Su-27 FM inconsistency in acceleration & turn performance?

[TaxDollarsAtWork]

The FM seems to be very off

Like in regards to trans sonic acceleration compared to IRL

This video puts a Su-27 in similar conditions to the video of that ill fated Su-30MK2 test run video and its severely off
More info in the original post here
 

How about when the Su-27 is unable to match the G figures above 600kmh in the manual?
Or even Chinese test data as pointed out by a deka dev
 

Can ED give us a straight answer.

it does seem ED has over done things regarding transonic acceleration or wave drag I am not sure.

The forum has quite good info Im not sure why they've ignored it

[BIGNEWY]

please add a track replay and your unclassified evidence

[Cmptohocah]

11 minutes ago, BIGNEWY said:

please add a track replay and your unclassified evidence

Does that RL video qualify as "unclassified evidence"?
You can find it here

 

[okopanja]

Hi @BIGNEWY,

I just skimmed through the references forum topics from last year between end users and developers. It seems that both tracks files and flight charts were supplied but still dismissed, despite even flight recordings being available.

As a side note: I always get shocked at the exchanges occurring on Russian part of the forum ( ) . Although I use google translate, I can not avoid to notice lack of respect on both side and rather direct confrontations. As a user by reading this topic I frequently witness the information being exposed on internal functioning of ED that no company would like to see public. It would be cool if this topic would stay civil and professional so the discrepancies observed between Su-27_documented/Su-27_IRL/Su-27ED can be properly addressed.

I am well aware that there limitations on modern RED aircraft, as well that likely there is a company level decision on keep FC3 in frozen state, but in the absence of better (more modern FF), the existing should be better maintained. Blue on blue situations we are facing on modern servers its kind of boring and I would say unsustainable. Recent polls on the desired aircrafts show certainly the tendency toward blue in ratio of 2:1, but I would say that 1/3 of DCS population is still very much interested in RED airplanes topic. You would off course be in a better to judge what level of income would such effort generate, but perhaps alternatives can be found in following directions:

- possible externalization of the effort (e.g. bounties, 3rd party, reuse/integration of certain mods like FC3 clickable cockpits project etc)

- providing alternative financing. E.g. paid (mini)-upgrades,, crowdfunding, etc.

Surely there has to be a way to keep these birds (FC3) flying and still make sure ED does not loose money on it.

 

Edited July 13, 2022 by okopanja

[BIGNEWY]

1 hour ago, Cmptohocah said:

Does that RL video qualify as "unclassified evidence"?
You can find it here

 

Video unfortunately does not always help, you have no idea what suite it is using, or its weight for example 

57 minutes ago, okopanja said:

Hi @BIGNEWY,

I just skimmed through the references forum topics from last year between end users and developers. It seems that both tracks files and flight charts were supplied but still dismissed, despite even flight recordings being available.

As a side note: I always get shocked at the exchanges occurring on Russian part of the forum ( ) . Although I use google translate, I can not avoid to notice lack of respect on both side and rather direct confrontations. As a user by reading this topic I frequently witness the information being exposed on internal functioning of ED that no company would like to see public. It would be cool if this topic would stay civil and professional so the discrepancies observed between Su-27_documented/Su-27_IRL/Su-27ED can be properly addressed.

I am well aware that there limitations on modern RED aircraft, as well that likely there is a company level decision on keep FC3 in frozen state, but in the absence of better (more modern FF), the existing should be better maintained. Blue on blue situations we are facing on modern servers its kind of boring and I would say unsustainable. Recent polls on the desired aircrafts show certainly the tendency toward blue in ratio of 2:1, but I would say that 1/3 of DCS population is still very much interested in RED airplanes topic. You would off course be in a better to judge what level of income would such effort generate, but perhaps alternatives can be found in following directions:

- possible externalization of the effort (e.g. bounties, 3rd party, reuse/integration of certain mods like FC3 clickable cockpits project etc)

- providing alternative financing. E.g. paid (mini)-upgrades,, crowdfunding, etc.

Surely there has to be a way to keep these birds (FC3) flying and still make sure ED does not loose money on it.

 

 

Bugs can be looked at but we have no plans for upgrading FC3. 
If you want me to investigate I need evidence, if I go to the team with feelings and opinion It wont go anywhere. 

[BIGNEWY]

thanks, I believe the team have already seen this document. 

[Cmptohocah]

7 hours ago, BIGNEWY said:

Video unfortunately does not always help, you have no idea what suite it is using, or its weight for example 

Bugs can be looked at but we have no plans for upgrading FC3. 
If you want me to investigate I need evidence, if I go to the team with feelings and opinion It wont go anywhere. 

