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Su-27 Flight Model Discussion


DarkFire

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All this talk about the Su-27's flightmodel in DCS -- which I, as a layman, think is phenomenal -- got me thinking if there are any real Su-27 drivers out there on the Russian-speaking side of the ED forums that ever gave any feedback on it? I am super curious about what they have to say. :)

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I really don't get the constant need for heavy trimming, seems unlikely that the real aircraft suffers so badly from this. I mean the thing has got a FBW stability system.

 

Never heard a Russian pilot say he constantly needs to trim the aircraft.

 

As SiThSpAwN and GGTharos have confirmed trimming is essential, here's another huge evidence :smilewink:

 

s9dmKCH.jpg

 

The trim command sits right as one of the most used button on the stick. Let's say its use is more intensive than its modern counterparts ;)

 

(it has the same function on my stick and it's what I use to land smoothly when it's possible)

 

Learning to pilot the Su-27 is now much more interesting with the PFM and explains an important part of the HOTAS commands logic.

 

It would be immensely valuable to have access to a Su-27 flight manual with detailed piloting techniques.

 

(online-su27-flying-lessons.com ?) :pilotfly:


Edited by Bourrinopathe

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How does the DCS Su27 trim effect the DCS Su27 stick position in context with our real Stick?

Something interesting happened for me!

I train the real Su27UB "random display" but with 60% fuel and a full load of weapons.

Ok, with a full load of weapons the Su27 is a bitch, but you will never fight with no weapons, so I train all this maneuvers with weapons.

With a well trimmed plane, the DCS Su27 is very hard to fly in turns (how to trim the Su27 in and for turns?). Her butt wants to come around all of the time (show me your ass bitch ;)).

If I trim the DCS Su27 a way more nose heavy, so I must hold the DCS Su27 till 600 kph+ (average speed over the whole flight could be 450 kph) by myself, with pulling the Stick, at level, I can easy fly the display without any strange stall effects and the butt of the DCS Su27 don't want come around. And I can turn much faster with less energie lost.... surprise! huh.gif

 

I have the feeling, that trim effects the sensitivity of our real stick inputs. The same Stick way gives me different sensetives in addiction of the current trim. So if I trim the DCS Su27 well, my stick inputs are much more direct and I always oversteer in turns with nearly no warning (Corba behavior). If I trim the plane a way more negativ, so I must hold the stick back to fly level, I have much more fine control in turns and can "feel" a hughe way more and much better the limits of the plane. Extrem more fine control! The DCS Su27 feels now a way more like the real plane. With a real "good" negativ trim, the DCS Su27 flys like a dream in turns. Two completely different planes because of this negativ trim. You must only trim her nose "very" heavy and she becomes a "turn bitch". What a fun to fly this plane.

OK, with this negativ trim the level flight is a real mess, but the dogfighting is so much better, I wouldn't believe it by myself If I had not tried it.

Now I can fly the real SU27UB displays with "ease" (but have to fine tune it), but only If I trim the Su27 a way more nose heavy.

The question I ask myself is, why? Or better why must I trim the DCS Su27 so nose heavy to take this "easy butt turn around mode" off?

 

Ok, now I can fly this beauty a WAY better as before, but it would be nice if I could do it with a well trimmed plane too!

Any suggestions?

 

 

HOTAS = Warthog

Stick curve for nick = 33 for Roll 38


Edited by Nedum

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2. I'm suspicious of the accuracy of the aerodynamic and kinematic modelling of missiles. Yes, that is a very different discussion but I do suspect that weapons loaded on the Su-27 are causing an exaggerated amount of parasitic drag. At present the change in the way the aircraft handles between an empty condition and even having say 4 x AA missiles is astounding. I think this could benefit from further review by the dev team.

After flying the A-50 escort mission in the Ultimate Argument campaign where I had to escort an A-50 to 9000m altitude, I had to go into afterburner to keep up with the A-50 in the climb once above 7000m.

 

I haven't tried this scenario with an empty jet but this doesn't seem right with a loaded one.

 

Edit... just tried at test at 9000m after climbing from take-off with full fuel. Got to altitude and needed to maintain afterburner to hold cruise at .80Mach IAS. I dumped all the missiles and still needed afterburner, although the EGT was a little less in order to maintain .80Mach. Funny thing is when I went to an external fly-by the jet was supersonic. Why would it be supersonic at .80Mach IAS?

Screen_150130_030340.thumb.jpg.cf1a38d40ff5aa69cf26aecb01b4de22.jpg

Screen_150130_030528.thumb.jpg.e0fc1540d0ec9b2391e992c695306024.jpg


Edited by Shepski
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...

If I trim the DCS Su27 a way more nose heavy, so I must hold the DCS Su27 till 600 kph+ (average speed over the whole flight could be 450 kph) by myself, with pulling the Stick, at level, I can easy fly the display without any strange stall effects and the butt of the DCS Su27 don't want come around. And I can turn much faster with less energie lost...

 

Any suggestions?

 

 

HOTAS = Warthog

Stick curve for nick = 33 for Roll 38

Almost sounds like the in-game equivalent of increasing the curvature for your stick under the Axis settings, doesn't it?

 

... Why would it be supersonic at .80Mach IAS?

Good question.

 

 

Rich

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The correct answer is..because it's still beta.. :)

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I don't think so.

 

The correct answer looks more like: "because you use a modded (english) cockpit, and it appears the machmeter in that cockpit is wrong".

 

With the default (russian) cockpit, standard day at 9000m and 700-720 KIAS, you're at M1.06 ;)

Screen_150131_112805.thumb.jpg.f2c6479873b24b11f5fdecc4d3d915f7.jpg

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I don't think so.

 

The correct answer looks more like: "because you use a modded (english) cockpit, and it appears the machmeter in that cockpit is wrong".

