What is the benefit of Sukhoi-37's back swept wings?

Question

What do they do? Why they were designed like that?

Answer 1

Forward swept wing have the advantage of permitting a higher sweepback effect as the effective sweepback is at quarter chord in subsonic and trans-sonic speed. And since wing sweep is to delay the chordwise supersonic transition, you can achieve the same effect as a very swept-back wing with a moderately swep-forward wing, which makes it better at slower speed. Additionally, the virtual spanwise flow is towards the fuselage, which acts as an endplate; the effect is that there will be less vorticity at the wing tip, cutting down drag, and thus improving lift (and as a consequence: performance and agility).

So, why don't we see more forward swept wing aircraft? Because of the flexion force of lift is causing the wing twist to increase at the tip, leading to diverging forces. Overly loaded, a forward swept wing will tend to stall at the tip first, removing any aileron control authority; also if it does not stall, the load at the tip will increase faster than at the root, and because of the moment arm, the structure will be more heavily loaded.

Basically, forward swept wing is less stable, heavier to manufacture, and usually requires advanced material -- composites, for instance -- that is rigid in one direction (chordwise torsion) and flexible in another(spanwise flexing). So in the end, it is a matter of cost.

Answer 2

Simply, swept wings reduce drag making the aircraft easier to slide through air and as a result more maneuverable.