PLA next/6th generation fighter thread

[AndrewS]

Internal mounting and advanced ducting mitigates quite a few problems with 3 engine designs. 3 won't take up less space and weight than 2 large, but it can take less fuel. If you design the ducting to be robust and lightweight enough, you can channel air entirely to the 2 lateral engines during cruise and close off the centerline engine, eliminating its drag. That's going to use less fuel than 2 larger engines. When more power is needed - like during takeoff and combat maneuvers - you open the flow to the centerline engine.

This is a very interesting point.

Yes, they could shut off the centerline engine to save fuel and it should still be more efficient.

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An added benefit is that the air ducts can be sized - based on the highest airflow requirements of the possible operating modes below:

a) Subsonic cruise speed to maximise range and fuel efficiency. 2 engines in high-bypass airflow mode. 1 engine is shut off.

b) Supercruise. 2 or 3 engines at maximum non-afterburning thrust, in a low-bypass airflow mode.

c) Maximum thrust. 3 VCE engines with afterburners on, in a low-bypass airflow mode.

d) Loiter mode. Only 1 Centerline Engine operating to really reduce fuel consumption to the absolute minimum. But would this be enough thrust?

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We can see definite advantages here over a 2 engine design - which always has to keep 2 engines operating.

There's some weight penalty with the duct flaps and the auxiliary power unit to restart the centerline engine, but the fuel savings in most flight scenarios make it worthwhile.

An engine probably represents 2.5-3? tonnes of weight. But the advantage is additional thrust, presumably supercruise and a larger MTOW. And there's already an APU to restart engines anyway?

If we use the F-35 engine as a baseline an example, we're looking at about 2? tonnes of fuel consumption per hour.

And if the requirement is to operate to the 2IC, that's a 6000km round-trip from mainland China which would take 6+ hours of flight
That would mean 12 tonnes of fuel saved by shutting off an engine
And if they can shut off 2 engines on the return journey (because most of the weight in fuel has been burned off), that's another 6 tonnes of fuel saved.

 

[kriss]

no one else was really raising the possibility of J-XD having three engines might reflect a limitation of industry

Just saying that's also some very far fetched thesis along with some other assumptions for why a three engines design.

We all know J-20 have been flying with underpowered engine for the past decade and only recently rumored to be equipped WS-15. No reason why J-XD couldn't make do with less powerful engine (even if it's WS-15 in this case).
Even if they deems it's really impossible to power the plane with only 2 engine, the natural next step would be put 4 engines on it (could also be 4 smaller engine if that's favorable). It's a tried solution in many other aircraft designs and are way simpler than make whole 3 engine thing work.

I believe if J-XD turns out to indeed have three engines it would have some good reasons for adding a third engine instead of "China can't make good engine".

 

[Gloire_bb]

I believe if J-XD turns out to indeed have three engines it would have some good reasons for adding a third engine instead of "China can't make good engine".

Lack of engine is the best reason possible. And I don't see it as something insulting.

We may love it, hate it, run in rage, but you're either flying with 3 or there's no aircraft you want.

It's common sense.

 

[Deino]

Lack of engine is the best reason possible. And I don't see it as something insulting.

We may love it, hate it, run in rage, but you're either flying with 3 or there's no aircraft you want.

It's common sense.

Exactly: IF - and again I would prefer to wait for its unveiling - it is indeed a huge fighter due to its-range-, sensor- and weapons-load-requirements, then a third engine may make sense simply since no current Chinese engine is powerful enough to power such a "monster-fighter"! That is in no way a testimony that the engines it uses are not good, not modern or whatever ... it only is that no powerful-enough engine is available.

But again: I would prefer to wait for its unveiling and then start making conclusions on why what or what not and what to deduct from it.

 

[siegecrossbow]

I don’t think so. If a more powerful engine is developed you guys serious think it can go back to a two engine configuration? I don’t think the amount of redesign is possible.

 

[latenlazy]

I don’t think so. If a more powerful engine is developed you guys serious think it can go back to a two engine configuration? I don’t think the amount of redesign is possible.

It will depend on how the engines and air inlet ducting is mounted.

 

[siegecrossbow]

It will depend on how the engines and air inlet ducting is mounted.

With a tri-engine configuration I don’t see how it can be done without belly intakes.

 

[latenlazy]

With a tri-engine configuration I don’t see how it can be done without belly intakes.

You can still do two side intakes. It would be a 2-1-3 tunnel shape.

 

[tphuang]

I beg you all to be patient and even more rationale!

As much as I admire China's progress and you all surely know me, how much - sometimes over- excited I am, I beg you to calm down a bit: Is China indeed "taking the lead in global fighter aircraft"?

Surely if they will show the J-XD-demonstrator soon it is a major "breakthrough in PLAAF history", but we all know, that the USAF already has similar "demonstrators" flying since years! They only did not unveil them to the public yet.

Again, I do not want to downrate this "breakthrough", but to immedealtly jump the bandwaggon and call it "China is leading" is IMO too early ... As such you are correct with your second part: It is surely "Symbolically taking the lead in global fighter aircraft" development but to make a conclusion we simply do not know enough!

... even more so, it hasn't been unveiled yet.

I actually think it's quite rational

USAF does not have "demonstrators" flying since years? It had maybe 1 or 2 YF or X type of aircraft that flew a couple of years ago. That's a huge difference. At this point, NGAD hasn't even picked a winning design yet. You can look up how long it took from Lockheed being picked as prime contractor for F-35 to when it achieved IOC.

Whereas based on CAC history, once the first "demonstrator" flies, it's about 7 years from joining service. Surely, you must see the difference here. We've both followed Chinese military aviation for about 20 years now.

This is a major moment when it gets revealed. There has been a lot of negative talks on NGAD program recently. You can bet that funding for NGAD will be flowing in once J-XD flies.

I think asking people to check themselves a bit is probably healthy. Hype is the mind killer.

well, you are the one that has written multiple articles on this topic on Western media.

Also true, but I nonetheless think "a brief moment of polite interest at most" is too much to ask. There will be at least some amount of cheering.

Very true, but I maintain that asking people not to celebrate out of an abundance of caution for a hypothetical future aircraft (as opposed to a very real, if inevitably overhyped* one) is probably asking too much.

* Every next-generation breakthrough is always ridiculously overhyped as some miracle wunderwaffe, don't take it personally anyone.

Well, advancement is only part of this. But as anyone that has seen my zero posting in 054B or CV-18 thread can see, most of these military projects are not that significant.

Just understanding how PLAAF sees future air warfare is a pretty big deal here.

5th gen, we all had some expectations of what J-20 would look like.

But with J-XD, just the 3-engine part is already a huge surprise to me and making me having to fully re-evaluate how future air fleet will look like.

It's entirely possible that PLA will see 6th gen differently than US military. And that's kind of exciting factor on its own.

 

[ACuriousPLAFan]

I don’t think so. If a more powerful engine is developed you guys serious think it can go back to a two engine configuration? I don’t think the amount of redesign is possible.

Indeed. Like, how would the aerodynamics even work here??

Even with the inlet and nozzle of the midline 3rd engine somehow blocked/covered up that are streamlined with the surrounding airframe body (in the case of reverting from a 3-weaker-engine configuration to a 2-powerful-engine configuration in the future) - The aerodynamic properties involved are still going to be very much different than having a fully functional engine inlet + operational midline 3rd engine + nozzle.

You can still do two side intakes. It would be a 2-1-3 tunnel shape.

Are there any examples of turbofan/turbojet aircrafts with shared engine intakes (i.e. number of intakes < number of engines)?