It's not *that* hard to say. We have math. The B-58 could get away with such a morbid T:W because it's threats looked different at the time. You need better acceleration to escape today's threats.
Our notional JH-XX would also be stealthy as well, and operating with stand off weapons, which substantially lowers its kinematic requirements.
But sure, I'll have a go below.
And the point I'm making is that the math tells us roughly where the lines are. Some very straightforward physical factors limit how arbitrary the sliding of that scale is. Weight and thrust classes and how they dictate capability are pretty big determinants in those unknowns, and we already know what different weight and thrust combinations will roughly look like.
EDIT: Let's say you have an 80 ton design but you'll compromise and keep its TOW with payload and fuel to 60 tons. You're still going to be flying something 40-50% heavier than a Su-34 using the same class of engines. I don't think this works out.
Okay, let's use 80 ton MTOW as the top weight for JH-XX. That is the weight of the aircraft if it's fully loaded, externally and all. But for the missions against a high intensity opponent, we would naturally be obliged to preserve stealth, thus it will be only limited to internal weapons. In other words, the MTOW number for a stealthy aircraft capable of hauling large loads externally (which JH-XX in my mind is almost certainly expected to do) is not very useful for standard stealthy strike missions.
But, we can use the MTOW to guestimate what the empty weight, internal fuel weight, and internal payload weight may look like.
-Based on various similar aircraft including stealthy airframes such as F-35, F-22 and YF-23, as well as less stealthy airframes but aircraft in the supersonic bomber role such as B-58 and B-1, I'm going to list this thing's empty weight as 40% of its MTOW, let's say 32 tons.
-Internal fuel I will derive from as a % between the F-35A's internal fuel (8.4 tons which is 64% of its empty weight of 13.1 tons), and the B-1Bs internal fuel (93 tons which is 108% of its empty weight) -- so let's say we want JH-XX to have an internal fuel load of 75% of its empty weight, which is 24 tons, and let's call that 1200km combat radius with a normal internal land attack payload.
-Internal payload, I will say to be six JSM sized stand off missiles, or two YJ-12 sized AShMs, as well as two MRAAM/LRAAMs.
One JSM sized missile is under 500kg, so six would be under three tons. YJ-12 is anywhere up to 4.5 tons heavy, but let's call it 3 tons per YJ-12.
I don't know how much internal hardpoints will add, but let's say they're 20% of the weight of each munition. (I don't think it would actually scale this way, and it may actually be an exaggeration of the necessary hardpoint weight, but let's just go with it)
For six JSM sized missiles, that is thus under 3 tons for the weight of the munitions + 600kg of the hardpoints; for two YJ-12s, that is 6 tons for the weight of the munitions + 1.2 tons of the hard points... so 3.6 tons for a six JSM payload ans 7.2 tons for a two YJ-12 payload.
Two MRAAMs/LRAAMs would add no more than 400kg together given the weight of a single MRAAM is about 150kg and the necessary launch rail probably no more than 50kg
So, empty weight + internal fuel + internal weapons load (let's assume the six JSM loadout, as I doubt they would be too keen on using a JH-XX with interim engines as a high demand anti shipper) + crew
So, 32 tons empty weight + 24 tons internal fuel + 3.6 tons for six JSM+hardpoints + 400kg for two AAMs with rails + let's say 200kg for two crew and their equipment...
That takes me to 60.2 tons, for a stealthy, full internal fuel, land attack loadout -- this is the TOW for a land attack mission without any compromises in payload or fuel, btw.
Of course, let's say we need to compensate for less powerful engines, and it just so happens that they don't need it to have full internal fuel, let's say only 75% -- maybe the target is not only 900km+300km away, or maybe they will be refuelled on the way home, whatever. That would be 18 tons of fuel rather than 24 tons, or, in the above loadout, it's a TOW of 54.2 tons. Maybe we're going to be even more conservative, and desire survivability a little more than payload haul on a single trip, and make it 4 JSMs rather than 6 JSMs -- that reduces the internal payload weight by another 1.2 tons, to 53 tons TOW.
Assuming WS-10A engines (if there is a higher thrust version actually on J-11D it's possible it would also be used for JH-XX as well, but let's use WS-10A for this), that is similar to the Al-31Fs currently aboard Su-34s.
Two WS-10As will be powering a 53 ton aircraft on only internal stores and at 75% internal fuel and 2/3 internal payload, versus two Al-31Fs powering a hypothetical Su-34 fully loaded at 45 tons MTOW. JH-XX obviously doesn't look too good here.
However, JH-XX would be much lower drag than Su-34, which is burdened by high air resistance external stores, and JH-XX is also stealthy, meaning even if it is unable to accelerate away as fast as Su-34, it has RF stealth to improve it survivability. Depending on just how lacklustre JH-XX's acceleration and top speed is, they could quite conceivably change the mission profile or SOP to compensate.
But let's take the worst case scenario, let's say JH-XX in the 53 tons loadout, can only reach Mach 1.5, and it takes a long time to get there. In the worst case scenario, the air force still ends up with a large, stealthy bomber operating at (presumably) high subsonic cruise for a mission, with supersonic dash during the egress phase, and more importantly it can get to the launch point for any stand off weapons against a distant, well defended target in a way which is far harder to detect than any other aerial platform China currently has.
So at worst, JH-XX using interim engines will be similar to a stealthy H-6K able to carry 4-6 300km range cruise missiles, but with slightly shorter range but also with the ability to reach low-mid supersonic speeds but with the need for greater acceleration time to get there compared to if it were using intended engines.
I would consider such a capability very worthwhile and the air force currently has nothing like it in its inventory -- when we consider that WS-10As would only be interim engines and that JH-XXs would likely be re-engined with WS-15s, then JH-XXs even with interim engines become an even more worthwhile investment... though this depends on how long it would take for WS-15s to be ready, which is why I harped on about it so much in the last few posts. If it's a 3 year delay, that's not bad at all, if it's 5 years I think it's acceptable but not optimal, but if it's something like 10 years then they should consider maybe investing the money elsewhere.
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Now, there are a lot of numbers above, and if one changes just a few of them slightly, that could drastically modify how viable JH-XX with interim engines is as a bomber and its opportunity-cost. That is why I thought it would be difficult to get anywhere too meaningful, because even if we disagree on every number by only 10%, that could be the difference between viable and non-viable.