 

With the default (russian) cockpit, standard day at 9000m and 700-720 KIAS, you're at M1.06 ;)

Even better answer. :)

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ill be annoying and bumb my question, since it really interests me

 

http://forums.eagle.ru/showpost.php?p=2304886&postcount=171

Is this the one in which you were continuously cycling the FBW system on and off with the "S" key? If so, then the answer is "yes".

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Strange roll behaviour.

 

Something that I've noticed since the last patch is that below 900 kmh IAS applying bank and returning the control column to neutral results in the aircraft returning to level flight, i.e. the bank angle gradually reduces back to zero, however above 900 kmh IAS this behaviour is not exhibited.

 

I mention IAS specifically as it does not appear to be dependant on TAS or SOG, only on the indicated airspeed.

 

It feels as though if the pilot applies bank the FCS applies an opposite control input, requiring the pilot to maintain a steady stick input for a given bank angle. Is this correct behaviour or an artefact? I feel that this increases my pilot workload at the worst possible times, i.e. low speed close combat, flying accurate landing patterns etc.

 

Attached is an illustrative track.

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Is this the one in which you were continuously cycling the FBW system on and off with the "S" key? If so, then the answer is "yes".

 

no its the one where you pull high g and have the stick all the way back, then in the plane the stick starts jumping back and forth, as if the FBW system is letting go and grabbing the stick.


Edited by karambiatos
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I don't think so.

 

The correct answer looks more like: "because you use a modded (english) cockpit, and it appears the machmeter in that cockpit is wrong".

 

With the default (russian) cockpit, standard day at 9000m and 700-720 KIAS, you're at M1.06 ;)

 

Thank you!

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@ Shepski: You're welcome :)

I guess the bright side is you don't need A/B to sustain M0.8 "anymore". I can't tell about escorting the A-50 as you described earlier.

 

@ Yo-Yo:

Guys, what is the point to discuss the matter that obviously is not completed? I mean this 55g, 155g, etc...

Can you confirm that negative g behaviour is also "not completed"/WIP, is that correct?

 

We got lots of trouble with the negative g tricky behavior when the aircraft is heavily loaded. More than once, experimented pilots (including me) "dumbly" lost our aircraft because we weren't able to recover from our initial "tiny" mistake.

Problem & track posed here by bolek, acknowledged/better described by Ironhand (who flies far better than me) there.

 

Thx,

Az'


Edited by Azrayen

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no its the one where you pull high g and have the stick all the way back, then in the plane the stick starts jumping back and forth, as if the FBW system is letting go and grabbing the stick.

 

It's AFAIK the FCS trying to prevent you from over G'ing.

I think it's called a stick pusher or something like that.

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I'd like to ask when you are pulling high G, the stick starts jumping back and forth, as if the FBW is grabbing and then letting go of the joystick, is this normal behavior for the su-27?.

 

 

track in 1.2.14.36041

Just reviewed the track. The behavior doesn't start until you over-G the aircraft. And it's definitely tied to the G-channel of the FBW. If you lower your landing gear (which turns off the G-channel), the behavior disappears when you over-G. I'm guessing that it's there to tell you to stop doing what you're doing before you break something important. :)

 

EDIT: Svend beat me to it. Guess I should have checked first. Go figure. First you get no response to your Q and now you've got two in rapid succession. :)


Edited by Ironhand

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What luck i have :)

 

yeah, i was more asking about the way it bounces the stick, more than there actually being a system that stops the aircraft from doing it.

 

but Svend answered it, so thanks to the both of you.

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s9dmKCH.jpg

 

 

Regarding the Su-27 Flightstick -- what close air combat mode is enabled when switching to it?

 

- Close Air Combat Vertical Scan Mode?

- Close Air Combat Bore Mode?

- Close Air Combat HMD Helmet Mode?

 

Thanks.

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Afaik, that slide switch on the stick is not used to select the different modes.

It's a weapon type selection based on the range:

 

Д. БОЙ --> ДРБ дальний ракетный бой

(long-range missile combat)

 

Б. БОЙ --> БМБ ближний маневренный бой

(close-range maneuver combat)

 

The actual mode selector is on the left console, below the clock:

 

ecP3pXb.jpg

 

My only source is the Su-27SK flight manual:

На ручке управления самолетом (РУС) установлены:

− переключатель Б.БОЙ-Д.БОЙ, для выбора вида ракет ближнего боя, при наличии вместе с ними другого оружия;

 

So, I may be wrong about the general slide switch function. I have no idea if it changes anything other than the weapons (general/group) selection. (there is a specific weapon selection button on the Su-27's throttle)

(I use the 3-position slide switch on my Black Mamba for the BVR / Navigation / Vertical Scan Mode - and the other modes are on a hat on the throttle)

 

If anyone has more details, feel free to share (in a relevant thread) :thumbup:


Edited by Bourrinopathe

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(I use the 3-position slide switch on my Black Mamba for the BVR / Navigation / Vertical Scan Mode - and the other modes are on a hat on the throttle)

 

Really would dig that Black Mamba stick! I envy you ;)

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Regarding the Su-27 Flightstick -- what close air combat mode is enabled when switching to it?

 

- Close Air Combat Vertical Scan Mode?

- Close Air Combat Bore Mode?

- Close Air Combat HMD Helmet Mode?

 

Thanks.

I believe it is whatever mode is selected on the dial on the forward left side console.

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Trim

 

Take a look at this video from the Su27 owned by Pride Aircraft.

 

Notice that the pilot never used the trim button!

 

 

 

 

iHsoo9B029o


Edited by wasserfall

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Hardly conclusive proof. Look at his stick action. He makes literally hundreds of little corrections per minute!

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