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

[MiG-29]

View attachment 8067

what a flying cigar may look like.

actually they are called fuel tanks and JDAMs

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A shape which is far far away from F-117 and slightly closer to J-20 but not as close as it is to Su-27, concorde, B-787, JDAMs or fuel tanks and our old friend V-2

 

[MiG-29]

No plane has an ideal sears-haack shape. SH shape is used to demonstrate the concept of minimum drag. Aircraft need to be designed with more criteria than that in mind.

Good luck trying to maneuver a perfect sears-haack shaped object using aerodynamic forces.

I don't want to hear no more about the words sears-haack body. We should use it's more useful derivative when talking about aircraft designs, which is the area rule.

[video=youtube;HvL2m4qQ85c]https://www.youtube.com/watch?v=HvL2m4qQ85c[/video]

why do not you tell that to the guys who developed the JDAMS or the X-1, probably their first tought was the hopeless diamond and later J-20

here we have the X-1 rocket plane which basicly is a sears-haack body with airfoils

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[latenlazy]

Look, you ae simply intelectually dishonest, in fact you simply can not even accept the sears-haack body is used.

I will give you 3 simple examples.

1-V-2, yes the german V weapons uses that shape.

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2-Most of modern external fuel tanks

3-smart weapons
open the link

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Su-27 is a modification of that shape, take the wings, tailplanes and vertical fins off and you find the Su-27 central fuselage is a modification of the sears-haack body.

J-20 like F-22 are closer to the hopeless diamond, and they need to be, since the hopeless diamond is based upon a pyramid shape.

The su-27 has area rule, treatment, if you look at the change in diameter of the radome and tail sting in the air brake junction .


Your basic theory is Al-31 will propel the J-20 to supercruise but will keep the Su-27 subsonic, which is unlikely since the only advantage of J-20 is a lower ratio wing, the rest of the fuselage is farther than Su-27 to an ideal sears-haack body and it weighs more

Yes indeed. I and the entire interwebs are hopelessly dishonest. I indeed do not believe that a sears-haack body can be used because that is exactly what I said, word for word. That is also why I suggested that both the su-27 and j-20 try to conform to a sears-haack shape but neither are ideal.of course it is because of my intellectual dishonesty, because how could the great mig be wrong about anything including what I have said, word for word.

The hopeless diamonds aerodynamic problems have absolutely nothing to do with a bad sears-haack body shape. Sears-haack isn't the only reason why aerodynamic designs employs round shapes. If you must know though both the j-20 and f-22's cross sectional areas taper off after their midpoint too. The su-27 isn't special in those regards.

 

[no_name]

here we have the X-1 rocket plane which basicly is a sears-haack body with airfoils

Then it is not a sears-haack body. It is not a body of revolution or whatever the hell you are trying to spin it - more ridiculously trying to arbitrarily classify Su-27 as somehow 'sears-haack' with its huge wings and unsymmetrical vaguely cylindrical cockpit, while arbitrarily dismiss J-20 because it got 'edges'.

They follow the area rule - a derived approximation of the sear-haack body principle.

You try to simplify aircraft design as if it's simply about stucking wings onto a 'sears-haack' body, Then use eyeballing/being completely subjective about what should be a SH body. whatever the hell that means.

 

[MiG-29]

The hopeless diamonds aerodynamic problems have absolutely nothing to do with a bad sears-haack body shape. Sears-haack isn't the only reason why aerodynamic designs employs round shapes. If you must know though both the j-20 and f-22's cross sectional areas taper off after their midpoint too. The su-27 isn't special in those regards.

Look mathematically you could not prove your point, JDAMS use such shape, J-20 flies thanks to its air foils, it has trade off between the sears-haack body shapes and hopeless diamond.
But most of its fuselage is based upon the hopeless diamond.


You went to this because you claim with 3D printing you get so much savings in weight that it will supercruise with Al-31.
Some people even claim Su-27 is much draggier, when is know Su-27 needs 117s engines to supercruise, a sharper tail sting without its chaff flares as even the original Su-27s, the Su-27 is lighter than J-20 and Su-27 uses a more aerodynamic fuselage.


