Chengdu next gen combat aircraft (?J-36) thread

[KFX]

If it was 3 engines for a smaller plane the “inefficient engines” line of thinking would have more cache. But this is a very large plane, easily 50% bigger by volume than any flying 5th gen today, which tells you they’re not simply trying to compensate for lower thrust. The actual reason has far more to do with electrical power. This plane is designed to have a massive amount of available electrical power to power its hungry sensor and EW capabilities, and the higher the electrical power demands the more beneficial it is to have an always available power source. A third engine simplifies the power architecture to enable this since you won’t have to constantly optimize power availability between thrust and electrical demands.

Sure, but B-21 (from my understanding) will make do with a pair of modified F-135s. Sure, B-21 doesn't have afterburners, but if the requirement had called for B-21 to be more of a fighter (as with J-36) they could have souped up the engines. Also the J-36's ventral intake will have air flow issues with high angles of attack. If the third engine is about electricty, sensors and so forth...wouldn't sharp changes of AoA disrupt this?

 

[vincent]

Sure, but B-21 (from my understanding) will make do with a pair of modified F-135s. Sure, B-21 doesn't have afterburners, but if the requirement had called for B-21 to be more of a fighter (as with J-36) they could have souped up the engines. Also the J-36's ventral intake will have air flow issues with high angles of attack. If the third engine is about electricty, sensors and so forth...wouldn't sharp changes of AoA disrupt this?

B-21 can’t fly supersonic

 

[latenlazy]

Sure, but B-21 (from my understanding) will make do with a pair of modified F-135s. Sure, B-21 doesn't have afterburners, but if the requirement had called for B-21 to be more of a fighter (as with J-36) they could have souped up the engines. Also the J-36's ventral intake will have air flow issues with high angles of attack. If the third engine is about electricty, sensors and so forth...wouldn't sharp changes of AoA disrupt this?

The B-21 isn’t designed to fly fighter maneuvers, and you’re talking about something like doubling the thrust for a B-21 sized plane to meet fighter requirements. The B-21 uses medium bypass engines and there are currently no low bypass engines either in production or development in the US that could meet such requirements.

*IF* there are occasional choked flow issues for the ventral intake they’re at best going to be intermittent. Any kind of high capacity electrical power architecture is going to have batteries and capacitors for load balancing anyways. Plus the other two can easily still supply power. This is not a real limitation.

 

[Nevermore]

One thing to say is that although some anti China elements internationally always say that the J-36 adopts a three engine design because Chinese engines are garbage. However, by the standards of the current three WS15s, this 50 ton fighter jet would have a very excellent thrust to weight ratio, to the point where if this aircraft were to use a variable cycle engine in the future, it would even feel quite 'thrust surplus'.

 

[Nx4eu]

Garbage Chinese engine theory falls flat with the existence of the J-XDS. Which not only is also humongous, and larger than any jet of the previous generation. But it is also equipped with 2D TVC which has a small thrust penalty. If the J-XDS was as famous as the J-36 we wouldn't be hearing these comments, but because the J-36 became mainstream first, the haters will always try and make up issues on anything developed by China, that just so happens to be the third engine on the J-36. Personally I don't even think the haters can find any big issues on an aircraft like the J-XDS. The J-XDS don't seem to fit in any of their cookie cutter stereotypes.

 

[Blitzo]

But why three engines? Wouldn't it make more sense to have two and reserve space along the centreline for fuel, weapons? Could this suggest that Chinese engine technology isn't quite ready to power such an aircraft with two engines? Or given the experimental nature of this jet, do they want to test with three, and if J-36 is proven move to two engines?

It's actually quite easy to logically check whether the question you're asking is valid in the first place.

1: what do we think the kinematic/thrust requirements, and power and cooling requirements of J-36 are?
2: do we think there is any nation on earth that is able to develop and produce engines that are able to meet the above requirements for J-36 in a manner that allows for two engines to be installed (rather than three), at realistic timespans, cost, risk and cross sectional diameter?

Based on your subsequent posts, your answer to 1., suggests that you think the B-21 with the idea with two uprated F135s would be able to meet the totality of those requirements, in which case that is the first flaw of your thinking. I.e.: you underestimate or misunderstand the kinematic/thrust, and power+cooling requirements for J-36.

