• Hi Guest! Forum rules have been updated. All users please read here.

Chengdu J-20 news and analysis Part III

T

TomcatViP

Hellcat
Joined
Feb 12, 2017
Messages
3,357
Reaction score
2,136
The picture discussed in above link:
e0ead781-42ff-4333-8d30-6293fb305519.jpeg


Notice also the different shape of the sensor on the inlet lip (below the twin bypass outlets)
 
FighterJock

FighterJock

ACCESS: Top Secret
Joined
Oct 29, 2007
Messages
1,756
Reaction score
519
TomcatViP said:
The picture discussed in above link:
e0ead781-42ff-4333-8d30-6293fb305519.jpeg


Notice also the different shape of the sensor on the inlet lip (below the twin bypass outlets)
Click to expand...

I wonder what the range of the twin seat variant of the J-20 will be over the single seat variant? Considering that there will obviously be less space for fuel tanks.
 
I

Inst

ACCESS: Restricted
Joined
Oct 18, 2019
Messages
29
Reaction score
6
Josh_TN said:
Is there any public range figure for the single seat version?
Click to expand...
Nothing official, estimates range from 1250 km (slightly higher than F-35C) to 2000 km combat radius. There's a claim somewhere of a tanked range of 5500 km. Compare over 3000 km F-22 ferry range, 4500 km Su-57 ferry range with external tanks.

For all the J-20's short-comings, it has very good range.

===

As for your comment about interceptor / fighter bomber, the J-20 has too poor a weapons bay to be either. Its weapons bay volume is roughly comparable to that of a F-35, except that an F-35 is a much smaller jet.

Interceptor -> can't dogfight, but can strike / intercept
Striker -> can dogfight, can strike, but can't intercept
Air superiority fighter -> can't strike, but can intercept or dogfight.

The poor weapons bay is a major short-coming, but air superiority fighters can and have been developed into strike fighters (Su-30, F-15E).

===

The bigger question, of course, is whether it's a good air superiority fighter (mediocre kinematics despite having essentially the Eurofighter AMK's layout). But that's more a function of the engine (surprised that they haven't tried stuffing TVC onto some operational fighters) and engine output (WS-10C is apparently in the same range as the Su-57's engines).
 
Last edited:
I

Inst

ACCESS: Restricted
Joined
Oct 18, 2019
Messages
29
Reaction score
6
GARGEAN said:
Inst said:
WS-10C is apparently in the same range as the Su-57's engines
Click to expand...
Eeeeeegh... That's optimistic)
Click to expand...
Erm, should have specified AL-41 / 117S, not Izdeliye 30. Should be in the 137-142kN range. Note that the intended WS-15 engine is supposed to be in the 17-18 ton range, and that the Chinese really screwed up by developing AL-31 / F110-class engines, instead of F404-type engines, where the smaller engine would have presented lesser technical challenges and allowed the Chinese to compensate for technological inferiority by simply using more, but smaller engines.
 
I

Inst

ACCESS: Restricted
Joined
Oct 18, 2019
Messages
29
Reaction score
6
Here's an important and relevant question:

Chinats on Chinese websites seem to attach a combat radius of 2000 km to the J-20. How viable is this on internal fuel?

For instance, a F-106 Delta Dart, on about a 30% internal fuel fraction, can make 930 km combat radius with a turbojet. The J-20 is certainly a draggier design, and has a higher wing loading to boot, but it uses a canard-lerx-delta-body lift design, which purports, for its 75 m^2 of wing-body lifting area, to achieve 80% higher lift (vs delta only and 20% vs Gripen/J-10-type canard-delta, and has a likely 40% fuel fraction.

In such a set-up, can the J-20 reach 2000 km combat radius on internal fuel alone?

===

The point is basically the F-35's point. The F-35 is a high fuel fraction fighter whose T/W and wing loading (although the wing loading should be decreased by about 23% due to tail lift in unstable parts of its regime) is terrible at maximum range, but excellent when engaging at "normal" ranges. In other words, it can be treated as having CFTs built in. If the J-20 has an even higher combat radius on internal fuel, first, the extreme combat radius allows it to afterburner in on defensive missions and later supercruise in. Second, since the J-20 needs much less of its fuel to get home, it can fight at very low fuel fractions and improve its wing loading / thrust to weight to Eurofighter levels even on a WS-10C.

===

One additional point is that the F-35, on an air to air mission, can reach about 1410 km. Since it's not designed for high speeds like the J-20, it's further possible that the J-20 can reach or near 2000 km on internal fuel on an air to air mission.

