Su-27 Flight Model Discussion

[tagge]

What do the DEV's think? Is the Su-27 ok? Are they really claiming that this is the AFM of the SU-27? I do believe in DCS but an answer to my questions By them would be much appreciated...

[OnlyforDCS]

What do the DEV's think? Is the Su-27 ok? Are they really claiming that this is the AFM of the SU-27? I do believe in DCS but an answer to my questions By them would be much appreciated...

 

The biggest complaint right now seems to be the non existant damage model under high-g loads. The dev's are aware of the issue, but your request for them to come to this thread is very unrealistic and I have to say quite entitled. The PFM is WIP and it needs some tweaks, but it is produced to the highest standards with the input of actual Su27 pilots. If you dont believe that they are trying their best I have to ask you what are you doing here? Despite the lack of full systems modeling, and some quirks (like the aformentioned damage model, or the strange taxi/tyre behavior) I find the Su 27 FM one of the best I have tried.

[Toxic]

Su27's FM

 

I really don't want to start a huge thing on the forums, but why does the Su-27 fly like such an unstable beast?

 

Where did ED get the information about how the Su-27 like that?

 

Having a degree in aerodynamics and commercial aviation I know quite a bit on how aircraft fly. The aircraft in the game just doesn't make any sense. Fly-by wire technology works in a way to make the flight very comfortable and easier on the pilot so he/she can focus on the task at hand CRM (ie ground attack or blowing someones face off with an Archer).

 

Is it just because this is an older version of the Su-27 and the fly-by wire technology in the world just wasn't that great at the time. Or is it because the aircraft is still in beta?

 

I would like to learn from the developers and supporting members, but I know a lot of "desk pilots" are going to chime in too. :pilotfly:

 

Also, am I myself doing something wrong inside DCS. (curves, etc.)

Edited January 21, 2015 by Toxic
Didn't want to sound insensitive to desk pilots.

[Solty]

It is "virtual pilots"...and that was just mean.:pain:

[NineLine]

Probably search the forums some, you might find the exact issues you are facing, we saw similar issues with the F-15 when it first came in with the PFM... these flight models are like nothing we have seen before, and they show our bad habits from the SFM real quick...

 

I really don't want to start a huge thing on the forums, but why does the Su-27 fly like such an unstable beast?

 

Where did ED get the information about how the Su-27 like that?

 

Having a degree in aerodynamics and commercial aviation I know quite a bit on how aircraft fly. The aircraft in the game just doesn't make any sense. Fly-by wire technology works in a way to make the flight very comfortable and easier on the pilot so he/she can focus on the task at hand CRM (ie ground attack or blowing someones face off with an Archer).

 

Is it just because this is an older version of the Su-27 and the fly-by wire technology in the world just wasn't that great at the time. Or is it because the aircraft is still in beta?

 

I would like to learn from the developers and supporting members, but I know a lot of "desk pilots" are going to chime in too. :pilotfly:

 

Also, am I myself doing something wrong inside DCS. (curves, etc.)

[tagge]

No, don´t get me wrong. I do believe that they are doing their best. Who I am to say, I'm just a FOW (flying on the weekends) type of pilot. The thing is I was shocked about the difference between the old SU-27 and the new AFM. Just barely managed the old one... Seems like I have to totally reset and reprogram my head for this one.

 

BTW, do you by any chance have Anatoly Kvochurs telephone number? He could take a quick spin with the SU-27 an tell me what he thinks... ;-)

[zaelu]

You should press S mid flight to see her true stability :D .

 

 

I think the PFM are still in fine tuning and many things will be polished in time. The last Froogle VLog here was quite informative in this part as it mentions the fact that with F15C and Su27 the AFM/PFM from ED and BST can now truly go supersonic.

 

 

At first I also find her very unstable but after you smooth your hand a bit she flies true.

[tagge]

If you dont believe that they are trying their best I have to ask you what are you doing here?

 

 

BTW, didn't quite like that argument. Let's keep it nice and polite here.

