J-20 5th Gen Fighter Thread IV (Closed to posting)

[Engineer]

I was thinking in the lines that planes have full load when mentioning maximum speeds which means of course also external armament. I thought it would cause so much drag that it is not practical to go for more powerful engines. I admit that I should have mentioned that point in earlier post.

F-22 would surely go some 2.x Mach if needed and with only internal armament. F-35 is coming out more and more lumpy with every iteration and I doubt it could do more than 1.8 mach even with clean sheet plane. Even thought, that F115 engine IS a monster for an engine. And there is the problem with Chinese planes, engine technology is not yet even near what USA can manufacture. (Or UK, referring to canceled F116 engine).

If you assume China to be 20 years behind US in engine technology, it would put China's current abilities to at US's level at 1990's. That happens to be the time when the F-119 engine first came out.

However, Chinese engineers know perfectly well that China's engine technology is far behind the US, which is why the J-20 exploits as much aerodynamics advantage as possible. A low aspect ratio configuration will allow the J-20 to cruise faster with a lower engine power as a jet with equivalent T/W ratio. At the same time, vortex interactions enable higher lift to be created and be more maneuverable versus an aircraft with equivalent wing loading.

 

[MiG-29]

If I were to compare sizes between two aircraft, I'd much rather rely on a satellite picture that contains both. Then both aircraft would unequivocally be pictured from the same distance, angle and resolution. The pictures you have used comparing cockpits etc are highly inexact, as there is ample room for differences in angles, distances etc. One should always use the tools that gives the best equal representation of the measuring stick and the aircraft in question. As of now, that is Deino's pic. Remember how we landed on a more considerable length using more dubious and erroneous pics earlier? Well, now we finally have the best tool we can have short of official measurements or actually standing next to the aircraft.

Let us start for what we are really doing we are guessing, yes that is what are we doing, by pixelation you get when you zoom the image is a bunch of squares that disfigure the shape of those aircraft, to complicate this even more some tones and shades prevent you to know the real shape and limits of the radomes and nozzles or tail stings.


So there is where subjectivity plays the biggest role, those squares and tones do not give you the real shape.

No one here has an official figure all are guesses.

The canopies pretty much are the same i told all of you that is also a guess, since obviously there is a marging for error.
The J-20 and F-22 canopies are pretty much almost the same size, enough to make a rough estimation of the size, but far from being official data.

You are free to choose the best method for you to calculate which is the closest measurement to the official one, but pixalation only will work if you have a perfect drawing of the J-20 shape viewed from top and try to overlap it to the picture as Paralay did

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however paralay`s drawing is not perfect so his drawing does not show the real shape of the J-20 and you can see it in the canard, see that his measurments even say 19.8 meters, which even a bit much smaller that what even the Chinese TV says

 

[MiG-29]

I was thinking in the lines that planes have full load when mentioning maximum speeds which means of course also external armament. I thought it would cause so much drag that it is not practical to go for more powerful engines. I admit that I should have mentioned that point in earlier post.

F-22 would surely go some 2.x Mach if needed and with only internal armament. F-35 is coming out more and more lumpy with every iteration and I doubt it could do more than 1.8 mach even with clean sheet plane. Even thought, that F135 engine IS a monster for an engine. And there is the problem with Chinese planes, engine technology is not yet even near what USA can manufacture. (Or UK, referring to canceled F136 engine).

Edit: Fixed the F-35 engines to correct numbers. I shouldn't trust my menory.

the engine thrust is not the problem.

MiG-25 has engines rated at 10 tonnes of thrust each and it has a mass over 30 tonnes, but still it will fly Mach 2.8.
Mirage lll or MiG-21 have engines of barely 7 tonnes and reach Mach 2.


Always is inlet design what limits the speed

DSI are fixed so they will allow around Mach 1.8, J-31 with official data shows you that same is F-35 and JF-17.

Supercruise is the result of low drag, high thrust at dry power and inlet design.

J-31 needs engines of 10 tonnes very likely to supercruise.

Eurofighter supercruises with engines of 9 tonnes but it is lighter and only when it has a fraction of its weapons.

J-20 will need an engine at least as good as 117 to achieve similar speeds to Su-35 or PAKFA, something in the range of 15 tonnes
Also the engine must be cleared for supercruise.

MiG-29K has engines as powerful as EJ-200s but does not supercruise at least up to what i know, but i know Russia is working in a 9.5 tonnes RD-33 derivative for the MIG-29/MiG-35 perhaps this will allow to supercruise to the MiG-35, but who knows

 

[Skywatcher]

the engine thrust is not the problem.

MiG-25 has engines rated at 10 tonnes of thrust each and it has a mass over 30 tonnes, but still it will fly Mach 2.8.
Mirage lll or MiG-21 have engines of barely 7 tonnes and reach Mach 2.


