J-20... The New Generation Fighter II

Planes do not change their roles just like that once theyre in service. There are no actual evidence for either side but there are plenty of indications for the fighter/interceptor role of j20. First there is a clear need for such a plane. That goes hand in hand with official statement of deputy of plaaf that such a plane IS in development. He was quoted two years ago that such an advanced air superiority fighter will fly soon and be fieleded within 8 to 10 years. Two years later, lo and behold, a plane seemingly very fitting flew. And was built by CAC, which we know from news bits has the job of developing new gen fighter. While it is possible there is another project lined up i say it is VERY unlikely, thus its very probable what we saw is indeed the next gen fighter.

Dedicated Striker/bomber does not need maneouvrability. In fact, excess control surfaces are not benefitial for such role as they add weight and drag while 99% of the mission of such a plane is a silent approach and quick egress. On the other hand, we can cleary see large canards, all moving tails and a very bulbous canopy. Which dedicated striker has those?

Some people may claim stuff about center of gravity and lift and what not but truth of the matter is without knowing the schematics of the plane one cant just guess such things from the images. The plane may not have standard internal layout. Who knows which materials are used? How do we know how much lift is gained by the fuselage or/and canards?

Powerful engines are definitely a must but one would not embark on a project of this scale and build a plane without being able to do the engines right. Now, the engines may or may not be on par with the western equivalents, but it is most likely they will be powerful enough for a fighter. Even 4th gen engines will provide j20 with enough thrust to do its mission, albeit with some capability missing. It may happen that only a midlife refit will provide the plane with the engines that fully unlock its potential, something like what went on with Tomcat throughout its service life.

Oh and j20 isnt that huge. I wont argue with anyone, but im willing to bet a hundred dollars its in the 20 meter range, length wise. One cant cram in a lot of ordenance in that. That is because it is not designed as a dedicated striker.

Oh and j20 isnt that huge. I wont argue with anyone, but im willing to bet a hundred dollars its in the 20 meter range, length wise.

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Seems you have read this too!

09:32 GMT, March 3, 2011 Aerospace experts scrutinizing images of the Chinese J-20 fighter that first began appearing on the internet in late December have developed a more nuanced view of the plane's features than what was available in early reports. Although the J-20 resembles the outline of the stealthy F-22 Raptor when viewed head-on in its forward aspect, the plane clearly lacks many of the features that make Raptor the most capable air-to-air combat system in history. On the other hand, these same experts believe that over time the Peoples Liberation Army Air Force can evolve the J-20 into a formidable combat aircraft -- especially given the fact that it is expected to operate in or near Chinese airspace, where it will greatly outnumber any attacker's planes.

Early reports that the J-20 exceeds 70 feet in length appear to be wrong. By comparing the scale of the aircraft with adjacent reference objects whose dimensions are known, experts have determined that the fighter is 62 feet long -- the same length as the F-22, and not much different from the 64 feet of the F-15C fighter. Based on overhead imagery and other inputs, wingspan looks to be about 41 feet, also similar to F-22 (45 feet) and F-15C (43 feet). However, the wing area of roughly 630 square feet much more closely resembles the 608 square feet of the F-15C than the 840 square feet on the F-22; this matters a great deal in terms of range since fuel is stored in wing areas.

The J-20's top speed is judged to be below Mach 2, meaning it is significantly slower than an F-22 or F-15C. Little is known about the performance features of the J-20's twin jets, which may be based on technology from the western CFM-56 commercial powerplant first exported 30 years ago. The steady-state thrust provided by the engines is probably similar to the 29,000 lbs of the F-15C, but greatly inferior to the 48,000 lbs generated by the two F119 engines on the Raptor (J-20 maximum thrust of 60,000 lbs comes closer to the 70,000 lbs of F-22, and surpasses the 48,000 lbs of F-15C). The J-20 does not have the supercruise feature of the F-22 that allows the latter plane to fly at high speed without consuming excessive amounts of fuel, which puts the J-20 at a decided disadvantage given that it carries about 25 percent less fuel internally than the F-22. It also does not have the vectored thrust of the F-22 that provides enhanced aerial agility; the Chinese appear to have modified the fixed exhaust nozzles on the J-20 with an eye to misleading western observers concerning how capable the propulsion system is.

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I read the "analysis" yo mention, but i discarded it for having to many incongruences, their conclusions differ wildy form other assessments, the problem with those so call "analyst " is that you can find them on every flavour:
* "The It's just a fiber glass mock-up and wont even fly" flavor:
defensetech.org/2010/12/31/j-20-vs-f-35-one-analysts-perspective
* "It`s the final weapon and will bring civilizarion to an end" flavor
ausairpower.net/APA-J-XX-Prototype

Some time ago i saw a documentary of the ATF Program in the USA, it started like a program to build an advanced striker, but they realize that a fighter (suited accordingly) can perform strike missions with relative ease but no the other way around.

