J-20 5th Generation Fighter VII

by78 said:

A procurement document that was posted today. It announces an open bid for a comparative radar signature test to be carried out on the rear aspect of a certain technology demonstrator (某工程验证机后向雷达隐身多方案对比测试及弱散射源雷达散射特性研究采购需求采购公告). If I'm reading this correctly, the bid implies that there are multiple competing designs, which necessitates a comparative test to find the design with the best radar signature reduction performance. Unfortunately, the screenshot partially obscures the name of the entity that submitted the bid; it only says "中国航发四", which could be AECC Sichuan Gas Turbine Research Institute/624 Institute (中国航发四川燃气涡轮研究院) or AECC Factory 402 (中国航发四二〇厂) or some other entity.

If indeed the document was submitted by the 624 Institute, then this could be for testing a new engine nozzle. WS-15 with a 2D and/or 3D TVC nozzle perhaps? If this bid has nothing to do with engines, then this could be about anything from H-20's rear fuselage design to J-20A's rear fuselage design.

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siegecrossbow said:

If the BPR is really 0.25 then it is even more of a leaky turbojet than F-119. J-20 is truly the ultimate J-8.

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CMP said:

Can you elaborate in more detail?

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Blitzo said:

Very simplistically:
Higher bypass ratio in general means better fuel efficiency but means the engine (and thus the aircraft it's attached to) is intended to operate at lower speeds.
Lower bypass ratio (say, 0.25 if WS-15 has that, compared to 0.3 of F119 which is already relatively low) means the fuel efficiency is not as good but the engine (and thus the aircraft it's attached to) is intended to operate at higher speeds.

So what Siege is joking is that J-20 is kind of the ultimate form of a "high speed combat aircraft" of which J-8 was best known for.

But "J-8" is an aircraft with such a complex history and whose role is ultimately still very different to J-20, that I think comparing the two even in a cavalier way just introduces room for misunderstanding and confusion @siegecrossbow

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CMP said:

That design philosophy sounds suitable for expectations of fighting within the first island chain. Wouldn't speed be much more important than fuel efficiency in that kind of scenario?

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Blitzo said:

Finding a balance between kinematic performance and endurance/range is always important, and is not dependent merely on the performance of the engine but rather on the requirements of the overall aircraft and the design of the airframe.

I for one, do not think that J-20 will be asked only to be able to operate within the first island chain, but also beyond.

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Blitzo said:

Very simplistically:
Higher bypass ratio in general means better fuel efficiency but means the engine (and thus the aircraft it's attached to) is intended to operate at lower speeds.
Lower bypass ratio (say, 0.25 if WS-15 has that, compared to 0.3 of F119 which is already relatively low) means the fuel efficiency is not as good but the engine (and thus the aircraft it's attached to) is intended to operate at higher speeds.

So what Siege is joking is that J-20 is kind of the ultimate form of a "high speed combat aircraft" of which J-8 was best known for.

But "J-8" is an aircraft with such a complex history and whose role is ultimately still very different to J-20, that I think comparing the two even in a cavalier way just introduces room for misunderstanding and confusion @siegecrossbow

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CMP said:

Agreed, but perhaps this was just the best compromise they could find.

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