J-20 to supercruise needs more powerful engines, in fact is funny that the jet has weapons bays similar to those of F-22 but has a longer fuselage.

 

[MiG-29]

Then it is not a sears-haack body. It is not a body of revolution or whatever the hell you are trying to spin it - more ridiculously trying to arbitrarily classify Su-27 as somehow 'sears-haack' with its huge wings and unsymmetrical vaguely cylindrical cockpit, while arbitrarily dismiss J-20 because it got 'edges'.

They follow the area rule - a derived approximation of the sear-haack body principle.

You try to simplify aircraft design as if it's simply about stucking wings onto a 'sears-haack' body, Then use eyeballing/being completely subjective about what should be a SH body. whatever the hell that means.

in terms of air drag, Su-27 has a more ideal fuselage shaping than J-20 except in the fact the J-20 has internal weapons bays.

To suggest J-20 supercruises with Al-31 without considering its trade off in aerodynamics well, well ..... is not realistic.

And you were wrong, JDAMs do fly, you simply can not admit you forgot to see how sear-hack bodies are used in modern times.

My premise was J-20 needs better engines and is unlikely to supercruise with Al-31.

And yes, Concorde uses the basic principles of aerodynamics like Su-27 and they use sears-haack theories, the bodies are modified due to needs of propulsion, airfoils and crew accomodation, but still they use those principles

 

[andyhugfan]

I'm no shrink but there are some serious autistic forces at work in this thread.....

 

[Engineer]

The cross sectional area can be calculated as follows:

[A(x) = \frac {16V}{3L\pi}[4x-4x^2]^{3/2} = \pi R_{max}^2[4x-4x^2]^{3/2}

The volume of a Sears–Haack Body is:

V = \frac {3\pi^2R_{max}^2L}{16}

The radius of a Sears-Haack Body is:

r(x) = Rmax(4x − 4×2)3 / 4The derivative (slope) is:

r’(x) = 3Rmax(4x − 4×2) − 1 / 4(1 − 2x)

The 2nd derivative is:

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Next time give a better read, going to wikipedia and paste does not mean you understand the theory,

Fishing a single word from a website while ignoring the rest of the theory does not show you understand the content. It only shows your desperation. If an engineer wants to make the body circular, then he can use r(x). If he wants the body to be square, he can define the length of one side of a square s(x) as:
s(x) = \pi^{1/2}r(x) = \pi^{1/2}Rmax(4x − 4×2)3 / 4

The shape of the fuselage does not have to be circular.

The first equation that you have quoted describes the cross sectional area. The equation is in fact the same one as I have posted earlier, which is independent of shape.

No where in the web page you quoted from does it states a fuselage has to be circular before matching Sears-Haack body. So, allow me to quote for you again:

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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stealth modifies the cross section of aircraft for a reason the hopeless diamond was called hopeless and the F-117 faceted body was a brick flying.

If F-22 or J-20's airframe is hopeless, than a Flanker airframe is even more hopeless. After all, the F-22 can supercruise at Mach 1.8, while your beloved Flanker can't even come close to matching such performance.

See you continue dreaming J-20 has the ideal sears-haack body and with Al-31 supercruises better than Su-35BM or F-22

Nope. Firstly, the J-20 follows the Sears-Haack body. It does not require any dreaming on my part just as it does not require dreaming to call the Earth round. By the same analogy, when you claim a stealth airframe cannot be a Sears-Haack body, it is no different than arguing the Earth is not round due to mountains. It makes you look extremely silly.

Secondly, for the J-20 to supercruise, all the aircraft needs to do is to fly above Mach 1 without afterburner. Flying faster than F-22 is never definition of supercruise and was never part of my argument. Your tactic of shoving words into people's mouth is exposed once again.

 

[Engineer]

Look, you ae simply intelectually dishonest, in fact you simply can not even accept the sears-haack body is used.

I will give you 3 simple examples.

1-V-2, yes the german V weapons uses that shape.

Please, Log in or Register to view URLs content!

2-Most of modern external fuel tanks

3-smart weapons
open the link

Please, Log in or Register to view URLs content!

Su-27 is a modification of that shape, take the wings, tailplanes and vertical fins off and you find the Su-27 central fuselage is a modification of the sears-haack body.

