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

[latenlazy]

The sears-haack body is basicly the aerodynamic body with least drag, the Von Karman ogive is also the least drag body of revolution you can get.

J-20 has not such type of cross section in fact is not even a body of revolution, in the other hand corcorde and Su-27 do have sears-hack bodies and von Karman ogives, plus concorde and SU-27 have ventral podded engines.

If you want data go to the Yefim Gordon`s book Su-27, which was made with extensive help by the Sukhoi Bureau, go to page 515 and look at tables 2 and 3 and will see the Flanker has the lowest fuselage relative cross section even lower than F-16 and F-15.

F-35 like any stealth fighter has a large cross section due to weapons bays.

The F-22 supercruise thanks to its engines that have 4 tonnes more thrust than Al-31.

The likelihood the J-20 supercruises with Al-31 are so low, that is hard to believe a machine with the same engines and heavier weight with a no sears-haack body of revolution will supercruise while the Su-27 does not supercruise.

Su-35BM supercruises but has 117s engines and PAKFA will fly with type 30 engine that is supposed to replace 117 because the 117 is not as powerful to be economical for the T-50 to compete with F-22.

You are welcome to believe it supercruises, i differ.

You need finite element analysis in order to determine how closely a complex shape conforms to a sears-haack body, not imaginary eyeballing skills. Unless you've done the differential calculus necessary to determine the distribution of the J-20's volume, it's impossible to tell just by looking.

We don't even know the weight of the J-20, and operational weight itself varies depending on load, so even if the J-20 had a higher empty weight than the Su-27, it doesn't mean it is always going to be heavier when during operation.

 

[MiG-29]

You need finite element analysis in order to determine how closely a complex shape conforms to a sears-haack body, not imaginary eyeballing skills. Unless you've done the differential calculus necessary to determine the distribution of the J-20's volume, it's impossible to tell just by looking.

We don't even know the weight of the J-20, and operational weight itself varies depending on load, so even if the J-20 had a higher empty weight than the Su-27, it doesn't mean it is always going to be heavier when during operation.

There are already equations for the Sears-haack body and Von karman ogive.

J-20 does not fit the bill, stealth has played big part in its design, they can try to fix it but is easy to see it is not a sears-haack body, with simple inspection you can see the Su-27 does conform to such concept better.

You are just giving excuses.

Any way, you are welcome to believe it supercruises.

No need discuss this further regards

 

[Engineer]

The sears-haack body is basicly the aerodynamic body with least drag, the Von Karman ogive is also the least drag body of revolution you can get.

J-20 has not such type of cross section in fact is not even a body of revolution, in the other hand corcorde and Su-27 do have sears-hack bodies and von Karman ogives, plus concorde and SU-27 have ventral podded engines.

Wong, J-20 has a Sears-Haack body. The Whitecomb's area rule from which the Sears-Haack body is derived never concerns with the actual shape of the aircraft. All that matter is the distribution of cross sectional area along the longitudial axis matches that of the Sears-Haack body.

The area rule says that an airplane designed with the same cross-sectional area distribution in the longitudinal direction as the Sears-Haack body generates the same wave drag as this body, largely independent of the actual shape.

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Your belief that a Sears-Haack body literally refers to the fuselage shape shows your complete misunderstanding in the subject.

If you want data go to the Yefim Gordon`s book Su-27, which was made with extensive help by the Sukhoi Bureau, go to page 515 and look at tables 2 and 3 and will see the Flanker has the lowest fuselage relative cross section even lower than F-16 and F-15.

F-35 like any stealth fighter has a large cross section due to weapons bays.

Having actually counted the pixels with a computer program, I can tell you that Flanker and J-20 has nearly the same frontal cross sectional area. The F-35 being a smaller aircraft than J-20, actually has smaller frontal cross section than a Flanker. Your use of the word "large" to describe F-35's frontal cross section is unsubstantiated.

The F-22 supercruise thanks to its engines that have 4 tonnes more thrust than Al-31.

The likelihood the J-20 supercruises with Al-31 are so low, that is hard to believe a machine with the same engines and heavier weight with a no sears-haack body of revolution will supercruise while the Su-27 does not supercruise.

Su-35BM supercruises but has 117s engines and PAKFA will fly with type 30 engine that is supposed to replace 117 because the 117 is not as powerful to be economical for the T-50 to compete with F-22.

You are welcome to believe it supercruises, i differ.

Weight, or more specifically thrust-to-weight ratio has little to do with supercruise. This has already been shown with the Concorde, as well as P-42. The latter has a thrust-to-weight ratio of 2:1 yet has no supercruise ability. Whether J-20 being heavier is entirely irrelevant. With substantial weight saving from 3D printing and more modern manufacturing techniques, I wouldn't be surprise that J-20 turns out to be slightly lighter.

Supercruise has as much to do with low drag as it does with powerful engine. Fitting F-22's engines on to the Flanker won't make the latter supercruise at Mach 1.8, because the Flanker's airframe simply isn't designed to supercruise. On the other hand, the J-20 is designed to supercruise, achieved by reduction drag at supersonic speed. That is evident by the low aspect-ratio and thin wing, as well as a high fineness ratio body. So naturally, the J-20 is going to be able to fly faster given the same amount of thrust as a Flanker. Like I said earlier, I wouldn't be so quick to dismiss current J-20 prototypes' ability to supercruise.

 

[Engineer]

There are already equations for the Sears-haack body and Von karman ogive.

J-20 does not fit the bill, stealth has played big part in its design, they can try to fix it but is easy to see it is not a sears-haack body, with simple inspection you can see the Su-27 does conform to such concept better.

You are just giving excuses.

Any way, you are welcome to believe it supercruises.