By the way, some calculations: the F-35 can reach around 274 kg / m^2 wing loading using tail lift in unstable (about -23% to wing loading) flight regimes to a combat radius of 600 km. The J-20 can likewise reach 271-282 (depending on whether canards are adding lift or neutral in the flight regime) kg / m^2 wing loading. The respective thrust / weights would be 1.22 and 1.32 T/W (using 137 kN for the J-20, mind you).
 
Last edited:
E

Evgeniy

ACCESS: Confidential
Joined
Mar 30, 2020
Messages
82
Reaction score
99
Inst said:
Erm, should have specified AL-41 / 117S,
Click to expand...
The Su-57 has a 117M engine with 15 tons of thrust.

How many tons of thrust the WS-10 has, as far as I remember, was not officially reported. It is unlikely that it is fundamentally different from the latest versions of the AL-31.
 
red admiral

red admiral

ACCESS: Top Secret
Joined
Sep 16, 2006
Messages
662
Reaction score
138
Just use Breguet range equation to do some calculations for range estimates. Feed in some feasible L/D, SFC or fuel fraction (e.g. compare with other aircraft published data) then see what you get out.
 
S

stealthflanker

ACCESS: Top Secret
Senior Member
Joined
Feb 12, 2010
Messages
741
Reaction score
437
red admiral said:
Just use Breguet range equation to do some calculations for range estimates. Feed in some feasible L/D, SFC or fuel fraction (e.g. compare with other aircraft published data) then see what you get out.
Click to expand...

Well it's actually bit more complex than that.. Used as it is. The breguet range would give "ferry range" which is... the "1 way" range. More iterations are needed. Like fuel utilizations, calculations of SFC during combat and returning to base, the aircraft's L/D's.

But anyway did that in excel with following assumptions :

Empty weight : 17000 Kg
Fuel weight of : 11000 Kg
L/Dmax of : 11 (looks reasonable, as far as i see typical fighters are about 10-13)
Cruise L/D is assumed to be 93.4% of the L/D max
Payload of 4000 Kg (weapons, pilot, etc)
Mission altitude of 12000-15000 m

Also Fuel utilizations need to be defined too. The radius or combat range is then effectively the cruise fuel.

The plane will "supercruise" throughout the mission at Mach 1.2. and doing afterburner during the combat as it would need some maneuvers. Then RTB, the fraction for RTB can be less than cruise phase one as the plane would drop payload. so it's lighter.

So what i got was that the combat range for my hypothetical J-20 there is 1384 Km. With enough fuel for 10 minutes of combat or dogfight with afterburner, and enough fuel for RTB with 6 minutes allowance for loiter awaiting landing.
 

Attachments

  • J-20 Mission.png
    J-20 Mission.png
    52.4 KB · Views: 41
T

Trident

ACCESS: Top Secret
Senior Member
Joined
May 8, 2006
Messages
1,089
Reaction score
399
Double digit L/D at Mach 1.2 seems optimistic... as does OEW of 17t.
 
red admiral

red admiral

ACCESS: Top Secret
Joined
Sep 16, 2006
Messages
662
Reaction score
138
Also need to consider the SFC values you're using. SFC at SLS uninstalled is very different from what you'll actually get at cruise conditions. The value you're currently using is more representative of a modern civil high bypass ratio turbofan
 
S

stealthflanker

ACCESS: Top Secret
Senior Member
Joined
Feb 12, 2010
Messages
741
Reaction score
437
red admiral said:
Also need to consider the SFC values you're using. SFC at SLS uninstalled is very different from what you'll actually get at cruise conditions. The value you're currently using is more representative of a modern civil high bypass ratio turbofan
Click to expand...

My sheet also take account of that. This is the "calculated parameters" section of the sheet.

Notice that i do Specify Altitude. That can be used to predict the SFC of the Jet engine.

The Atmosphere model i use is based on ICAO. Which should be good until 22000m.

The SFC or Specific Fuel Consumption of the engine roughly follows the following simple relationship RElationship-Engine.png

Where Ct is the SFC at SLS condition. a is the speed of sound in the operating altitude while the asl is the speed of sound in sea level condition.

Thus for given parameters (SLS SFC : 0.75) and cruising altitude of 15000 m. the estimated SFC of the engine at that altitude would be :

a(15000 m) : 924.9 ft/s
a(SLS) : 1115 ft/s

SFC(15000m) = 0.75 *(924/1115)
SFC(15000m) = 0.621 lb/lbhr.
 