[OnlyforDCS]

I really don't want to start a huge thing on the forums, but why does the Su-27 fly like such an unstable beast?

 

Where did ED get the information about how the Su-27 like that?

 

Having a degree in aerodynamics and commercial aviation I know quite a bit on how aircraft fly. The aircraft in the game just doesn't make any sense. Fly-by wire technology works in a way to make the flight very comfortable and easier on the pilot so he/she can focus on the task at hand CRM (ie ground attack or blowing someones face off with an Archer).

 

Is it just because this is an older version of the Su-27 and the fly-by wire technology in the world just wasn't that great at the time. Or is it because the aircraft is still in beta?

 

I would like to learn from the developers and supporting members, but I know a lot of "desk pilots" are going to chime in too. :pilotfly:

 

Also, am I myself doing something wrong inside DCS. (curves, etc.)

 

I believe I read somewhere that the FBW tech in the Su27 is setup to give the pilot positive stability in the aircraft, so you will need to trim the aircraft whenever you are not flying at a fixed speed.

[rrohde]

The only thing that I have an issue with is the wobbly autopilot. Is that a glitch with the old autopilot not coping with the new AFM, or is that based in reality?

[amigastar]

While i love flying the SU 27, me as a layman also thinks the Flight Model might be flawed to a certain degree. I'm falling way to easy into stall.

But, I'm 100 percent positive they will sort and balance it out.

[ShuRugal]

While i love flying the SU 27, me as a layman also thinks the Flight Model might be flawed to a certain degree. I'm falling way to easy into stall.

But, I'm 100 percent positive they will sort and balance it out.

 

I think the problem going around with so many people stalling "too easily" is that the old SFM gave unrealistic expectations as to the stability of a fighter aircraft.

 

A true fighter aircraft is unlike any other thing that flies, all the way from conception to final product. Civil aircraft, transport planes, and even (dedicated) ground-attack aircraft are all designed to be aerodynamically stable. There is no need to change attitude rapidly, so the aerodynamic design trades this ability away in exchange for aircraft which, when flown inside their design envelop, are virtually impossible to place in unrecoverable situations.

 

A fighter, on the other hand, must be able to fly fast and turn rapidly, above almost all other considerations. The speed requirement means low-aspect, deeply-swept wings. The maneuverability requirement means large control surfaces and low(ish) wing loadings. The only feature in that list which leads to more stability is designing for low wing loadings, but there is a limit to how much that can be achieved with the need to carry fuel and weapons.

 

The end result of fighter design requirements is an aircraft which is capable of changing attitude significalntly faster than direction of flight. Coupled with low aspect wings (enters stall easier) and high-sweep (stall spreads rapidly spanwise) you now have an aircraft which is very easy to maneuver into out-of-envelope situations. In real life, this is handled through the application of hundreds of hours of flight training, until the pilot knows exactly what his aircraft can be asked to do under any given set of conditions.

 

TL;DR version: Flying a fighter is like operating linux as root: the machine can and will do anything you ask it, including fly tail-first into the ground (rm -rf /)

[Shepski]

Having several Flanker books and a video on the design, development, and chronology of the Su-27, reading and listening to interviews by test pilots and demonstration pilots the way they describe flying the real jet is not what we have in the DCS Flanker.

 

Some quotes by pilots were "best aircraft they ever flew", "Flys like a dream", and "very easy for the pilot".

 

Just watch some Youtube videos of in-cockpit footage when the jet is pushed around and you can see how stable it is.

 

I'm looking forward to flying *that* jet in DCS!

[SFJackBauer]

Not dismissing your arguments, but isn't that a bit difficult to base your expectations off on videos? For example, I am a fanatic Formula One fan, and participate on some F1 fan communities. One of the arguments that always pops up is that the onboard F1 videos shows the racing drivers pushing hard those machines so easily... that it makes almost possible for we regular folks to drive one of those. Yet when regular folks jump into these machines they almost kill themselves in the first 100 meters.

