Chinese Stealth bomber program - XAC H-X (H-20)

[Tomboy]

Oh, there are zillion reasons to use low bypass engines still.

Isn't high hypass turbofans better for long range subsonic aircraft,?

 

[Sferrin]

Oh, there are zillion reasons to use low bypass engines still.

Yep. Even the B-2 and B-21 uses them.

 

[Sferrin]

Isn't high hypass turbofans better for long range subsonic aircraft,?

Depends what you mean by "high". What most people think when they say high-bypass:



But the F101 on the B-1B is lower, though still high compared to something like an F119, at 2.1:1

 

[Nx4eu]

Yep. Even the B-2 and B-21 uses them.

Isn’t it speculated that the B-21 uses a medium bypass engine for more efficiency?

PW9000 with a bypass ratio of 4:1 is on the edge of medium bypass and high bypass.

 

[Sferrin]

Isn’t it speculated that the B-21 uses a medium bypass engine for more efficiency?

From Aviation Week:

"Engines The Air Force has confirmed that Pratt & Whitney is the engine supplier for the B-21, but it has not revealed the number or type of engines. The options include two, three or four engines inside each bomber. Pentagon officials approved the B-21 program on the condition that the Air Force use off-the-shelf technology as much as possible.


That may limit the candidates to the Lockheed Martin F-35’s Pratt & Whitney F135 engine or the PW9000, a hybrid engine concept unveiled by Pratt in 2010. The PW9000 integrates the high-pressure core of the commercial PW800 engine and the low-pressure section of the F135. The B-21 entered development more than five years before a new generation of adaptive-cycle turbofans reached the ground-testing stage, which likely rules them out for at least the baseline version of the bomber."

The B-2, by comparison, uses the F118, a non-afterburning variant of the F110 that is also used by the U-2.

 

[Nx4eu]

I remember awhile back that the H-20 could potentially use an improved WS-18/D-30KP-2. Of which is medium bypass but lower bypass than PW9000. This is a pretty old rumor though.

 

[Tomboy]

I remember awhile back that the H-20 could potentially use an improved WS-18/D-30KP-2. Of which is medium bypass but lower bypass than PW9000. This is a pretty old rumor though.

It's going to be high bypass since there was a order calling for analysis of large S bend intake for high bypass turbofan. Which means BPR>4

 

[Josh_TN]

For those that says it'll take China years to make a B-2 sized conventional flying wing because engine or whatever, you guys are clearly forgetting WZ-X and GJ-X two bomber sized flying wing already flying.

Clearly large composite structure and efficient powerplant is no issue right now.

The payload requirements are quite different. Also I am not saying they cannot make H-20, just that the reason we have not seen it yet is because it is a challenging project.

And I think it will not be a leap ahead supersonic broadband aircraft for those reasons.

 

[Josh_TN]

Sure it can. We could start with adopting a CFM-56 or clone. IIRC China has been license-producing those since the 1990s. Or you could take some of the new high-performance turbofans and remove the afterburners, like how the US F118 is basically an F110 sans afterburner.

If payload and endurance are no issue, sure.

 

[1635yankee]

The original WS-10's core itself is based on a locally reverse-engineered CFM-56. It powers almost all Chinese-built, manned jet aircraft in the PLA fleet and has evolved into a legitimate 5th-gen engine thanks to the integration of technologies developed for the first WS-15 design.



It's likely already in use as an interim engine on both the GJ-X and WZ-X.

View attachment 793414View attachment 793415

The delay in the H-20 project and its redesign is due to the changing requirements of the PLA. With these drones, PLAAF is already capable of delivering stand-in payloads to the 3IC reliably(the WZ-X likely also has a shallow, small IWB). If the H-20 project is to continue, it must be capable of striking CONUS and returning safely.

This is what the insiders have been hinting at, and it’s also the consensus within the PLA-watching community.

I don't think striking the continental US is necessary; they have ICBMs for that. Attacking surface ships may be a more important role, as may non-nuclear power projection. Right now, most of China's goals may be achievable by soft power, more so since the current administration has conceded that particular field of conflict.

 

[Josh_TN]

Isn't high hypass turbofans better for long range subsonic aircraft,?

Yes, though my understanding is at very high altitudes they lose power and efficiency. I think the PW-9000 is thought to be a medium bypass more like 4:1.