Always is inlet design what limits the speed

DSI are fixed so they will allow around Mach 1.8, J-31 with official data shows you that same is F-35 and JF-17.

Supercruise is the result of low drag, high thrust at dry power and inlet design.

J-31 needs engines of 10 tonnes very likely to supercruise.

Eurofighter supercruises with engines of 9 tonnes but it is lighter and only when it has a fraction of its weapons.

J-20 will need an engine at least as good as 117 to achieve similar speeds to Su-35 or PAKFA, something in the range of 15 tonnes
Also the engine must be cleared for supercruise.

MiG-29K has engines as powerful as EJ-200s but does not supercruise at least up to what i know, but i know Russia is working in a 9.5 tonnes RD-33 derivative for the MIG-29/MiG-35 perhaps this will allow to supercruise to the MiG-35, but who knows

Supercruise depends on the velocity of the exhaust.

 

[Player99]

Hehe, I don't know why you good gentlemen bother to keep arguing/debating with Mr. Mig-29. His mind is set to hold on to his belief no matter what. And he's been like this as far as I remember.

If your intention is to inform, educate, and delight other forum members, lurkers, and yourselves with your diligent work, I'd highly praise your effort, but it is really, I'd say, not worth arguing with Mr. Mig-29 or his likes along this line any more.

Let's just enjoy what we see and let time unveil the facts in an accelerated rate... By some time in 2015, I believe people will change their attitude toward J-20 and other things of this nature from China, just as they have toward J-10 between today and 2006.

 

[latenlazy]

the engine thrust is not the problem.

MiG-25 has engines rated at 10 tonnes of thrust each and it has a mass over 30 tonnes, but still it will fly Mach 2.8.
Mirage lll or MiG-21 have engines of barely 7 tonnes and reach Mach 2.


Always is inlet design what limits the speed

DSI are fixed so they will allow around Mach 1.8, J-31 with official data shows you that same is F-35 and JF-17.

Supercruise is the result of low drag, high thrust at dry power and inlet design.

J-31 needs engines of 10 tonnes very likely to supercruise.

Eurofighter supercruises with engines of 9 tonnes but it is lighter and only when it has a fraction of its weapons.

J-20 will need an engine at least as good as 117 to achieve similar speeds to Su-35 or PAKFA, something in the range of 15 tonnes
Also the engine must be cleared for supercruise.

MiG-29K has engines as powerful as EJ-200s but does not supercruise at least up to what i know, but i know Russia is working in a 9.5 tonnes RD-33 derivative for the MIG-29/MiG-35 perhaps this will allow to supercruise to the MiG-35, but who knows

Yano, a few weeks ago I found a few forum discussions that discussed the F-22's fixed inlets, and it was mentioned that the F-22 uses its dorsal air bleed vents to regulate pressure recovery, doing away with the need for a variable inlet. If you want to see the discussion, I can post it.

Otherwise, that's really all I'm going to say on this topic, a poor horse so beaten and flayed the sinew is stripping itself off bone.

 

[Engineer]

the engine thrust is not the problem.

MiG-25 has engines rated at 10 tonnes of thrust each and it has a mass over 30 tonnes, but still it will fly Mach 2.8.
Mirage lll or MiG-21 have engines of barely 7 tonnes and reach Mach 2.

Always is inlet design what limits the speed

DSI are fixed so they will allow around Mach 1.8, J-31 with official data shows you that same is F-35 and JF-17.

Wrong, and you are repeating nonsense. It is the thrust and drag that limit the speed, not air inlet design. This is simple flight dynamics, and you aren't going to find a source that says otherwise. F-22 can supercruise and exceed Mach 2 despite having a fixed inlet, so your Mach 1.8 speed limit myth is debunked. F-35, JF-17 and 31001 are not heavy weight fighter, so naturally they are going to fly slower. However, DSI can achieve similar performance to a variable-geometry inlet used on the F-4D at Mach 2.0, as the comparison below shows:

Supercruise is the result of low drag, high thrust at dry power and inlet design.

Wrong. "The real secret to supercruise is thrust minus drag" as

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. That's real flight dynamics speak from a real pilot who flown a real supercruise capable aircraft, not your pseudo flight dynamics nonsense.

J-31 needs engines of 10 tonnes very likely to supercruise.

Eurofighter supercruises with engines of 9 tonnes but it is lighter and only when it has a fraction of its weapons.

J-20 will need an engine at least as good as 117 to achieve similar speeds to Su-35 or PAKFA, something in the range of 15 tonnes
Also the engine must be cleared for supercruise.

