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Old 02-08-2018, 02:58 PM   #1
Maverick Su-35S
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Default Degraded Su-27 aerodynamic lift

Hello,

After some update (don't know in which one), changes have been made to both the F-15 and Su-27 in terms of aerodynamic simulation (lift capabilities being easier to spot).

Initially (after the PFM came out), both the F-15 and Su-27 were capable of achieving quite authentic turn rates compared to the real planes (of course, depending on IAS and weight). The F-15 only had some critical AoA handicap (initially, now is better) as the plane's lateral-directional control was almost impossible to attain above 20 AoA (30 on the F-15's in cockpit indexer), while the Su-27 was worked quite well from the start in this area.

For whatever reason, after later updates (didn't stand to test aerodynamic parameters after each update) the Su-27's wings produce a quite lower lift for a given AoA (lower lift slope) while the F-15 does exactly the opposite.

Now, (a bit absurd one will find it), the F-15 turns better than the Flanker at both low (full aft stick full AB) and high speeds (around the best turn corner). For short, with both planes fueled the same (30% fuel), the F-15 completes the fastest (full aft stick from around corner speed) 360 turn in about 14.4 seconds, while the Flanker in no less than 15.8. How did this happen?

Here is a track and some output data from it:

Su-27 turns badly after latest updates.trk

Click image for larger version

Name:	F-15 lifting performance (turning capabilities).jpg
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Click image for larger version

Name:	Su-27 lifting performance (turning capabilities).jpg
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ID:	178379

And here's a video of the Su-27's proven turning capabilities:
https://youtu.be/6mOAkNC3GSc

Aerodynamic modelers, can you please tell us what's going on?

Kind regards!
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Last edited by Maverick Su-35S; 02-13-2018 at 01:43 AM.
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Old 02-08-2018, 03:32 PM   #2
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Haven't noticed any loss in performance myself except that temperature now has an effect on available thrust at lower altitudes. But this should effect on the F-15 similarly. Then again I also haven't been specifically testing for anything either.
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Old 02-08-2018, 04:17 PM   #3
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Your graph shows quite impressive lift for Su-27.(24deg/s at 550km/h)
Try to use Stick Deflection Limiter Override( Y is default).
Su-27's FLCS only allows very slow onset G so there may be problem.

Last edited by opps; 02-08-2018 at 04:21 PM.
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Old 02-08-2018, 07:02 PM   #4
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Quote:
Originally Posted by opps View Post
Your graph shows quite impressive lift for Su-27.(24deg/s at 550km/h)
Try to use Stick Deflection Limiter Override( Y is default).
Su-27's FLCS only allows very slow onset G so there may be problem.
I know what you are talking about with the G limitation, but this is not the problem. If people still can't see the difference between the initial PFM and the latest updates, I have to detail things a bit more thorough.

24deg/s at 550km/h with 30% fuel is impressive? Then what do you say about the F-15, did you look at it? Sorry, but you prove to not know how these values are in reality.
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Old 02-09-2018, 01:12 AM   #5
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Quote:
Originally Posted by Maverick Su-35S View Post
I know what you are talking about with the G limitation, but this is not the problem. If people still can't see the difference between the initial PFM and the latest updates, I have to detail things a bit more thorough.

24deg/s at 550km/h with 30% fuel is impressive? Then what do you say about the F-15, did you look at it? Sorry, but you prove to not know how these values are in reality.
Sorry completely misunderstood graph.
But Stick Deflection Limiter is key.

Simple math gives that F-15 pulling 10.75G at 750km/h and your track shows around 10.9G. Su-27 doing about 8G due to FLCS limiting G, Not LIFT limitation.
While one aircraft clearly pulling OverG, you bring another FBW controlled aircraft and complain about you cannot pull OverG is not just fair.
I hope you just try Stick Deflection Override and draw graph again. You will see.

Last edited by opps; 02-09-2018 at 05:20 AM.
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Old 02-09-2018, 02:48 PM   #6
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Quote:
Originally Posted by Maverick Su-35S View Post
I know what you are talking about with the G limitation, but this is not the problem...

24deg/s at 550km/h with 30% fuel [for the Su-27] is impressive?...
No, it's not. Had you pulled thru the AoA limiter (modeled as the "Y" key) you would have been in the 30°/sec range just before that.

Speaking of 30°/sec, that video you linked has me puzzled. It seems to suggest that the Flanker in question turned 360° in 12 seconds. If that's actually the case, then it somehow held its max instantaneous turn rate for the entire turn which seems to be a contradiction.
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Old 02-13-2018, 12:53 AM   #7
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Quote:
Originally Posted by Ironhand View Post
No, it's not. Had you pulled thru the AoA limiter (modeled as the "Y" key) you would have been in the 30°/sec range just before that.

Speaking of 30°/sec, that video you linked has me puzzled. It seems to suggest that the Flanker in question turned 360° in 12 seconds. If that's actually the case, then it somehow held its max instantaneous turn rate for the entire turn which seems to be a contradiction.
Correct. It seems to be in contradiction to DCS, in which you said you were just able to achieve 30 deg/s as ITR (that is maximum capable for a split of a second at very low fuel, no loadout and rapid AoA onset), which in reality is the average turn rate, below the highest ITR (at corner speed where it started turning) and above the lowest ITR (where the turn ends).

Guess for yourself which is wrong, reality or...? The video is untouched in terms of frames/second or timing and it's not the only video proving the same qualities of the Flanker's turning performance.

Regards.
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Old 02-08-2018, 04:45 PM   #8
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opps I bet you're right.
But personnaly I won't use the override, because since last update from 02-06-2018, I can break my Su-27 wings in a hard turn without it ^^
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Old 02-08-2018, 06:44 PM   #9
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only red air that ever worked well for me was mig29.

su family all flamed out with nose down attitude, very nose heavy aircraft, into inverted flat spin death. also had problems with wings ripping off and rear stabs dying when a little rudder applied.

Shes made of glass, or I need more practice, maybe a bit of both. its interesting to see your graphs. the flanker should crank the eagle in comparison, but I can't say if its slow or fast contrasting IRL.
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Old 02-08-2018, 06:53 PM   #10
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Quote:
Originally Posted by proletariat23 View Post
only red air that ever worked well for me was mig29.

su family all flamed out with nose down attitude, very nose heavy aircraft, into inverted flat spin death. also had problems with wings ripping off and rear stabs dying when a little rudder applied.

Shes made of glass, or I need more practice, maybe a bit of both. its interesting to see your graphs. the flanker should crank the eagle in comparison, but I can't say if its slow or fast contrasting IRL.
Right control + enter and a lot of trim change in pitch/AOA changes.

As for cranking Eagles...Think combat configurations.
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