To my amateur eye, there appears to be limited fuselage on the engines for Sukhoi fighters from Su-27 on. That is, the fuselage follows the curvature of the engines closely and there is a definite material difference between the adjacent fuselage.

enter image description here

This seems to be a characteristic specifically of Sukhoi fighters or their clones.

What is the purpose of such a feature?

I realise might be a state secret as to the actual design decision and will accept such an answer but I suspect there is a straight-forward engineering reason. And perhaps I am mistaken on my assessment.

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    $\begingroup$ The metal finish in the afterburner region is simply because paint will not endure the peak temperatures there. If that does not answer the question it is because I have a hard time to understand what you want to ask. $\endgroup$ – Peter Kämpf Feb 15 '18 at 23:38
  • $\begingroup$ @Dave appears to have understood my question. Perhaps my vocabulary is wrong. F-14 from the straight back view does appear to have a very similar appearance, was not aware. The limited 'skin/fuselage' or the low cross-sectional area of the aircraft near the engine area is what I was curious about. I guessed the paint difference was from the heat, but I reasoned that was decided because the skin is so close to the burner. $\endgroup$ – RomaH Feb 16 '18 at 13:50
  • $\begingroup$ That is, why are they able to place the skin so close to the engines? I was expecting something like: Sukhoi engines are generally simpler and they can get away with it, or it just performs better in wind tunnels, easier to get to in the field, or all! Help clarify? $\endgroup$ – RomaH Feb 16 '18 at 14:05

In a fighter you generally want to optimize fuel and ordinance capacity as well as have competitive performance. This use case generally leads to a design that is different than your average transport category aircraft. The SU-27 has some similar characteristics to the F-14 Tomcat and it should be noted

The aircraft had a large wing, clipped, with two separate podded engines and a twin tail. The ‘tunnel’ between the two engines, as on the F-14 Tomcat, acts both as an additional lifting surface and hides armament from radar.

Here is a good picture of the engines from the back

enter image description here (source)

You can see that they could connect the engines but that would increase cross sectional area, disturb the center portion which helps add lift and add weight. If there is nothing they need to stick in there, there is no reason to have such an area on the aircraft. Its also worth noting this is not terribly different from the back of an F-14.

There is not necessarily a whole lot of metal surrounding any aircraft engine.

In the case of the SU-27 it also looks like the engine coverings are unpainted, this may be for heat related reasons.

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