 

[snne]

The payload requirements are quite different.

How so? I get that the payload is a combination of fuel and bombs/missiles but the GJ-X is quite literally a B-21-sized UCAV, almost certainly with a comparable bomber-sized IWB. By contrast, what the PLAAF really needs from the H-20 isn't heavier/larger (weapons) payload, but rather bigger combat radius and more sensors (in addition to a cockpit). This isn’t just a guesstimate either; it’s what we've been hearing for a while now.

I don't think striking the continental US is necessary; they have ICBMs for that.

Theoretically, the US in this current situation could just "lob" JASSM-ERs at the mainland (right in China’s backyard!) with impunity, while China would have to rely on expensive ICBMs to deliver a payload to the CONUS (which would trigger a nuclear retaliation!). Don’t you think any country with adequate resources would want to level out the playing field? It won't have to cross the Pacific in a straight line either...

Spoiler:

(From China's view) without showing ordinary Americans and decision-makers that the war could come to their doorsteps if they don’t keep a leash on their hawkish-leaders, there wouldn’t be much incentive for them to avoid a war (keeping nukes and economic impact out of this scenario).

 

[flateric]

Isn't high hypass turbofans better for long range subsonic aircraft,?

before you are trying to feed them via lo ducts and fly high

 

[Tomboy]

before you are trying to feed them via lo ducts and fly high

I don't think there is any issue with large S bends as B-21 uses PW9000 with a 4:1 ratio and there is a XAC tender calling for a S bend for high bypass turbofan. I also don't think there is any utility for a manned bomber to fly high enough for low bypass turbofans to truly shine.

 

[Nx4eu]

It's going to be high bypass since there was a order calling for analysis of large S bend intake for high bypass turbofan. Which means BPR>4

I just know that Ayi and Orca both agreed that the the H-20 is/was powered by 4xWS-18/D-30KP-2 engines. Perhaps it was like this when the bomber was first envisioned, and there has been major redesign and a switch to using high bypass engines, this could also explain the massive delay in it's appearance.

 

[Elysium]

Are we even sure they're gonna make this thing?

This is just a guess, but if the H-20 is B-21 sized, then the payload difference might not be meaningful enough to justify a new aircraft.
I think there's a chance the project got internally cancelled, and if we ever get a H-20, then it's going to be an entirely distinct aircraft from what was being built so far.

 

[Tomboy]

Are we even sure they're gonna make this thing?
View attachment 793503
This is just a guess, but if the H-20 is B-21 sized, then the payload difference might not be meaningful enough to justify a new aircraft.
I think there's a chance the project got internally cancelled, and if we ever get a H-20, then it's going to be an entirely distinct aircraft from what was being built so far.

2D dimension of bays doesn't mean much, B-21 has deeper bays and much larger combat radius. Payload is one thing but the range you csn carry that payload is also important.

 

[Scott Kenny]

No reason to use low bypass engines anymore, China has medium to high bypass engine available. It's likely powered by four engines with bypass ratio >4 with GJ-X/WZ-X using two of the same engine.

I mean, B-2 is 4x low/medium-bypass turbofans. B-21 is 2x low/medium-bypass turbofans.

Isn't high hypass turbofans better for long range subsonic aircraft,?

In terms of sheer fuel economy, yes. If you're just setting the throttles and leaving it alone for the whole flight like a commercial plane, the higher the bypass ratio the better.

But high-bypass fans are slow to spool up. Even the small-fan CFM56s (60 or 61" fans) are very slow to respond to throttle changes. Which is not desirable for a military aircraft. F101s are about the highest bypass you'll want for a combat aircraft.

 

[Tomboy]

In terms of sheer fuel economy, yes. If you're just setting the throttles and leaving it alone for the whole flight like a commercial plane, the higher the bypass ratio the better.

But high-bypass fans are slow to spool up. Even the small-fan CFM56s (60 or 61" fans) are very slow to respond to throttle changes. Which is not desirable for a military aircraft. F101s are about the highest bypass you'll want for a combat aircraft.

I don't forsee any reason for rapid maneuver for a large strategic bomber hence I doubt fast throttle response is really weighed over than having better fuel efficiency. In fact I expect the flight profile of these bombers to be more like airliners with a long high efficiency cruise to and back from the targeted area.

PW9Ks have a BPR of 4 already.

