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Fox One

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@Alfa Exactly strong stuff there :)

When I translated the russian DCS forum (topic Su-27) with google translate, I found out that Yo-Yo said, he hasn't got a sausage and his samurai skills are to blame hahahhaha. I'm sure google mixed up, with or without advertising!!

But who can be sure about that??? :P

 

Please do not smoke this hahahha substance too much! :)

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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^^^ Where from can I get such telemetry?

+1

Tacview?

 

Just lines of script.

 

Export data with export.lua, pretty easy way for precise in-game data.

No eyeball-metering:)

 

1.

Backup your C:\Users\[YOUR NAME]\Saved Games\DCS\Scripts\export.lua

Put files in Scripts.zip to dir C:\Users\[YOUR NAME]\Saved Games\DCS\Scripts

 

Then you can start mission and do the flight test.

Test mission: Su27_TurnTest.miz

 

When you exit the mission, flight data will be logged in file: C:\Users\[YOUR NAME]\Saved Games\DCS\Logs\FlightData-YYYYMMDD-HHMMSS.log

 

2.

Extract graphic_Flighdata.zip

Open the top .html (with MS.IE please) in the dir

Click 'CHOOSE LOG FILE', choose your flight data log file

Click 'draw me' button

 

Now there it is.


Edited by L0op8ack
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Just lines of script.

 

Export data with export.lua, pretty easy way for precise in-game data.

No eyeball-metering:)

 

1.

Backup your C:\Users\[YOUR NAME]\Saved Games\DCS\Scripts\export.lua

Put files in [ATTACH]107597[/ATTACH] to dir C:\Users\[YOUR NAME]\Saved Games\DCS\Scripts

 

Then you can start mission and do the flight test.

Test mission: [ATTACH]107600[/ATTACH]

 

When you exit the mission, flight data will be logged in file: C:\Users\[YOUR NAME]\Saved Games\DCS\Logs\FlightData-YYYYMMDD-HHMMSS.log

 

2.

Extract graphic_Flighdata.zip

Open the top .html (with MS.IE please) in the [ATTACH]107598[/ATTACH]

Click 'CHOOSE LOG FILE', choose your flight data log file

Click 'draw me' button

 

Now there it is.

Thanks!

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  • 2 weeks later...

I am sorry to bring this topic again, but it still seems very strange to me, so I would like to confirm that the behaviour is realistic.

 

The thrust with open nozzles is apparently immensely less than with nozzles open, and it doesn't seem to really increase with RPMs (which is to say, 70% or 78% doesn't seem to make any difference in thrust).

 

I did a little acceleration testing (in flight, so nothing about wheels friction here) to illustrate what I mean, using an export script. I maintained 7 000 m during the whole maneuver. What I did was start idle, and advance the throttle slowly (by increments), until 85%, then retard the throttle slowly back to 70%, all the while recording the time, IAS (in m/s) and RPM (left engine). Here are the results:

 

RPM%201.png

 

As you can see:

- the aircraft (nozzles open) starts at 70% and decelerating.

- as the throttle advances from 70% to 79% it keeps decelerating at a steady pace, as if RPM didn't matter.

- when when reaching about 80%, nozzles close* and thrust kicks in, instantly resulting in a significant acceleration.

- as the throttles is advanced to 85, the aicraft accelerates faster and faster

- with the RPM going back, acceleration decreases slowly until speed as approximately constant at about 75% RPM

- when RPM goes under 74%, nozzles open* and the aircraft immediately starts decelerating at a great pace

- once again, as the throttle is retarded from 4% to 70%, no change in the pace of deceleration is noticed.

 

* I suppose

 

What I would gather from that is that it would seem as if thrust was kept constant at idle thrust in the whole region where nozzles are open.

 

I may be interpreting this wrong, of course, and maybe the engine model is absolutely allright, but I wanted to share this tests with you so that a confirmation could be made that this is realistic for the Su-27.

