Chinese UAV/UCAV development
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kwaigonegin
Colonel
Not just the engines but a lot of cases, to reduce IR signature the airframe itself has to be well designed to divert and disperse the hot exhaust properly. You can still have a regular engine inside any bird but you can significantly reduce it's heat signature by hiding all of the engine parts including the nozzles internally and then vent the hot exhaust out in a way to better blend with the cold air outside.
A good example is the F-117.. those who have seen it up close can tell they made HUGE efforts in hiding the exhaust. That has little to do with engine but everything do to with the chassis design.
Exhaust vents of F-117
exhaust X47B
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Not just the engines but a lot of cases, to reduce IR signature the airframe itself has to be well designed to divert and disperse the hot exhaust properly. You can still have a regular engine inside any bird but you can significantly reduce it's heat signature by hiding all of the engine parts including the nozzles internally and then vent the hot exhaust out in a way to better blend with the cold air outside.
A good example is the F-117.. those who have seen it up close can tell they made HUGE efforts in hiding the exhaust. That has little to do with engine but everything do to with the chassis design.
View attachment 7829
Exhaust vents of F-117
exhaust X47B
Everything you say is 100% correct, but to be fair it seems the Chinese are pursuing a twin track of both revolution and evolution. Clearly the overall airframe shaping would seem to conform to current 'best practices' in VLO shaping and signature reduction. Assuming this is an early stage prototype, the Chinese have closed a pretty massive gap pretty quickly and it would be fairly safe to assume that they'll undertake comprehensive testing of the prototype and then incorporate ever more sophisticated exhaust / IR reduction into their future prototypes.
Testing it all in one go would seem to be a fairly high risk strategy, especially with technology that is this new.
IR reduction measures come with thrust penalties. I wonder if they've simply decided not to incur those penalties during the testing phase, maybe because of the engine problem.Not just the engines but a lot of cases, to reduce IR signature the airframe itself has to be well designed to divert and disperse the hot exhaust properly. You can still have a regular engine inside any bird but you can significantly reduce it's heat signature by hiding all of the engine parts including the nozzles internally and then vent the hot exhaust out in a way to better blend with the cold air outside.
A good example is the F-117.. those who have seen it up close can tell they made HUGE efforts in hiding the exhaust. That has little to do with engine but everything do to with the chassis design.
View attachment 7829
Exhaust vents of F-117
not to
exhaust X47B
plawolf
Lieutenant General
I have a feeling the engine arrangement may be permanent. Look at the main fuselage at the back. There is very little downwards tapering, and more significantly, no room available for the fuselage hull to taper to fine point because the engine is mounted a lot further back than comparable designs.
If they intended for a stealthy exhaust to be installed at a later date, the current engine should be around half a meter more forward than it is now to allow for the space to install a tapered nozzle and IR suppressor.
I think the designers have chosen to sacrific IR suppression and some sideways and aft RCS for increased available internal volume for bigger payloads and more fuel as well as a more efficient engine exhaust (giving better thrust per unit of fuel burnt, which should hopefully translate to better range) in addition to reduced complexity and cost (both in terms of unit cost and operational cost).
From the front and from below, the Sharp Sword would be just as stealthy as ever, its only when you look at it from directly behind or from the air that you might get a bigger RCS compared to if it had a stealthy exhaust.
Since this would be a ground attack UAV, the current engine layout does not really compromise its effectiveness in its primary role. We have to bare in mind that the F35 exposes more of its engine nozzle and also does not have IR suppression, so what if the Sharp Sword might have a bigger RCS from behind or above compared to other western stealthy UCAV? It should still have a smaller RCS than the F35, which should be more than good enough, especially if settling for less than complete all aspect stealth gives the Sharp Sword a noticeably bigger weapons bay and/or combat range. The cost savings should also not be overlooked.
UCAV, even the top of the range stealthy ones, are ultimately expendable assets. If you loose sight of that and want all the bells and whistles to the extent that their price approaches or maybe even exceeds that of manned stealth fighters, well then, you might get top marks in terms of the engineering, but you still fail when it comes to meeting the design criteria.
If they intended for a stealthy exhaust to be installed at a later date, the current engine should be around half a meter more forward than it is now to allow for the space to install a tapered nozzle and IR suppressor.