MiG-29K has engines as powerful as EJ-200s but does not supercruise at least up to what i know, but i know Russia is working in a 9.5 tonnes RD-33 derivative for the MIG-29/MiG-35 perhaps this will allow to supercruise to the MiG-35, but who knows

More pseudo flight dynamics theories. I do not know what engine various aircraft will need to supercruise. What I do know is the following. First of all, an engine does not need to "be cleared to supercruise" for an aircraft to supercruise, since the air speed going into the engine is always subsonic. Secondly, an aircraft with low aspect ratio wing is going to have lower drag than a similar sized aircraft with higher aspect ratio. In other words, aircraft such as the J-20 is going to have easier time supercruising than the Su-35 or PAKFA. Simple flight dynamics.

 

[Engineer]

Yano, a few weeks ago I found a few forum discussions that discussed the F-22's fixed inlets, and it was mentioned that the F-22 uses its dorsal air bleed vents to regulate pressure recovery, doing away with the need for a variable inlet. If you want to see the discussion, I can post it.

Otherwise, that's really all I'm going to say on this topic, a poor horse so beaten and flayed the sinew is stripping itself off bone.

The purpose of inlet design is to maximize pressure recovery thus engine performance. However, with sufficiently powerful engines, you can overcome poor pressure recovery. At the end of the day, thrust and drag are the two players that determine the speed of an aircraft. That's basic flight dynamics.

 

[latenlazy]

The purpose of inlet design is to maximize pressure recovery thus engine performance. However, with sufficiently powerful engines, you can overcome poor pressure recovery. At the end of the day, thrust and drag are the two players that determine the speed of an aircraft. That's basic flight dynamics.

Just thought I'd bring up something I thought was interesting.

 

[siegecrossbow]

An interesting bit of wingloading calculation. Courtesy of Kryptid from secretprojects. What do you guys think?

Assuming the reference image I used to calculate wing area was fairly accurate, I arrived at these approximate figures for overall reference wing area based on the speculated dimensions provided above:

Length - Wing Area
19.2 meters (63 feet) - 71 square meters (763 square feet)
20.35 meters (66.75 feet) - 79.9 square meters (860 square feet)
20.7 meters (67.9 feet) - 82.6 square meters (889 square feet)

For comparison, the F-22 has a length of slightly above 18.9 meters (62 feet) and a wing area of 78.4 square meters (840 square feet).

If (and this is a big if) the J-20 has a similar weight per unit length as the F-22, the following wing loadings can be calculated. These figures may not be that unreasonable since the two are in roughly the same size range and have similar design elements (the boxy fuselage, closely-spaced engines, low aspect ratio wings, fixed inlets, internal weapons, same canopy, etc). Take note that I did some rounding with the numbers.

Length - Loaded Weight - Wing Loading

19.2 meters (63 feet) - 29,700 kilograms (65,400 pounds) - 418 kilograms/square meter (86 pounds/square foot)
20.35 meters (66.75 feet) - 31,500 kilograms (69,300 pounds) - 394 kilograms/square meter (81 pounds/square foot)
20.7 meters (67.9 feet) - 32,000 kilograms (70,500 pounds) - 387 kilograms/square meter (79 pounds/square foot)

You may have noticed that the larger values for length generate lower values for wing loading. Due to scaling laws, this is almost certainly incorrect. Using the square-cube law (and using the lowest length value as a baseline) more realistic wing loadings may be calculated:

Length - Loaded Weight - Wing Loading

19.2 meters (63 feet) - 29,700 kilograms (65,400 pounds) - 418 kilograms/square meter (86 pounds/square foot)
20.35 meters (66.75 feet) - 35,400 kilograms (77,900 pounds) - 443 kilograms/square meter (91 pounds/square foot)
20.7 meters (67.9 feet) - 37,200 kilograms (82,000 pounds) - 450 kilograms/square meter (92 pounds/square foot)

For comparison, the F-22's loaded weight is 29,300 kilograms (64,460 pounds) and its wing loading in this state is 375 kilograms/square meter (77 pounds/square foot). All of these estimates put it at a higher wing loading than the F-22. However, I would also like to point out the the range of wing loadings calculated is still rather "fighter-like". Compare these values with those of the F-16C Block 30 (at 431 kg/m2 or 88.3 lb/ft2), the F-35A (at 526 kg/m2 or 107 lb/ft2), the F/A-18E/F (at 459 kg/m2 94 lb/ft2), and the Su-35S (at 408 kg/m2 or 84.9 lb/ft2).

It should also be remembered that there are many other factors that affect an aircrafts lift than just wing loading alone. There is also leading edge sweep, taper ratio, camber, airfoil profile, types and sizes of leading edge/trailing edge flaps/flaperons, wing interactions with other aircraft structures (such as LERX and canards), thickness ratio, how it is integrated with the fuselage, etc.

In the end, I believe that the J-20 was designed with agility as a high priority. Not just the theoretical wing loading calculations, but the all-moving canards, tails and the canopy design lead me to this conclusion as well. If speed, supersonic cruise and range were all they cared about, a tailless delta would probably have been both a stealthier and a less-draggy option than a canard-delta.