Russian aircraft questions. Educate me please!

[At Sea]

Hello,

A question I have always had about Russian fighters is why are some of Mig and Sukhoi's designs so outwardly similar.

To my eye it always looks like Sukhoi make a bigger version of whatever Mig make. Almost as if Mig made 3 series BMW's and a few months later Sukhoi bring out the 7 series.

Is this intentional sharing of aerodynamic data and principles?

Is this a by-product of the command economy (this is a good fighter, better make our fighter look the same or it will not get built) thing?

Is it just a massive co-incidence?

examples;

Mig 21 & SU-22 I know the SU-22 has VG but the silhouette is similar.

Mig 23 & SU-24 size is the biggest difference here.

Mig 29 & SU-27 size again.

On other designs such as the SU-15 Flagon & Mig 25 the solution to the same problem was very different and both succesful in their own right, so why the similarities elsewhere?

The US aircraft industry has some similar designs from different designers, F-14 & F-15 both use twin tail & wide spaced engines but don't share a silhouette.

The best non Soviet example is the Dassault Mystere and North American Sabre which are very similar, but the Mirage went a very different way from the Lightning. Though not admittedly the Corvair Dart.

The 3 examples above have always made me wonder if the design similarities are deliberate or not, can anyone enlighten me?

Thanks.

[Knight_Flyer]

I vaguely remember another thread saying at the time of the Soviet planes some central bureau put together a general design that was passed on to the aircraft manufacturers. Hence the similarities are much more prevalent. Could be wrong though as I read a lot of threads.

Not entirely sure the Su-15 and MiG-25 were developed for the same "problem". Both are certainly interceptors and my understanding was, Su-15 replaced obsolete aircraft. While the MiG-25 came about because of a concern about the XB-70 Valkyrie being a threat which in the end never entered service.

[Arachnid]

Because the russians use a "design dept" they come up with better ideas than the west, hence the SU34

[At Sea]

I vaguely remember another thread saying at the time of the Soviet planes some central bureau put together a general design that was passed on to the aircraft manufacturers. Hence the similarities are much more prevalent. Could be wrong though as I read a lot of threads.

Not entirely sure the Su-15 and MiG-25 were developed for the same "problem". Both are certainly interceptors and my understanding was, Su-15 replaced obsolete aircraft. While the MiG-25 came about because of a concern about the XB-70 Valkyrie being a threat which in the end never entered service.

The 'problem' being point air defence. But yes very differnt times and specs.

The central planning bureau sounds rational as an explanation. The "why are western designs so diverse?" " because of competition" is maybe a better way of looking at it.

[At Sea]

Because the russians use a "design dept" they come up with better ideas than the west, hence the SU34

Are they better? There is always an element of group think that can blinker a big organisation.

SU-34 is a great aircraft, but so are many western designs. I am not convinced by the above logic.

[Jessica]

The general design work for both the MiG-29 and the Su-27 was done by TsAGI, and then given to each to build. MiG was tasked to do the Frontal Aviation (tactical fighter-bomber) variant while Sukhoi was tasked to develop an air superiority fighter which could defeat the F-15. Thus the two designs' great similarities.

Edited December 13, 2015 by Jessica

[At Sea]

Does that also apply to the Mig-23 / SU-24 and the Mig-21 / SU-22?

[Flankerman]

TsAGI (the Central Aerodynamics and Hydrodynamics Institute) was a research organisation involved with aerodynamics, stress testing, wind tunnel work, theoretical studies etc etc.

It did not DESIGN aircraft and hand them down on tablets of stone for the OKB's to make.

Why would each OKB (MiG, Sukhoi, Yakovlev etc) have their own design teams if it was all done by TsAGI ???

TsAGI advised - the OKB's designed - a bit like NACA in the US - or the RAE in the UK

The fact that they produced similar designs is coincidental - similar requirements producing similar designs.

In the case of the Su-27, Pavel Sukhoi set up two rival teams to study varying layouts - one team going with a 'converntional' F-15 style layout, the other with a more radical 'blended wing/body' shape.

Testing was done using models of both shapes using TsAGI's wind tunnels - and the very convervative scientists at TsAGI recommended the F-15 style layout.

Pavel Sukhoi stuck to his guns and went with the shape we know today as the Su-27 Flanker.

So TsAGI were overruled by the Sukhoi OKB.

Ken

TsAGI's homepage is here...... http://tsagi.com/

Recommended reading (if you can get hold of it)... 'Su-27 - Beginning of Story' by Ildar Bedretdinov

Edited December 13, 2015 by Flankerman

[Giorgio N]

There's another important aspect that has to be considered: each moment in the history of aviation has witnessed "fashions" of one kind or another. Of course these are not fashions in the same way as wearing blue or red but result from recent developments or discoveries made by companies, research groups or advisory institutions. As a result often aircrafts designed in the same era show similarities as each design team tried to implement the latest "fashion" in their work.

