The history of Flanker

[Евгений Ожогин]

To whom it may concern.

Ivan the Bear
=Nothing per-r-rsonal, just business...=

By Andrei Fomin (AIR FLEET #6).

Su-
27: History

The Su-27, a Russian fourth-generation single-seat supersonic fighter, is
recognised all ver the globe as one of the best combat aircraft of the 20th
century. Due to its perfect flight performances and operational
characteristics, the fighter is rightfully popular with pilots and
technicians. Top piloting capabilities of the Su-27 fighter demonstrated
during multiple air shows around the world did not leave anyone indifferent.
The Su-27 is in the top lines of the aviation record tables of the
International Aircraft Federation. To the date, the Su-27 is a record-holder
of 27 world class flight achievements. The Su-27 is a forefather of a combat
aircraft family of various functionality, including the Su-27UB trainers,
Su-27K shipborne fighters (Su-33), Su-30 twin-seat interceptors, Su-30MK
twin-seat multirole fighters, Su-34 tactical bombers, Su-35, Su-37 and other
high-maneuverability multirole aircraft.
To achieve such impressive results, the developers of the fighter had to
follow a long and difficult way. Creation of the fighter in its modern
appearance with its current performances to guard the Russian aerospace as
well as that of the Su-27 buyers would not have been possible without
strenuous efforts made by many engineers, designers, scientists,
researchers, pilots and military test experts. The most significant input in
the Su-27 development has been made by teams of the Sukhoi Design Bureau and
Komsomolsk-on-Amur Aircraft Manufacturing Plant, developers of its power
plant, radar sight system and guided missile system from the Lyulka-Saturn
Company, Tikhomirov Instrumentation Research Institute and Vympel
State-owned Design Bureau respectively. In addition to the above
organisations, the Su-27 fighter development was performed by a variety of
other scientific and research institutions, including the TsAGI, CIAM,
GosNIIAS, CNII, a range of other design bureaus and research institutes that
designed and manufactured various systems for the Su-27 fighter. This
article is dedicated to some aspects of the Su-27 development history which
began 30 years ago.

Advanced Frontline Fighter Programme

A team of developers from the Kulon machine-building plant headed by Pavel
Osipovich Sukhoi initiated development of an advanced new-generation fighter
for the Soviet Air Force and Air Defense Forces' aviation in 1969. By the
mid-seventies, a general concept of the new fighter was formulated in
cooperation with a number of science and research institutions. This concept
provided for a high-manoeuvrability long-range fighter with a powerful
weapon system and perfect sighting and navigation system that would allow a
pilot participate efficiently in both long-range missile exchange and
dogfights. Basic flight performances of the new fighter were to be of top
class globally while a number of characteristics was to exceed those of its
American counterpart F-15 fighter the American leadership was reasonably
vesting their high hopes in. The design bureau was planning to introduce a
number of major innovations and solutions into the design of the new fighter
designated T-10.
In 1970 engineers of the Sukhoi design bureau developed the first version of
the fighter airframe incorporating the key features of the integrated
aerodynamic configuration. The aircraft was to have a lifting body featuring
a smooth coupling of the wing and fuselage, two turbojet engines located in
isolated belly-mounted engine nacelles and two vertical stabilisers. Such
and integrated design allowed a significant improvement of the fighter's
aerodynamics and provided for a more spacious interior to accommodate fuel
tanks and various equipment. For the fighter to achieve intended flight
performances within a wide range of altitudes and speeds, the new fighter's
wing had ogyval shape and a leading edge extension. According to the
developers, the leading edge extension was supposed to ensure required
high-lift characteristics during the aerodynamic focus shifting at
supersonic speeds and generate vortice increasing wing, tail unit and
control surface efficiency. At the same time, Sukhoi was engaged in
developing a traditional non-integrated version of the same fighter powered
by two adjacent engines located in the fuselage's aft part, side-mounted air
intakes and two vertical stabilisers. In 1972, both versions were submitted
to the Air Force board for examination and consideration. The board was to
assess proposals submitted by three aircraft design bureaus (Sukhoi, Mikoyan
and Yakovlev) regarding development of an advanced tactical fighter slated
for entering the service with the Soviet Air Force in the early eighties.
As a result of thorough evaluation and assessment of all versions submitted
for consideration, the proposals presented by Sukhoi and Mikoyan were
approved by the board for further development. The Su-27 (T-10) programme
was to be developed into a heavy multirole advanced tactical fighter, while
the MiG-29 programme was to produce a series-built light advanced tactical
fighter. Among the major combat objectives the both fighters were to meet,
there was the dogfight and medium-range aerial combat capability,
interception of aerial targets in the front and rear hemispheres both
against the sky and ground as well as the secondary task of ground target
destruction. The Su-27 which had a better fuel endurance, more weapons load
and more sophisticated navigation, self-defense and communication systems
was intended to operate independently within an air group deep behind the
enemy lines at an operational-tactical range of up to 250-300 km, while a
lighter and cheaper MiG-29 would operate only at ranges of up to 100-150 km
into the enemy-held territory. The Su-27's weapons control system was
expected to ensure successful countering the F-15 fighter, the most capable
fighter of that time available to a potential opponent, as well as
successful engagement when outnumbered by less capable but numerous fighters
(for instance, YF-17, YF-16 and J-6). Besides, the Su-27 fighter was
intended for entering the service with the Soviet Air Defence Forces after
its appropriate reequipping and rearmament.

