Shenyang FC-31 / J-31 Fighter Demonstrator

latenlazy · Mar 2, 2021

ougoah said:
Not the fairest comparison - F135 with EJ200. Wonder what the difference is between a Al-31 and RD-33. It's probably nowhere near 2 times greater. Then there's twice the maintenance man hours and material consumed. Also more chances of aircraft being grounded or at least a lower serviceability rate since twin engined fighters have twice the chance of engine drama that reduces their readiness. These are all cost factors, not only the purchase price of the engine. If this weren't such a big deal, the Americans wouldn't have bothered with the F-16 or F-35.

Well, two RD-33s provide more thrust than one AL-31. That’s why I went with the EJ-200 to F135 comparison. Much more comparable total thrust between two EJ-200s and one F135 than two RD-33s and one Al-31. You’re talking about using a single engine to power a *mid-weight* fighter, not a light weight one. Again, the internal bays disqualifies the possibility of a single engine fighter being light.

Double the maintenance perhaps, but you don’t need a 1:1 reserve of engines for your maintenance schedule to maintain readiness. Smaller engines also tend to have better service schedules since being smaller means less mechanical strain on the parts. And also you don’t need to invest in a *third* fighter development program and a *third* supply chain in the specific case we’re talking about, if this is really all about the money.

Deino · Mar 2, 2021

Kejora said:
... It seems they confident that they could produce enough engines for both Su 57 and LMFS.

Yes, they were confident in the 1990s to have five carrier battle groups until the early 2020s, they were confident to have the Su-57 already operational since years ... jet's wait and see what happens, but I won't hold my breath.

Atomicfrog · Mar 2, 2021

Deino said:
Yes, they were confident in the 1990s to have five carrier battle groups until the early 2020s, they were confident to have the Su-57 already operational since years ... jet's wait and see what happens, but I won't hold my breath.

Optimism aspiration is always bigger than truth... it's why the cautious approach in China pay well.

We can just look at the f-35 with huge engine problems right now when the fighter have been build in the hundred... The way China handle is jet engines progression give them plenty of good fighters with high increment possibility. If they would have jumped the ladder with risky approach, maybe the j-20 would not be implemented in units right now. The same with J-31, they will take the time necessary to have something that works or to decide to kill it in the egg before putting to much time and money on it.

davidau · Mar 2, 2021

Atomicfrog said:
Optimism aspiration is always bigger than truth... it's why the cautious approach in China pay well.

We can just look at the f-35 with huge engine problems right now when the fighter have been build in the hundred... The way China handle is jet engines progression give them plenty of good fighters with high increment possibility. If they would have jumped the ladder with risky approach, maybe the j-20 would not be implemented in units right now. The same with J-31, they will take the time necessary to have something that works or to decide to kill it in the egg before putting to much time and money on it.

A famous Chinese saying....small steps [cautious], quick pace [fast]. My interpretation is ...do everything cautiously but [once all debugged] move at fast pace to catchup

Blitzo · Mar 2, 2021

ougoah said:
Yeah a midsize fighter with one engine though. Not a twin engine midsize. Midsize doesn't necessarily mean twin engine. Of course China will need the WS-15 to mature and be in twin engine service for a while before this can be realistic. WS-10 may or may not offer enough thrust.

Two medium thrust engines are just a lot more costly than one high thrust.

There was an extensive discussion about a medium weight single engine versus twin engine 5th generation fighter a couple months ago.

Future PLA combat aircraft composition

And yes, what you described -- a "worse" J-20, with commonality with the navy, and a larger production run, more maintainable stealth, more advanced production method -- sounds like a hell of an aircraft to me, especially as such an aircraft would not need the additional development time needed...

www.sinodefenceforum.com

The position I held, and I continue to hold, is that it is true in general principle that a single engine fighter of a given weight class would offer lower operating costs than a twin engine fighter of the same weight class, assuming we can hold all else equal.

But for the PLA, a "single engine medium weight 5th gen" versus a "twin engine medium weight 5th gen" is more complex than that, and not everything is held equal.
Things like development time, reduced costs in terms of commonality of systems and upgrades (given the PLAN will be procuring J-XY itself, and any "twin engine medium weight 5th gen" would be a land based derivative of J-XY), engine availability (how available would WS-15 be if it was asked to fulfill both J-20 production and a single engine medium weight 5th gen fighter), as well as distribution of aerospace resources.

My conclusions were:

Single engine strengths:
- Operating cost and maintainability benefits of a single engine

Twin engine strengths:
- Operating costs and upgrade costs/paths and certain shared logistics benefits of having a close carrier based variant
- Greater speed from project initiation to service and reduced risk
- Will not have same degree of engine bottleneck (WS-15 production/availability) as a single engine aircraft
- More sensible distribution of aerospace resources in context of SAC and CAC's other respective ongoing projects

Common strengths of both:
- Non engine related operating costs intrinsic to both aircraft's design and production

In other words, IMO it is a red herring to focus so much only on the number of engines that a prospective medium weight 5th gen fighter has, from the PLA's perspective.
There are other confounding factors at play which may drive them more towards a twin engine solution than a single engine solution, with some of those including operating cost that are not engine related.

NiuBiDaRen · Mar 2, 2021

Interesting that the official prize of this week's episode on CCTV7 is a model of "FC-31". Curious that Chinese state media would release an official model of FC-31 before the plane is in service.

