Su-27 FM inconsistency in acceleration & turn performance?

[draconus]

7 hours ago, Ironhand said:

Thank you.

Found the other one - Совместные государственные испытания (СГИ) - actual aircraft tests.

[Cmptohocah]

Found here that Su-27 should accelerate from 600km/h to 1100km/h in 15s at 1000m. Slide name is 0012.jpg.

From this test it looks like our DCS version is 3.3 seconds slower:

 

 

Edited July 19, 2022 by Cmptohocah
Added the test reference.

[Ironhand]

3 hours ago, Cmptohocah said:

Found here that Su-27 should accelerate from 600km/h to 1100km/h in 15s at 1000m. Slide name is 0012.jpg.

From this test it looks like our DCS version is 3.3 seconds slower:

….

 

Thanks for the link. I’ll check it out.

I’m seeing about 3 seconds difference myself at the 2,000 m altitude for both the 600-1100 and 1100-1300 km/h marks but the latter mark especially depends on whether you’re measuring IAS or TAS. My runs have been with 4 AAMs and 2622 kg fuel.

[Cmptohocah]

18 hours ago, Ironhand said:

 

Thanks for the link. I’ll check it out.

I’m seeing about 3 seconds difference myself at the 2,000 m altitude for both the 600-1100 and 1100-1300 km/h marks but the latter mark especially depends on whether you’re measuring IAS or TAS. My runs have been with 4 AAMs and 2622 kg fuel.

Data in the acceleration table is valid for:
 

Quote

50% fuel load of internal tanks; 2xR-27 and 2xR-73 (in the manual they are called "K" for some reason); full after burner.

Slide 0011.jpg, paragraph 10.

[Ironhand]

13 hours ago, Cmptohocah said:

Data in the acceleration table is valid for:
 

Slide 0011.jpg, paragraph 10.

Yes. Ran across that while reading last night. Still haven’t found any indication of whether the V is Vпр (IAS) or Vист (TAS). Have yet to see it in any of the materials I’ve looked at. Our Flanker is much closer, especially for the 1100-1300 bracket, if it’s TAS.

Edit: K-27 is the GRAU identifier for the R-27 (perhaps while in prototype?), something I didn’t know until today.

Edited July 20, 2022 by Ironhand

[Cmptohocah]

14 hours ago, Ironhand said:

Yes. Ran across that while reading last night. Still haven’t found any indication of whether the V is Vпр (IAS) or Vист (TAS). Have yet to see it in any of the materials I’ve looked at.

 

I have never seen any aircraft manual that uses TAS as a reference for performance. It makes sense to be used in engagements as it describes the geography better, but when it comes to performance IAS/Mach is the thing to look for.

I will sift through the docs again, but I am almost certain that they are talking about indicated airspeed.

[Ironhand]

9 hours ago, Cmptohocah said:

I have never seen any aircraft manual that uses TAS as a reference for performance. It makes sense to be used in engagements as it describes the geography better, but when it comes to performance IAS/Mach is the thing to look for.

I will sift through the docs again, but I am almost certain that they are talking about indicated airspeed.

If you have the time, do sift through. But, since ED has already said that how it behaves is more accurate than the charts, it may be a moot issue.

The reason I’m so curious is that, while it doesn’t make too much difference in the 600-1100 speed range, it makes a tremendous difference in the 1100-1300 sped range. In the latter, it’s the difference between 14 sec and ~50 sec at 2000 m. I believe in the “Сопротивлeниe” (Drag) video you posted above, he came in at 49 sec. No matter how you look at it, the speeds don’t line up with the charts. But in TAS, they end up a hell of a lot closer in the higher speed range.

Edited July 21, 2022 by Ironhand

[Cmptohocah]

On 7/21/2022 at 8:24 PM, Ironhand said:

If you have the time, do sift through. But, since ED has already said that how it behaves is more accurate than the charts, it may be a moot issue.

On the slide named 0055.jpg, for example, you can see that they have used Vpr (IAS) for their performance data.

[Ironhand]

21 hours ago, Cmptohocah said:

On the slide named 0055.jpg, for example, you can see that they have used Vpr (IAS) for their performance data.

Thanks. I’m not sure what to make of that in terms of proof. While it’s specified there, it isn’t throughout. It could, I suppose, be an indication that, unless indicated otherwise, velocities are TAS. If everything is IAS, though, then our Su-27 is extremely out of line with publicly available specifications. There’s a world of difference between 13 sec (expected) and 49 sec (delivered).

[F-2]

On 7/20/2022 at 2:59 AM, Cmptohocah said:

Data in the acceleration table is valid for:
 

Slide 0011.jpg, paragraph 10.

Keep in mind 50% does not mean 50% of the flankers total fuel as it can’t pull 9g still under 50% total. Note the weight is listed 18920kg. You are likely aware but readers might not be.

[Cmptohocah]

18 hours ago, F-2 said:

Keep in mind 50% does not mean 50% of the flankers total fuel as it can’t pull 9g still under 50% total. Note the weight is listed 18920kg. You are likely aware but readers might not be.

From what I know, Su-27 is limited to 8G, but that's for the export version - not sure if there is any differenece though.

[Ironhand]

23 hours ago, F-2 said:

Keep in mind 50% does not mean 50% of the flankers total fuel as it can’t pull 9g still under 50% total. Note the weight is listed 18920kg. You are likely aware but readers might not be.

The 50% is 50% of the basic fuel load which is defined in the manual as filling tanks #2 and #3 with fuel having a specific gravity of 0.785. So 4160+1060/2=2610 kg or thereabouts. I suppose the other possibility is 50% of a partial fuel load which is tank #2 filled to at least 3400 kg with a top limit of around 4160.

Which fuel load, though, doesn’t matter too much because the difference would equate to fractions of a second rather than many multiple seconds. And especially not the 40+ sec difference in the 1100-1300 acceleration range.