J-20 5th Generation Fighter VII

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taxiya

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minime said:
Now WS-15 is officially confirm for J-20 flight testing, any info out for what kind of engine WS-15 is?
1, more of F-119 small bypass ratio for high altitude high speed
2, or between F-119 and F-135 for a balance approach?
3, what kind of thrust WS-15 is aiming for and implication of performance impact on J-20?
Click to expand...
Low bypass ratio according to Liu Daxiang in the recent video. It was a known information from the early requirement paper (around 0.25:1).
1671217800777.png

In the requirement, thrust in the class of 15000kgf with afterburner, same as F-119.

J-20 is aiming at F-22's role and performance. The US made F-135 for F-35 because they have F-22, there is no compromise (balancing) on either aircrafts. If China want a bomb truck like F-35, China will make something else, not to compromise J-20(WS-15).
 
sunnymaxi

sunnymaxi

Major
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taxiya said:
Low bypass ratio according to Liu Daxiang in the recent video. It was a known information from the early requirement paper (around 0.25:1).
View attachment 103524

In the requirement, thrust in the class of 15000kgf with afterburner, same as F-119.

J-20 is aiming at F-22's role and performance. The US made F-135 for F-35 because they have F-22, there is no compromise (balancing) on either aircrafts. If China want a bomb truck like F-35, China will make something else, not to compromise J-20(WS-15).
Click to expand...
outdated information. 15,000kgf thrust was the target of early WS-15 version.

this WS-15 is totally a different machine.

WS-15 wet thrust will be in the range of 38,000-40,000 lbs

minime said:
Now WS-15 is officially confirm for J-20 flight testing, any info out for what kind of engine WS-15 is?
1, more of F-119 small bypass ratio for high altitude high speed
2, or between F-119 and F-135 for a balance approach?
3, what kind of thrust WS-15 is aiming for and implication of performance impact on J-20?
Click to expand...

Low bypass ratio

Dry thrust - 25,000 lbs
Wet thrust - 38,000 lbs - 40,000 lbs
 
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gelgoog

Lieutenant General
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High bypass ratio = increased engine frontal area. Which basically kills high speed performance of the aircraft.
That is why you won't see it in fighter aircraft.
 
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Tirdent

Junior Member
Registered Member
The killer for a high-BPR engine in the J-20 would specific thrust, long before cross sectional area became an issue. You can build a Mach 2.0 (dash) aircraft with *reheated* engines having BPRs in excess of 1.0, e.g. Tornado or Tu-160. The MiG-31 hits almost Mach 3.0 on engines with a BPR of ~0.6. Only when you reach BPRs in excess of 2.0 does fan diameter start to make decent airframe area ruling for low supersonic drag difficult. It's the supercruise requirement that truly precludes high BPR in the WS-15.

Net thrust = gross thrust - inlet momentum drag: F = m9*c9 - m0*c0, where 0 indicates inlet and 9 nozzle exit. Fuel mass flow is quite negligible compared to air mass flow, so you can reasonably simplify to F = m*(c9 - c0). Specific thrust is thrust per mass flow, i.e. F/m - now you can rewrite as Specific thrust = exhaust velocity - inlet velocity, and inlet velocity is flight speed. A fast-flying aircraft needs high exhaust velocity to develop any net thrust at all due to high inlet velocity, and high BPR engines move lots of air but at low velocity for a given net thrust. That is to say they have low specific thrust, good for subsonic fuel consumption, but they require afterburner to increase exhaust velocity if they are to attain supersonic speed. That is obviously incompatible with supercruise.

Depending on how high fan pressure ratio and turbine inlet temperature are (both increase specific thrust at constant BPR), the WS-15 might not need to go all the way down to 0.2, but <0.5 is a given. It's also why a dry WS-15 where you only chop off the reheat (as opposed to re-design the LP shaft) makes little sense as a powerplant for the H-20. Fuel consumption would probably be *worse* than the older but higher-BPR WS-10.
 
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