J-35 coming out soon?

Military aircraft - Post cold war aircraft, including for example B-2, Gripen, F-18E/F Super Hornet, Rafale, and Typhoon.
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weasel1962

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Unread post04 Aug 2022, 00:41

Had the impression that drag due to lift is affected by the aspect ratio which includes wing area. Realized this may be a common mistake. Thanks for the clarification spurts.
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element1loop

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Unread post04 Aug 2022, 01:05

tphuang wrote:
element1loop wrote:'J-35' is closer to a 2005 level JSF prototype, but with adapted 4th-gen engine thrust levels and a far bigger weight problem, plus tiny implied useable internal payload. Doubt it could even carry pylons externally with a full internal fuel load and internal weapons. It's main advantages over the SH are newer LO, a much cleaner airframe, and WVR SA.


J-35 is about 4 years from joining service. It does not have a weight problem. It has close to 20t of thrust between the two engines and isn't expected to carry anything other than AAMs. It's a little longer and have possibly larger wingspan, but is a lot skinnier than F-35C. As such, I don't see it taking off with heavier weight than F-35C. So, why would it have a weight problem? Does F-35C have a weight problem?


Yes, it did, before the production version was built.

J-35 will have a MUCH larger weight problem, and thus curtailed performance envelope.

And as has been pointed out, the kit which will make it heavy, has not been included yet.

And I hope you don't think two engines, with the structural mass and fittings of two engines, will be lighter than having one engine.

4 years ... yes, the Chinese are magic, and the west is not. :mrgreen:
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weasel1962

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Unread post04 Aug 2022, 01:11

The F-135 is a pretty heavy engine and the F-35C is designed to carry a lot of fuel. The Chinese may not have the same requirements.
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jessmo112

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Unread post04 Aug 2022, 04:49

This is laughable.
I bet the designers of The J-35 finally convinced, someone above them that the T/W issue was fixed. They likely convinced them that with the newer engine they could do it. I bet they left out the part about it being a navy fighter, and they would have to hang new heavy stuff on the plane. I can't wait to see how it handles around the boat on a hot day. I'd like to discuss corrosion resistance next. That's going to be difficult for the Chinese to crack.
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weasel1962

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Unread post04 Aug 2022, 09:27

There is evidence of corrosion awareness in the PLANAF. J-35 is seen in same green primer.
https://www.globaltimes.cn/page/202002/1181026.shtml
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sprstdlyscottsmn

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Unread post04 Aug 2022, 11:15

weasel1962 wrote:Had the impression that drag due to lift is affected by the aspect ratio which includes wing area. Realized this may be a common mistake. Thanks for the clarification spurts.

Aspect ratio is a factor, but remember that for a fixed wing area a higher aspect ratio means more span. My equations (man the forums suck for equations) show where it all fits in.
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spad_s.xiii

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Unread post04 Aug 2022, 14:59

sprstdlyscottsmn wrote:I won't say I'm an expert, but I am an Aerospace Engineer. I insist on just wing span because drag due to lift is wing span dependent. This is why gliders have long skinny wings instead of short fat ones.

When L=nW, and we assume n=1 then W=ClqS where q=.5*rho*V^2. From this Cl=W/(qS) and since S is b*c (span times mean chord) Cl=W/(q*b*c)
Di (induced drag from lift) = CdiqS or Cdi*q*b*c
Cdi = Cl^2/(pi*e*AR) and based on out above Cl definition that means Cdi = W^2/(q^2*b^2*c^2*pi*e*AR) oh wait AR is b/c so now Cdi=W^2/(q^2*b^3*c*pi*e)
putting this back in Di we get Di=W^2/(q*b^2*pi*e) or simplified to Di = (W/b)^2/(q*pi*e)
So, for a given G and dynamic pressure drag due to lift is directly related to the square of Span Loading. Wing loading is irrelevant. Wing area is irrelevant. Wing area only matters in that you need enough Cl*S to make the lift in the first place, but drag due to lift is "100%" about the span.

