The work on evolving operational
requirements for an attack aircraft went further on for quite some time; not
until 1972 was the customer, at last, in a position to present their final version.
In accordance with the new specifications issued by the WS it was necessary to
develop a subsonic attack aircraft possessing a maximum attainable
survivability, high manoeuvrability, and an ability to be committed to action
at the shortest possible notice when required by ground troops.
Although the IL-42 project had been
rejected, the Ilyushin OKB, at its own initiative, continued working on the
concept of a subsonic armoured attack aircraft intended for supporting ground
troops on the battlefield. As a result, the IL-42 project was considerably
reworked.
An analysis conducted with due regard to
the peculiarities of combat aviation activities in the Arab-Israeli conflicts
of those years showed that the two-seat IL-40 and IL-42 aircraft would represent
the closest possible response to novel elements of the new military doctrine
which gave up the use of mass destruction weapons on the battlefield and marked
a transition to the use of precision-guided munitions. This was accompanied by
a further increase of the pilot's workload, especially at low altitudes; in the
opinion of the OKB's specialists, this workload was already in excess of what
was humanly possible. This was corroborated also by the assessment of the
combat efficiency of foreign single-seat attack aircraft which proved to be
some 25% lower than expected. On the other hand, having a second crew member
enabled the attack aircraft to spend more time attacking the target. The pilot
sought out the target and attacked it on a head-on course, the gunner/ operator
continued to bring his gun to bear on the target while the aircraft was leaving
the scene; at the same time he protected the aircraft from being hit by an
artillery shell or rocket launched in pursuit of the aircraft. There was one
more point to be taken into account: the progress of avionics could enable the
gunner/operator, despite his aft-facing position, to conduct observation of the
battlefield together with the pilot. Using information from his display, the
gunner/ operator could aim and launch rocket weapons against ground targets
relieving the pilot from this operation and enabling him to concentrate on
piloting, especially at extremely low altitudes, and on firing the guns. The
participation of the gunner/operator in the attack made it possible to hit not one,
but several targets during one pass, which served still further to enhance the
attack aircraft's combat efficiency.
The new version of the project for a close
support aircraft which was being developed as a 'private venture' under the
guidance of Ghenrikh V. Novozhilov (who became General Designer of the OKS upon
retirement of S. V. Ilyushin in 1970) received the designation IL-102. In
comparison with the IL-42 it featured the following changes:
- cockpit visibility was improved;
- engines with thrust-vectoring nozzles
were installed;
- the airframe incorporated a system of
autonomous maintenance means which ensured the attack aircraft's high mobility
in conditions of front-line deployment at short unprepared airstrips with a
bearing strength of 5 kg/cm2 (71 Ib/sq in).
In designing the IL-102, special attention
was paid to precluding the possibility of a situation in which firing the
onboard weapons would affect engine operation, the aircraft's structure and the
view from the pilot's cockpit. The mutual location of the cannon installation,
the air intakes and the cockpit, dictated by these considerations, determined
the general layout.
The aircraft was configured as a twin-engined
low-wing monoplane with thick swept wings and dihedral tail planes mounted on
top of the rear fuselage. The powerplant comprised two Klimov (Izotov) RD-331
turbofans (I stands for izmeneniye vektora tyagi vniz - downward thrust
vectoring) with a take-off rating of 5,200 kg (11,466Ib) each. The RD-331 was a
non-afterburning version of the production RD-33 engine developed by the Klimov
OKS and manufactured in series for the MiG-29 fighter. The engines flanked the
centre fuselage, breathing through individual air intakes which protruded
slightly ahead of the wing leading edge. The nozzles could be deflected
downwards both for take-off and in level flight, thus improving the aircraft's
manoeuvrability and field performance considerably.
The thick swept wings developed for the
IL-102 under the guidance of G. G. Muravyov jointly with TsAGI featured a new
aerodynamic configuration. The wings enabled the aircraft to attain a speed of
950-1,000 km/h (559-621 mph) at sea level while keeping the minimum control
speed down to a mere 250 km/h (155 mph). Such a wide range of speed
characteristics enabled the crew to arrive quickly at the battle area in
response to any request from ground forces. It could fly at an altitude of
30-100 m (100-330 ft) under conditions of ground fire, low visibility and
uneven terrain, make a stealthy approach to the target and reliably identify
it. The wing parameters in combination with the thrust/weight ratio, coupled
with the availability of airbrakes, made the aircraft capable of performing a
banking turn with a radius of only 400 m (1,310 ft); this enabled the pilot to
make a second pass without losing sight of the target.
