Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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mixelflick

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Unread post09 Jan 2019, 15:31

How is it the SU-27 or SU-35 can maintain such high mach speeds with external missiles? Is this due to the fact they're carried in the "tunnel" between the engines?

Their AAM's have those big honking fins, you'd think they'd be a lot more draggy than say, 4 AMRAAMS fit flush against the F-15's fuselage. Shame those CFT's on the F-15 can't be jettisoned. They add a lot more fuel (bringing capacity up to about an SU-27's full internal), and she sounds real fast with them (vs. the external tanks). Of course, as one pilot told me once - We'll just punch the tanks when it's time. Still, wasn't the LA guard flying with CFT's on their F-15C's not long ago as an experiment?

Did anything ever come of that??
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Unread post09 Jan 2019, 15:32

garrya wrote:Andraxxus is very well known for his knowledge about aerodynamic so that i guess we can take his word, in the mean time i will try to contact him to see if we can get the manual

Ah, yes, Andraxxus. He and I have butt heads by proxy (as we do not attend each others forums but many other users here do). He has been critical of my past works. I appreciate that he is critical of my work from a standpoint of aerodynamic evaluations and logic instead of passion and "fanboy"-ism. Where we tended to differ was in our assumptions. We both agree that assumptions have to be made when trying to tease the meaning out of public data, we just chose different assumptions and thus came to different conclusions. I do respect his posts, even when I disagree with them.

I have the Su-27K manual. It doesn't actually have much in it compared to western manuals. If he has anything on air-to-ground stores limits I would be interested.

That said, the quote you boxed for me is interesting. Those sound like air to air stores carriage limits, the same kind of placard limits I deal with with the F-15. I will take them as such and add this to my data.

To add visuals to what I am saying I have added the following. From the below graphic we can see from the Flight Manual that a CFT Mounted AIM-7 has a 660/1.4 carriage and employment limit on the F-15E. On the F-15C it is listed as BAL for Basic Aircraft Limits, meaning no additional speed restrictions, like the Pylon Mounted AIM-9s shown beneath the AIM-7s.
Eagle Stores 1.PNG


The next graphic shows many structural limits, notably the CFT limits.
Eagle Limits 1.PNG


Taking these images I can confidently and correctly make the statement that "An F-15E is limted to Mach 2 with CFTs and only Mach 1.4 with missiles on them." Someone might interpret that as a thrust limit. Yet with the -220 motors the F-15E with CFTs, CFT mounted AIM-7s, and pylon mounted AIM-9s can get past 1.4 on standard day based on thrust limits.
Eagle Limits 2.PNG


Now, this next part is relevant to the Su-27 vs Su-35 discussion. With -229 motors, the F-15E is subject to the exact same carriage limitations but it has more power. Now it can blow through Mach 1.4 with ease.
Eagle Limits 3.PNG
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Unread post09 Jan 2019, 15:43

mixelflick wrote:How is it the SU-27 or SU-35 can maintain such high mach speeds with external missiles? Is this due to the fact they're carried in the "tunnel" between the engines?

I don't think they can. The F-16 Flight Manual will tell you that the F-16 has no speed restriction with air-to-air missiles, just like the statement "An Su-27 can go up to M2.35 (max speed) with missile on pylons 5,6,7,8"

Care to wager the top speed an F-16 can reach with 6 AMRAAMS/Sidewinders? closer to Mach 1.85. Conversely the F-15E, well, see the above post.

There are CAS limits, Mach limits, and Drag limits. The first two are "placard" limits. "You better not try and go faster than this or else bad things will happen" limits. The last one is "You are never going to exceed this"
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Unread post09 Jan 2019, 17:38

From the below graphic we can see from the Flight Manual that a CFT Mounted AIM-7 has a 660/1.4 carriage and employment limit on the F-15E. On the F-15C it is listed as BAL for Basic Aircraft Limits, meaning no additional speed restrictions, like the Pylon Mounted AIM-9s shown beneath the AIM-7s.


Why would the CFT shod F-15E have an AIM-7 hard speed limit and the CFT shod F-15C not ? Would the AIM-120 be similarly limited ? The limit seems pretty close to the thrust speed limit indicated by the flight test envelope chart for -220 engines with that configuration, wonder if it was just an oversight to hardwire that number in the F-15E manual ? I also can't understand how they tested and graphically tabulated a CFT/AIM-7 -229 F-15E close to Mach 2 if it was flying well past its certified structural limit for that configuration.
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Unread post09 Jan 2019, 17:52

marsavian wrote:
Why would the CFT shod F-15E have an AIM-7 hard speed limit and the CFT shod F-15C not ? Would the AIM-120 be similarly limited ? The limit seems pretty close to the thrust speed limit indicated by the flight test envelope chart for -220 engines with that configuration, wonder if it was just an oversight to hardwire that number in the F-15E manual ? I also can't understand how they tested and graphically tabulated a CFT/AIM-7 -229 F-15E close to Mach 2 if it was flying well past its certified structural limit for that configuration.

