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-   -   Degraded Su-27 aerodynamic lift (https://forums.eagle.ru/showthread.php?t=202030)

Maverick Su-35S 02-08-2018 03:58 PM

Degraded Su-27 aerodynamic lift
 
3 Attachment(s)
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:

Attachment 178377

Attachment 178378

Attachment 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!

Ironhand 02-08-2018 04:32 PM

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.

opps 02-08-2018 05:17 PM

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.

toutenglisse 02-08-2018 05:45 PM

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 ^^

proletariat23 02-08-2018 07:44 PM

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.

Sweep 02-08-2018 07:53 PM

Quote:

Originally Posted by proletariat23 (Post 3388404)
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. :smilewink:

Maverick Su-35S 02-08-2018 08:02 PM

Quote:

Originally Posted by opps (Post 3388225)
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.

Sweep 02-08-2018 08:09 PM

Why 30%?

Is that what the real charts are for (obviously, the ones available!)? Haven't looked at the Flanker charts in a while...

Maverick Su-35S 02-08-2018 08:16 PM

Quote:

Originally Posted by proletariat23 (Post 3388404)
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.

Su-27/33s don't flame out cause of attitude angles, if this is what by mistake you refer to, but below a given G-load, no matter the plane's orientation from the Earth. Nose heavy? Just the opposite. If it would be nose heavy then it couldn't reach high angles of attack, maybe not even reach the critical AoA (less to say the supercritical). Sorry, don't look bad at me, but you have to learn / understand a bit of flight dynamics. The plane's CG (center of gravity) seems realistic where it is, the only problem that comes on when you push the stick until reaching an AoA below -20 is that the elevators become shadowed (turbulent and inefficient airflow) by the wing due to the relative position between the wing and elevators in the plane's vertical plane. The way to get out of the negative deep stall is quite simple, but you need a bit of altitude (at least 2000 meters). Set the controls to direct pitch (needed for high alpha or cobra), fully pull the stick and wait until the AoA goes as much negative as it can get, then release it to neutral once the AoA wants to reduce. If the AoA managed to get below -20, pull the stick and get out of this unstable region. If not, repeat the process..., full stick pull until the AoA reaches a maximum negative value, then release until it drops to below -20.

On the other hand, yes, the Flanker won against the Eagle in real tests and beat it in turns. The Eagle had an impossible chance to stay or get behind the Flanker. Now (after latest updates) in DCS we see the opposite, so we need a fix.

Maverick Su-35S 02-08-2018 08:17 PM

Quote:

Originally Posted by Sweep (Post 3388413)
Right control + enter and a lot of trim change in pitch/AOA changes.

As for cranking Eagles...Think combat configurations. :smilewink:

Very good pointing! Yes, think combat configuration..., it still beats the Eagle in turns if both have dogfight missiles left (usually those are the missiles they remain with).


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