No need discuss this further regards

Nope. The J-20 conforms to the Sears-Haack body.

 

[kyanges]

Just wait and see guys. This exact scenario has played out every single time someone says the J-20 can or can't do something.

 

[Quickie]

Engineer is correct. In aircraft design, having a streamline body that conforms to the Sears-Haack body has to be seen in the context of the Area Rule because of the complex design of an aircraft that involve not only the fuselage, as someone here would want us to believe otherwise, but also control surfaces like the wings, canards, horizontal/vertical stabilizers and a whole lot of the rest of the aircraft's components.

 

[MiG-29]

as someone here would want us to believe otherwise, .

Sears-haack bodies are bodies of revolution, if you understand that, then you can see why aircraft without stealth requirements have round or oval cross sections in example F-18, Concorde, Su-27 and so on.

Stealth requieres other types of non bodies of revolutions, J-20 like F-22 needs economical engines, in few words no external clutter like external stores or weapons and high thrust at dry power.

Can J-20 supercruise with Al-31? maybe, do i think it does? no i do not, concorde also uses afterburner from transonic speeds to Mach 1.7, but here lies a secret you have not think, variable geometry intakes and speed actually add thrust as air is compressed like in SR-71.

J-20 has a fixed intake and only a body of revolution on the jet nozzles, the main cross section is diamond shaped or semi-trapezoidal and has no Von karman ogive radome.

F-35 has been modifided not because they do not know stealth requieres flat surfaces, but because that new shape is more aerodynamic

F-22 has also engines that have higher thrust at dry power than Al-31 ad 4 tonnes more of thrust than Al-31.

Does it supercruise? who knows but in reallity is highly unlikely it does with Al-31.

 

[Quickie]

Sears-haack bodies are bodies of revolution, if you understand that, then you can see why aircraft without stealth requirements have round or oval cross sections in example F-18, Concorde, Su-27 and so on.

Stealth requieres other types of non bodies of revolutions, J-20 like F-22 needs economical engines, in few words no external clutter like external stores or weapons and high thrust at dry power.

Can J-20 supercruise with Al-31? maybe, do i think it does? no i do not, concorde also uses afterburner from transonic speeds to Mach 1.7, but here lies a secret you have not think, variable geometry intakes and speed actually add thrust as air is compressed like in SR-71.

J-20 has a fixed intake and only a body of revolution on the jet nozzles, the main cross section is diamond shaped or semi-trapezoidal and has no Von karman ogive radome.

F-35 has been modifided not because they do not know stealth requieres flat surfaces, but because that new shape is more aerodynamic

F-22 has also engines that have higher thrust at dry power than Al-31 ad 4 tonnes more of thrust than Al-31.

Does it supercruise? who knows but in reallity is highly unlikely it does with Al-31.

Strictly speaking, if you look at them in 3 dimension, the F-18, Concorde and Su-27 nose sections do not have the Sears-haack shape. Try look at them from the side view and you'll see they're not close to the Sears-Haack shape. In any case the front section is only a part of the aircraft that has to be considered as part of the whole design.

 

[latenlazy]

There are already equations for the Sears-haack body and Von karman ogive.

J-20 does not fit the bill, stealth has played big part in its design, they can try to fix it but is easy to see it is not a sears-haack body, with simple inspection you can see the Su-27 does conform to such concept better.

You are just giving excuses.

Any way, you are welcome to believe it supercruises.

No need discuss this further regards

Wow, you must have done great in math class. You do know that Sears-haack is ultimately about cross sectional area along the entire longitudinal axis of the plane right? The frontal cross section is less important than the change in cross section along the length of the plane. I could have a plane with a bigger frontal cross section than the su-27 like the Concorde with better wave drag because how much bigger or smaller a cross section gets in proportion to the cross section in front or behind it's ultimately what determines how closely a shaped conforms to a sears-haack shape. Frontal cross section by itself tells us nothing.

No one's making any excuses here. We're simply pointing out a nonsense understanding of science

 

[MiG-29]

Wow, you must have done great in math class. You do know that Sears-haack is ultimately about cross sectional area along the entire longitudinal axis of the plane right? The frontal cross section is less important than the change in cross section along the length of the plane. I could have a plane with a bigger frontal cross section than the su-27 like the Concorde with better wave drag because how much bigger or smaller a cross section gets in proportion to the cross section in front or behind it's ultimately what determines how closely a shaped conforms to a sears-haack shape. Frontal cross section by itself tells us nothing.

No one's making any excuses here. We're simply pointing out a nonsense understanding of science

Sears-haack bodies are bodies of revolution, you have not got me in any contradiction.

Basicly a AIM-120 is a body of revolution, a better example is an aircraft external fuel tank or Ohio class Submarine.

Su-27 like any fighter that had little or none stealth treatment has those shapes.

You can see that in the fact Su-27 main fuselage is a boulbous ogive and has a tail sting ending like a ogive, plus to podded engine nozzles with similar shape.

J-20 has other requierements, basicly flat platforms to reflect radar signatures at some specific angles.
F-35, T-50, F-22, F-117, J-20, J-31 and B-2 are huge radar mirrors.

F-22 needs a very powerful engine at dry power and no external clutter such as external stores.
The F119 needs extremely high dry power to allow F-22 to supercruise.

J-20 needs something better than Al-31s for sure, is Su-27 a perfect body of revolution of course not, but is an aircraft based upon such shape.

J-20 is based upon the pyramid shape with a diamond cross section to reduce RCS at different angles.

Su-27 is an aircraft designed for aerodynamics, F-22 and J-20 are for stealth with some trade offs between aerodynamics and stealth, as such they need good engines.

WS-15 will be needed, Al-31 is basicly a test engine to test the aircraft basic concept, in the same way EAP did for Eurofighter