Almost ALL CFT mounted stores on the F-15E have a 660/1.4M limit with the exception of an 11 GBU012 loadout that has 525/0.90 limit listed. This is a CAS/Mach limit for stores carriage, not a thrust limit. Any time there is a difference between the -220 and the -229 it is called out, stores limits is not one of them. I do not have an answer for how they make envelopes that go past these placard speeds, only speculation.
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Unread post09 Jan 2019, 18:20

Speculation ... indication of emergency limits ? Any idea why it was changed for the same configuration from F-15C to F-15E ? Nice work btw, like an F-15 driver said it will be exchanging long range missile shots with opponents once detected like an old fashioned pistol duel.
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Unread post09 Jan 2019, 18:33

I don't have my F-15C manual on me so I can't verify that CFT mounted AAMs are cleared for BAL or 700/2.0. Possible reasons for the difference could be 1) blanket limit of "not to exceed 1.4M" to save time on certification 2) all the extra pylons on the F-15E CFT generate shockwaves that interfere with stores above 1.4M.
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Unread post09 Jan 2019, 18:39

Thanks, but if it is just carrying wing pylon missiles with CFT like AIM-9/AIM-120 then no limits apart from actual flight performance apply ?
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Unread post09 Jan 2019, 19:15

The CFT limit of 700/2.0 applies, but yes, both types of wing mounted AAMs have a BAL carriage and employment limit.
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Unread post10 Jan 2019, 11:36

sprstdlyscottsmn wrote:
mixelflick wrote:How is it the SU-27 or SU-35 can maintain such high mach speeds with external missiles? Is this due to the fact they're carried in the "tunnel" between the engines?

I don't think they can. The F-16 Flight Manual will tell you that the F-16 has no speed restriction with air-to-air missiles, just like the statement "An Su-27 can go up to M2.35 (max speed) with missile on pylons 5,6,7,8"

Care to wager the top speed an F-16 can reach with 6 AMRAAMS/Sidewinders? closer to Mach 1.85. Conversely the F-15E, well, see the above post.

There are CAS limits, Mach limits, and Drag limits. The first two are "placard" limits. "You better not try and go faster than this or else bad things will happen" limits. The last one is "You are never going to exceed this"

So the limit for Su-27/35 as well as F-16 in manual is placard limit?
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Unread post10 Jan 2019, 13:18

Verified CFT limit for AIM-7s on the F-15C is 700/2.0 as limited by the CFT. Any guesses about drag limits?
F-15C CFT clean.PNG



Three 610gal gas bag limit is 660/1.5 with or without CFT, AIM-7 limit is 700/2.0 with CFT, AIM-9 limit is BAL (800/2.5). So, according to stores limits, we are looking at 660/1.5 with tanks and 700/2.0 without. Too bad loaded with three gas bags was never run through the wringer for the FM, but we can see what it is if all the EFTs are dropped.
F-15C CFT loaded.PNG


So we can see that the stores limit for the F-15C of CFTs with 8AAMs of 700/2.0 is academic unless you are flying a plane with engine trim set to 102% and you are flying in Alaska (STD-10C). Standard trim and standard atmo? You will barely hit the 1.5 limit of the gas bags even after you drop them.

I am unable to find my source doc for the original comparison I did that said on the F-16 AAMs had a 2.0M limit and AG stores had a 1.2M limit. Sorry.
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Unread post10 Jan 2019, 13:26

garrya wrote:So the limit for Su-27/35 as well as F-16 in manual is placard limit?

I have as much evidence proving the Su limits are placard as Andraxxus has saying they are drag limits. None. But when I look at what is written it makes the most sense to me. Otherwise the 10-AAM Su-27 with six of them being Alamos is a 1.7M plane. BS. An F-15C with 8-AAMs and four of them being conformally carried on the fueselage is a 1.8M plane from a drag standpoint even though it's limits are 2.5M, which it can't even reach with uptrimmed engines on a Std-10C day (2.25M)
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Unread post10 Jan 2019, 13:56

The conclusion I get from all these charts is that the -229 engine is really good at overcoming the drag of stores and getting close to clean structural performance. It gets the best dynamically out of the Eagle.
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Unread post10 Jan 2019, 15:06

Definately. The 8AAM with CFT loadout for the -229 F-15E can hit ~1.9M from 35,000ft to 45,000 ft at a weight 8,000lb heavier than the above F-15C chart of the same load.

Based on the HAF F-16 manual, the GE-129 is even better than the PW-229 at altitude in the 1.2-1.6M range. Granted that is a different inlet and the F-15 has a variable one, but I suspect the difference would be similar.
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Unread post10 Jan 2019, 16:26

sprstdlyscottsmn wrote:
mixelflick wrote:How is it the SU-27 or SU-35 can maintain such high mach speeds with external missiles? Is this due to the fact they're carried in the "tunnel" between the engines?

I don't think they can. The F-16 Flight Manual will tell you that the F-16 has no speed restriction with air-to-air missiles, just like the statement "An Su-27 can go up to M2.35 (max speed) with missile on pylons 5,6,7,8"

Care to wager the top speed an F-16 can reach with 6 AMRAAMS/Sidewinders? closer to Mach 1.85. Conversely the F-15E, well, see the above post.

There are CAS limits, Mach limits, and Drag limits. The first two are "placard" limits. "You better not try and go faster than this or else bad things will happen" limits. The last one is "You are never going to exceed this"


I would concur. The fact is any legacy fighter flying with 6 AAM's is going to struggle to get to supersonic, waste a ton of fuel in doing so and won't stay there for long. There may be isolated incidences where it's necessary (one Iranian F-14 got to mach 2.2 chasing a Foxbat - no air to air loadout noted, but assume it had to have at least 1), but you can count them on one hand.

Which makes the F-35 limit of mach 1.6 with 5,000lb weapons load all the more impressive. Actually, I think the mach 1.2 supercruise with minimal burner is the most impressive of all..
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