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

[MiG-29]

Funny, you proved no mathematical point either. .

Mathematically i proved it, it has an r for radius, if you can not read that mathematically or you refuse to accept it well that is not my problem.

The Sears-Haack area distribution graph in fact has diameter fixed value, this detail shows that mathematically speaking a diameter only exist as a result of a radius.

Click to see and see the graph says Radius and values 1 to .0

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Since aircraft have more requirements than JDAMs or ICBM they also sacrifice the ideal shape by adding canopies, wings, intakes.


J-20 has sacrificed more the Sears-haack ideal shape for the sake of stealth.


YF-22 had even more stealthy lines than the operational F-22, but they decided to go back a bit to Von Karman ogive in the radome, X-35 had a flatter underbelly, more stealthy from some angles, but the series F-35 has rounded lines more in line with the sears-hack body streamlining even more the series F-35, but forcing some sacrifices in stealth.

Now let us move on an wait when they unvail the 2003 J-20 regards

 

[Engineer]

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.

Look, you cannot prove that a Sears-Haack body must have circular cross sections. Not only so, but claiming that there is a trade-off between a 2D geometry and a 3D body shows you are simply engaging in mud-slinging rather than having an intellectual debate.

You went to this because you claim with 3D printing you get so much savings in weight that it will supercruise with Al-31.

Wrong. Latenlazy never claimed reduction of weight would result in supercruise. The issue of weight got brought in because some people like yourself are lacking in flight dynamics knowledge, and were confused between thrust-to-weight ratio and thrust-to-drag ratio. The first ratio has little to do with supercruise ability, as Concorde and the P-42 have shown. Nevertheless, with the weight saving due to 3D printing, combined with trading away fuel and payload will enable to J-20 to achieve the kind of kinematic performance as if WS-15 engines were used.

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.

The assumption that Su-27 being less draggy than J-20 is based on nothing more than Su-27's fuselage being round, which is an extremely weak argument.

The Flanker was optimized for transonic speed, as evident by the use of higher aspect-ratio wing. This will be more draggy than the lower aspect-ratio wing on the J-20. The length-to-width ratio is also larger for the J-20 than for the Flanker. This is beneficial to J-20's fineness ratio, allowing the airframe to be less draggy. Let's not forget that the canard arrangement will result in lower trim-drag for the J-20. For this last factor, the Flanker is aerodynamically inferior and must use thrust-vectoring engines to compensate. Let's not forget that these comparisons are done assuming the Flanker to have a clean configuration. With weapons, the Flanker airframe will be even more hopeless.

To achieve supercruise, the Su-35 uses more powerful engines. There is nothing that prevents the J-20 to match that level of thrust-to-drag ratio with reduced supersonic drag.

 

[latenlazy]

Mathematically i proved it, it has an r for radius, if you can not read that mathematically or you refuse to accept it well that is not my problem.

You cannot read English. Let's make this simple.

"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."

Whatever mathematical point you think you've made is wrong, simply because you are ignoring the definition of the principle you're arguing about.

The Sears-Haack area distribution graph in fact has diameter fixed values, this detail shows that mathematically speaking a diameter only exist as a result of a radius.

Click to see and see the graph says Radius and values 1 to .0

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Since aircraft have more requirements than JDAMs or ICBM they also sacrifice the ideal shape by adding canopies, wings, intakes.

ICBMs are one thing, but you must be joking when you talk about JDAMs. JDAMs don't have to worry about wave drag. Either way, you're simply sidestepping a point that is definition to the point about sears-haack, which is that the shape doesn't matter! It's the cross section area distribution, not the shape! Don't believe me? Read the link above.

J-20 has sacrificed more the Sears-haack ideal shape for the sake of stealth.

YF-22 had even more stealthy lines than the operational F-22, but they decided to go back a bit to Von Karman ogive in the radome, X-35 had a flatter underbelly, more stealthy from some angles, but the series F-35 has rounded lines more in line with the sears-hack body streamlining even more the series F-35, but forcing some sacrifices in stealth.

Now let us move on an wait when they unvail the 2003 J-20 regards

[/QUOTE]
*facepalm* You don't seem to get that conformity to sears-haack shape is about cross sectional area, despite every source saying this.

 

[Engineer]

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.

Your reference to ideal fuselage is based nothing more than the fuselage being circular. Any body sharing the same cross-sectional area distribution as the Sears-Haack body will have the same wave drag as a Sears-Haack body. Shaping is irrelevant.

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

A trade-off occurs when one performance parameter increases at the expense of another parameter. Aircraft like the F-22 achieves the best of both world by having stealth and superb aerodynamics. The performance of a Flanker is doesn't even come close to the F-22. In the context of supercruise, there is very little to believe that J-20 cannot match the F-22 in terms of drag characteristics, especially with J-20's longer body and higher fineness ratio. Less drag means the aircraft can fly faster with the same level of thrust. It isn't our problem that you cannot accept reality.

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

Look, the issue here is you keep on referring to Sears-Haack body yet has absolutely no clue as to how it is used. You are so blinded by pride, so you argue for the sake of arguing even though your understanding is incorrect.

Sears-Haack body is used one way or another in the design of on all transonic and supersonic aircraft. This includes F-22, F-35 as well as J-20, not just the Su-27 and the Concorde. The Sears-Haack body takes in account of cross-sectional area of the wing, engine pods, airfoils, and all other extrusions. For minimum wave drag, the engineers then optimize the placement and size of these components so the combined cross-sectional area matches the corresponding section of on a Sears-Haack body.