The speed claims are particularly amusing, because speed is often influenced more by the escape velocity of gases leaving the engine rather than the T/W ratio and maximum power output.

The fastest achieveable speed depends on both how much and how fast air can be expelled from the engine, so in a sense thrust does matter, so does speed:


The motion impulse of the engine is equal to the fluid mass multiplied by the speed at which the engine emits this mass:

I = mc

where m is the fluid mass per second and c is the exhaust speed. In other words, a vehicle gets the same thrust if it outputs a lot of exhaust very slowly, or a little exhaust very quickly. (In practice parts of the exhaust may be faster than others, but it is the average momentum that matters, and thus the important quantity is called the effective exhaust speed - c here.)

However, when a vehicle moves with certain velocity v, the fluid moves towards it, creating an opposing ram drag at the intake:

mv

Most types of jet engine have an intake, which provides the bulk of the fluid exiting the exhaust. Conventional rocket motors, however, do not have an intake, the oxidizer and fuel both being carried within the vehicle. Therefore, rocket motors do not have ram drag; the gross thrust of the nozzle is the net thrust of the engine. Consequently, the thrust characteristics of a rocket motor are different from that of an air breathing jet engine, and thrust is independent of speed.

The jet engine with an intake duct is only useful if the velocity of the gas from the engine, c, is greater than the vehicle velocity, v, as the net engine thrust is the same as if the gas were emitted with the velocity c − v. So the thrust is actually equal to

S = m(c − v)

This equation shows that as v approaches c, a greater mass of fluid must go through the engine to continue to accelerate at the same rate, but all engines have a designed limit on this. Additionally, the equation implies that the vehicle can't accelerate past its exhaust velocity as it would have negative thrust.

Conservation of energy means at max speed, all the power from the engine will be used to counter drag.
Also momentum needs to be conserved.

S = m(c − v)

If there is no air resistance on the body of the plane, then eventually v will equal to c irrespective of m, since max speed is reached when S becomes zero. However in reality a (quite large) part of the thrust needs to counter drag on the body of the plane, so while c determines the max speed of the plane, m will also have an effect.

If c is kept the same while m increases, you will have larger thrust and therefore larger acceleration at the same starting speed, you will also have a higher top speed v.

So it should be like:

S = m(c − v) - Dv, where Dv is the counter impulse generated at speed v as the plane tries to push an equivalent mass of air out of it's way (crudely speaking)

S = mc -mv - Dv

And maximum speed is reached when S = 0

Highere speed will have higher Dv so part of mc will need to counter that, so v can never be as high as c, but v can approach closer to c if you increase m, which is why the need for higher thrust engines, although you can also will increase c if m is kept constant, or better still increase both, so both m and c is important.

c (engine exhaust speed) determines the maximum speed limit, but you need m to push you closer to that limit (and it has a increasingly diminished return the closer you try to get to that value, like y=1/x plot)

The volume, and thus area, of the wings is indeed important for the amount fuel they can contain, but that is also influenced by the amount of flap area on the leading and trailing edges. How do they compare?
Beside this type of aircraft will stow a considerable part of its fuel in the fuselage.
The engines used are bound to be of an interim type, as there is a lot of time to go before 2017, when the aircraft is to become operational at the earliest, so the definitive version of the engine now used or even an entirely new engine van appear in the mean time.

The heads up display used by the J-20 may appear, in a modified form, in China's spacestation Tiangong I.

Source from Xinhua:

zoom said:

Seems you have read this too!

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Surprising how they already knew what engine, and the power, T:W ratio are already, before any info was leaked

siegecrossbow said:

The heads up display used by the J-20 may appear, in a modified form, in China's spacestation Tiangong I.

Source from Xinhua:

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one translation stated that data can also display in the helmet,hint of new gen. of HMS/HMD.the original HMS clone copy of soviet arsenal HMS already obselete.

Asymptote said:

Russian analyst who analyzed the aspect ratio, aerodynamics and center of gravity of the J-20, think it's not very maneuverable, and is design as a strike fighter (or strike bomber). Go back about 20 - 30 pages, I think there is a link to that article.

I personally think this issue will largely depend on the engine itself. Will CAC be able to develop a very powerful thrust vectoring engine is the root of the matter. Will the engine be able to do thrust vectoring? Will it have 190 kn thrust? Will it have high thrust to weight ratio?? If engine cannot meet these requirements, it will become a strike bomber. A stealthy one.

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Russian analysts also collectively suffer from a server case of sour grapes syndrome which cripple their ability to think neutrally or rationally when it comes to Chinese defense and the J20 in particular.