LMAO! The Su-27 does not have a Sears-Haack body even according to your flawed definition. People who lie eventually stumbles on their own lies, and you illustrate this so perfectly.

By the actual definition, a Sears-Haack body is the ideal shape with the lowest wave drag. The calculation of wave drag takes in account of every part on the aircraft, as

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. No engineer would take away the wing, tailplanes and all other extrusions when using Sears-Haack body. The fact that you came up with such nonsense as above shows you have absolutely no clue as to what you are talking about.

Having said that, I will now give you three counter examples where Sears-Haack body is applied and where the airframe is not circular.

1. F-22.
2. F-35.
3. J-20

J-20 like F-22 are closer to the hopeless diamond, and they need to be, since the hopeless diamond is based upon a pyramid shape.

The su-27 has area rule, treatment, if you look at the change in diameter of the radome and tail sting in the air brake junction .

It's funny how those aircraft you mentioned with hopeless diamond flies better than the Flanker.

Sears-Haack body only concerns with the distribution of cross sectional area. It is independent from the actual shape of the cross section, so whether an aircraft's cross section is based on a diamond or whatever is irrelevant. From

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:

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.

Your basic theory is Al-31 will propel the J-20 to supercruise but will keep the Su-27 subsonic, which is unlikely since the only advantage of J-20 is a lower ratio wing, the rest of the fuselage is farther than Su-27 to an ideal sears-haack body and it weighs more

Unlike the Flanker which is optimized mostly for transonic performance, the J-20 has a requirement to supercruise, which means the J-20 would follow the Sears-Haack body closer than the Flanker. This combines with the use of low aspect-ratio wing means the J-20 sees lower drag at supersonic speed. This is why it would not be impossible for the J-20 to supercruise with Al-31 engines.

 

[latenlazy]

Look mathematically you could not prove your point, JDAMS use such shape, J-20 flies thanks to its air foils, it has trade off between the sears-haack body shapes and hopeless diamond.
But most of its fuselage is based upon the hopeless diamond.


You went to this because you claim with 3D printing you get so much savings in weight that it will supercruise with Al-31.
Some people even claim Su-27 is much draggier, when is know Su-27 needs 117s engines to supercruise, a sharper tail sting without its chaff flares as even the original Su-27s, the Su-27 is lighter than J-20 and Su-27 uses a more aerodynamic fuselage.


J-20 to supercruise needs more powerful engines, in fact is funny that the jet has weapons bays similar to those of F-22 but has a longer fuselage.

Funny, you proved no mathematical point either. You asserted a claim that can be measured, and you refuse to provide actual measurements. The sears-haack body shape is meant to reduce wave drag. It's about the distribution of cross sectional area. That is what the theory pertains to by definition. It has nothing to do with why JDAMs are round in shape or why the F117 is a flying brick. JDAMs don't even experience wave drag because they're not traveling at transsonic+ speeds! Again, the sears-haack shape doesn't even tell us why it's better to have rounded geometry to reduce aerodynamic drag, because it has nothing to do with being rounded! You can ignore academic definitions if you want, but that doesn't make you less wrong.

You're now imaging what I'm saying instead of actually reading what I'm saying. This discussion about the sears-haack shape has absolutely nothing to do about weight savings from 3D printing. I did not even assert that the J-20 must be able to supercruise due to some miraculous weight savings from 3D pointing. I was merely pointing out that the amount of weight savings from 3D printing could potentially be more than what one person claimed. This silly off tangent about the sears-haack shape is purely based around your fantasy notion that seems to be 1) a sears-haack shape is about looking like a cigar and not about the distribution of cross sectional area along a shape, and 2) that the sears-haack shape is the ideal shape to reduce all aerodynamic drag, and not just wave drag, which only applies to a specific flight regime.

This argument, fundamentally, is not even about what the J-20 can or cannot do. It's purely about pointing out how wrong your understanding of a science is. If you don't believe any of us take a class on aerodynamics, and use your faulty definitions and see what kind of grade you get. These silly debates you bring about aerodynamics is particularly embarrassing because you're arguing with people who're actually employed for their knowledge on a field you seem to profess knowing so much about, yet exhibit zero nuanced understanding for.