J-20 5th Gen Fighter Thread VIII

[latenlazy]

Increasing static thrust wouldn't really matter if it could not match true 5th generation engines at flight regimes where it actually matters like attaining good supercruise speed and efficiency or good transonic acceleration which IMO is far more important for J-20.

You think that increases in static thrust don’t also translate to increases in thrust across the whole flight envelope? If so please explain your rationale.

4th generation turbofan is usually designed more around subsonic flight regime and is relatively inefficient at supersonic speeds while 5th generation turbofans are designed to sacrifice some subsonic cruise efficiency (F-119 is very fuel thristy) for higher supersonic efficiency and performance like allowing for high supercruise. Next generation VCE are suppose to provide the best of both worlds by offering both good subsonic cruise efficiency and high supercruise speed and performance.

And yet both the F-16XL and Su-57 (and also the proposed but unrealized F-14 Super Tomcat) can supercruise using 4th generation engines. The F-106 needed burners to break past the sound barrier but could also cruise on dry thrust once it was in the supersonic regime, off “3rd generation” engines. What you’re nitpicking over has nothing to do with engine generations but overall pressure ratios and bypass ratios. I would recommend not oversimplifying how these things work.

 

[sequ]

I'll never forgive Lockheed for sticking us with these "generation" marketing terms. What even is a "5th gen" turbofan vs a "4th gen?"

IMO, a 5th gen engine should have at least 2 of the 3 following requirements:

1. Able to make the aircraft for which it was designed for fly supersonic without the use of the afterburner
2. Reduced radar cross-section
3. Reduced IR emission

 

[latenlazy]

IMO, a 5th gen engine should have at least 2 of the 3 following requirements:

1. Able to make the aircraft for which it was designed for fly supersonic without the use of the afterburner
2. Reduced radar cross-section
3. Reduced IR suppression

2 and 3 have nothing to do with the engine.

Edit: If your laughing emoji is meant to be mockery @sequ I would like for you to explain to me why you can’t add IR suppressors and radar blockers to 4th generation engines.

 

[sequ]

2 and 3 have nothing to do with the engine.

Edit: If your laughing emoji is meant to be mockery @sequ I would like for you to explain to me why you can’t add IR suppressors and radar blockers to 4th generation engines.

I would like to add a 4th requirement for 5th gen engines.

4. The engine should be able to put forth straw man arguments or able to shift goalposts.

 

[latenlazy]

I would like to add a 4th requirement for 5th gen engines.

4. The engine should be able to put forth straw man arguments or able to shift goalposts.

Answer my questions about points 2 and 3 first please. Petty smarm is not substantive and you’re not really helping your case with it.

 

[Blitzo]

I would like to add a 4th requirement for 5th gen engines.

4. The engine should be able to put forth straw man arguments or able to shift goalposts.

No, it just means that your original points were somewhat poorly made to begin with.

One could meet points 2. and 3. by modifying a 3rd generation turbojet -- this specific hypothetical is not meant to be obstinate, rather it is meant to demonstrate that one can serve to be more discerning with the criteria of what a "5th generation engine is".

(And even then, if this chain of discussion is continued it should probably occur in a different thread, and I will probably move them to a different location if this conversation does meaningfully continue)

 

[Tomboy]

You think that increases in static thrust don’t also translate to increases in thrust across the whole flight envelope? If so please explain your rationale.

Correct me if I'm wrong but IMO it depends on how you increased the thrust in the first place, if it's from dumping more fuel into the afterburner or running it hotter I doubt it'll provide any help for supercruise which relies on high dry thrust while improving TIT while adding some improvements in compressor design helps but improvement usually still can't match fully (AFAIK WS-10C basically does this). You'd need some serious modification to fully match a purpose designed engine's performance there, which sure isn't impossible but at that point you might as well as just swap in a completely new core and I don't think there are any evidence that WS-10C2 uses a brand new core.

 

[siegecrossbow]

Useful metric of different engine generation is thrust to weight ratio (dry/wet thrust produced vs weight of the engine). If you want to continue debating this then go to the engine thread. This is not the appropriate place.

 

[Deino]

Are we still in the J-20 thread?

IMO especially the discussion of US engines is irrelevant and should end.

 

[latenlazy]

Correct me if I'm wrong but IMO it depends on how you increased the thrust in the first place, if it's from dumping more fuel into the afterburner or running it hotter I doubt it'll provide any help for supercruise which relies on high dry thrust while improving TIT solely helps but improvement usually still can't match fully (AFAIK WS-10C basically does this). You'd need some serious modification to fully match a purpose designed engine's performance there, which sure isn't impossible but at that point you might as well as just swap in a completely new core and I don't think there are any evidence that WS-10C2 uses a brand new core.

To use a concrete example, the F110-132 is not getting more thrust over the F110-129 from dumping more fuel into the afterburner, and the F-16XL and Super Tomcat are both specced for supercruise on lower thrust variants of the F110 than the 132. Iterative thrust improvements in the F110 family don’t just come from higher TIT but aerodynamic improvements in the compressor section, and supercruise is not exactly a function of thrust alone. You don’t actually need a brand new core.