H-20 bomber (with H-X, JH-XX)

High bypass engines are crap for stealth because you get a larger frontal aspect and more radar signal return from larger fan blades.
There is like zero chance the H-20 will use the WS-18 or WS-20.

The PAK-DA is supposed to use a lower bypass engine. NK-32 is low bypass.

gelgoog said:

High bypass engines are crap for stealth because you get a larger frontal aspect and more radar signal return from larger fan blades.
There is like zero chance the H-20 will use the WS-18 or WS-20.

The PAK-DA is supposed to use a lower bypass engine. NK-32 is low bypass.

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According to Wikipedia (I know I know), NK-32 has the same fan diameter as D30KP2.

gelgoog said:

High bypass engines are crap for stealth because you get a larger frontal aspect and more radar signal return from larger fan blades.
There is like zero chance the H-20 will use the WS-18 or WS-20.

The PAK-DA is supposed to use a lower bypass engine. NK-32 is low bypass.

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An amateur question: what if the blades are 100% synthetic fibre? In the old days, I learned that large military aircrafts such as tactical striker/bomber would use medium bypass turbofan. Is there such a thing now?

OppositeDay said:

A few years back people seemed genuinely uncertain whether H-20 would be powered by WS-10 or WS-18, but judging from recent posts WS-10 has since become the expectation. Was this change a result of news/rumors, or was it because of the increased production rate of WS-10 equipped J-20?

Russia is going with a NK-32 derivative for PAK DA instead of the 117S->Izdeliye-30 path. That likely means a twin-engine aircraft. B21 is expected to have twin F135s. Without counting in H-20, B2 will soon become the exception among flying wing bombers for its quad engine configuration.

D30KP2 is an early 1970s Soviet low pressure engine, old tech compared to F135 or even NK-32, but AECC have been working on WS-18 for a while now. It took PW 6 years (1979 - 1985) to get from JT8D-209 to JT8D-219, increasing pressure ratio and thrust by 11% without touching the basic design. WS-20's fan blades have been estimated to be at a tech level similar to early-mid 1990s CFM56 variants. If an improved variant of WS-18 is at a similar tech level as WS-20 re material and blade design, we can expect substantial improvement in thrust, going from early 1970s Soviet level tech to early-mid 1990s Western level tech.

Y-20's chef designer said at last year's Zhuhai Airshow that two domestic engines were being tested on Y-20, one of them was almost certainly WS-18 . A WS-18 variant with substantially increased thrust could serve as as H-20's test/backup engine before a WS-10 derived design becomes ready. If a WS-10 derived D30KP2 sized engine began development at the same time as H-20, the new engine could be ready before H-20's serial production given the experiences gained from WS-10 and WS-20. A second higher bypass WS-10 derivative should be a much easier project for China than China's first original flying wing, stealth, strategic, bomber (four separate firsts if we don't count JH-7 as a pure bomber).

This is not claiming H-20 will definitely feature a twin engine design. I'm just suggesting engine availability should not be a deal breaker for a twin engine H-20.

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China is now the proper aero engine manufacturer in the world. WS-10/WS-20 are just peanuts what China currently doing in aero engine sector. there are plenty of engine projects under development simultaneously.

someone posted on engine thread. AECC has built 2 test rigs supporting 250kN. saying Chinese version of NK-32. really interesting of true.

OppositeDay said:

According to Wikipedia (I know I know), NK-32 has the same fan diameter as D30KP2.

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The NK-32 is a much larger and more modern engine. The fan diameter of both engines is roughly the same but the NK-32 engine is overall much larger, heavier, and more powerful. The NK-32 has less frontal aspect in relative terms of overall dimensions. Check the bypass ratio of both engines.

4Runner said:

An amateur question: what if the blades are 100% synthetic fibre? In the old days, I learned that large military aircrafts such as tactical striker/bomber would use medium bypass turbofan. Is there such a thing now?

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Supposedly using fiber would help somewhat.

gelgoog said:

The NK-32 is a much larger and more modern engine. The fan diameter of both engines is roughly the same but the NK-32 engine is overall much larger, heavier, and more powerful. The NK-32 has less frontal aspect in relative terms of overall dimensions. Check the bypass ratio of both engines.