I completely agree about the video, however the main point of it is to show that Su-30MK2, that uses the same engines and is known to have higher drag than the Flanker, has better performance in RL than or Su-27 does in DCS.
So even if adjustments are made to match the Su-30, this will still not be 100% accurate, but it will be better than what we have now.

Thanks again for your answers.

[TaxDollarsAtWork]

 

Possibly this chart could be of some help?
I don't think any of my information is classified.

[strelok2014]

4 часа назад, Бойовий Сокіл сказал:

https://dcs.silver.ru/Diagram/Su27

The charts are in the F15/Su27 comparison document and 27SK doc.

The fact is that the ED considers the diagrams in the Su-27SK documents to be incorrect, so they did it their own way.

[TaxDollarsAtWork]

How about asking Deka for more thorough test data like this?

 

[okopanja]

Since trk file is what is needed, can you please upload it?

[Ironhand]

4 hours ago, okopanja said:

Since trk file is what is needed, can you please upload it?

Here's the track but it matches the RL video time pretty closely. Video 500-1300 km/hr in 46 sec. TRK 500-1300 km/hr 44 sec.

Su-27 Trans-sonic.trk

Edited July 14, 2022 by Ironhand

[okopanja]

9 hours ago, Ironhand said:

Here's the track but it matches the RL video time pretty closely. Video 500-1300 km/hr in 46 sec. TRK 500-1300 km/hr 44 sec.

Hi, I took a look at your reply and noticed the following:

1. aircraft is unarmed, it appears the referenced document contains partially armed aircraft with 5000kg of fuel
2. you start with 3500 kg of fuel
3. you climb slightly higher and are actually loosing the altitude, where the other guy was probably more precisely following slightly climbing pattern

 

 

Edited July 14, 2022 by okopanja

[Ironhand]

46 minutes ago, okopanja said:

Hi, I took a look at your reply and noticed the following:

1. aircraft is unarmed, it appears the referenced document contains partially armed aircraft with 5000kg of fuel
2. you start with 3500 kg of fuel
3. you climb slightly higher and are actually loosing the altitude, where the other guy was probably more precisely following slightly climbing pattern

 

 

 

Not flying the reference material. I am flying the Su-30 crash video that keeps being posted to prove that the DCS Su-27 transonic flight profile is wrong. How many missiles does that Su-30 have? How may kg fuel onboard? And how many seconds difference do you think the slight difference in flight profile add or subtract?

BTW, I’m not saying that our Su-27 is correct. I don’t know if it is or isn’t. I do know that ED claims the charts are missing the transonic drop.

Edited July 14, 2022 by Ironhand

[okopanja]

1 hour ago, Ironhand said:

Not flying the reference material. I am flying the Su-30 crash video that keeps being posted to prove that the DCS Su-27 transonic flight profile is wrong. How many missiles does that Su-30 have? How may kg fuel onboard? And how many seconds difference do you think the slight difference in flight profile add or subtract?

BTW, I’m not saying that our Su-27 is correct. I don’t know if it is or isn’t. I do know that ED claims the charts are missing the transonic drop.

I am not claiming anything but let's try to establish healthy baseline, before trying to replicate, possibly by more than one person, and with some variants.

There are actually 2 issues reported here in a single topic.

Issue 1: acceleration of Su-27ED (to designate what we have in game) vs Su-30 crash video at ~ 3100m with level flight with slight drops and climbs

Unknown:

- the exact fuel state of SU-30

- precise temperature

Known facts:

- season

- altitude

- IAS matches the real aircraft roughly until 02:19 into overlayed recording (from first post), when the downward trend changes into climb, and IRL aircraft starts to rapidly accelerate, where SU-27ED lags behind

- from following we would expect Su-27ED to be faster: yet it appears to be slower

  - same engines, and almost the same thrust (found something online, but would appreciate more solid input)

  - Su-30 is heavier (someone have the exact numbers?)

- we have @Ironhand's reproduction with 3500 kg fuel which starts from slightly higher altitude with downward trend, but we would need to overlay these speeds to be certain.

Issue 2: Ny graph different between chart and Su-27ED

Unknown:

- standard temperature conditions (maybe I am missing here something?)

Known facts:

- loadout of missiles

- fuel capacity

In addition we have several diagrams I am not clear to which case they apply, and what do they exactly represent.

So, guys anything else to contribute/comment on this?

( I will edit the comment or perhaps @TaxDollarsAtWork can do that in initial post?)

 

[Ironhand]

1 hour ago, okopanja said:

Issue 1: acceleration of Su-27ED (to designate what we have in game) vs Su-30 crash video at ~ 3100m with level flight with slight drops and climbs

Unknown:

- the exact fuel state of SU-30

- precise temperature

Known facts:

- season

- altitude

That video's acceleration starts at 3390 m and he drops from there. If I'm at a significantly higher altitude, my IAS would be less, not more, than his all things being equal.

