Su-27 Flight Model Discussion

[wasserfall]

Yesterday a flew the whole evening on the Virtual Aerobatic server in the Su27.

And yes you have to trim at any speed change, but i love the slow flying characteristic

Even did some touch an go's on the Kuz, a bit bumpy and my right main gear would't retract anymore

But landed safely at Gudauta, did some repairs and took off again did some aerobatics and returned her safely to Sochi.

I really enjoyed it!

 

Just my thoughts

Edited April 3, 2015 by wasserfall

[Nedum]

Yes it is. You ran out of airspeed and spun the aircraft. What you want to do in simple terms is cut power to idle (power-on exacerbates and extends the stall/spin - this is why the nose pitched up again and the spin continued), let the nose down (as far as it wants and let airspeed build. Rudder opposite the spin, and NO aileron or elevator inputs. These will again propagate the spin.

Once the aircraft is stabilized, gently pull the nose to the horizon, regain straight and level flight and then add power.

 

Edit: leave the ACS on but again get out of the power. The ACS is a good thing.

 

 

The problem is, the nose pitch up behavior at any speed.

I have tracks with blow outs only climb into the sky (no negativ g's).

Nose ups at landig because the landig speed was so slow I was stalling 1 meter above the ground.

The explanation why the nose is always lifting up during a stall I wisch to hear!?

He said "the nose of the Su27 pulled up suddenly" for me that is the problem for the whole FM of the DCS Su27.

Why the heck is the nose most of pulling up?

Landing with 240 kph, get in a stall and the nose pitches up without any reaction on the elevator.... ? :music_whistling:

Which strange forces doing that strange things?

The Su27 has really big wings closer to the back, but a small aerodynamically nose flips the whole 20 tons plane around and during the nose gives more lift as the elevators, the extrem large elevators giving non reaction even the plane is still getting hight at full AB?

Or why is it, with the DCS Su27 and with full AB, not possible to raise the speed if she is already stalled inverted with the nose pitching slightly to the ground. Which strange forces hinders the DCS Su27 to speed up for minutes?

Full AB on and NO single reaction!

One is for sure, here is something strange with the FM.

This extrem nose up bevior is overall the Modell.

If I take off, the DCS Su27 needs a extrem nose down trim, if I retract the landing gear, the DCS Su27 needs a extrem trim down again. Every little speed change I must extrem trim this bird.

If I am loosing speed, trimmed up, some strange thing happen again.. the DCS Su27 becomes extrem sensitive around the stick middle position. Suddenly there are no forces to fight with.. up or down. With a tiny little small stick input the DCS Su27 rides a small dot of her centerpoint. Every tiny little stick input gives a big reaction.

If you look from outside of the plane, it looks really funny how the Su27 reacts, you can make her "shiver" without any reaction change! The Black hole of forces. :music_whistling:

 

But for me that's a forum problem I think.

The more strange and harder a plane is, the more good/right the plane must be! :huh:

 

A 20+ tones plane drifting a 10 m/s wind on the runway with all three wheels on the ground.. make the start harder = must be right.

 

A modern jet, harder to trim as a WWII fighter... make the flight harder = must be right.

 

A modern jet stalls 100 times more and without any reason as every older plane.. make flying harder = must be right.

 

Wingtips lost on the BF109 at 4G's, never heared before from any pilot of both sides, but in DCS it must be right, because it makes the flying unatural harder.

Now it's fixed and all the "it's total ok so, it must be so" are all gone. No pedition to let the wingtips rip off again. Why? :huh:

 

I don't get this "looks, feels and plays unatural so it must be right" behavior!

 

AC are not as hard to fly as many people here try to believe!

And a Su27 will never react as here in this game.. that's for sure!

I would really know the names of the russian real Su27 pilots testing this FM!

Would be nice to talk with them. Perhaps they could explain why the Su27 is the only modern russian jet with this extrem trim and nose pitch up behavior?

Edited April 3, 2015 by Nedum

[OnlyforDCS]

Nedum you are completely ignoring large parts of this thread (AGAIN) and discussion and coming to the WRONG conclusions, for what end I do not know.