 

[Nx4eu]

I mean, B-2 is 4x low/medium-bypass turbofans. B-21 is 2x low/medium-bypass turbofans.



In terms of sheer fuel economy, yes. If you're just setting the throttles and leaving it alone for the whole flight like a commercial plane, the higher the bypass ratio the better.

But high-bypass fans are slow to spool up. Even the small-fan CFM56s (60 or 61" fans) are very slow to respond to throttle changes. Which is not desirable for a military aircraft. F101s are about the highest bypass you'll want for a combat aircraft.

F118 has a bypass ratio of 1.3:1,
F101 has a bypass ratio of 2.1:1,
PW9000 has a bypass ratio of 4:1,

I don’t know why you keep calling B-21’s engines as “low/med” bypass. The PW9000 4:1 bypass ratio is by all accounts on the high end of medium bypass, and could be classified as low-high bypass. So by all means it should be referred to as med/high-bypass turbofan.

For a subsonic long range bomber fuel efficiency trumps whatever small advantages you’d get from accelerating a bit faster. If the B-21 is being shot at, its primary defense has already failed. How can you say F101s are about the highest bypass you’ll want, while ignoring the fact that the B-21 already has engines with nearly double its BPR?

If the H-20 has a requirement to hit the CONUS, it’s going to need more efficient engines.

For reference the current H-6 flies with WS-18/D-30KP-2. Those have a BPR of 2.24:1.

That should be the floor BPR for any engine a subsonic H-20 may be installed with, already higher than your F101s are about the highest BPR you’d want for a combat aircraft.

 

[chimeric oncogene]

I think the main issue is just going to be range; CONUS is very, very far from the PRC. Combat radius requirements are like 8,000 to 10,000 km, which means nearly 16-20,000 km of range.
Tankers might help, but you need to push your tankers very far over Russia (hah!) or over Japan (hahahaha!) to make this work.
So you need a very, very big flying wing with either a buddy tanker variant or something, and that's a huge mess. It's much worse in this day and age of space-based sensors, and in either case the enemy can hunt your tankers with Blue A2/AD/Golden Dome etc.

 

[Scott Kenny]

I don’t know why you keep calling B-21’s engines as “low/med” bypass. The PW9000 4:1 bypass ratio is by all accounts on the high end of medium bypass, and could be classified as low-high bypass. So by all means it should be referred to as med/high-bypass turbofan.

Because I do not trust those reports describing the PW9000. An F135 LP section does not fit on an engine core that has a 9:1 bypass ratio with a 56" fan. That's a ~19" diameter core, give or take, assuming I have done my math correctly.

For a subsonic long range bomber fuel efficiency trumps whatever small advantages you’d get from accelerating a bit faster. If the B-21 is being shot at, its primary defense has already failed.

It's not how fast the aircraft accelerates, it's how fast the engine accelerates or decelerates.

If the H-20 has a requirement to hit the CONUS, it’s going to need more efficient engines.

The B-2 goes that far with 4x F118s. Haven't we already talked about "H-20 has 4 engines"?

 

[Nx4eu]

Because I do not trust those reports describing the PW9000. An F135 LP section does not fit on an engine core that has a 9:1 bypass ratio with a 56" fan. That's a ~19" diameter core, give or take, assuming I have done my math correctly.



It's not how fast the aircraft accelerates, it's how fast the engine accelerates or decelerates.



The B-2 goes that far with 4x F118s. Haven't we already talked about "H-20 has 4 engines"?

F135 Fan inlet is 43in. Assuming this is used as the LP stage for the PW9000, a 4:1 BPR translates to roughly a 86in diameter Fan. Actually less due to the shaft.

I measured 2 separate images of the B-21 from the front view, assuming a 48m wingspan which using the theorized serpentine intake layout shown in the sample graphics below. The B-21 could possible accommodate a 84in diameter engine.
(The thickness is not the thickness of the entire fuselage, it is measured from bottom of the fuselage to the perceived top of the inlet lip.)

 

[Nx4eu]

I think the main issue is just going to be range; CONUS is very, very far from the PRC. Combat radius requirements are like 8,000 to 10,000 km, which means nearly 16-20,000 km of range.
Tankers might help, but you need to push your tankers very far over Russia (hah!) or over Japan (hahahaha!) to make this work.
So you need a very, very big flying wing with either a buddy tanker variant or something, and that's a huge mess. It's much worse in this day and age of space-based sensors, and in either case the enemy can hunt your tankers with Blue A2/AD/Golden Dome etc.