 

[Engineer]

Mathematically i proved it, it has an r for radius, if you can not read that mathematically or you refuse to accept it well that is not my problem.

I have to concur with Latenlazy that you have not proven anything mathematically. Furthermore, the presence of radius in the equation not prove that the shape is required to be circular. Firstly, radius is a dimension and does not describe the shape. Your insistence otherwise is like claiming measurement of width makes the object being measured a rectangle. For example, measuring the width of an aircraft doesn't turn the aircraft into rectangle. Secondly, a circle means there is a measurement of radius, but the is not true. Radius is often used to define the points in a geometry with respect to the center, such as the tip of a pentagon.

The Sears-Haack area distribution graph in fact has diameter fixed values, this detail shows that mathematically speaking a diameter only exist as a result of a radius.

Click to see and see the graph says Radius and values 1 to .0

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Nope. The vertical axis can represent values other than radius. The following graphs only use areas for the vertical axis.

What matters is the enclosed area of the shape. Area is independent of shape, so the Sears-Haack area distribution is also independent of shape.

Since aircraft have more requirements than JDAMs or ICBM they also sacrifice the ideal shape by adding canopies, wings, intakes.


J-20 has sacrificed more the Sears-haack ideal shape for the sake of stealth.


YF-22 had even more stealthy lines than the operational F-22, but they decided to go back a bit to Von Karman ogive in the radome, X-35 had a flatter underbelly, more stealthy from some angles, but the series F-35 has rounded lines more in line with the sears-hack body streamlining even more the series F-35, but forcing some sacrifices in stealth.

Now let us move on an wait when they unvail the 2003 J-20 regards

Nope. Paying lip services to aerodynamic terms does not show your understanding of these terms. The way you have applied these terms show you have no idea what they are about. If you were to write the above nonsense in an University exam, you would be flunked.

Firstly, the application of Von Kármán Oglive is in the side profile of the radome, describing the curve from the tip to the base. It is not about cross section. Whether the radome is round or faceted is of little relevance. Secondly, the F-35 incorporates bulges because there wasn't enough internal space for certain systems. In fact, adding bulges will result in a worse match to Sears-Haack body, because it causes the cross-sectional area distribution to be non-optimal.

Application of Sears-Haack body is not about adding curves to external contour, as the actual shape is irrelevant. It is the cross-sectional area distribution, not the contour, that matters in the application of Sears-Haack body. As such, a stealthy airframe is not mutually exclusive with a Sears-Haack body. A rounded body does not automatically make it a Sears-Haack body either. Allow me to quote it to 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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[Lezt]

While all the discussion on Sears-Haack is fascinating and a good brush up to my aerodynamics; Why get so fed up over it?

It is not like an airplane cannot super-cruise without a sears-haack body, and without the actual geometry and some proper CFD, we won't begin to know how well the sears-haack body is acheived.

More importantly, if a fighter is to engage in a dogfight and not just cruising, sears-hacck does not mean much, but TVC and control airfoil does.

 

[kwaigonegin]

While all the discussion on Sears-Haack is fascinating and a good brush up to my aerodynamics; Why get so fed up over it?

It is not like an airplane cannot super-cruise without a sears-haack body, and without the actual geometry and some proper CFD, we won't begin to know how well the sears-haack body is acheived.

More importantly, if a fighter is to engage in a dogfight and not just cruising, sears-hacck does not mean much, but TVC and control airfoil does.

yup.. I was going to ask the same thing. Far from being an aeronautical engineer (although I did dabble in it somewhat during college) an aircraft shape doesn't have to comply and conform 100% to a S-H body to achieve supercruise capability which I believe prompted this entire OT discussion.

Also one cannot truly discuss S-H body design without talking about the viscous effect on the body itself but we're talking real geeky stuff here and far from what this forum was designed for

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Either way I hope J-20 has something new soon because as enlightening as Mig 29/Engineer and LatenLazy's verbal sparring is I hope we get to see 2003 or something soon!!!!!!!!

 

[latenlazy]

It's really about the terrible understanding and reckless application of science. Thus is like one of those crazy anti evolution or climate change denier debates.

 

[MiG-29]

yup.. I was going to ask the same thing. Far from being an aeronautical engineer (although I did dabble in it somewhat during college) an aircraft shape doesn't have to comply and conform 100% to a S-H body to achieve supercruise capability which I believe prompted this entire OT discussion.

Also one cannot truly discuss S-H body design without talking about the viscous effect on the body itself but we're talking real geeky stuff here and far from what this forum was designed for

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Either way I hope J-20 has something new soon because as enlightening as Mig 29/Engineer and LatenLazy's verbal sparring is I hope we get to see 2003 or something soon!!!!!!!!

Of course no aircraft can have a perfect sears-haack body, all aircraft have need for wings, engines, cockpit and canopies, intakes, those things affect its shaping.

And to supercruise you are right, you just need good engines, but always, less air drag helps, the less air drag and weight, the engines can match easier the airframe thrust needs to supercruise and the more effective and cheaper supercruise that was the whole point.

But yeah let us move on i hope we see it soon.

 

[Hyperwarp]

Any, I mean any tiny tiny rumors on 2003?

Either something has gone wrong or there are some substantial aerodynamics changes?