design went from canard to quad-tail shortly before the CDA RFP deadline (which was in 1996). The main reason was that the carrier version was going to need a larger wing than the span-restricted (LH-class parking) CV/STOVL aircraft, and larger control surfaces. Scaling up a delta wing, while keeping its sweep angles constant (LO constraint) is difficult configuration-wise because the increase in root chord - in feet and inches - gets very large... so where do you put the (also larger) canard? A wing with less sweep and taper, and an aft tail likewise, made it easier to accommodate two wing designs on the same body shape.”

Also
“besides carrier suitability, one driving consideration for switching to a conventional configuration from the original canard was a question of weapons bay placement. the bays ended up "too far aft" (i'm assuming because they have to straddle the cg; this could have all sorts of implications in aerodynamics and structures ). The other reason, was that the canards could, under some conditions, mask the field of view of air launched weapons.”

So for whatever reason the J-20 is in high alpha and with deflecting canards and it needs to shoot at a target +\- off axis, the PL-10 seeker from the side bays would have trouble looking through them. With helmet cueing through the IRST and LOAL capabilities that is moot but it does make sense from a 90s design perspective.

@gambit , any thoughts?

I agree with you -- that the removal of the canards had more to do with RCS considerations than with the lift fan.

Canards are not large flight controls surfaces to start. Their deflections, from arcs to rate, can be the same as the larger rear horizontal stabs, but because of their smaller sizes which mean lighter mass, the hydraulics subsystems will be smaller.

Flight controls surfaces have mass and a mass in motion have momentum. Once a flight control surface reached a commanded deflection point, it must be stopped else there would be airplane overshoot of the maneuver. But there is an additional issue/problem that is unique to the flight control surface that rarely exist elsewhere. Keep in mind that the airplane is in flight. Using a rear horizontal stab as example, when the stab deflect LE up, now there is a low pressure area that try to force the stab to return to neutral or inline with the fuselage. The rear stab have its own CG which must be at the rotation point else with that low pressure there would be flutter which mean departure from controlled flight. Imagine the stab shakes as it rotate LE up/down. This is why we have 3000 psi hydraulics to maintain flight control surface steady state throughout its deflection.

Canards being smaller still have the same issue but easier to control. With a relaxed stability design, the canards will already be active flight controls elements, but now add in the intent to reposition the airplane's nose via direct lift instead of the conventional method of pushing the tail down, canard deflection will be greater and sooner than with a positive or neutral stable design. Hence, the RCS issue.

 

[ZeEa5KPul]

It seems the myths regarding the J-20 are harder to kill than the J-20 itself. That's quite an accomplishment. But let's dispel the myths all the same:

1. The J-20 is an all-aspect VLO air superiority fighter with a multirole capability.
2. The J-20's canard delta wing configuration does not impose an RCS penalty relative to a conventional delta wing.
3. This simulation gets macroscopic details like the shape of the canopy and where the strakes attach to the body wrong. It is useless in its entirety in reaching any conclusion about the J-20's RCS relative to any other aircraft.

 

[FuturePAF]

I think the reason for that is when the Chinese designed this thing, they weren't sure of their engine tech's advancement. So they gave up some RCS / stealth on frontal due to canards to achieve agility. If I was to design it, I'd have used 2D TVC in achieving the agility. This option rarely is used, primarily in a dog fight for pointing the nose towards the opponent.

The WS-15 is currently in testing and we have seen 2D TVC nozzles at the latest Zhuhai air show, so a lower RCS redesign may not be far off of desired by the PLAAF.

https://twitter.com/x/status/1602687065749131271

Here is the translation

https://twitter.com/x/status/1602704732899971075

If I’m reading this correctly there is a 10-20% increase in thrust over the WS-10C?

And here is the J-20 supposedly fitted with the WS-15

https://twitter.com/x/status/1603401886941720576

A wider view of the conference

https://twitter.com/x/status/1602906232871854080

The TVC nozzle

https://twitter.com/x/status/1589170930722701314

With the TVC nozzle it could remove the canard and turn all the aft control surfaces (twin tails and twin stabilizing fins) into a couple of Pelican tails, as envisioned for the X-32’s final design. The improvements to stealth and maneuverability could be considerable. Remember the X-32 design called for the use of a 2D TVC nozzle along with a pelikan tail. If China matures this design feature and applies it to the J-20 and J-35 it could offer significant performance as well as signature reductions, and if it’s applied to a redesign of the J-10 they could have the basis for a new design that would be even better then what the X-32 was envisioned, which was suppose to be a match for the x-35, now F-35. This could help China build up their numbers quicker in terms of lower RCS (especially if the canard can be removed) single engine fighters.

 

[Flaming Sabre]

The J-20 is a static instability aircraft, completely different from the StaticStability aircraft, requiring canard balancing torque, each layout has profound implications, a prize tested by countless top experts and instruments, and it cannot be evaluated by simple opinions and tests.

For example, the canard of the J-20 is due to lack of power.
These kinds of rumours are false.

Regarding the RCS test of the J-20, a professional scholar published a report back in 2014 to provide a reference, link↓

A Preliminary Assessment of Specular Radar Cross Section Performance in the Chengdu J-20 Prototype

APA Analysis Paper APA-2011-03; Title: A Preliminary Assessment of Specular Radar Cross Section Performance in the Chengdu J-20 Prototype; Abstract: This study has explored the specular Radar Cross Section of the Chengdu J-20 prototype aircraft shaping design. Simulations using a Physical Optics...

ausairpower.net

Note that the physical optics test method in this report has limitations and cannot test the diffracted wave, cavity and seam sections, also, the shape of the J-20 before 2014 is very different from now and does not take into account wingtip tip scattering etc., but the theoretical data in this report is more realistic and reliable.

I am not a professional academic and cannot do tests to provide theoretical data, but I can carry some official Chinese data reports and try to briefly describe the performance of this aircraft.

There are three types of RCS for canard, wingtip tip scattering, edge scattering, and butt seam scattering.
To be more accurate, Chinese scholars did not use absorbing coatings and used the multi-layer fast method of integrating Maxwell's equations for detection.

1.7GHZ L-band, canard frontal 0° pitch 0°~30° average values.↓
Red is the canard layout

5.6GHZ C-band.↓

Conclusion: canard increases or decreases RCS at specific angles with very little effect, cutting off the wingtips, reducing wingtip scattering, applying wave absorbing coatings and special materials closes this gap even more.↓

Some may ask, when the J-20 does manoeuvres, the duck wing deflection increases the RCS value, and if the 5th generation aircraft needs to do high manoeuvres, it means it finds the enemy actively attacking, or is found to evade the lock, and stealth will not be considered when it is already exposed.

The above is just the most controversial topic of the J-20. When China minimises the RCS of the canard through reasonable angles and calculation methods, this technology will also be applied to the full fuselage of the J-20, whose true RCS is not as large as rumoured, and the aerodynamic layout of the fifth-generation aircraft, the avionics, engines, fuel tanks, missiles and pilots are all complex and large systems that require comprehensive consideration.
Finally: suppression of wingtip tip scatter is the most basic 5th generation technology, which AMCA does not have.