Birth of the T-10

Proceeding from the updated and more specific requirements the client set
for the tactical fighter of the eighties, Sukhoi started in 1972 developing
a preliminary design of the T-10 fighter subsequently followed by the
conceptual design stage. During 1970-75, over 15 options of the fighter
configuration were given a consideration. Those configurations varied not
only in general approaches to the problem (integrated or classic
configuration) but differed in solutions suggested for individual problems
(engine and air intake positioning, landing gear design, type of the control
system, etc.). Finally, preferences were given to the aircraft design with
an integrated statically unstable configuration. The Su-27 was to become the
first Soviet unstable fighter with longitudinal in-flight balancing to be
provided by the fly-by-wire control system. Accepting the longitudinal
static instability concept (in other words, "electronic stability") promised
a lot of advantages: for aircraft to balance at a high angle of attack, the
leading edge flap's upward deflection was required with its lift being added
to the wing lift, which allowed significant improvement of the fighter lift
with minor increase in its drag. Due to the use of the integrated statically
unstable configuration, the Su-27 was to acquire exclusive manoeuvrability
allowing the fighter altitude changes unavailable to typical configuration
fighters and an increase in its range of up to 4,000 km without external
fuel tanks. There were no other series-produced fighter in the world with
similar performances.
The Su-27 fighter powerplant included two powerful and economical AL-31F
bypass turbofan engines producing thrust of 12,500 kg each. They were
developed by the Saturn Mechanical Plant headed by Arkhip Mikhailovich
Lyulka and supposed to ensure take-off thrust-to-weight ratio exceeding 1.
Low specific fuel consumption along with about eight tonnes of fuel stored
in internal tanks filling most of the airframe inner space was to ensure
required operational range of the fighter.
The Su-27 fighter weaponry which included 30 mm high-rate cannon, K-27
medium-range air-to-air missiles and K-73 or K-14 short-range missiles was
to be standardized with that of the MiG-29 light tactical fighter. The only
difference in armament was the warload carried: while the MiG-29 could house
only six missiles, including two K-27 missiles, the Su-27 was capable of
carrying eight, including four K-27s, as well as the K-27E improved
longer-range radar-homing and heat-seeking missiles. Development of the
missile weaponry for the Su-27 and MiG-29 was awarded to the Vympel and
Molniya mechanical plants (headed by chief designers Andrei Lyapin and Matus
Bisnovat, later by Gennady Sokolovsky and Gleb Lozino-Lozinsky). Finally,
the R-27 medium-range missile developed by the Vympel design bureau and the
R-73 close combat missile devloped by the Molniya mechanical plant was
selected for installation on both fighters (from 1982 on, further
improvement and development of new versions of the R-73 missile was carried
out by the Vympel design bureau).
An integrated weaponry control system of both fighters was substantially
standardised and, for the first time in the history of aviation, included
two complementing channels - a radar sighting system and an optoelectronic
sighting system, as well as a helmet-mounted sight. The sighting system
initially designed for the Su-27 fighter had a higher characteristics.
Development of the SUV-27 weapons control system was delegated to the NIIP
Institute which along with the NIIR Institute was part of the Phazotron
Research and Development Assocoation. The weapons control system development
was headed by Victor Grishin, Designer General. In addition to developing a
radar for the Su-27 fighter (Tamerlan Bekirbayev was appointed Chief
Designer of the radar development programme), the NNIP Institute was
involved in development of the computer and tasked with developing some
standardized units to be used in the MiG-29's SUV-29 weapons control system
as well (the NIIR Institute was appointed a head developer). An OLS-27
optics-based detection and ranging system combining an acquisition and
tracking IR locator and a laser rangefinder was developed by the
Moscow-based Geophysics Central Design Bureau headed by Chief Designer D.
Khorol.