In comparison with the first prototype
IL-40, the IL-102's maximum Mach number was reduced from 0.9 to 0.82, while the
operational g-Ioad was reduced from 5.45 to 5.0. At the same time more
effective airbrakes were fitted. The first prototype IL-40 needed one minute to
decelerate from maximum speed to half of this value, whereas the IL-102 used
only 45 seconds to bring the speed down from maximum to minimum.
The moderate wing loading, efficient
high-lift devices, high thrust/weight ratio and reworked landing gear featuring
twin wheels on each main unit, coupled with the thrust-vectoring engines,
enabled the IL-102 to operate from ad hoc dirt strips in the frontline area.
The IL-102's design characteristics included a take-off run of a mere 250-300 m
(820-980 ft), while the landing run with the use of reverse thrust was expected
to be 300-350 m (980-1,150 ft).
As distinct from Sukhoi's T-8 project, the
designers of the IL-102 decided to relinquish the concept of an armour shell
protecting all the vital components of the aircraft. Instead, a layout was
evolved in which the vital structural elements and units were located in such a
way as to provide mutual shielding. Armour plating was used only for the
separate crew cockpits fitted with zero-zero ejection seats developed by NPP
Zvezda (a standard K-36L for the pilot and a K-36L-102 for the gunner). Also,
the engines and the fuel system were provided with partial armour plating. The
fuel tanks had no armour protection - from the front and from the rear they
were protected by armoured crew cockpits, while from below and from the sides
they were shielded by the cannon installation and the engines. In addition, to
prevent a fire and explosion, should a tank be pierced by a bullet, the empty
space in the tank was filled with explosion-suppression polyurethane foam (as
was the case with the Sukhoi T-8, too).
The IL-102 possessed a very potent
complement of offensive armament. There were no fewer than 17 hardpoints for
the carriage of external stores and chaff/flare dispensers; this enabled the
aircraft to use a wide range of weapons. The aircraft's special feature was the
versatile armament bays in the fuselage and the wings. The fuselage bay housed
the easily detachable NU-102-1 cannon mount which could be deflected to an
angle of 150 downwards; it carried the GSh-30 twin 30-mm cannon which had a
1,500-rpm rate of fire.
Eventually the NU-102-1 could also be
equipped with a single-barrelled 30-mm (1.18 calibre) or 45-mm (1.77 calibre)
aircraft cannon firing shaped-charge rounds intended for destroying heavy
tanks. Gun pods housing 12.7-mm, 23-mm and 30-mm weapons could be carried
externally under the wings. Bombs weighing up to 250 kg (551 lb) apiece could
be carried in six wing bomb bays. The use of internal stowage of the bombs
considerably enhanced the aircraft's performance and reduced its radar
signature. Six underwing and two under fuselage versatile weapons racks could
be used for the carriage of air-to-air and air-to- surface missiles, unguided
rocket pods, bombs, gun pods and other weapons.
Additionally, two attachment points for the
carriage of defensive armament were placed at the downturned wingtips. Mounted
here were chaff/flare dispensers and radar warning receiver antennas. All this
equipment provided passive protection from ground-to-air missiles with IR and
radar homing warheads. Active protection from the rear hemisphere was provided
by the tail barbette with a twin-barrel 23-mm cannon remote-controlled by the
gunner/operator.
The availability of versatile internal
weapon bays incorporated into the fuselage and the wings, and of the external
racks, made it possible to modernise the armament complement without
introducing changes into the airframe. The weight of the IL-102's rocket and
bomb armament totalled 7,200 kg (15,880 Ib).
The aircraft was fitted with special
equipment enabling it to operate efficiently under all weather conditions in
the daytime and at night, making use of the full complement of its armament.
One more special feature of the IL-102 was
its ability to operate autonomously and at the shortest possible notice when
called into action by the ground forces. Engine starting was catered for by jet
fuel starters mounted on each of them; there was a drive from the jet fuel
starter to the on board generator and the hydraulic pump which made it possible
to check the units and systems without making use of ground sources of electric
power supply. Inbuilt onboard mechanisms for lifting and taking down the
weapons and the possibility to lower the fuselage cannon mount for maintenance
made it possible to prepare the aircraft for the next sortie very quickly. The
IL-102 and its systems were notable for their utmost simplicity in manufacture
and maintenance, earning for the aircraft the nickname 'a soldier aircraft'.
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