I think the designers have chosen to sacrific IR suppression and some sideways and aft RCS for increased available internal volume for bigger payloads and more fuel as well as a more efficient engine exhaust (giving better thrust per unit of fuel burnt, which should hopefully translate to better range) in addition to reduced complexity and cost (both in terms of unit cost and operational cost).
From the front and from below, the Sharp Sword would be just as stealthy as ever, its only when you look at it from directly behind or from the air that you might get a bigger RCS compared to if it had a stealthy exhaust.
Since this would be a ground attack UAV, the current engine layout does not really compromise its effectiveness in its primary role. We have to bare in mind that the F35 exposes more of its engine nozzle and also does not have IR suppression, so what if the Sharp Sword might have a bigger RCS from behind or above compared to other western stealthy UCAV? It should still have a smaller RCS than the F35, which should be more than good enough, especially if settling for less than complete all aspect stealth gives the Sharp Sword a noticeably bigger weapons bay and/or combat range. The cost savings should also not be overlooked.
UCAV, even the top of the range stealthy ones, are ultimately expendable assets. If you loose sight of that and want all the bells and whistles to the extent that their price approaches or maybe even exceeds that of manned stealth fighters, well then, you might get top marks in terms of the engineering, but you still fail when it comes to meeting the design criteria.
I'm not so sure the sacrifice for a stealthy nozzle isn't worth it. Tail end RCS and IR suppression are important for deep strike mission roles. Of course, the Lijian may not be designed for those.
If you want to reduce visibility from aft you would lengthen the fuselage in both directions to bury the engine and to keep the center of gravity in the same place. But if that is the intention you're probably looking at a different engine with a higher by-pass ratio. It would then make sense to design and build a smaller test aircraft with say an engine as used in the L-15.
Conclusion: this aircraft is probably intended for use as it looks now.
Conclusion: this aircraft is probably intended for use as it looks now.
plawolf
Lieutenant General
Weapons design criteria are shaped by the operational environment they are intended to operate in. Casing your eyes around China, which potential adversaries besides Russia and maybe India would really require deep strike capabilities?
Western UCAVs may have deep strike as a major design criteria, but that is because they are designed with the kinds of strategic depth and top end integrated air defences possed by the likes of Russia, and now more increasingly, China.
From a Chinese prospective, Russia is not really a remotely likely military adversary, and India simply does not have the kind of integrated air defences that would necessitate the kind of top end all aspect stealth capabilities western UCAVs are aiming for.
US installations in the Pacific. Taiwan. Japan. Okinawa. We also can't discount the possibility that the ASEAN countries will seek to acquire or develop more comprehensive IADs over time. There's a question of range with some of these targets of course, but I would argue there is a place for deep strike mission role in the PLAAF and PLAN, either now or in the near future.
plawolf
Lieutenant General
Taiwan simply lack the strategic depth to necessitate deep strike capabilities. Any high value targets in Taiwan would be covered by cruise and ballistic missiles and the sheer volume of firepower the PLA would pour at Taiwan in the event of war would quite simply overload and quickly smash Taiwan's air defences if they tried to hold the line.
The Sharp Sword lacks the speed and reliability to be relied upon as a first strike weapon for high value targets deep in Taiwan. But if used as part of a second wave follow-on strike force, there wouldn't be enough of Taiwan's AD network left intact and operational to warrant full aspect stealth. Besides, as I said earlier, UCAVs are expendable assets, in that respect, it would be better for enemy AD to pick up on the UCAVs and engage them, thus revealing their own location rather than for manned aircraft to find out the hard way that there are AD assets let operational in the area later if the UCAVs were too stealthy for those AD assets to even realise they were overhead.
Similarly, Japan and other potential targets like Okinawa and Guam lack real strategic depth. They are far away, but they are mainly isolated and small islands and there are no supporting bases from which land based radar might get a peek at the aft of incoming Sharp Swords before they turn for home for the RCS spikes there to matter.
As you mentioned, there is also an issue with range when it comes to most of those bases, and in most scenarios, strikes against those targets would be carried out by cruise missiles rather than UCAVs (unless they are carrier based).
As for ASEAN, well with no disrespect intended towards them, but they are hardly the kind of opponents the PLA would really need to specifically tailor its procurement strategy to defeat. I seriously doubt they are even considered when drawing up requirements for future PLA weapons.
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