 

Note: I did not made this tests in the new Open Beta, so if things have changed, I will redo them later with the new version.

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I don't know if the two things are connected in some way with state of the PFM ground handling, but at times the Eagle will actually continue to accelerate on the ground at idle power.

 

That would be in extreme cold temperatures i think.

[sIGPIC][/sIGPIC]

Win10 64, Asus Maximus VIII Formula, i5 6600K, Geforce 980 GTX Ti, 32 GB Ram, Samsung EVO SSD.

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Ok, so.

 

After a couple more flight tests, I have come to the conclusion that the (current) engine always produce the same thrust when the nozzles are open, ie. having your RPM at 70% or 78% produces exactly the same thrust if the nozzles are open. See attached charts with a comparison of speed* and acceleration** against time (also, for reference, altitude* and left engine RPM*).

 

* extracted by export script

** computed by derivation of the velocity

 

For all the parameters (except obviously RPM), both curves are pretty much exactly superimposed, indicating that the 8.5% difference in RPM does not change anything. I might try plotting the same for 80% and 88%, for comparison purposes, although I strongly expect it would show a much better acceleration for 88% than for 80%.

 

Note that I have tested on a light aircraft in order to have a better sensivity to thrust.

 

I know I may seem obsessed about the matter, but I'm simply intrigued by the current behaviour (also, I like to do flight tests and charts). Also, note that I am not at all trying to belittle the huge work that was done on the Su-27 flight model, which is very impressive.

1827111947_Flighttest.thumb.png.d1d3f323031b2ab741a26b1fdf7654de.png

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From the DCS SU-27 manual: "When the landing gear is extended, the nozzles partially closed in order to preserve the power margin and to avoid nozzle contact with the runway during the touchdown. Due to this, the thrust is increased when on the glide path. In order to decelerate, the speedbrake should be used."

 

Has anyone observed this behavior in DCS?

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Yes, it's there.

 

Could someone help me to explain the taxiing technique with the new PFM? When the nozzles close (going above 78%), the thrust increase seems to be very significant (which I think is not entirely correct), but the thrust doesn't decrease when you throttle down, until the nozzles open again. I have noticed on some videos that Flanker pilots sometimes taxi by using just one engine, but if anybody among testers or developers could shed some light into this, I'd be extremely grateful.

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  • 3 months later...

I am happy to report that the issue has been fixed in the latest update (1.2.16.38741), as you can see by comparing the quick test I just did with the earlier ones (like post #32):

 

RPM_1.2.16.38741.png

 

Now you can see that before, when the nozzles were open, the velocity decreased in a straight line, no matter the RPM, indicating no change in thrust. But now, the acceleration can clearly be seen to depend upon the RPM.

 

Thank you for fixing the issue. By the way, this has also fixed the taxiing problem (where the aircraft would suddenly jump forward at 80% RPM), so now taxi will be a lot easier.

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  • 4 months later...

Hi, it was interesting to watch you to solve the problem of idle thrust. In fact the accuracy of idle thrust doesn't bother me at all. What I suppose not to be accurate is the idle thrust at low temperatures. Try to simulate siberia conditions with temp around -20°C. The idle thrust is so high, that the aircraft accelerates on idle.

What i would like to be solved is high fuel consumption of Su-27. According to engine charts and aircraft datas it seemed to be approx. 20% higher in the whole envelope. Does someone know, how to fixed it?

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Hi, it was interesting to watch you to solve the problem of idle thrust. In fact the accuracy of idle thrust doesn't bother me at all. What I suppose not to be accurate is the idle thrust at low temperatures. Try to simulate siberia conditions with temp around -20°C. The idle thrust is so high, that the aircraft accelerates on idle.

What i would like to be solved is high fuel consumption of Su-27. According to engine charts and aircraft datas it seemed to be approx. 20% higher in the whole envelope. Does someone know, how to fixed it?

 

 

It's alright. It is realistic. The higher the temperature difference upstream of the engine and the output power increases.


Edited by UVP/Mechan
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