I remember I did some basic calculations awhile back where i assumed that an H-20 with a similar estimated L/D ratio of the B-2 while being powered by 4xWS-18 would get something like 16,000km range with 118,000kg of fuel. That's a lot of fuel, and a huge plane.

 

[snne]

Are we even sure they're gonna make this thing?
View attachment 793503
This is just a guess, but if the H-20 is B-21 sized, then the payload difference might not be meaningful enough to justify a new aircraft.
I think there's a chance the project got internally cancelled, and if we ever get a H-20, then it's going to be an entirely distinct aircraft from what was being built so far.

https://www.secretprojects.co.uk/th...bomber-program-xac-h-x-h-20.28076/post-855782

 

[baseball801802]

https://www.secretprojects.co.uk/th...bomber-program-xac-h-x-h-20.28076/post-855782

My theory was the "redesign" was them pivoting the R&D into HALE bomber/ISR drones like the WZ-X and the GJ-X.

 

[snne]

My theory was the "redesign" was them pivoting the R&D into HALE bomber/ISR drones like the WZ-X and the GJ-X.

 

[Elysium]

2D dimension of bays doesn't mean much, B-21 has deeper bays and much larger combat radius. Payload is one thing but the range you csn carry that payload is also important.

Do we have any good guesstimates of the respective ranges and payloads of the 2 aircraft? My guess would be 15 tons payload and 6000km combat range for the B-21, and 10 tons and 3000 km for the J-36. Both fit huge bombs/missiles.
While the B-21 can carry more stuff further by a significant margin, 3000km combat range is more than most combat aircraft, and is more than enough for most combat theaters imo, including the South China Sea.
The huge range of the B-2 has been used for boutique capabilities, like taking off from the middle of the US, flying to the middle east, dropping some specialist payload (MOAB) and flying back. The B-2 was also a highly exotic aircraft, and I guess there are very few airbases in the world it can operate from. The B-21 won't be, and the J-36 likely won't be as well.
And if the Chinese decided to do a 'redesign', build a new plane essentially that only shares its name with the old one, I think it's reasonable to consider the old design cancelled.

 

[Tomboy]

Do we have any good guesstimates of the respective ranges and payloads of the 2 aircraft? My guess would be 15 tons payload and 6000km combat range for the B-21, and 10 tons and 3000 km for the J-36. Both fit huge bombs/missiles.

J-36 can maybe hit 3500 km with VCE and air to air payload and a reasonably bit less with heavier strike payload although the types of strike payload it could possibly carry are far inferior to B-21 owning to limited bay depth. B-21 could carry more proper strike weapons to ranges likely twice as far.

H-20 that they would want would likely be carrying 20-30 ton oversized payload across the third island chain, they might want to stuff it full of HCMs for mass conventional strike and nuclear strike against CONUS which also means a very long bay will be required along with minimal refueling for an unrefueled combat range of atleast 8000 km and very good stealth. H-20 already has suffered a complete redesign in the late 2010s so you are probably right the H-20 we'll see in the near future will be completely different from the H-20 we would've seen in the last decade.

 

[Sferrin]

F118 has a bypass ratio of 1.3:1,
F101 has a bypass ratio of 2.1:1,
PW9000 has a bypass ratio of 4:1,

I don’t know why you keep calling B-21’s engines as “low/med” bypass. The PW9000 4:1 bypass ratio is by all accounts on the high end of medium bypass, and could be classified as low-high bypass.

There are a couple variants of the CF6 in the 4+ - 5 BR.

 

[Josh_TN]

If the H-20 has a requirement to hit the CONUS, it’s going to need more efficient engines.

+1

The issue is not can any engine be used in a bomber; the issue is how far can you carry a heavy payload? And for that, you likely need a medium-to-high bypass engine of very high efficiency tuned to the cruise altitude of the airplane. That is probably a major development item for the PRC.

For comparison, B-2 has a combat radius of ~3000 miles/5000 km, which would get you to about Midway or the northern edge of Australia in a straight line. Plenty of range for Guam, but I assume the PLAAF is thinking bigger.

