Chinese Engine Development

minusone

Junior Member
Registered Member
Something about those numbers doesn't sound right to me, especially if we take @sunnymaxi 's 25,000lbf (~11 tons) dry thrust into the picture. J-20 was specifically designed to do well even with underpowered engines. I can believe that if the dry thrust was around 11 tons, it can reach mach 1.8 in supercruise; 11 tons isn't much less than the wet thrust max of the original AL-31 and Su-27 can get to mach 2.35 on it, so mach 1.8 kinda makes sense, especially to someone who isn't trained in aero-engineering. (Obviously, they're totally different designs but J-20 has decades of aerodynamic research to its advantage though stealth shaping and internal bay requirements to the detriment of kinematic performance compared to the Su-27.) But how to you bump up the thrust to a monstrous 18 tons, making the J-20 the most well-powered fighter jet in the world by far, and end up with a max speed of only just over mach 2.2??? Unless they want to stay very far away from revealing the true speed (highly likely) and just threw 2.2 in there instead of saying, "classifed," I'd say it sounds off. With 2 engines of 18 tons thrust, I'm expecting something like Mach 3, though I'm really not qualified in the field.
well, PLA never revealed the real numbers on max speed.
 

siegecrossbow

General
Staff member
Super Moderator
I know it's far from linear and not calculable with what we have but I'm just saying it sounds weird compared to other jets. Logically, the J-20, desgined on a premise that it must prioritize high kinematic performance even with underpowered engines, should not have a lower max speed than basically every other twin-engined heavy fighter while also miraculously getting engines that are significantly more powerful than every other twin-engined fighter. Although the caveat to this is that they could have prioritized maneuverability, agility, subsonic and transonic performance at the detriment of max speed since this is one of the less useful envelopes.

They said that the max speed of J-20 is over mach 2.2 with two 18.5 ton WS-15s, not with WS-10C.

You don't want your fifth gen to fly at Mach 2+ speeds for too long. Heat would cause the RAM to fracture and strip off.
 

manqiangrexue

Brigadier
You don't want your fifth gen to fly at Mach 2+ speeds for too long. Heat would cause the RAM to fracture and strip off.
Yes, true, hopefully, Chinese material science is at it improving on that but then I'm thinking they should be quite happy with a lower powered engine (maybe the latest WS-10 variant)and focus on dry thrust to improve supercruise. I'm saying something doesn't seem to add up that they went out of their way to develop a 5th gen fighter the emphasizes excellent performance with lesser engines, then went through GREAT pains to make a 180kN engine for it, only to end up with a fighter with a top speed of around mach 2.2 either by natural or imposed limit. Something doesn't seem right.
 

ZeEa5KPul

Colonel
Registered Member
I wouldn't take this information too seriously. That person thinks the H-20 will get WS-20 engines so whatever he has to say can be completely discounted.
They said that the max speed of J-20 is over mach 2.2 with two 18.5 ton WS-15s, not with WS-10C.
Whatever the J-20's max speed with WS-10Cs is, expect the max speed with WS-15 to be around 10% higher.
 

manqiangrexue

Brigadier
It is confirmed to be Mach 2.0 at Zhuhai Airshow.
They seriously declassified the top speed??? By official channel instead of a leak? Or did they say something like, "Above mach 2"? That's crazy if they did! Why would they do that? I don't know of any benefit or instance where a nation declassified such performance parameters of a top fighter jet that isn't for export and isn't ready to be replaced.
 

siegecrossbow

General
Staff member
Super Moderator
They seriously declassified the top speed??? By official channel instead of a leak? That's crazy! Why would they do that? I don't know of any benefit or instance where a nation declassified such performance parameters of a top fighter jet that isn't for export and isn't ready to be replaced.

I don’t see what the big deal is? It isn’t as if they revealed the flight envelope.
 

HereToSeePics

Junior Member
Staff member
Moderator - World Affairs
Registered Member
You don't want your fifth gen to fly at Mach 2+ speeds for too long. Heat would cause the RAM to fracture and strip off.

It’s less about heat causing RAM coating damage(and I doubt this hasn’t been solved by advancements in material science and application techniques), but heating of the aircraft surfaces makes it more susceptible to IR detection and reduces stealth from the IR aspect.
 

latenlazy

Brigadier
I know it's far from linear and not calculable with what we have but I'm just saying it sounds weird compared to other jets. Logically, the J-20, desgined on a premise that it must prioritize high kinematic performance even with underpowered engines, should not have a lower max speed than basically every other twin-engined heavy fighter while also miraculously getting engines that are significantly more powerful than every other twin-engined fighter. Although the caveat to this is that they could have prioritized maneuverability, agility, subsonic and transonic performance at the detriment of max speed since this is one of the less useful envelopes.

They said that the max speed of J-20 is over mach 2.2 with two 18.5 ton WS-15s, not with WS-10C.
Max speed is not determined by thrust. Thrust tells you acceleration, not speed limit.

I have other reasons for not believing the numbers. The dry to wet thrust ratio looks more in line with a higher bypass engine than I would have expected. But let’s wait and see what details emerge.
 
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