 

There are a lot of variables missing from our desktop simulations - beginning even with the control hardware. How many pounds of pressure on the stick is needed to get it into full deflection, at speed, to do the kind of maneuvers we do on our desktops with a flick of the joystick? One USAF pilot in exchange with the Luftwaffe, said this about the handling qualities of the MiG-29:

 

Of the four fighters I have flown, the MiG-29 has by far the worst handling qualities. The hydro-mechanical flight control system uses an artificial feel system of springs and pulleys to simulate control force changes with varying airspeeds and altitudes. There is a stability augmentation system that makes the aircraft easier to fly but also makes the aircraft more sluggish to flight control inputs. It is my opinion that the jet is more responsive with the augmentation system disengaged. Unfortunately, this was allowed for demonstration purposes only as this also disengages the angle-of-attack (AoA) limiter. Stick forces are relatively light but the stick requires a lot of movement to get the desired response. This only adds to sluggish feeling of the aircraft. The entire time you are flying, the stick will move randomly about one-half inch on its own with a corresponding movement of the flight control surface. Flying the Fulcrum requires constant attention. If the pilot takes his hand off the throttles, the throttles probably won't stay in the position in which they were left. They'll probably slide back into the 'idle' position.

 

The Fulcrum is relatively easy to fly during most phases of flight such as takeoff, climb, cruise and landing. However, due to flight control limitations, the pilot must work hard to get the jet to respond the way he wants. This is especially evident in aggressive maneuvering, flying formation or during attempts to employ the gun. Aerial gunnery requires very precise handling in order to be successful. The MiG-29’s handling qualities in no way limit the ability of the pilot to perform his mission, but they do dramatically increase his workload. The F-16’s quadruple-redundant digital flight control system, on the other hand, is extremely responsive, precise and smooth throughout the flight regime.

 

There is no auto-trim system in the MiG-29 as in the F-16. Trimming the aircraft is practically an unattainable state of grace in the Fulcrum. The trim of the aircraft is very sensitive to changes in airspeed and power and requires constant attention. Changes to aircraft configuration such as raising and lowering the landing gear and flaps cause significant changes in pitch trim that the pilot must be prepared for. As a result, the MiG-29 requires constant attention to fly. The F-16 auto-trims to one G or for whatever G the pilot has manually trimmed the aircraft for.

 

The MiG-29 flight control system also has an AoA limiter that limits the allowable AoA to 26°. As the aircraft reaches the limit, pistons at the base of the stick push the stick forward and reduce the AoA about 5°. The pilot has to fight the flight controls to hold the jet at 26°. The limiter can be overridden, however, with about 17 kg more back pressure on the stick. While not entirely unsafe and at times tactically useful, care must be taken not to attempt to roll the aircraft with ailerons when above 26° AoA. In this case it is best to control roll with the rudders due to adverse yaw caused by the ailerons at high AoA. The F-16 is electronically limited to 26° AoA. While the pilot cannot manually override this limit it is possible to overshoot under certain conditions and risk departure from controlled flight. This is a disadvantage to the F-16 but is a safety margin due its lack of longitudinal stability. Both aircraft have a lift limit of approximately

35° AoA.

 

I know it is a different aircraft but I'm not sure if the flight control system is entirely different. I would love to see some objective assertions on the Flanker.

[esb77]

I find the Su-27 to be very easy to fly and very well behaved.

 

Key difference: I never had FC:3, I got the standalone after the new flight model hit.

 

My references for comparison are the Su-25, A-10 C, and P51 modules, and long ago memories of a workaround for GraphicSumulation's hornet 3.0 back in the late 1990's that would let you fly a flanker (though with a C block Hornets cockpit interior).

 

So aside from possible hardware configuration issues, I think most people are just used to a model that wasn't very representative of how a Flanker behaves in the more dangerous and difficult portions of the flight envelope.

 

Aside from botched Cobra attempts I generally find it difficult to make the Su-27 misbehave.

[otto]

@Toxic.

