T-10 Flanker-A
The first prototype of Su-27, T-10-1 has made his first flight on 20 May 1977 from runway of Institute of Flight Test in Zhukovski. Later the plane received the NATO code-name Flanker-A. Analysis of the capabilities of the first prototype and their comparisons with the capabilities of F-15 has showed that prototype of Su-27 was inferior to his counter-partner.

A new prototype
T-10S Flanker-B In this situation, despite the decision about starting the industry production of T-10, constructors had decided to thoroughly rebuild the plane, and have developed the almost new plane T-10S (T-10-7).

T-10S Flanker-B
The main changes were in following areas(refer to the picture below):

The wing(1)has no longer ogival edge, also the mechanization of the wing edge was introduced, ailerons(7) were moved toward the fuselage and wing has received full adaptive mechanization(6) (later also automatic)

The area of transversal cut was decreased to about 80% of previous. This last change was achieved by the reconstruction of engines mount(3), in the new design the gears(2) boxes were on the top of both engines, it was also necessary to move vertical tail planes(11) into another place. Finally the aerodynamic hackles were removed from the wings.

Aerodynamic brake(10) was removed from the under-fuselage position, and in the new design it became a big hatch on the top of fuselage.

In order to protect the engines from the dirt on runway the front undercarriage(4) was moved to the rear, and the additional protecting nets were implemented in the air intakes of the engines.

The canopy(5) was fully redesigned.

One of the most significant changes was the introduction of the new engines(8) Al-31F (the new engines were used also in previous T-10 prototypes, starting from the number T-10-3).

Two T-10S were build: T-10S-1 (T-10-7) and T-10S-2 (T-10-12) both in Sukhoy’s construction factory.