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.
Sukhoi Su-27/30/33/35/37 Flanker series & Su-34 Fullback - History, Design, Performance & Dissection
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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.
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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
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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
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Can you show us where you got the data for Su-27 vs later models from?
Look in publication Andrei Formin.
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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
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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?
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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?
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As Su-27 is being build into “lift body”. So you can have bigger wing area without change wing.
And like always changes are in details usually not visible at first. Distinguished changes in wings have Su-35
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You’ve been asked multiple times for a valid source of your information. A magazine editor is not a valid source of your information.
This magazine editor (as you call him) have access to these machine’s. And published more books and articles than you.
Still waiting for your paper from TsAGI. I’m looking in whole internet can’t find documents made by Director this institute. At last can you give me author?? It’s will be mutch raiser to find or titile of document
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It shows a graph, discusses topics similar to what you have already been presented. It is not new information, simply additional information confirming that instability is the reason for the Su-27’s maneuverability.
https://sci-hub.ru/https://arc.aiaa.org/doi/abs/10.2514/6.1993-4737
It is obvious, in my opinion. The Su-27 is statically unstable even if by a small margin as mentioned previously by both BBCRF and explained to you by MAV_JK.
Now please, if you have information to share… stop hiding it.
Thank you! I will read whole. But If I can please different link. Russian domain its blocked (lol) by my provider
But from Figure 7. If Im read this graph in proper way (if not please explain what we can see in it) that plane go into instability ABOVE 30 Deg AoA?
What is missing in my opinion is a graph of instability across speed range from low to max. Including different fuel load.
I’m mostly use monographs of Su-27. What you can easily find in Amazon.
You will not be able to observe it without paying this website otherwise;
https://arc.aiaa.org/doi/abs/10.2514/6.1993-4737
So if you don’t have this data and are only quoting books on amazon then why are you arguing against people who are discussing data from the primary sources?
You are joking right??
What is difference to have book Vs library book??
Btw some translation from “Spanish Su-27 manual” is not primary…
Ps. How meany pages have this document 25$ it’s quite expensive if have 5 pages…