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NK-32 is three spool and a bit longer at 10% increased length. Bypass ratio is 1.4 for NK-32 and 2.24 for D30KP2. While D30KP2 has significantly less thrust than NK-32, its thrust can be improved by improved pressure ratio. As a older/much lower pressure engine, D30KP2 has more room for improvements in this regard.

In my original post I was focusing on better blade material/design for WS18, but adding new stage(s) is not out of question either. One or two additional compressor and/or turbine stages should be possible given how long AECC has been working on WS18 since the development of the first WS-18 model's completion in 2015. F135-PW-100 gained quite a bit of length from F119 partly because of an additional low pressure turbine stage. While we do not have evidence of a longer WS-18 variant, we cannot rule out such an engine is being tested from satellite photos because the second half of the engine would be obscured by wings. Not saying such an engine is currently being tested, just that the lack of photographic evidence does not rule out such a possibility.

In any case, in the scenario I described WS-18 should only be a stopgap engine before a WS-10 derivative is ready, and one of my points was a second WS-10 derivative after WS-20 should see much smoother development. If more serious modifications involving additional compressor/turbine stages is being pursued for WS-18, they might skip the WS-10 derivative and wait for a WS-15 derivative. I think WS-15 is supposed to have lower bypass with a bigger core than WS-10.

Again this is not to suggest a twin engine H-20 is more likely than quad engine, my point is we should not rule out a twin engine H-20 with D30KP2/WS-18 sized engines, and there is definitely a trend in both US and Russia to move toward twin engine strategic bombers.

Just did a quick check, D30KP2's compressor has 3 LP stages + 9 HP stages. Better fan + one additional LP compressor stage at the front and optimizing the rest of compressor/turbine design could significantly improve airflow & pressure ratio at the cost of lower bypass ratio and increased length. China in the late 2010s had better materials, cooling techniques and computing power than early 1970s USSR.

Between 2B1 and 5B3 variants, CFM56 saw a 50% increase in take-off thrust while keeping the same fan diameter by implementing improvements listed above (including an additional low LP compressor stage). One analysis on Zhihu suggests WS-20's latest public display model showed a technology level similar to that of CFM56-5B3. Applying similar level of technology to D30KP2 could see substantial increasing in thrust as D30KP2's technology was behind 2 series CFM56 to begin with (D30KP2's overall pressure ratio is at a very modest 20, compare that to about 30 for 2 series CFM56). They probably can't or don't want to increase WS-18's pressure ratio to CFM56-5B3 level (let's roll in the H-20 dumb bombs memes), but given the low base of D30KP2, I don't see why they can't get at least a 30% increase in thrust at the cost of increased length and decreased bypass.

Throwing in FADEC, and we'll have a modernized D30KP2 probably no worse than Russia's latest NK-32 variant. The original NK-32 already had a high overall pressure ratio at 28.4 so less room for improvements in that regard.

Development timeline wise, if full development for the improved WS-18 started in earnest in 2015 (after the first WS-18 model's project completion) and used only technologies developed for WS-20, I think it's possible for the new variant to be in flight testing by the time of Y-20 chief designer's interview in September 2021.


Also, the chief designer claimed the two engines under testing were results of self-led development (自主研制). It's questionable whether a close copy of D30KP2 could qualify as self-led development. A significantly improved variant just might. Not enough to prove anything. But a hint...

Anyway, not claiming twin engine H-20 is more likely than quad engine, what I'm suggesting is use scenarios, doctrinal/operational considerations should have been the deciding factors between twin engine and quad engine, not engine availability.

4Runner said:

An amateur question: what if the blades are 100% synthetic fibre? In the old days, I learned that large military aircrafts such as tactical striker/bomber would use medium bypass turbofan. Is there such a thing now?

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Closest to “synthetic fiber” fan blades is carbon composite. Carbon composite fan blades help a bit but not that much.

W20 said:

I don't know what is allowed in this thread

If

"we have NO information on the H-20‘s size and dimensions"

and

"stop these what if speculations until we get a first image of the real one or some sort of official data"

I suggest at this point that it would be simpler to make a list of those who can post in this thread.

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Right ON THE HEAD!

Former test pilot said that he thinks H-20 will take its maiden flight within next two years.

Take it with a grain of salt as Xu has left the service for nearly a decade.