26:06 in the video. Wonder if the serial number means anything that you plane watchers know things about.

ougoah · Mar 2, 2021

Bltizo said:
There was an extensive discussion about a medium weight single engine versus twin engine 5th generation fighter a couple months ago.

Future PLA combat aircraft composition

And yes, what you described -- a "worse" J-20, with commonality with the navy, and a larger production run, more maintainable stealth, more advanced production method -- sounds like a hell of an aircraft to me, especially as such an aircraft would not need the additional development time needed...

www.sinodefenceforum.com

The position I held, and I continue to hold, is that it is true in general principle that a single engine fighter of a given weight class would offer lower operating costs than a twin engine fighter of the same weight class, assuming we can hold all else equal.

But for the PLA, a "single engine medium weight 5th gen" versus a "twin engine medium weight 5th gen" is more complex than that, and not everything is held equal.
Things like development time, reduced costs in terms of commonality of systems and upgrades (given the PLAN will be procuring J-XY itself, and any "twin engine medium weight 5th gen" would be a land based derivative of J-XY), engine availability (how available would WS-15 be if it was asked to fulfill both J-20 production and a single engine medium weight 5th gen fighter), as well as distribution of aerospace resources.

My conclusions were:

In other words, IMO it is a red herring to focus so much only on the number of engines that a prospective medium weight 5th gen fighter has, from the PLA's perspective.
There are other confounding factors at play which may drive them more towards a twin engine solution than a single engine solution, with some of those including operating cost that are not engine related.

@latenlazy

Right but my original position is that J-35 is a PLAN only project because being twin engined, it is quite unlikely for it to suit PLAAF needs as some low cost, number filler 5th gen fighter. So if it fits anywhere in PLA, it fits with the prospective PLAN carriers and nowhere else.

Single engined 5th gen for China is not going to happen because the pace at which air combat is moving at means by the time one is ready, it can potentially be obsolete already. A WS-15 or WS-10 with enough thrust and reliability for a single engine application questions whether 1. it will even be enough thrust for a midsize and 2. whether it can be developed and proven reliable in time since we know the FC-31 is designed as twin engined but the peripheral skills of 5th gen fighter development have already been around (well we assume anyway since it's been years since J-20 service intro).

stannislas · Mar 2, 2021

Crang said:
Interesting that the official prize of this week's episode on CCTV7 is a model of "FC-31". Curious that Chinese state media would release an official model of FC-31 before the plane is in service.

View attachment 69417

26:06 in the video. Wonder if the serial number means anything that you plane watchers know things about.

why not, this thing was in the Zhuhai airshow since 2014, it's not a classified PLA jet

Blitzo · Mar 2, 2021

ougoah said:
@latenlazy

Right but my original position is that J-35 is a PLAN only project because being twin engined, it is quite unlikely for it to suit PLAAF needs as some low cost, number filler 5th gen fighter. So if it fits anywhere in PLA, it fits with the prospective PLAN carriers and nowhere else.

Single engined 5th gen for China is not going to happen because the pace at which air combat is moving at means by the time one is ready, it can potentially be obsolete already. A WS-15 or WS-10 with enough thrust and reliability for a single engine application questions whether 1. it will even be enough thrust for a midsize and 2. whether it can be developed and proven reliable in time since we know the FC-31 is designed as twin engined but the peripheral skills of 5th gen fighter development have already been around (well we assume anyway since it's been years since J-20 service intro).

That's a question of whether they're going to pursue a land based medium weight 5th gen fighter.

My position is that if they do, it will likely be a land based J-XY derivative.

And for the reasons stated in the subsequent replies in that thread, I believe a land based J-XY derivative will be cheaper to operate than J-20s as well.

That is to say -- and let me be clear -- that I think a land based J-XY can fit the role of a lower cost medium weight 5th generation fighter for the PLA. It doesn't have to be a single engine aircraft.

latenlazy · Mar 2, 2021

ougoah said:
@latenlazy

Right but my original position is that J-35 is a PLAN only project because being twin engined, it is quite unlikely for it to suit PLAAF needs as some low cost, number filler 5th gen fighter. So if it fits anywhere in PLA, it fits with the prospective PLAN carriers and nowhere else.

Single engined 5th gen for China is not going to happen because the pace at which air combat is moving at means by the time one is ready, it can potentially be obsolete already. A WS-15 or WS-10 with enough thrust and reliability for a single engine application questions whether 1. it will even be enough thrust for a midsize and 2. whether it can be developed and proven reliable in time since we know the FC-31 is designed as twin engined but the peripheral skills of 5th gen fighter development have already been around (well we assume anyway since it's been years since J-20 service intro).

All low cost “filler” stealth fighters will end up looking something like the F-35, aka a medium weight fighter. Whether it uses one engine or two engines it’s going to end up becoming a mid weight fighter by function of all the stealth imposed requirements. The number of engines is not a significant qualifier or disqualifier for such a class of fighters.

Shenyang FC-31 / J-31 Fighter Demonstrator

latenlazy

Brigadier

Deino

Lieutenant General

Atomicfrog

Major

davidau

Senior Member

Blitzo

Lieutenant General

Future PLA combat aircraft composition

NiuBiDaRen

Brigadier

ougoah

Brigadier

Future PLA combat aircraft composition

stannislas

Junior Member

Blitzo

Lieutenant General

latenlazy

Brigadier