Attachments

  • Altitude.png
    Altitude.png
    82.5 KB · Views: 43
Last edited:
overscan (PaulMM)

overscan (PaulMM)

Administrator
Staff member
Joined
Dec 27, 2005
Messages
12,771
Reaction score
4,455
GARGEAN said:
overscan (PaulMM) said:
WS-10C is analogous to Izdeliye 117, WS-15 to Izdeliye 30.
Click to expand...
May be. But from what I see we don't know enough about either WS-15 or Izd. 30 to make such claims.
Click to expand...
WS-10C is a developed WS-10. WS-15 is a new design.

Izd. 117 is a developed AL-31F. Izdeliye 30 is a new design.

Analogous doesn't mean comparable.
 
I

Inst

ACCESS: Restricted
Joined
Oct 18, 2019
Messages
29
Reaction score
6
stealthflanker said:
red admiral said:
Just use Breguet range equation to do some calculations for range estimates. Feed in some feasible L/D, SFC or fuel fraction (e.g. compare with other aircraft published data) then see what you get out.
Click to expand...

Well it's actually bit more complex than that.. Used as it is. The breguet range would give "ferry range" which is... the "1 way" range. More iterations are needed. Like fuel utilizations, calculations of SFC during combat and returning to base, the aircraft's L/D's.

But anyway did that in excel with following assumptions :

Empty weight : 17000 Kg
Fuel weight of : 11000 Kg
L/Dmax of : 11 (looks reasonable, as far as i see typical fighters are about 10-13)
Cruise L/D is assumed to be 93.4% of the L/D max
Payload of 4000 Kg (weapons, pilot, etc)
Mission altitude of 12000-15000 m

Also Fuel utilizations need to be defined too. The radius or combat range is then effectively the cruise fuel.

The plane will "supercruise" throughout the mission at Mach 1.2. and doing afterburner during the combat as it would need some maneuvers. Then RTB, the fraction for RTB can be less than cruise phase one as the plane would drop payload. so it's lighter.

So what i got was that the combat range for my hypothetical J-20 there is 1384 Km. With enough fuel for 10 minutes of combat or dogfight with afterburner, and enough fuel for RTB with 6 minutes allowance for loiter awaiting landing.
Click to expand...

Thanks for doing the work, although I'd dispute the empty weight (Trident elsewhere thinks it's around 21 tons, Chinats came out with a rumor of 15 tons and 17.5 tons, I work with 18.5-19.5 tons based on rough dimensions and 3D-printed titanium weight reduction) and payload (it's an air superiority / air defense fighter, it won't be carrying heavy strike missiles because it literally can't).

That said, I'm more interested in non-supercruising combat radius than supercruising combat radius. I think it's interesting that most Western analysts are thinking about the J-20 as an offensive and aggressive interceptor aimed at shooting down AEW&C and tankers. But on a defensive mode, speed and range are actually quite interesting.

For instance, if you have 2000 km non-supercruising range, you can now put rudimentary bases on the periphery of your territory, but base the aircraft with their weapons perhaps 1000-2000 km inland. The intent is that the aircraft take off from inland bases, cruise or supercruise to the border, dogfight, then return not to their original bases but the rudimentary frontline bases, allowing you to slash combat T/W while at the same time reducing your vulnerability to enemy attacks on your airfield.

Likewise, the speed and range allows you to attempt defeat in detail tactics; because you're faster than your opponent, you can concentrate the entire PLAAF onto a small portion of the enemy force. If you're in a range of 0.8 vs 1.2 equivalency to enemy fighters you can easily achieve 2:1 numerical superiority in a small area so that even if you don't have a qualitative or big qualitative advantage, quantity has a quality all its own. The quantitative advantage can help you minimize losses, then move on to the next segment of the enemy force.

===

Moreover, a 2000 km combat radius allows the J-20 to reach, from Chengdu basing (where, incidentally, the J-20 is produced), both Lhasa and Shanghai. This allows the Chinese to put a reserve force in Lhasa and Shanghai and allow them to handle both the Indian and Taiwan theaters simultaneously, perhaps even supercruising onto a combat mission using reduced fuel reserves with the aim of landing at a front airbase instead of the original airbase.
 