Variable geometry wings were one of these fashions and it's not a coincidence that all aircrafts with this feature have been designed in roughly the same decade as back then this kind of wing was considered ideal for a number of reasons. Once different concepts emerged, VG became a thing of the past.

Another thing that must be kept in mind is that every designer will always look at what's around before starting a new project. The material analysed will include data from centres like TsAGI, configurations used on other aircrafts designed for similar missions, experience from previous designs. Very few aircrafts can be really considered to have been born from a totally white sheet.

Then there's the fact that similar problems will most times require similar solutions. The "two-dimensional" intakes used by F-14, F-15, Su-27 and others (and first pioneered by the A-5 Vigilante) are simply the most efficient intake system for a combat aircraft required to fly over M2, no surprise if most aircrafts designed with such specifications in mind use them. The same can be said for the MiG-21 and Su-22 mentioned by the OP... or better, for the MiG-21 and the Su-7/9 family from which the Su-22 derives. These aircrafts are actually very different but some traits are common because some specifications were similar so we have on both a simple intake with a central cone... and nothing else in case of the Su-7 but on both the MiG-21 and the Su-9 a delta wing with conventional taiplanes. The simple intake arrangement works well enough for the performance required however has a disadvantage in that limits the size of the radar antenna. Not too much of a problem for the MiG but a serious problem for an interceptor like the Su-9 and the reason for which the following Su-15 did not use this system

Now as the Lightning has been mentioned, this too has a simple frontal intake. And also has high swept wings not too different from a Su-7... the Soviets used a very powerful engine on this aircraft and got some good performance, EE used two engines to get even higher performances. Try to think of what a single engined Lightning would look like and we have something not too dissimilar from the Su-7.

The Mirage III looks very different because from a certain point of view it's a more advanced design compared to both the Lightning and the Su-7 and was designed with more operational flexibility in mind. In any case nothing was really new on the Mirage: here we have side mounted intakes with moving cones (F-104 style), a delta wing (F-102 or FD.2 style), an "area ruled" fuselage (again think F-102).. all features of this aircraft had been used on other fighters of the late '50s, Dassault's merit was to blend them together in the right way to achieve a great design as a result.

[Graham Boak]

Certainly TsAGI didn't design the planes, but none the less the similarity in configurations over the years make it quite clear that there was a central guiding hand in the initial project stage. This is not just the postwar jets but the WW2 twins and single-engined fighters. Look at the layouts of the Pe2/Yer2/Tu2 or the Yak1/LaGG3/Mig3, The similarities in general layout and particularly wing taper ratios make it quite clear that there was a central guiding hand. The manufacturers were told which was the best way to go in terms on wing tapers and general layout. The specific roles dictated the size, and often the engine choice when this was open. This doesn't mean that manufacturers couldn't apply their own imaginations - such as the short-coupled MiG3 which clearly shows his experience in the Polikarpov design team.

You don't see the variety that came out of the more independent Western companies, where the RAE or Langley were free to advise but not dictate. Where is the major WW2 Russian design with no taper on the leading edge, or with an elliptical wing?

The one time where a wide variety in aircraft shapes does appear is in the immediate pre-war years, where the best ways of integrating jet engines and transonic aerodynamics were unknown in the USSR (or indeed elsewhere). However once past the initial stage we get the La17/MiG15 and the Il28/Tu14. The sheer number of such similarities, and the lack of alternatives, makes it naive not to recognise a guiding hand - and if not TsAGI then whom?

[At Sea]

Genuinely thank you all for your contributions above.

It is an area of modelling I have never really looked at and after having grown up during an era when soviet aircraft were at best the 'super bogeyman' and at worst a badly replicated guess at what the actual aircraft looked like it is very interesting ti to hear the information above and start my own research.

I think at worst I will come out of this line of enquiry more knowleable, at best with a Soviet shelf in my collection and the ability to use Alclad! :-D

[Giorgio N]

I think at worst I will come out of this line of enquiry more knowleable, at best with a Soviet shelf in my collection and the ability to use Alclad! :-D

And here's another bit that for many years we didn't consider in the west: most Soviet aircrafts were coated with a clear lacquer that while allowed some panel variation to show through, gave the finish a more uniform appearance compared to a true natural metal. Many aircrafts were later painted with a mix of clear paint and aluminum paste (mine is s short summary, the details can be found in the Cold War section). So Alclads are sure useful, but no need to add all those variations that would be seen for example on a '50s USAF fighter. This makes painting models of these aircrafts a little bit easier