Good presentation, especially in this not so equation friendly forum, but "e", the "planform/span/Oswald efficiency factor" depends on planform, aspect ratio, wing sweep angle, et cetera. https://en.wikipedia.org/wiki/Oswald_efficiency_number

The Prandtl Lifting-line Theory, where the equations comes from, has several other assumptions, like small AOA: https://en.wikipedia.org/wiki/Lifting-line_theory
It works fine for airplanes with high aspect ratio, straight, clean, wings with an elliptic lift distribution. Then e=1. Unfortunately, no sorts airplanes exists. But e can be calculated and real airplanes can have e as high as 0.9, but not fighters. Drag will still be dependent on other things then span, although span will be predominant in many cases. Drag from canard-delta wing configurations at high AOA, with complicated vortices, will probably not be as span dominated.

Below a couple of examples of how to calculate e (from https://mediatum.ub.tum.de/doc/1283438/file.pdf )
OswaldSpanEfficiency.png
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Unread post04 Aug 2022, 16:09

I've looked over wind tunnel data for an F-15 model that included CL/AoA and CD/AoA. taking the two together I gather that the Eagle planform has e values from .95 to ~.3 as AoA increases. You can see where the vortexes start forming as the value plummets. But yes, e is variable but for the purpose of THIS discussion of fighter v fighter we can assume they are close. Thanks for the pdf! Nice to see ways to estimate a low AoA value for it without having to calculate the actual lift distributions nd comparing it to the elliptical ideal.
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tphuang

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Unread post08 Aug 2022, 13:12

element1loop wrote:
tphuang wrote:
element1loop wrote:'J-35' is closer to a 2005 level JSF prototype, but with adapted 4th-gen engine thrust levels and a far bigger weight problem, plus tiny implied useable internal payload. Doubt it could even carry pylons externally with a full internal fuel load and internal weapons. It's main advantages over the SH are newer LO, a much cleaner airframe, and WVR SA.


J-35 is about 4 years from joining service. It does not have a weight problem. It has close to 20t of thrust between the two engines and isn't expected to carry anything other than AAMs. It's a little longer and have possibly larger wingspan, but is a lot skinnier than F-35C. As such, I don't see it taking off with heavier weight than F-35C. So, why would it have a weight problem? Does F-35C have a weight problem?


Yes, it did, before the production version was built.

J-35 will have a MUCH larger weight problem, and thus curtailed performance envelope.

And as has been pointed out, the kit which will make it heavy, has not been included yet.

And I hope you don't think two engines, with the structural mass and fittings of two engines, will be lighter than having one engine.

4 years ... yes, the Chinese are magic, and the west is not. :mrgreen:


The original FC-31 prototype flew with RD-93s. The current iteration uses WS-21, which probably has 15 to 20% more power. I'm not really sure how you can conclude J-35 have a weight problem based on 31001.

There is a SAC paper out there that discussed they reduced drag on J-35 by 10% (vs FC-31v2) through several design optimizations, including the enlarged hump, modified intake inlets, and reshaped afterbody. 9 years passed between FC-31 first flew to when J-35 first flew. It would be rather silly for them to not be able to improve on its aerodynamic properties.

Engine weight is a very small part of an aircraft's weight. J-35 was not built to be multi-functional like F-35C. It does have very large wings (much larger than FC-31 prototypes) similar to F-35C, but it is simply not bulked up like F-35C to be able to carry same amount of payload. Just look at the pictures. J-35 is a lot skinnier than F-35C.

China decided to sacrifice strike capabilities and range in order to have lower weight and adequate T/W ratio with WS-21. With WS-19, it will have very good T/W Ratio. The latter should be ready in a few years.
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jessmo112

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Unread post08 Aug 2022, 13:50

[

J-35 is about 4 years from joining service. It does not have a weight problem. It has close to 20t of thrust between the two engines and isn't expected to carry anything other than AAMs. It's a little longer and have possibly larger wingspan, but is a lot skinnier than F-35C. As such, I don't see it taking off with heavier weight than F-35C. So, why would it have a weight problem? Does F-35C have a weight problem?
[/quote]

Yes, it did, before the production version was built.

J-35 will have a MUCH larger weight problem, and thus curtailed performance envelope.

And as has been pointed out, the kit which will make it heavy, has not been included yet.

And I hope you don't think two engines, with the structural mass and fittings of two engines, will be lighter than having one engine.