 

1.Some of us desk pilots don't live in US where you have endless possibilities ...

My country offered me 400 dollars a month to become a fighter pilot and that was too low for my ... talents.I'm glad i became a desk pilot it's a lot more fun for me at least.

 

2.I have t16000 and it feels stable to me.

[Witchking]

I agree... the flanker feels pretty natural to fly..it feels weighty as an aircraft is supposed to be. The engines behave exactly as expected with the sudden jolts of thrust as the throttle cone closes. It is easier to fall into a stall if you do not manage your speed correctly. But just because that happens doesn't mean it is wrong. Unless you are a pilot who has actually flown a flanker, trust ED that they have more information that you do in what they have implemented. Just because it was easier flying the flanker in 1.0, 2.0, 2.5, lomac and pre-AFM days, doesn't mean that was correct and this isn't. This is the first representation of the flanker and its engines in a simulation. I see someone was talking about pilots who said "it is a breeze to fly". But those are pilots...they have years of experience flying aircraft...dealing with the edge of envelope feedback. I would imagine the physical G-forces and actually being in a aircraft has that feedback which we will never get in a simulation. There is an element of subconscious compensation for the responsiveness of the aircraft. The experience becomes second nature to actual pilots. So just because it feels harder....doesn't mean it is wrong. Get an actual flanker pilot who flew "the early generation Su-27 Flanker B variant from 1989? 1990? and ask him if the jet behaves as expected....that is the answer we are looking for. Either way... ED.. or ED representatives....please do not dumb down this amazing aircraft just because people are finding it harder to fly/manage. Keep up your standards and just focus on providing the most realistic experience as possible. ;) :)

 

I find the Su-27 to be very easy to fly and very well behaved.

 

Key difference: I never had FC:3, I got the standalone after the new flight model hit.

 

My references for comparison are the Su-25, A-10 C, and P51 modules, and long ago memories of a workaround for GraphicSumulation's hornet 3.0 back in the late 1990's that would let you fly a flanker (though with a C block Hornets cockpit interior).

 

So aside from possible hardware configuration issues, I think most people are just used to a model that wasn't very representative of how a Flanker behaves in the more dangerous and difficult portions of the flight envelope.

 

Aside from botched Cobra attempts I generally find it difficult to make the Su-27 misbehave.

[Bourrinopathe]

Either way... ED.. or ED representatives....please do not dumb down this amazing aircraft just because people are finding it harder to fly/manage. Keep up your standards and just focus on providing the most realistic experience as possible. ;) :)

^

Absolutely!

But I'm pretty confident a PFM has no reason to be dumbed down in any way. Fortunately.

 

As a virtual pilot with not much experience in flying (fighter) aircrafts, I'm really enjoying the Su-27 so far and the few acrobatics I pulled didn't end in a stall (yet).

Obviously, I still have to explore the flight envelope limits. I shut off the engines several times though ;)

I messed up a take off once but it was because I pulled the stick like a savage beast, and was punished accordingly.

My very first landing was surprisingly easy (from what I recall the SFM was not so imperfect).

 

As I'm now lucky enough to own a very precise and smooth stick (VKB Black Mamba), I tend to think a good control device is part of the key to fly the Su-27 with confidence.

Edited January 22, 2015 by Bourrinopathe

[OnlyforDCS]

The thing is I was shocked about the difference between the old SU-27 and the new AFM. Just barely managed the old one...

 

And right there is your problem. The old FM was (sorry to say this) complete garbage.

[BitMaster]

I have just had a few hours in the new Su-27 FM and it is quite challenging, up to a point where I ask myself how many RL pilots killed them selves by negative G's. It doesn't need a lot of negative G's to permanently harm your body, most relevant is your brain's blood pressure and no suite yet can hinder the blood going UP. The more sudden you apply negative G's the more harmful they are.

 

This leads me to the conclusion that IF this was the real Su's behaviour, then how many dead russian pilots have been caused by this, it can't be zero. How many planes got destroyed by this ?

