J-20... The New Generation Fighter II

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delft

Brigadier
Interesting but subsonic aircraft have the upper camber near the leading edge so their aerodynamic centers are near the leading edge, however to be true, then the J-20`s wing profile must be quit fat, not a very good wing for a supersonic jet, the J-20`s wing profile is supersonic then its wing camber can not be so close as you claim because supersonic wing cambers are rather thin without too much camber.
The F-22 `s wing has a tip twist to increase lift and leading edge flaps.
The Lifting bodies are also different concepts too they are basicly work like kites, so the J-20 also does not work like that, the J-20 is not unique in having a LERX and canards the Rafale does it too and a detail you missed the Rafale vectors a compressed vortex generated by its inlet and forebody plus it has a better positioned canard.


The J-20 has like the F-22 a semi blended fuselage-wing but its design is not unique.
The remarks on wing profiles are notably uninformed.
 

MiG-29

Banned Idiot
Actually,

No other plane has lerx/delta combination.
No other canard/delta has them on the same level.

We don't need to look far to see the uniqueness.

And it is reflected in it's center of lift. No other plane has it as close to the front edge of the main wing as J20.

It's aerodynamic design is not something we (armchair designers) can talk out of thin air. Even real designers will have to build models to test in wind tunnels to give a judgement. That's why I see no point discussing this.
The Rafale has LERXes




Having a LERX and a Delta with canards is not unique to the J-20, what is unique to the J-20 is it is a stealth fighter with canards, besides that is not unique,

Now compare the J-20 to the Rafale

The first think it will strike you is the wing of the Rafale is positioned further forward from the engine nozzles and the main landing gear is farther back from the wing root and leading edge.
This shows easily tha all Eurocanards are unstable longitudinaly and the J-20 is closer to the Viggen in configuration

the Rafale also has LERXes but its canards are closer to the wing and above it, this means their vortices re-energize better the wing (if you disagree you can read technical documentation about canards and see all fighters J-10, Gripen Eurofighter, Rafale, MiG1.44 have the same configuration)


the conclusion is the J-20 is more a striker than a fighter and only with advanced avionics and missiles will be able to fight, this is not to minimize or belittle it, it is a tornado adv type fighter with modern stealth

in this picture you can see the vortex formation on the Rafale and you can see its LERXes and inlet forebody do create Vortices increasing AoA handling
 
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Quickie

Major
Your statement is not correct, the SR-71 achieves Mach 3.4 thanks to ramjets and a inlet cone design that moves backwards allowing supersonic flow to the engines, the F-22 has fixed inlets.
You know it's no coincidence that real-life examples of high mach aircrafts like the Blackbird, Concorde, Space Shuttle (which is applicable during reentry to the atmosphere) all have relatively small aft wings and a longer body compared to other slower supersonic aircrafts.

Jet engine power aside, I can't imagine something in the shape of the F-22 flying at more than 3 mach without breaking up.

Long is not good, bigger is not good, the SR-71 is long just to carry lots of fuel in a very narrow fuselage, but the engines are not buried type, they are not part of the fuselage mainbody, but separate entities, thus alowing for a narrow fuselage.
The SR-71 has a much narrower fuselage than the F-22 and it has wing-fuselage blending with its chines that are basicly LERXes.
Are you now alluding to the point that being longer and narrower is better?

the J-20 cross section is not smaller than the F-22`s cross section and it has longer fuselage than the F-22`s, both cross sections are similar basicly the same with the exception of the inlet and engine nozzle separation at the end of the fuselage.
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I think you still miss the point. A body that's slightly wider and longer than another body, can still be more streamlined than that other body. i.e. The shape of the 2 bodies also have to be taken into account. Furthermore, an aircraft fuselage is just one of the many components contributing to drag, with the wings contributing a large part of it.
 
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siegecrossbow

Brigadier
Staff member
Super Moderator
Let me summarize MIG-29's arguments:

1) J-20 has poor manoeuvrability
2) J-20 can't super-cruise
3) J-20 can't go above Mach 2

If all of the above were true why didn't the CAC go and design a plane along the lines of the JH-7 flying leopard? The latter has a conventional configuration so the flight control would be a lot easier. Why go with the one piece canopy when visibility is less of a concern in dogfights. Why putting so many control surfaces on the plane when it is only capable of strike missions?
 

johnqh

Junior Member
Let me summarize MIG-29's arguments:

1) J-20 has poor manoeuvrability
2) J-20 can't super-cruise
3) J-20 can't go above Mach 2

If all of the above were true why didn't the CAC go and design a plane along the lines of the JH-7 flying leopard? The latter has a conventional configuration so the flight control would be a lot easier. Why go with the one piece canopy when visibility is less of a concern in dogfights. Why putting so many control surfaces on the plane when it is only capable of strike missions?
Based on Mig-29's logic, by eyeballing, JH-7 is a fighter.
 

johnqh

Junior Member
By the way, those who are really interested in the J-20 design can find the paper I mentioned here:

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It is all Chinese. So I am summarizing some major points:

Increase in lift:
LERX: 20%
Canards: 30%
LERX+Canards:60%
Blending lifting body+LERX+Canards:81%

Unstable to 10% (other planes generally limited to 3%)
Increasing the size of canards to 15% of main wing (generally limited to 10%)
Able to turn canards to 90%
Small vertical stabilizers

The funny thing is, at the end of the paper, it talked about a design with underbody intake, so it wasn't specifically about J-20. It is really about the result of general wind tunnel testing about aerodynamic designs.

It also means, CAC has at least one other design with lifting body+LERX+canards+delta+underbody intake+small dual vertical stabilizers.
 
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johnqh

Junior Member
In China they refer to two types of LERX. One of them they call "bian tiao" and the other they call "bian tiao yi". I don't know how to properly translate the two.
The thing Rafael has is really "Zheng liu zhao" - fairing (based on Google translate).

I guess some people could can it "Small LERX". We have to look at it from the purpose of design. I doubt it is there for the increased lift. Rather, it is simply part of the blending between the body and the wings.
 
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