 

The nose UP pitching behavior at stall speed is due to the bird being TAIL heavy, since there is NO lift generated at stall (Look up the definition of stall if you don't know what Im talking about).

 

The rest of your points are all moot, and if you had bothered to read the thread you would know why.

 

Every single airplane that has positive stability has a pitch up tendency with increasing airspeed. You completely ignore the fact that the FBW system of the Su27 is configured to respond in the exact same way. Oh man why do I even bother...

[Svend_Dellepude]

WIP, BETA!!

 

And some reading:

http://www.digitalcombatsimulator.com/en/products/flanker/?PAGEN_2=2#1037031

[pepin1234]

Well!! here we go again.

 

The Su-27 AFM is the most strange I have seen since I play this Sim. Honestly I don't believe the Su-27 have this behavior in real life.

 

PD: Just in case, What mean ACS?? maybe this is my problem!!

[GGTharos]

The control augmentation system. It's abbreviated ASC but I don't recall what it actually stands for.

 

ASC provides the trajectory control laws for the aircraft to keep it predictable and 'stable', so that the pilot can fly it safely.

 

This system is turned off in an emergency, or to perform a cobra.

 

People have been using it as a combat system, which it shouldn't be. You're flying beyond critical AoA when you do this, so you should be paying the price for any asymmetry on your aircraft (Asymmetry should cause roll-off).

 

Also, the FM for the Su-27 is not finished, still WIP AFAIK so you can still expect tweaks.

 

Most people are running into problems because they put a lot -pitch input. Keep it positive!

[pepin1234]

ok. then I have to test some combat with ASC off.

 

Anyway when I take-off I have to trim the aircraft, if I don't the aircraft stay uncontrollable with the nose up.

 

Thanks u

Edited April 3, 2015 by pepin1234

[GGTharos]

Yes, trimming is necessary. I don't know the specifics for Su-27 but I believe they have been discussed either in this or other threads.

[Weta43]

from another thread dealing with this question..

 

http://forums.eagle.ru/showthread.php?p=2354959#post2354959

 

Also - the flaps increase lift, but also cause a nose down pitch (by moving the center of lift backwards). As you lift the gear and flaps, you have to trim the nose down to remove the pitch up that occurs as you lift the flaps (& the opposite as you drop the gear and flaps to land). You should start doing this as soon as you hit "G & F"

[pepin1234]

Sorry but I tested the combat with ACS off and the aircraft is completely uncontrollable. We cant do any movement well done. This is completely wrong!!

 

We look like a sheet falling when we get into blackout while others fighters can kill us with cannon.

 

This is ridiculous!!

[GGTharos]

No, this is completely correct.

 

ASC OFF is not meant for combat. It is an emergency mode. If you fly too roughly with ASC OFF you will put the aircraft out of control.

 

You're simply not flying the aircraft carefully enough. Flying with ASC OFF requires that you understand exactly what ASC does and why, and how it differs from flight with ASC OFF.

 

The Su-27 already has a lot of good performance with ASC ON, there is no need to use ASC OFF at all.

 

Sorry but I tested the combat with ACS off and the aircraft is completely uncontrollable. We cant do any movement well done. This is completely wrong!!

 

We look like a sheet falling when we get into blackout while others fighters can kill us with cannon.

 

This is ridiculous!!

[pepin1234]

No, this is completely correct.

 

ASC OFF is not meant for combat. It is an emergency mode. If you fly too roughly with ASC OFF you will put the aircraft out of control.

 

You're simply not flying the aircraft carefully enough. Flying with ASC OFF requires that you understand exactly what ASC does and why, and how it differs from flight with ASC OFF.

 

The Su-27 already has a lot of good performance with ASC ON, there is no need to use ASC OFF at all.

 

No way any try. The performance of this aircraft has become horrible after this AFM. Even with ASC on we can not use the Vertical mode appropriately because the target some time get unlocked cuz the extremely pitching.

 

When you try to fix the situation we get in blackout quickly right at the combat moment. No way!!

[GGTharos]

By vertical mode you mean Vertical Search for radar/EOS?