Last edited:
MC72

MC72

ACCESS: Confidential
Joined
Oct 17, 2010
Messages
79
Reaction score
28
Collecting all the possible information in dozens of forums and at the risk of some initial imprecision, I include this cutaway that anticipates the Chengdu J-20 version B, when it incorporates the new Chinese WS-15 engine since one of its problems is the lack of super cruise and its new BVR PL-15 missiles, 4 in the central interior warehouse, (the F-22 can already carry 6 new AIM-120s, and with the future AIM-260 Peregine this capacity will be much greater) I am also surprised that this dragon still need parachute braking on landing, which lengthens work on the ground.
Regards MC72
PD: The infographic is currently in Spanish
j37bh1P.jpeg
 
Last edited:
H

Helix88

ACCESS: Confidential
Joined
Mar 4, 2020
Messages
55
Reaction score
64
MC72 said:
Collecting all the possible information in dozens of forums and at the risk of some initial imprecision, I include this cutaway that anticipates the Chengdu J-20 version B, when it incorporates the new Chinese WS-15 engine since one of its problems is the lack of super cruise and its new BVR PL-15 missiles, 4 in the central interior warehouse, (the F-22 can already carry 6 new AIM-120s, and with the future AIM-260 Peregine this capacity will be much greater) I am also surprised that this bird still need parachute braking on landing, which lengthens work on the ground.
Regards MC72
PD: The infographic is currently in Spanish
j37bh1P.jpeg
Click to expand...
I was unaware of any evidence of thrust vectoring in future versions. Where did that particular tidbit come from?
 
MC72

MC72

ACCESS: Confidential
Joined
Oct 17, 2010
Messages
79
Reaction score
28
Helix88 said:
I was unaware of any evidence of thrust vectoring in future versions. Where did that particular tidbit come from?
Click to expand...
WS.jpg (Traduction from Mandarin) https://www.wautom.com/2017/08/engine-ws-15-for-j-20/
''The full name of WS-15 is turbofan 15 "Emei" turbofan engine. It is a small bypass ratio thrust vectored turbofan engine developed for my country's fourth-generation heavy/medium fighter. WS-15 is mainly used for the twin-engine heavy stealth fighter J-20. WS-15 was developed by experts from 606, 624, 614, 410, 430 and 113 factories. The “Emei” aero-engine technical verification machine was successfully tested in May 2006 for the first time. This indicates that my country has achieved a historic leap on the road of independent research and development of aero engines, and has taken a solid step in the development of my country's fourth-generation medium-sized fighter. In 2011, AVIC Liming completed the delivery of the ws-15 verification aircraft. The guarantee node will be completed in 2020.''

The 3d nozzle is of course accessory to the engine, but there is the possibility of including it in the J-20B version; Although the question may be, that without a cannon it is better to flee by push the accelerator to the maximum, than to do evasive acrobatic maneuvers.
Regards MC72
 
T

totoro

ACCESS: Secret
Joined
Jan 11, 2011
Messages
395
Reaction score
128
While WS-15 on J20 may very well feature TVC, I somehow don't really trust a random blog on Chinese cars (and other topics)...

The video itself may very well be of WS-15 but it doesn't really give out any info as to just what is it really showing. Anyone could take such a video and title it "WS-15".

Same for the refueling pod and side inlets MADL
Click to expand...

Refueling probe is pretty well documented by various older imagery.

MADL on the inlet however I am not sure about. Are you referring to the light gray protrusion below the hexagons? Is there any other probable use for such a protrusion? I guess RWR sensors would be within various leading and trailing edges on wings and rear parts of the plane...
 
BDF

BDF

ACCESS: Confidential
Joined
Mar 14, 2009
Messages
147
Reaction score
55
stealthflanker said:
red admiral said:
Just use Breguet range equation to do some calculations for range estimates. Feed in some feasible L/D, SFC or fuel fraction (e.g. compare with other aircraft published data) then see what you get out.
Click to expand...

Well it's actually bit more complex than that.. Used as it is. The breguet range would give "ferry range" which is... the "1 way" range. More iterations are needed. Like fuel utilizations, calculations of SFC during combat and returning to base, the aircraft's L/D's.

But anyway did that in excel with following assumptions :

Empty weight : 17000 Kg
Fuel weight of : 11000 Kg
L/Dmax of : 11 (looks reasonable, as far as i see typical fighters are about 10-13)
Cruise L/D is assumed to be 93.4% of the L/D max
Payload of 4000 Kg (weapons, pilot, etc)
Mission altitude of 12000-15000 m

Also Fuel utilizations need to be defined too. The radius or combat range is then effectively the cruise fuel.

The plane will "supercruise" throughout the mission at Mach 1.2. and doing afterburner during the combat as it would need some maneuvers. Then RTB, the fraction for RTB can be less than cruise phase one as the plane would drop payload. so it's lighter.