 

 

It is hard to believe that this was accepted by the Generals and Moscow elites.

 

Just my 2 cents

 

Bit

Edited January 22, 2015 by BitMaster

[Nedum]

I think the problem going around with so many people stalling "too easily" is that the old SFM gave unrealistic expectations as to the stability of a fighter aircraft.

 

A true fighter aircraft is unlike any other thing that flies, all the way from conception to final product. Civil aircraft, transport planes, and even (dedicated) ground-attack aircraft are all designed to be aerodynamically stable. There is no need to change attitude rapidly, so the aerodynamic design trades this ability away in exchange for aircraft which, when flown inside their design envelop, are virtually impossible to place in unrecoverable situations.

 

A fighter, on the other hand, must be able to fly fast and turn rapidly, above almost all other considerations. The speed requirement means low-aspect, deeply-swept wings. The maneuverability requirement means large control surfaces and low(ish) wing loadings. The only feature in that list which leads to more stability is designing for low wing loadings, but there is a limit to how much that can be achieved with the need to carry fuel and weapons.

 

The end result of fighter design requirements is an aircraft which is capable of changing attitude significalntly faster than direction of flight. Coupled with low aspect wings (enters stall easier) and high-sweep (stall spreads rapidly spanwise) you now have an aircraft which is very easy to maneuver into out-of-envelope situations. In real life, this is handled through the application of hundreds of hours of flight training, until the pilot knows exactly what his aircraft can be asked to do under any given set of conditions.

 

TL;DR version: Flying a fighter is like operating linux as root: the machine can and will do anything you ask it, including fly tail-first into the ground (rm -rf /)

 

If this would be the only Jet with PFM in DCS, I would say that your announcement could be right. But we have some planes we can compare with the Su27 (F15C, Mig21, A10, and so on). So I think, that there is much more around that "feeling" of the AC behavior.

One person in another thread said something very interesting about the "Pitch/Cobra" behavior.

The Su27 seems to be very/to tail heavy. I think that would explain most of the problems I have with the DCS Su27!

Perhaps we need this extrem heavy tail to do the Cobra?

This has nothing to do with, that a fighter jet is build aerodynamic unstable to be fast an agil. Even a fast and agil AC must have his point of the center of gravity at the right place.

I can land the DCS Su27 and hold and switch the nose hight of the DCS Su27 between an AoA of 4 and 12 even till 140 kph before the nose goes/falls down by herself. A real Su27 can do this too? I don't know, but compared to all other DCS AC with a PFM it feels very strange.

 

On the other side the DCS Su27 burns energie like hell at every turn, if I want to do that turn at the same speed and in the same time like the real plane! All other DCS planes feel more or less right and do not burn so much energie.

There is allways a very small point at which the butt of the DCS Su27 wants to come around. If you pull 0.001 degree to much, you do more or less a sudden air break maneuver. If this happens there is always an extrem speed loss, because the DCS Su27 pitches suddenly with the butt around with.

If I try the same with the F15C/Su25/F86F/A10C they all slowing down but they don't show any air breaking/drift car behavior, if you pull the turn the same way as with the DCS Su27.

The DCS Su27 wants to throw her butt around. She feels and acts like a drift car with not enough power.

It's a very tiny point at which this behavior will accour, and the point where this happend is not stabel and that would fit perfect with a wrong centerpoint of mass.

A wrong center of gravity could explain this and many other strange behaviors.

 

So more ore less, we can compare the DCS Su27 AC with those who are already insinde and if you fly them all and try to push them all to the limit, you can see that the Su27 acts very different to all other DCS AC at some points (where all planes should have to act more or less the same way).

A small difference at this point is good, an extrem different behavior not so!

They are all AC, so at some points they must/should act the same way!

[Nedum]

The "override key" (S) function seems to be wrong.

I would bet all of my money that this key don't resett/override the trim function. This where stupid like hell. A harakiri/sepuko switch? Really?