 

For the pitching: You're supposed to trim your aircraft. This is correct. You have to change your flight technique. The Su-27 will out-turn anything out there, you just need to know how to fly it.

 

No way any try. The performance of this aircraft has become horrible after this AFM. Even with ASC on we can not use the Vertical mode appropriately because the target some time get unlocked cuz the extremely pitching.

 

When you try to fix the situation we get in blackout quickly right at the combat moment. No way!!

[Ironhand]

You know, I screwed up earlier. When talking about the FCS (Flight Control System), our beloved FBW system, I referred to it as the ACS (Automatic Control System) which is what actually controls the various autopilot functions. And others now seem to be referring to the FBW system as ACS. Or I'm even more confused than normal.

 

... The performance of this aircraft has become horrible after this AFM. Even with ASC on we can not use the Vertical mode appropriately because the target some time get unlocked cuz the extremely pitching...

Pepin, there must be something wrong with me because I don't find the aircraft difficult to fly at all. There are a few things you simply must not do, otherwise she seems to handle well. Could you, perhaps, post a track of you flying (without the "S" key pressed)? I'd like to see why our experiences are so different.

[pepin1234]

I will take apart the Su-27 for the moment.

 

The Mig-29S is becoming more interesting at the moment.

[IonicRipper]

Really? Even with the basic flight model and non-6dof cockpit?

 

I think the Su-27 is just a pure joy to fly. You just have to be careful at low speeds, she will bite back!

 

Like someone said on the 104th server: The Su-27 sacrifices safety for maneuverability. I think that accurately describes it.

Edited April 4, 2015 by IonicRipper

[Robin_Hood]

By vertical mode you mean Vertical Search for radar/EOS?

 

I think he is referring to the Longitudinal Mode (the IR missile-sensor mode), that requires you to have the target exactly on boresight.

 

As for maneuvering, I have no difficulty doing combat, with or without direct control (normally without, but when training I will sometime turn it on to very carefully gain a little more nose pointing authority at the expense of more energy bleeding - usually not needed against a dissimilar opponent).

 

There must be something wrong with how you fly the aircraft. You have to trim it a lot (especially at certain speed ranges, namely around 600 km/h and between 700-800 km/h, not so much beyond that), or maybe adding some curvature to the pitch could help.

 

PS: as far as the ACS/ASC/FCS is concerned, I think we should settle for the term used in the manual, namely, FCS, with its different modes : normal, landing, direct control. It may be less confusing than talking about ACS/ASC off or on (since technically, it is not really off, just in a different mode, from what I understand).

[ruddy122]

I agree,

 

The Su-27 can dogfight, personally I know that I would need to ease up on agressive maneuvering when you start going below 350 KMH if not you will bleed off all your airspeed, lose control and risk getting yourself shot down which I have learned the hard way.

 

The DCS Su-27 is one of the few aircraft that makes me really think about energy management and your control inputs.

 

Cheers,

[Hummingbird]

The biggest problem atm is that the upwards pitch starts too soon and rises too quickly IMO.

 

The real aircraft is supposed to require a fairly small amount of trim in pitch IIRC, mainly thanks to the ACS.

 

Also I am fairly certain that the ACS is supposed to prevent you from being able to enter a pitch down stall, whilst with ACS off you're obviously on your own.

 

Looking at cockpit videos of Su-27's in flight the pilots actually never seem to touch the trim controls at subsonic speeds, infact they don't even seem to have to move the stick forward to compensate for any pitch up as speed increases :huh:

[pepin1234]

You guy. Could be possible some of you guys that have already control well the Su-27 show in this thread the AXIS CONFI and the Joy you have for the actually Su-27????

[IonicRipper]

I use a Thrustmaster Warthog and dont have any axis curve. The Su-27 flies just fine with linear axis mapping, you just have to practice a bit, you'll get the hang of it.

[Exorcet]

You guy. Could be possible some of you guys that have already control well the Su-27 show in this thread the AXIS CONFI and the Joy you have for the actually Su-27????

I don't use any curves at all currently. Whatever axis settings the Su-27 comes with is what I've been using. While I don't fly it as much as the F-15, I don't find it hard to fly. It doesn't handle as crisply and it feels heavier (and it is heavier) but I can dogfight without losing control.

