I don’t know if you’ve discussed this here, but I was wondering, don’t you actually deal with three engines ?
First the F-404 GE 402, then the RM-12 and then the F-404 GE 402 EPE engine ?
The first is the oldest and the last is the youngest?
F-404-GE-400, which is the F/A-18A/B engine.
Then the F-404/RM12, a version improved for the JAS 39
Then the F-404-GE-402, the EPE engine for the F/A-18C/D.
mig23m has implied that because it’s slightly newer, the 402 should have all the improvements of the RM12 plus more improvements. The fact that it has a lower static thrust, and a lower flowmass even with a higher bypass ratio is indicative it is worse than the RM12 across the board. For example the F-414 engine for the SuperHornet, which produces much more thrust than any of these engines, has a much lower bypass ratio, meaning more of the air is getting used with fuel in the combustion chamber of the turbine.
EPE only had the last series of Hornet C and then the Swiss
You’d know more than me. I don’t know the details of which versions received which improvements and when.
The hornet will be a good plane when it comes, it just won’t be a pure dogfighter like the F-16 and Gripen. It wasn’t designed to be though, it’s much more of a multi-role aircraft. It should be able to pull incredible alpha though, so I can’t wait to see what the flight model looks like when it arrives.
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MiG-23M making up a million data points and traveling back in time to publish them to win an argument about the Grippen apparently.
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No, I haven’t implied anything. The sources discuss explicitly what was changed between the models. The F404-GE-402 has all of the improvements of the RM12, except in areas where it further improved upon the changes done to the RM12.
The RM12 has a higher flow fan, as expected, this results in a higher uninstalled static thrust. The -402 has the original fan, modified, with a better flowing core and higher RPM. The bypass ratio is higher… so more fresh air is usable for the afterburner section and temps are managed better until higher airspeeds. The lower pressure ratio means that friction heating is less of an issue, turbine inlet temperature is likely lower at the same speeds as that of the RM12.
Time travel baby ;)
The “EPE” or “enhanced performance engine” is the F404-GE-402. They are not two separate models. Simply put, the GE-402 utilizes a 2nd gen core for the F404 series which has +200 degree turbine inlet temps limit and flows air better with a lower pressure ratio than that of the RM12 to produce similar (likely better) peak thrust. The bypass ratio is lower, which means more air flows around the engine (improving cooling) but also providing more fresh air for the afterburner. This indicates to me that the F404-GE-402 should have a higher peak thrust ceiling than that of the RM12.
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Yes, that’s right, somehow I thought it was the -GE 402 model and the EPE is its stronger variant.
I think the GE 402 may be slightly more powerful than the RM-12 at a certain speed and altitude. But the RM-12 will have the same, maybe with a bigger difference for Volvo
I see two problems :
The performance of an engine varies greatly depending on its speed and altitude (air pressure/density). If we don’t have graphs, it will be hard to compare engines purely based on uninstalled thrust.
But moreover, we don’t know what the installed thrust is for the Hornet and Gripen :-/
The sources directly contradict this. For example it doesn’t incorporate the better intake fan from the RM12.
Using all of this logic the F-414, which they replaced the 402 with in the Super Hornet, would be worse. It has a higher pressure ratio, a higher static thrust, and a much lower bypass ratio than the 400/402.
Seeing we know they went with the F-141, we know who is right here.
The reality is that Saab and later BAe made improvements to the 400, resulting in the RM12, which far exceeded what GE were able to achieve in the 402 EPE program. Probably for cost reasons. Remember the Hornet was the ugly duckling of the US military-industrial complex for a long time.
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One interesting reason I can think of is fuel consumption; the Hornet didn’t meet range criteria, so a more fuel-efficient engine almost as powerful as the RM-12 would have been useful. And the -402 has a slightly lower fuel consumption than the RM-12.
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Already discussed, the better intake fan only improves performance in the upper left hand of the flight envelope.
The F414 has a much larger fan with 16% higher flow… the fan is also longer by 5 inches. Among a myriad of other changes it is a much different engine than the RM12 and F404-GE-402 which are quite similar (with the exception of the improvements the -402 made)…
That’s not true actually. It specifically makes a large improvement in the upper left of the envelope. But it provides a higher mass flow across the board according to the sources.
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Having higher mass flow through the core doesn’t make it magically produce more thrust with afterburner… it just means that it will have higher output in mil thrust w/out burner. Additionally, the turbine inlet temperature limit still exists… having higher flow doesn’t offset the fact that they will run into the hard temperature limit sooner due to the increased pressure ratio… whereas the GE-402 will be able to handle the higher flow at higher speeds without as much concern for the temp limit… since it won’t reach it until later than the RM12.
On the other hand, we know that the F404-GE-402 document states explicitly that the only place the RM12 fan would improve upon the GE-402 model is in the upper left hand of the envelope. I’m sure since they took the effort to say this it would imply that it indeed doesn’t benefit them in the rest of the envelope.
If you’re not familiar with journal articles, I’m sure it might seem that way. As someone who regularly reviews scientific papers I can tell you it is not the case.
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Going back to the “industry standard” issue… they clearly discuss more than just the static thrust increase for the -402, and likely aren’t generalizing here either. I think it is quite obvious that the -402 would have improved thrust over the RM12. If you think otherwise, you are clearly not reading the available materials… Probably deducing your opinion from the position that you won’t believe it until the numbers are publicly available directly from a primary source to prove it… in spite of the fact that sufficient evidence exists to already show this.
We can all agree we have different thresholds which we deem sufficient evidence.
Quite the contrary. I was unaware of the increased bypass ratio of the 402, so if anything you’ve only unearthed more evidence to convince me the RM12 is the superior engine. Thankfully, for once me and the devs are in agreement here.
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Why would you go through the effort of building a brand new engine with the stated goal of faster time to altitude and intercept, with the stated goal of more provided power, to then make the engine worse than the previous model? That doesn’t even make sense.
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He’ll point out the constraint of having to use the lower flow fan to be fit in the F/A-18 without modifications to the airframe. The issue with this response is that the document clearly states the RM12 only provides additional performance in a specific area of the flight envelope.
The RM-12 should be superior to the GE 402 in several very important ways. Someone correct me if I’m wrong, but the first and very important thing is that the RM-12 engine needs to be more reliable and safer because the Gripen has one engine - so the engine design is more geared in that direction.
The second important thing is more bird strike resistance.
More engine thrust in a certain area of the flight envelope, directly adapted to the intended use of the Gripen.
The RM 12 is not inferior to the GE 402, it is different and has its own advantages. Naturally the GE 402 has its advantages too.
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The -402 received the reliability enhancements and mechanical backup should the FADEC system fail. Aside from the bird strike issue, it has all of the same improvements but without the higher flow fan, as well as the improved core and a couple of other minor enhancements. The core has less friction and flows air better than the RM12’s -400 core w/ material modifications that enabled it to manage higher turbine inlet temps.
Of course the Gripen will have higher thrust than the -402’s in certain specific conditions… but those are likely limited to very slow airspeeds especially when combined with higher altitudes. This is what is stated and what I have covered in the discussion already to this point.
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