 

[KFX]

One thing to say is that although some anti China elements internationally always say that the J-36 adopts a three engine design because Chinese engines are garbage. However, by the standards of the current three WS15s, this 50 ton fighter jet would have a very excellent thrust to weight ratio, to the point where if this aircraft were to use a variable cycle engine in the future, it would even feel quite 'thrust surplu

One thing to say is that although some anti China elements internationally always say that the J-36 adopts a three engine design because Chinese engines are garbage. However, by the standards of the current three WS15s, this 50 ton fighter jet would have a very excellent thrust to weight ratio, to the point where if this aircraft were to use a variable cycle engine in the future, it would even feel quite 'thrust surplus'.

It's actually quite easy to logically check whether the question you're asking is valid in the first place.

1: what do we think the kinematic/thrust requirements, and power and cooling requirements of J-36 are?
2: do we think there is any nation on earth that is able to develop and produce engines that are able to meet the above requirements for J-36 in a manner that allows for two engines to be installed (rather than three), at realistic timespans, cost, risk and cross sectional diameter?

Based on your subsequent posts, your answer to 1., suggests that you think the B-21 with the idea with two uprated F135s would be able to meet the totality of those requirements, in which case that is the first flaw of your thinking. I.e.: you underestimate or misunderstand the kinematic/thrust, and power+cooling requirements for J-36.

Fair point, three WS-15s provide about 40% more thrust than two turbocharged F135s. That said, this three engine arrangement just seems bizarrely complex. These three engines will burn a ton of fuel. The dorsal intake will increase drag and make stealth more challenging. The third intake make the pilot's rear visibility (already bad with the J-36 cockpit) even worse. I guess rearward visibility isn't seen as an issue given that this thing will have a solid DAS capability and the aircraft will operate at stand-off ranges. Also, how will the dorsal engine affect air-to-air refuelling?

 

[amchan]

Fair point, three WS-15s provide about 40% more thrust than two turbocharged F135s. That said, this three engine arrangement just seems bizarrely complex. These three engines will burn a ton of fuel. The dorsal intake will increase drag and make stealth more challenging. The third intake make the pilot's rear visibility (already bad with the J-36 cockpit) even worse. I guess rearward visibility isn't seen as an issue given that this thing will have a solid DAS capability and the aircraft will operate at stand-off ranges. Also, how will the dorsal engine affect air-to-air refuelling?

Yes those are the disadvantages. What this probably means is that the additional capability was considered worth taking those disadvantages. Also air to air refueling is probably not a serious issue given the X-47B, which has a dorsal intake in the same position, was able to refuel with no pilot.

 

[KFX]

One thing to say is that although some anti China elements internationally always say that the J-36 adopts a three engine design because Chinese engines are garbage. However, by the standards of the current three WS15s, this 50 ton fighter jet would have a very excellent thrust to weight ratio, to the point where if this aircraft were to use a variable cycle engine in the future, it would even feel quite 'thrust surplus'.

Ai yah. It's not about being pro-China or anti-China, just discussing things objectively. One fault I have with these forums is the nationalistic assumption that Chinese aircraft designers are ten feet tall. Chinese aircraft designers screw up, Western designers screw up...and sometimes they get things right. J-36 is a fascinating aircraft, but its worth being objective about it...and admitting how little we actually know.

Yes those are the disadvantages. What this probably means is that the additional capability was considered worth taking those disadvantages. Also air to air refueling is probably not a serious issue given the X-47B, which has a dorsal intake in the same position, was able to refuel with no pilot.

Yeah, I'm sure they can sort out the air-to-air refuelling bit...maybe a bit more work, but doable...

 

[sevrent]

If it was 3 engines for a smaller plane the “inefficient engines” line of thinking would have more cache. But this is a very large plane, easily 50% bigger by volume than any flying 5th gen today, which tells you they’re not simply trying to compensate for lower thrust. The actual reason has far more to do with electrical power. This plane is designed to have a massive amount of available electrical power to power its hungry sensor and EW capabilities, and the higher the electrical power demands the more beneficial it is to have an always available power source. A third engine simplifies the power architecture to enable this since you won’t have to constantly optimize power availability between thrust and electrical demands.

Im curious but how big of an impact does electricity generation have on thrust? I feel like even with a high power requirement like say 1MW, that still represents a relatively small amount of total power an engine is capable of producing. Now amortizing that over 2 or even 3 engines I feel would probably be negligible per engine