B-21 range is undisclosed but estimates run in the 5,000-6000 mile / 10,000 km combat radius, which could put you over Alaska or Hawaii. Austin has stated that B-21 will not require any “in theater logistics”, which I take to mean no air refueling. And I believe there have been statements by PLAAF watchers that 20,000 km range is the requirement for H-20.

I think reaching the CONUS is unobtainable without refueling.outside China, though strikes might be carried out against west coast targets with long range cruise missiles.

 

[snne]

+1

The issue is not can any engine be used in a bomber; the issue is how far can you carry a heavy payload? And for that, you likely need a medium-to-high bypass engine of very high efficiency tuned to the cruise altitude of the airplane. That is probably a major development item for the PRC.

For comparison, B-2 has a combat radius of ~3000 miles/5000 km, which would get you to about Midway or the northern edge of Australia in a straight line. Plenty of range for Guam, but I assume the PLAAF is thinking bigger.

B-21 range is undisclosed but estimates run in the 5,000-6000 mile / 10,000 km combat radius, which could put you over Alaska or Hawaii. Austin has stated that B-21 will not require any “in theater logistics”, which I take to mean no air refueling. And I believe there have been statements by PLAAF watchers that 20,000 km range is the requirement for H-20.

I think reaching the CONUS is unobtainable without refueling.outside China, though strikes might be carried out against west coast targets with long range cruise missiles.

FYI, the PLAAF don't have to fly over San Diego or anything; they just need to get close enough with refuel to launch very long range missiles.

 

[Tomboy]

10000km combat radius for B-21 seems ridiculous, are you sure it's not total range?

 

[Rumil]

Combat radius requirements are like 8,000 to 10,000 km, which means nearly 16-20,000 km of range.

Not really, H20 is being built Primarily to deliver Nukes all other unguided bombs platforms talk is secondary and useless when they already have long range stealth platforms like GJX, So you have to include the range of nuclear vehicle in addition to bomber's CR and for now that would be JingLei-1 which has a range of 8000Km as stated by official media.

In other words, the PLA requires the H-20 to have a combat radius of 5000 km to be viable for their strategic goals.

 

[Josh_TN]

10000km combat radius for B-21 seems ridiculous, are you sure it's not total range?

I am sure of nothing. I have seen some estimates that run that high. I think it minimally extremely likely that it has a longer unrefueled range than B-2. Austin’s statement sounds like it could be refueled off AK/HI. The latter would skip the ascent/takeoff, so perhaps the numbers I am mentioning are in relation to that specific situation, or I misremembering, or it was simply an inaccurate estimate in the first place. My main point was just that a lot of the distances being mentioned on the thread require an extremely high efficiency.

 

[Josh_TN]

Not really, H20 is being built Primarily to deliver Nukes all other unguided bombs platforms talk is secondary and useless when they already have long range stealth platforms like GJX, So you have to include the range of nuclear vehicle in addition to bomber's CR and for now that would be JingLei-1 which has a range of 8000Km as stated by official media.

In other words, the PLA requires the H-20 to have a combat radius of 5000 km to be viable for their strategic goals.

View attachment 793550

JL-1 seems very unlikely to be an internal store or otherwise associated with H-20.

 

[Rumil]

JL-1 seems very unlikely to be an internal store or otherwise associated with H-20.

"For now that would be JingLei-1 which has a range of 8000Km as stated by official media"

Already explained the Primary role of H20, It will replace H6 as air leg of triad so we have to assume H20 will carry the only air launched nuke vehicle in service right now aka JL1.

I am not aware of any LRSO counterpart being in development for now and given the place of ALBMs in PLA doctrine I don't see one being developed anytime soon either so JL1 is our only option for the time being.

 

[lancer21]

JL-1 seems very unlikely to be an internal store or otherwise associated with H-20.

Actually, iirc the rumour mill was saying that the H-20 is designed around the capability to carry JL-1 class weapons, not necessarily the JL-1 per se but likely a somewhat miniaturized equivalent, so this still dictates a long bay and a big aircraft.

 

[Tomboy]

If B-21 can have combat ranges up to 10k km, no doubt H-20 which is much larger and newer having the range to directly overfly coasts of CONUS without refueling should be expected.

 

[FighterJock]

I would think that the H-20 was probably based on the size of the B-2 especially for the PLAAF's long term strategic goals of targeting beyond the second island chain as they currently see it, so anything being the size of the B-21 would just not be good enough.