Yes I’m in totally different page. Like I’m speaking about apple’s and you about pears.
All planes various stability depending from fuel. It’s just IN comparison to other aircraft in GAME odd to me that we have delta and unstable planes BEHAVING more generally gently at low speed and overall HANDLING is just lest difficult to maintain. IN COMPARISON to unstable by design planes…
The Su-27 is not stable in practically all ranges of fuel loading
From what little I’ve read about the Su 27, it should be more or less unstable only with a certain smaller percentage of fuel.
As a curiosity I attach an excerpt from the manual for those who would like to try the AoA characteristics of the Su 27.
"To ensure good maneuverability characteristics over the entire acceptable range of angles of attack at subsonic flight speeds, automatic control systems for wingtips and flaperons based on the angle of attack signal are introduced. As the angle of attack increases, the lateral stability and controllability characteristics remain satisfactory up to α up.
At speeds below 400 km/h and α ≥ 24°, the airplane has reduced lateral controllability. When climbing out of roll at speeds less than 400 km/h while performing maneuvers along the boundary of the ERP response, an angle of attack greater than α dop may occur.
Therefore, when climbing out of a roll, control the angle of attack without allowing αdop to be exceeded.
At angles of attack α > 28° up to stall the controllability of the airplane is absent.
Aerodynamic shaking occurs at angles of attack α=9°-5° at M=0.5-0.9, respectively. As the angle of attack increases, the intensity of shaking increases and stabilizes after Δα=2°-3°.
The nature of the shaking is soft. Over the entire range of angles of attack, shaking does not impede piloting and cannot serve as a warning sign of approaching α extra.
When the wingtip control system is deactivated and fails, piloting is safe and has no peculiarities up to α ∼10°.
Airplane behavior with deflected toes at 30° (landing gear retracted, flaperons retracted) has no peculiarities. Failure of control of the nosings and flaperons at subsonic speeds does not cause aircraft evolutions requiring pilot intervention. The maximum incremental overload at this ΔPu ≈ 0.5. The available roll angular velocity decreases with increasing angle of attack, but remains sufficient up to α extra (more than 20°/sec). The efficiency of lateral control in horizontal flight provides a roll angular velocity ωx ≥ 1.5°/sec.
At takeoff and landing modes with released wing and landing gear mechanization provides angular velocity ω 1.0°/sec.
Characteristics of stability and controllability of the aircraft without hangers and with all variants of missile armament remain acceptable up to angles of attack:
The limit is 24 AoA, you can’t really see it, there’s a green line.
Everything is wrong.
What does the alignment and control of the wing mechanization have to do with it?
I don’t know what you’re answering. The description is from the manual and refers to AoA.
Thanks for your contribution to subject.
Now @MiG_23M can we see any documents about instability during subsonic speeds ?? To be at the same page of course.
Mentioned by Sukhoi themselves on ICAS2002 congress:
• Su-27S/SK basic single seat configuration (typical role is interception) with neutral and small
negative margin of longitudinal stability, maximal Mach number up to 2.3 and airspeed up to 1350 km/h.
I was going to just post the paper by TsAGI director on supermaneuvrability as well. So many papers on it, kind of weird to declare I should present a source when the burden of proof for their claim that it was statically stable was on them in the first place.
As said, whether an aircraft is able to recover from a deep stall and not get hung up even with a full forward stick depends on the pitch recovery moments available by the elevator. It’s only unique to just a few aircraft because the effectiveness of the elevator is so lost that it cannot even generate negative Cm (a.k.a pitch-down moment) in the high AOA region.
For the small tail F-16A, there’s a wide AOA region where all three Cm curves go above zero and the aircraft is unable to pitch down at all. Pitch rocking technique is developed to rock the aircraft out of the deep stall. And I don’t think this is the case for Su-27.
A friend of mine works at Honeywell, he is involved in aircraft control design there, he has an older gentleman as a colleague who was in control design for the Su 27 in the 80s. I got from him that the Su 27 has some degree of instability at lower speeds and depending on the weight of the aircraft which is according to the amount of fuel.
He also said they had huge problems designing the controls for the Su 27 back then.
I am attaching an excerpt from a book on the Su 27 by Y.Goron.
I’ll digress to a slightly different topic.
It is from the manual:
Pilotage to execute only with the switch oned limiter of α and g. Output to the critical angles of the attack of g-force is escorted “by stop” (by stepped increase in the efforts on stick on 15 kgf) and by buffeting of control stick. In this case luminesces signal “α CRIT.”, the escorted by vocal information “critical angle of attack, the g tolerance”.
System [means limit system - OPR] with its correct operation ensures the high maneuverability of aircraft with the safe pilotage on the boundary of the critical angles of attack and g-force.
WARNING. The overriding limit alfa and g of a noticeable increase in the maneuverability does not give, but it is possible to lead to stalling aircraft or to hight G load.
Permissible angles of attack ( limit set by OPR, see text in figure)
for the aircraft without the suspensions or with [UR]
M AoA
0,5 24
0,6 23
0,7 22
0,8 20
0,9 19
1,0 18
2,0 8
for the aircraft with the bomber weapons :
M 0,6 20 AoA
0,7 18
0,85 15
For who ever would like to try AoA at Su 27 in the game, in real world above 28 AoA the lateral control is ineffective
It’s a big difference between Su-27 and Su-27S and later models. Especially with avionic weight and fuel containers distribution…% of materials including composits are also different… Su-27 compare to Su-27SK have wing area bigger by 5%. Nose and radar containment it’s lighter.
It’s loot of changes and differences between Su-27 and later models.
Please post TsAGI director paper. We all except you willing to learn new things, and I don’t know everything like you. So if it’s not a problem for you please post everything what you have
Can you show us where you got the data for Su-27 vs later models from?
Look in publication Andrei Formin.
I’ll take TsAGIs word over take-off magazine editors’…
I like read so if You can just put any docs about Su-27 because Im big fighter aviation fan. And you are specialists in the subject. So far I don’t see your report so I can’t confront data. Only cows don’t change their mind
So far Im not convinced that Su-27 is unstable because what I read Su-27 and it’s first iteration was stable platfor and SDU was major limitation
Nearly all 'modern ’ air superiority fighters are aerodynamically unstable for the sake of maneuverability, it wouldn’t be a surprise if the Flanker was unstable, like most everything else?
Absolutely all Flankers wings do not differ from each other in terms of wing area except for the Su-33
About radar and other nonsense, where do you get this from?