4 years ... yes, the Chinese are magic, and the west is not. :mrgreen:[/quote]

The original FC-31 prototype flew with RD-93s. The current iteration uses WS-21, which probably has 15 to 20% more power. I'm not really sure how you can conclude J-35 have a weight problem based on 31001.

There is a SAC paper out there that discussed they reduced drag on J-35 by 10% (vs FC-31v2) through several design optimizations, including the enlarged hump, modified intake inlets, and reshaped afterbody. 9 years passed between FC-31 first flew to when J-35 first flew. It would be rather silly for them to not be able to improve on its aerodynamic properties.

Engine weight is a very small part of an aircraft's weight. J-35 was not built to be multi-functional like F-35C. It does have very large wings (much larger than FC-31 prototypes) similar to F-35C, but it is simply not bulked up like F-35C to be able to carry same amount of payload. Just look at the pictures. J-35 is a lot skinnier than F-35C.

China decided to sacrifice strike capabilities and range in order to have lower weight and adequate T/W ratio with WS-21. With WS-19, it will have very good T/W Ratio. The latter should be ready in a few years.[/quote]

Translates:

Our plane doesn't have weight gain issues in development because, we are Chinese and we are majic.lol. and you wonder why the world mocks you.
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tphuang

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Unread post13 Aug 2022, 21:57

jessmo112 wrote:Translates:

Our plane doesn't have weight gain issues in development because, we are Chinese and we are majic.lol. and you wonder why the world mocks you.


Look, it's very possible that things are not all Chinese commentators claim it to be. It's still in testing. We also don't know how well FC-31 will work out. Not every Chinese project is as successful as J-20. I think we will find out how good this aircraft will be in a few years. I'm simply saying that they have sacrificed payload and range with the goal of attaining better A2A capability than F-35C. That is their goal. Most of China's military projects are developed to counter US military.

Xi apparently will be leaving China for the first time in 3 years and visiting Saudi Arabia next week. I've long speculated that Saudi Arabia will be locally producing FC-31 at some point. If they get Saudi Arabia signing up, it will be a huge endorsement of the entire project.
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madrat

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Unread post13 Aug 2022, 23:12

The Saudis will not build their own. They buy custom.
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Corsair1963

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Unread post14 Aug 2022, 23:23

tphuang wrote:
jessmo112 wrote:Translates:

Our plane doesn't have weight gain issues in development because, we are Chinese and we are majic.lol. and you wonder why the world mocks you.


Look, it's very possible that things are not all Chinese commentators claim it to be. It's still in testing. We also don't know how well FC-31 will work out. Not every Chinese project is as successful as J-20. I think we will find out how good this aircraft will be in a few years. I'm simply saying that they have sacrificed payload and range with the goal of attaining better A2A capability than F-35C. That is their goal. Most of China's military projects are developed to counter US military.

Xi apparently will be leaving China for the first time in 3 years and visiting Saudi Arabia next week. I've long speculated that Saudi Arabia will be locally producing FC-31 at some point. If they get Saudi Arabia signing up, it will be a huge endorsement of the entire project.


They sacrificed payload and range for the very same reason as South Korea (KFX), Turkey (TFX), and India (AMCA) did with their 5th Generation Fighter Programs. Because they don't have an engine in the class of the 5th Generation P&W F135. So, they were forced to settle on two 4th Generation Engines. In order to have adequate thrust to weight. Nor, by doing so give them somekind of performance edge!
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milosh

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Unread post15 Aug 2022, 18:21

Cool but it doesn't change fact that even with two ws13 J35 have similar thrust as F14A.

With two ws19 we are talking about F14B thrust level.
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charlielima223

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Unread post15 Aug 2022, 18:40

milosh wrote:Cool but it doesn't change fact that even with two ws13 J35 have similar thrust as F14A.

With two ws19 we are talking about F14B thrust level.


That is nice but that still isnt at the level of thrust and efficiency we see on the F-119 and F-135. Russia claims at max their current engines on their Su-35s are either equal to or more than the F-119s. Yet those engines are nowhere near efficient. My understanding is that 5th gen engines are a balance of high thrust and better efficiency over those used in 4th gen fighters.
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