If the DCS Su27 (s) key function is any near the original one, you must me pay several 100.000 dollars to be a Co on a Su27 hitting that switch to do a Cobra.

As I know, that switch only make the stick output more sensitive at the edges.

So around a normal input you cant feel any difference, you can only notice a difference if you push the stick to the limits. Thats why we always see the max way pull and push during a real Cobra.

So where does this "trim reset" coming from? Logic? Kill as many Pilots as an stupid engineer can?

I think it is more a change of center of gravity of the su27 to do the Cobra.

I can't believe that the ovveride key would act any near in RL like in DCS.

[FSKRipper]

I really don't want to start a huge thing on the forums, but why does the Su-27 fly like such an unstable beast?

 

Where did ED get the information about how the Su-27 like that?

 

Having a degree in aerodynamics and commercial aviation I know quite a bit on how aircraft fly. The aircraft in the game just doesn't make any sense. Fly-by wire technology works in a way to make the flight very comfortable and easier on the pilot so he/she can focus on the task at hand CRM (ie ground attack or blowing someones face off with an Archer).

 

Is it just because this is an older version of the Su-27 and the fly-by wire technology in the world just wasn't that great at the time. Or is it because the aircraft is still in beta?

 

I would like to learn from the developers and supporting members, but I know a lot of "desk pilots" are going to chime in too. :pilotfly:

 

Also, am I myself doing something wrong inside DCS. (curves, etc.)

 

In the Su-27 forum are several very good posts with example tracks or Tacview files.Just look for it

 

You don't expect private flight lessons from a developer because you paid 10 bucks for a module, don't you?

[OnlyforDCS]

The "override key" (S) function seems to be wrong.

I would bet all of my money that this key don't resett/override the trim function. This where stupid like hell. A harakiri/sepuko switch? Really?

If the DCS Su27 (s) key function is any near the original one, you must me pay several 100.000 dollars to be a Co on a Su27 hitting that switch to do a Cobra.

As I know, that switch only make the stick output more sensitive at the edges.

So around a normal input you cant feel any difference, you can only notice a difference if you push the stick to the limits. Thats why we always see the max way pull and push during a real Cobra.

So where does this "trim reset" coming from? Logic? Kill as many Pilots as an stupid engineer can?

I think it is more a change of center of gravity of the su27 to do the Cobra.

I can't believe that the ovveride key would act any near in RL like in DCS.

 

A test pilot was killed during the development of the SU27 when the FBW system failed (or was turned off) so Im not sure what you are getting at here?? The airframe is clearly capable of performing extreme manouvers which is why it needs a FBW system to fly safely and effectively.

[Bourrinopathe]

I'm not 100% sure about this, but the red rotary knob next to the "direct control" switch should be used to choose the proportional multiplier on the commands (while the direct control is ON).

That multiplier is shown on a semi-circular window with the values: 0.5 - 1 - 1.5 - 2

 

Of course, we don't have access to that button. That would be a DCS-level Su-27 ;)

 

 

The Su-27, like many other modern fighters, is designed to be inherently unstable; that is, the aircraft, if completely uncontrolled, will not tend to return to level, stable flight after a disturbance as an inherently stable design will. Such designs require the use of a "fly-by-wire" system where a computer corrects for minor instabilities while also interpreting the pilot's input and manipulating the control surfaces to produce the desired behavior without inducing a loss of control. Thus corrected for, the instability of the design creates an aircraft that is highly maneuverable; free from the self-limiting resistance that a stable design provides to desired maneuvers, an intentionally unstable design is capable of far higher rates of turn than would otherwise be possible.

(derived from wikipedia article: "Supermaneuverability")

(and apparently, the Flanker has a rear center of gravity)

 

What we have should depict the highly unstable behavior and violent command response. And based on the proportional value visible on the SDU (FBW) panel, it's a breeze compared to a higher value (but of course it may not represent the current implementation).

Nose bleeding may occur ;)

 

[EDIT:

(great video)]
Edited January 22, 2015 by Bourrinopathe