correct as is Current F-15 Speed

[GGTharos]

11 hours ago, Cmptohocah said:

Not what's happening now , which is I presume nothing.

Are you really that certain that it's something like that and not say, certification up to M1.5 because they didn't test further?

12 hours ago, okopanja said:

No clue on this, but your question made me wonder.

What happens in general with aircraft stability when the large draggy object is jettisoned at high mach speed?

Does the aircraft pitch up/down? If I remember correctly, with both F-15 and F-16 there is no effect at all,  but is this true in reality?

Reality is fickle and its fickleness is not simulated   There are a lot of fuel tank related things that aren't happening to anything that carries fuel tanks ... not just eagles or vipers.  Hint.

From the little I know, the greatest area of concern is transonic, that's where a tank is a little more likely to do something unexpected like come back up and take a couple of feet of wing off - it's happened, but it's also not exactly what you'd call a common occurrence.

Edited February 12, 2022 by GGTharos

[okopanja]

8 hours ago, draconus said:

https://www.digitalcombatsimulator.com/en/support/faq/general/

You can read on what is PFM. Does it sound like your "true simulation of aerodynamics" I can't say.

Quote from there: "Use a wider array of wind tunnel tests CFD methods for aerodynamics parameters calculations."

Essentially, I am pointed out that they do not do the CFD for frame rendered in the game for 50+ aircraft.

Instead its about the simplification that can be processed fast enough.

Occasionally people notice the discrepancy, just like @trenchfeet did and report it.

When this happens the issue should be reproduced by the developers, and then decided if they want to update the flight model or not, based on severity and status of the model (I believe that both F-15C and Su-27 are heavily in the maintenance phase with feature freeze). If they do even a single change of a constant, this can cause multiple unit tests (I mean software tests) to fail. They can try modifying few more parameters until hopefully all pass, but in worst case it may be proved that the flight model is not accurate enough. All these activities represent the human effort, and thus cost the money.

IMHO whenever we notice something that is awkward we should report it. This will help them validate and improve code quality and therefore simulation accuracy.

Please take a look how these parameters (I am pretty sure there are additional parameters that can not be extracted from LUA) look like here:

https://github.com/Quaggles/dcs-lua-datamine

Left is F-15C and right is Su-27

Edited February 12, 2022 by okopanja
typos...

[okopanja]

7 hours ago, GGTharos said:

Are you really that certain that it's something like that and not say, certification up to M1.5 because they didn't test further?

The process of airplane development starts on the whiteboard (or PC nowadays), where initial idea is refined, improved. This includes computer aided modeling, simulation, wind tunnel testing (and probably 10 more high level things I did not mention), and off course flight testing of the "final" product. Needless to say the "truth" is established iteratively, with final product more or less being different than the initial idea. The adherence to the initial requirements is assessed. Ideally issues are resolved, but sometimes in agreement with customer even undesired behavior can be accepted in some cases, which usually brings the limitations. Even with now current F-22/F-35 there are surely a number of limitations, just on observing publicized incidents.

As you can see from many of the documents you have probably so far amassed (), it is never the perfect picture. All due limitations are noted and surely this is not just because they did not test it. From what I got from that documents they tested pretty much everything that can be tested. I would see the document as something they assembled based on a rather comprehensive test results on what the real pilot needs to know.

7 hours ago, GGTharos said:

From the little I know, the greatest area of concern is transonic, that's where a tank is a little more likely to do something unexpected like come back up and take a couple of feet of wing off - it's happened, but it's also not exactly what you'd call a common occurrence.

Actually I believe you know quite a bit, it is always interesting to read your posts independent if I agree or not. I am pretty sure the pilots also ask: "hey why can not I drop the tanks?", and they do get the answer to that.

IMHO: this got reported, everyone here now have access to real profiles, so feel free to replicate and report your findings. I am pretty sure the developers will get back with the answer.

Edited February 12, 2022 by okopanja
typos

[cofcorpse]

On 2/11/2022 at 2:34 PM, BlackPixxel said:

I have made a comparison of the acceleration at 8.4 °C vs 40 °c in a level flight at 12 km altitude some days ago.

As you can see, the acceleration is just stretched a bit in time as it gets warmer. But the top speed stays the same.

Meanwhile the Su-27 shows massive differences:

Su-27 at warm temperatures accelerates alot slower and reaches a much slower top speed (look how the warm curve begins to show the approach of a max value with a bend, while the cold curve is growing linear at the same time.)

One of them is wrong (or both are wrong). ED needs to take a look at those FM's again.

I'm sorry, but I think your test is not quite correct in my opinion. You have different scale in X axis for F-15 and the same for Su-27, what causes the graphs of one to be similar and the other to be different. Your test of F-15 ends due to running out of fuel, but there is a lot of acceleration at this point, which will lead to more different results. And, as I can see, Su-27 doen't run out of fuel till the end of the test (or graph at least).

On 2/11/2022 at 9:20 PM, dundun92 said:

I was under the impression that this doc was OK as this was uploaded by Chizh himself on the DCS userfiles?

Apart from the rule 1.16 this document is not valid for our F-15 as we have PW-220, not PW-100.

 

Our F-15C is definitely not immune to changes in temperature, which I have easily seen by doing simple tests. The size of the temperature influence might be worth checking and adjusting if necessary, but this influence exists even now.

[Ironhand]

8 hours ago, cofcorpse said:

..You have different scale in X axis for F-15 and the same for Su-27, what causes the graphs of one to be similar and the other to be different. Your test of F-15 ends due to running out of fuel, but there is a lot of acceleration at this point, which will lead to more different results. And, as I can see, Su-27 doesn't run out of fuel till the end of the test (or graph at least)...

EDIT: Took BlackPixxel's original F-15 Low (Cold) TRK and ran it out to 5 minutes. Then opened it in the ME and changed the temp to 50°C and saved it. Then reran the TRK file, taking control after BP had punched into afterburner to maintain level flight and ran it for 5 minutes as well. Interesting result:

Blue: 8.4°C

Pink: 50°C

 

Edited February 13, 2022 by Ironhand

[BlackPixxel]

6 hours ago, cofcorpse said:

I'm sorry, but I think your test is not quite correct in my opinion. You have different scale in X axis for F-15 and the same for Su-27, what causes the graphs of one to be similar and the other to be different.

You have to compare speed at certain times, or time for certain speeds. Not just overlaying the graphs.

[dundun92]

9 hours ago, cofcorpse said:

Apart from the rule 1.16 this document is not valid for our F-15 as we have PW-220, not PW-100.

I linked that one because thats the only one I could find from a quick  search; IK at some point both the 220 and 100 performance charts were uploaded by Chizh there; the one I had linked in the deleted post came from the 220 doc