Testing
In 1980, when the new-version prototype assembly was in full swing at Sukhoi, the pre-production
batch assembly was nearing the end at the series production plant in Komsomolsk-on-Amur. As far as
their design was concerned, they were the deadringers for the T10-1 and T-10-2 prototypes with only
difference being their canted tails resembling those of the T10-3 prototype. Their powerplant still
retained the AL-21F-3AI engines. Despite the fact that the planes had little in common with the
future series-made Su-27, it was decided against cancellation of the pre-production batch. The
decision was made to use them for honing the weapons control system and other equipment as long
as first T-10S were being manufactured and put through initial stages of the testing programme. This
was intended to make up for inevitable dragging behind the schedule due to the need of reequipping
the production lines for manufacturing the new-configuration aircraft. The first aircraft of the pre-
production batch designated T10-5 was finished in July 1980 and followed in the same year by the
T10-6 and T10-9 (numbers 7 and 8 were assigned to first T-10Ss). In 1981, the Komsomolsk-based
plant produced another two fighters - the T10-10 and T10-11, thus making five flying prototypes of
the pre-series batch aircraft designated Su-27, Type T10-5 to discern them from future series-built
aircraft. By 1982, there have been produced nine initial-configuration aircraft and one for static tests
including those assembled at the Sukhoi plant.
Sukhoi completed the assembly of the first T-10S prototype designated T10-7 (a.k.a T10S-1) in early
1981 and in April 1981 it made its maiden flight piloted by test pilot V.S. Ilyushin. Also in 1981, the
static version (T10-8, or T10S-0) and the second flying prototype featuring new configuration were
built. From 1981 on, the Su-27 programme has been headed by Alexei Knyshev who has been the
aircraft's Chief Designer ever since. The T10-7 and T10-12 were used to determine main
performances of the new-configuration fighter, its stability and controllability, as well as to evaluate
the new powerplant featuring top-mounted accessory gearboxes. However, both aircraft were not
destined to fly long. On 3 September, 1981, the T-10-7 was lost due to a fuel system malfunction.
Vladimir Ilyushin had to punch out while the fighter with its tanks nearly empty hit the ground in a
fireball. On 23 December, 1981, the T10-12 crashed too due to entering uncontrolled spin while
performing deceleration from the max speed. The fore part of the air frame was destroyed resulting
in the aircraft hitting the ground. The test pilot, Aleksandr Komarov, died in the crash.
It proved to be impossible to determine all reasons for the crash. However, in 1983, Sukhoi's test
pilot Nikolai Sadovnikov found himself in a similar situation while flying one of the first series-
produced Su-27s - the T10-17. During the low-altitude high-speed level flight, Sadovnikov's fighter
suffered destruction of a leading edge slat and part of the wing panel with the debris damaging
vertical stabilisers. Thanks only to the high skills of the pilot (who was later awarded the title of Hero
of the Soviet Union and set quite a few world records), the sortie did not end up in a crash. Nikolai
Sadovnokov landed the damaged fighter with most of the wing panel missing and a tail clipped, thus
providing the developers with precious information to rake their brains over. It was found out later
that the
reason was a mistake in the calculation of the hinge moment emerging due to the deflection of the
adaptive leading edge flap in certain flight modes. Urgent measures were taken to rework the design,
including the reinforcement of the airframe and wings as well as the development of lesser-area
adaptive leading edge slats.
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