[SkateZilla]

I dont see what all the hooplah is about here....

 

I just spent all day with the Su-27 abusing it in everyway possible as i did with the F-15C AFM.

 

Are there some lile quirks? Yes, but I dont see the reason people are going nuts over them.

 

It's also in a WIP/Beta State, so things will likely be improved and adjusted.

 

Then Again, I saw the SAME exact reaction to the F-15C AFM, Seems people that have been flying the SFM from LockOn->FC3 are used to the way it flies w/ SFM, so they have to re-learn the aircraft and it's limitations.

[IvanK]

Playing around with this FM after wading through this discussion. What is the:

 

"stick to trimmer control mode" in the Options Flight control settings ?

 

Its an unassigned key as default. Enabling it results imo in a sort of pseuedo Auto trim in pitch in the higher IAS range .... though I have only briefly looked at it.

[esb77]

You guy. Could be possible some of you guys that have already control well the Su-27 show in this thread the AXIS CONFI and the Joy you have for the actually Su-27????

 

I use a Thrustmaster T-Flight Hotas X, that's about 2-3 years old and extremely difficult or perhaps impossible to get high precision with.

 

I use the default settings, which is linear axis for x, y, and z, and deadzones of 0.

 

I didn't get the Su-27 until after the PFM was released, and most of my experience in DCS has been with the Su-25T (at least 300 hrs), and the Mi-8. I have the Huey, A-10C, and Blackshark, but don't get around to flying them much.

 

I use trim in the Su-25T (via autopilot), and in the Mi-8 with the trim button, but haven't bothered using the trim in the Su-27 because even with modifiers my single hat button is at capacity with more important controls, and I prefer to fly HOTAS, so no keyboard trimming. My stick is sprung so that I don't find holding trim manually a problem in terms of effort, so the only time it's annoying is when I want to fly with both hands off of the controls (to take notes for instance).

 

I find the Su-27 to be very flyable. It likes to nose up at some speeds, but with manual stick you always have enough stick forward authority to nose down enough to get yourself into serious trouble if that's what you want to do. So at no point is there uncontrollable uncommanded nose up, the available nose down authority greatly exceeds the pitch up so it is always possible for the pilot to counteract it.

 

It has control traits that may not be what you are used to, but those traits are consistent, and therefore you can learn to fly plane. This is true with the FCS on or off.

 

Flying, or even fighting with the Su-27 is no worse than learning to hover in a Huey or Mi-8.

 

It's just a matter of unlearning bad habits you may have from the SFM, and learning how the airplane behaves currently in the sim.

 

There are a couple of special comments I'd add.

 

Turning off the FCS.

Turning off the FCS in flight is a suicidal piloting error. Even when you do it "correctly" it is an extreme high risk action that should be avoided if at all possible. Airshow demonstration pilots and test pilots are know for their great aviation skills, but they are also known for their high rates of fatal crashes.

 

Flying with the FCS off the entire flight is possible, but it GREATLY increases the pilot workload and reduces the margin for pilot error to almost nothing. With the FCS off, almost every piloting error can become a fatal piloting error. That's why turning it off is such a stupid thing to do. If you fly an error free flight, it is possible to fly and fight with it off, but the increased workload and risk of fatal pilot error is so high that attempting to do so is not rational.

 

Nose down inputs. The Su-27 has a great deal of responsiveness in negative pitch, and no safeties to prevent pilots from doing incredibly stupid things with that ability.

 

In real life a strong negative pitch input will create zero or negative perceived G forces on the pilot. This is very easy to feel, and for most people it is an extremely unpleasant sensation. In the real plane no special system is needed to handle this because the pilot can sense sharply unloading the plane very easily, and will be highly motivated to avoid it if at all possible.

 

In DCS we lack this sensory feedback, and this is a key reason that many virtual Su-27 pilots are making unrecoverable errors from excessive sudden nose down inputs. Keeping a close eye on the accelerometer can save you from many crashes as you learn the Su-27. If you always keep at least +1 G you are much less likely to have problems.