As for known facts, what season is it? I'm assuming winter given the look of the sky. That may or may not be snow on the ground.

1 hour ago, okopanja said:

Issue 2: Ny graph different between chart and Su-27ED

Our Su-27 does not match the charts. ED's response is that the charts are wrong. They have different information.

I can overlay the two flights in a video but I probably won't have an opportunity until sometime next week. You really don't need that, though, other than for a visual comparison. Just pick any speed range you want in the video and the TRK and compare the times.

Edited July 14, 2022 by Ironhand

[okopanja]

41 minutes ago, Ironhand said:

Our Su-27 does not match the charts. ED's response is that the charts are wrong. They have different information.

I can overlay the two flights in a video but I probably won't have an opportunity until sometime next week. You really don't need that, though, other than for a visual comparison. Just pick any speed range you want in the video and the TRK and compare the times.

Issue 1:

I will try to sample images from video every second when I get home. From there I will extract the IAS and altitude for both Su-30, and Su-27ED. From there I will plot both data series for each aircraft on a single time line. I hope 1 second range is enough to prove or disprove the case. Acceleration can be generated from this point.

However I think we should also generate one fateful trk file, since this is what ED asks for.

From video it looks like Su30 starts to depart the EDs model at 02:19. Since it is heavier but has same engines with same thrust, the only logical conclusion is that model is wrong.

[TaxDollarsAtWork]

26 minutes ago, okopanja said:

Issue 1:

I will try to sample images from video every second when I get home. From there I will extract the IAS and altitude for both Su-30, and Su-27ED. From there I will plot both data series for each aircraft on a single time line. I hope 1 second range is enough to prove or disprove the case. Acceleration can be generated from this point.

However I think we should also generate one fateful trk file, since this is what ED asks for.

From video it looks like Su30 starts to depart the EDs model at 02:19. Since it is heavier but has same engines with same thrust, the only logical conclusion is that model is wrong.

There are acceleration figures given in Su-27 Birth of a legend with more exact parameters such as weight and armament

 

Here is a video comparing the acceleration to these figures

 

[okopanja]

Here is the first iteration of charts based on first overlayed video. It took me nearly 2 hours to extract data.

Major difficulty was that the Su-30 recording has altitude saturated, and it took me a combination of gimp processing and multiple passes frame by frame to figure out the numbers.

Most notable is that at some point there is a significant dent in the altitude, which I can not explain. It as if the display of Su-30 glitched!

Whoever flew for reproduction video, deserves the credit, he almost nailed exact altitude profile.

First chart is altitude, second is IAS.

Edited July 14, 2022 by okopanja

[okopanja]

Added the spreadsheet with numbers...

If you modify to add more data, and/or calculate derived parameters, please bump the file version

IAS_Altituded_datapoints_v1.ods

[okopanja]

15 hours ago, Ironhand said:

I can overlay the two flights in a video but I probably won't have an opportunity until sometime next week. You really don't need that, though, other than for a visual comparison. Just pick any speed range you want in the video and the TRK and compare the times.

I think overlaying is unneeded effort you can simply extract the numbers for altitude and IAS from your flight with 1 second frequency. Most likely the simplest way to do it is to capture the video and then split it with FFMPEG.

E.g.

ffmpeg -i source.mp4 -vf fps=1 images2\frame_%03d.jpg

 

[Spurts]

17 hours ago, okopanja said:

 

Most notable is that at some point there is a significant dent in the altitude, which I can not explain. It as if the display of Su-30 glitched!

 

 

 

Compressibility going through the Mach.  Totally normal and aircraft with higher level systems modeling in DCS show the same thing.

[Ironhand]

On 7/14/2022 at 1:13 PM, TaxDollarsAtWork said:

There are acceleration figures given in Su-27 Birth of a legend with more exact parameters such as weight and armament

 

 

Anyone know which instrument/system or whatever ТТТ and СГИ refer to? I’m not familiar with either one and the numbers are different depending on the column you’re in. Also I don’t see the weight, armament etc listed in the image.

Also, are the airspeeds IAS or TAS?

[draconus]

1 hour ago, Ironhand said:

Anyone know which instrument/system or whatever ТТТ and СГИ refer to?

тактико-технические требования (ТТТ) - it's a tactical-technical requirement - a plan of parameters to achieve for a new fighter. This site helped me:

http://www.airwar.ru/enc/fighter/su27.html

[Ironhand]

1 hour ago, draconus said:

тактико-технические требования (ТТТ) - it's a tactical-technical requirement - a plan of parameters to achieve for a new fighter. This site helped me:

http://www.airwar.ru/enc/fighter/su27.html

Thank you.