So what i got was that the combat range for my hypothetical J-20 there is 1384 Km. With enough fuel for 10 minutes of combat or dogfight with afterburner, and enough fuel for RTB with 6 minutes allowance for loiter awaiting landing.
Click to expand...

How reliable are the empty weight(s) for the J-20 and Su-57? They seem awfully light given the Raptor is around ~19,650kg. I grant that they are newer designs and may benefit from more recent manufacturing and material technologies but both are larger than the Raptor is. I wonder if there's some confusion about the OEW and the weight of the airframe without engines for example. I recall the F-22 started out with a airframe goal of 13,750kg minus the engines. The F119s supposedly weigh in at 1,800kg each so this translates to a estimated OEW of 17,350kg. It gained about 2,300kg during EMD apparently. Anyway don't mean sidetrack the discussion just wondering how realistic the empty weight assumptions are.
 
T

TomcatViP

Hellcat
Joined
Feb 12, 2017
Messages
3,357
Reaction score
2,136
totoro said:
While WS-15 on J20 may very well feature TVC, I somehow don't really trust a random blog on Chinese cars (and other topics)...

The video itself may very well be of WS-15 but it doesn't really give out any info as to just what is it really showing. Anyone could take such a video and title it "WS-15".

Same for the refueling pod and side inlets MADL
Click to expand...

Refueling probe is pretty well documented by various older imagery.

MADL on the inlet however I am not sure about. Are you referring to the light gray protrusion below the hexagons? Is there any other probable use for such a protrusion? I guess RWR sensors would be within various leading and trailing edges on wings and rear parts of the plane...
Click to expand...
Why would someone use a stealthy fighter plane with a round refueling pod hanging below?
Also, the side meshed outlets are identical. Even the shape that we can guess behind the grids are similar (see the picture I cropped and posted). There is no way one to be a phased array...
 
S

stealthflanker

ACCESS: Top Secret
Senior Member
Joined
Feb 12, 2010
Messages
741
Reaction score
437
BDF said:
stealthflanker said:
red admiral said:
Just use Breguet range equation to do some calculations for range estimates. Feed in some feasible L/D, SFC or fuel fraction (e.g. compare with other aircraft published data) then see what you get out.
Click to expand...

Well it's actually bit more complex than that.. Used as it is. The breguet range would give "ferry range" which is... the "1 way" range. More iterations are needed. Like fuel utilizations, calculations of SFC during combat and returning to base, the aircraft's L/D's.

But anyway did that in excel with following assumptions :

Empty weight : 17000 Kg
Fuel weight of : 11000 Kg
L/Dmax of : 11 (looks reasonable, as far as i see typical fighters are about 10-13)
Cruise L/D is assumed to be 93.4% of the L/D max
Payload of 4000 Kg (weapons, pilot, etc)
Mission altitude of 12000-15000 m

Also Fuel utilizations need to be defined too. The radius or combat range is then effectively the cruise fuel.

The plane will "supercruise" throughout the mission at Mach 1.2. and doing afterburner during the combat as it would need some maneuvers. Then RTB, the fraction for RTB can be less than cruise phase one as the plane would drop payload. so it's lighter.

So what i got was that the combat range for my hypothetical J-20 there is 1384 Km. With enough fuel for 10 minutes of combat or dogfight with afterburner, and enough fuel for RTB with 6 minutes allowance for loiter awaiting landing.
Click to expand...

How reliable are the empty weight(s) for the J-20 and Su-57? They seem awfully light given the Raptor is around ~19,650kg. I grant that they are newer designs and may benefit from more recent manufacturing and material technologies but both are larger than the Raptor is. I wonder if there's some confusion about the OEW and the weight of the airframe without engines for example. I recall the F-22 started out with a airframe goal of 13,750kg minus the engines. The F119s supposedly weigh in at 1,800kg each so this translates to a estimated OEW of 17,350kg. It gained about 2,300kg during EMD apparently. Anyway don't mean sidetrack the discussion just wondering how realistic the empty weight assumptions are.
Click to expand...
It doesnt actually matter. I just pick some number which looks good. and run it. I wonder tho why not many more people use the breguet range equation, considering how widely it is the availability of the related materials.

On the empty weight respect however, there unfortunately no real figure released for both J-20 and Su-57 on that respect. All figures i see so far are estimates based on photographs and such. Unfortunately people are screwing around way too much on finding "accurate" estimate which they may never found unless official release by the respective company. It is not important that the first estimate to be accurate, just as close as one's ability or materials available. The more important thing are the methods being used to calculate the performance, the standard being used (OEW or any specified condition) and whether others can repeat the calculations.
 

Similar threads

Top