J-20 5th Generation Fighter VII

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enroger

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Rumored WS-15 powered J-20 will not have twin dorsal fins because in built TVC will compensate for loss of maneuverability. J-20 stealth will improve without those fins.

source =CMA Blog by Huitong:



There is even more stealth gains that can be made by reducing control surfaces especially vertical control surfaces. This is all made possible due to WS-15's TVC.

Do you have link for that blog?
 

sunnymaxi

Major
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Well … already now some say there are about 40 produced per year since 2020/21 but this does not fit to the number of J-20s in service … as such I‘m sceptical with this even higher number.
so we can expect 70+ units minimum from 2023 onward. that's huge for a stealth fighter jet. only US exceed this production rate.

now finally China showing their mass production skills. LOL
 

ZeEa5KPul

Colonel
Registered Member
Well … already now some say there are about 40 produced per year since 2020/21 but this does not fit to the number of J-20s in service … as such I‘m not only sceptical with the 40 but even more with this even higher number.
Although some degree of skepticism is always warranted, it's not outlandish that a platform that's been in service for five years and been flying for more than ten to be mature enough to manufacture at this scale. The question here is who this lyman2003 person is. What's his track record?
 

ougoah

Brigadier
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You don't need to be an aerospace engineer, just understanding some very basic principles about RCS optimization is sufficient:
View attachment 96819
One of the most important principles is to reduce the number of unaligned surfaces. Take a look at each strake and the V-tail on the opposite side - you'll see that they're parallel. There's a lot more to this, like the intakes, sides of the plane, and even a tangent line on the lower canopy are all parallel. The reflections from an EM emission source like a radar are all moving in the same direction, away from the radar.

You'll see this sort of "parallelism" everywhere. In fact, I just noticed that the side facets of the ETOS window under the J-20's nose are also parallel to the features I discussed. It's a very tight requirement for a VLO design, and removing the strakes exposes the cylindrical nozzles. A side-view cylinder is just about the worst thing you can present since a radar looking at it from any angle has a tangential plane on the surface reflecting back.

The take away is it's not the number of surfaces that's the issue, it's the number of unaligned surfaces.

Number of aligned surfaces do matter too because it amplifies the return signal but that's a smaller question than the major one of what direction your surfaces are in.
 

ZeEa5KPul

Colonel
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Number of aligned surfaces do matter too because it amplifies the return signal but that's a smaller question than the major one of what direction your surfaces are in.
I would guess that the bigger factor regarding the strength of the return signal is the total surface area exposed along a specific angle, not necessarily the number of surfaces. In this regard, it makes sense that the V-tails of the J-20 are relatively small since the total "reflection budget" has to account for reflections from the aligned strake at the opposite side of the aircraft.
 

ougoah

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I would guess that the bigger factor regarding the strength of the return signal is the total surface area exposed along a specific angle, not necessarily the number of surfaces. In this regard, it makes sense that the V-tails of the J-20 are relatively small since the total "reflection budget" has to account for reflections from the aligned strake at the opposite side of the aircraft.

That's what I mean. The number of aligned surfaces = surface area. The greater the number of aligned surfaces means greater area exposed in that specific angle.

This is a lower priority than orientation or surfaces for sure. Much less but still does factor in to stealth and RCS in a non zero way. I think deleting ventral fins may help RCS in the way that it minimises the surface area in that orientation BUT if may expose engine nozzle from more angles. Very slightly more lol but who knows. It's probably a balance overall unless someone has all the specifics hahaha. I'm sure CAC and PLAAF have exact details on how having it and not having it affect the J-20 wrt performance and stealthiness. In other words, they certainly know best and if it stays after WS-15 integration, we would have very good indication that ventral fins in this application do not constitute so much of a RCS penalty as to be worth deletion or the mission profiles for J-20s are in such a way that penalty does not matter.
 

stannislas

Junior Member
Registered Member
Do you think plane parts can go on and off like Lego pieces? The strakes are there to provide yaw stability so the small moving V-tails don't throw the plane into uncontrollable spins. Removing them fundamentally alters the J-20's aerodynamics to an extent where its entire FCS would have to be rewritten at the very least.

Why do you think the strakes need to be removed in the first place?

Removing the strakes would expose the nozzle from the side and worsen RCS.
That's what I mean. The number of aligned surfaces = surface area. The greater the number of aligned surfaces means greater area exposed in that specific angle.

This is a lower priority than orientation or surfaces for sure. Much less but still does factor in to stealth and RCS in a non zero way. I think deleting ventral fins may help RCS in the way that it minimises the surface area in that orientation BUT if may expose engine nozzle from more angles. Very slightly more lol but who knows. It's probably a balance overall unless someone has all the specifics hahaha. I'm sure CAC and PLAAF have exact details on how having it and not having it affect the J-20 wrt performance and stealthiness. In other words, they certainly know best and if it stays after WS-15 integration, we would have very good indication that ventral fins in this application do not constitute so much of a RCS penalty as to be worth deletion or the mission profiles for J-20s are in such a way that penalty does not matter.
one more thing to add on this is that the ventral fin, based on the primer color (same to the random), should be made in almost complete wave transmitting composite material, so theoratical, it should be invisible on the radar...
 

Deino

Lieutenant General
Staff member
Super Moderator
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so we can expect 70+ units minimum from 2023 onward. that's huge for a stealth fighter jet. only US exceed this production rate.

now finally China showing their mass production skills. LOL


Ähhhm ??? I say I doubt these numbers and even the currently often mentioned claim of 40 per year and you rate it as if even 70 - in fact even more than the 60 claimed - would roll off the line?!!!

Did I miss something?
 

stannislas

Junior Member
Registered Member
Well … already now some say there are about 40 produced per year since 2020/21 but this does not fit to the number of J-20s in service … as such I‘m not only sceptical with the 40 but even more with this even higher number.
well, it's not completely impossible to get the number of 40, at least for this year, we got from ~90- to 110-120 within a year, and there is still 3 months to go this year, so...
 

56860

Senior Member
Registered Member
Ähhhm ??? I say I doubt these numbers and even the currently often mentioned claim of 40 per year and you rate it as if even 70 - in fact even more than the 60 claimed - would roll off the line?!!!

Did I miss something?
I actually think China has been slightly muting production these last few years. It's not ideal to pump out lots of airframes utilizing an interim engine. Once WS-15 is finalized I can see production of J-20B ramping up to that number over 2-3 years. There's probably a laundry list of upgrades PLAAF are itching to make once WS-15 is available, and that will necessitate lots of flying hours which means lots of airframes.
 
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