The Maiden Flights

Conceptual and detailed design stages of the Su-27 fighter were completed in
1975-1976, and after issuance of required design documentation and drawings,
building of first prototypes was initiated at the Kulon plant.
Unfortunately, Pavel Sukhoi did not live long enough to see the fighter, he
died in 1975, and since then the design bureau named after him was led by
Yevgeny Ivanov. From 1976 on, the Su-27 programme was under immedeate
guidance of Chief Designer Mikhail Simonov. The first prototype designated
T10-1 was completed in early 1977. Due to the lack of the Al-31F turbofan
bypass engines, the prototype was equipped with two AL-21F-3AI engines - a
modified version of the series-production AL-21F-3A engine mounted on other
Sukhoi-developed fighters (Su-17, Su-24). After completion of the required
ground checks and run-ups, everything was ready for test flights and on 20
May, 1977 Vladimir Iliushin, Sukhoi's chief pilot, took the T10-1 off the
ground for its maiden flight. This first prototype was used to establish key
flight performances and determine stability and controllability of the new
fighter.
In 1978, the second prototype designated T10-2 was completed though life of
the second aircraft was not long. On 7 July, 1978, the fighter suffered a
mid-air accident resulting in death of test pilot Yevgeny Solovyov. The
crash was triggered by malfunction of the control system that occurred at a
supersonic speed. The black box recorder readings showed that the fighter
got into an unexplored resonant mode, which caused mid-air disintegration of
the aircraft. This was so fast that Yevgeny Solovyov, a merited test pilot
and Hero of the Soviet Union, did not have a chance to eject. The crash
analysis established the actual reasons for the tragedy and allowed to
introduce necessary changes into the fighter's design.
During 1978, preparations for preliminary production of the Su-27 were made
at the Gagarin machine-building plant situated in the Far Eastern city of
Komsomolsk-on-Amur. At the same time, the Sukhoi mechanical plant commenced
assembling another two prototypes of the Su-27. Unlike the first two
prototypes, those two fighters were to be powered by AL-31F engines. The new
powerplant had better weight characteristics being 500 kg lighter than the
previous engine, its thrust was 12 percent higher than that of the
predecessor with fuel consumption being better too. In comparison with the
AL-21F-3s, the AL-31F engines had smaller diameter and length while their
nozzles were accommodated with a secondary (bypass) duct control system. On
23 August, 1979, Vladimir Ilyushin took the T10-3 off for its maiden flight.
Two months later, the T10-4 equipped with a Mech radar for the first time
joined the flight test programme. At first, both aircraft were used for
in-flight engine testing. Then the T10-3 was remodeled to be further tested
on the Nitka training facility in the support of development of the Su-27
fighter shipborne version while the T10-4 was used for further refining of
the weapons control system.

The long way to series production

By the early 1980, as many as three prototypes (T10-1, T10-3 and T10-4) had
been taking part in the Su-27 testing programme with first pre-series
aircraft expected to join soon. It seemed that everything was in line with
the schedule and the new fighter would have been fielded in a couple years.
However, there were staunch objections against commencing series production
of the aircraft in the then airframe configuration made by the Siberian
aviation research institute's (SibNIA) aerodynamic experts and... Chief
Designer Mikhail Simonov himself. According to the SibNIA experts who had
been performing the bulk of aerodynamic research under the Su-27 programme,
a range of mistakes was made during the fighter's development stage.
Combination of the accepted wing planform and leading edge extensions
configuration caused premature vortex flow separation: the non-stationary
airflow around the wing would begin as early as at an eight-to-ten angle of
attack (AoA), which would ensue deterioration of the airframe's lifting
capability, buffeting and decrease in lateral stability. The tail unit
configuration designed for the T10 would fail to provide required
effectiveness of the longitudinal control surfaces, lateral and directional
stability devices. The SibNIA-held T-10's wind tunnel tests performed in
1975-76 indicated that there was a slim chance of developing a highly
manoevrable fighter without dealing first with the above problems.
The necessity of the Su-27 programme's radical reconsideration was looming
ahead. Such fundamental elements of the fighter's design as the form and
area of the wing, leading-edge extension configuration, horizontal and
vertical control surfaces' arrangement were have to be redesigned. Mikhail
Simonov was a staunch supporter of such an approach but the Aviation
Industry Ministry's brass had a different opinion. As a result, first Su-27s
were tested in their initial configuration. The flight tests of the T10-1
and T10-3 corroborated to the Siberian aerodynamics experts' doubts.
The T-10 testing also revealed the failure of the fighter's certain other
characteristics to match those of the performance specifications. First of
all, that was true for the range: the difference between the required and
actual ranges exceeded 20 percent. The Designer General reported to the
ministry that there were two main reasons for non-compliance with certain
requirements set in the performance specifications. Firstly, avionics
developers failed to meet the weight limits set out in the avionics
performance specifications. The avionics summary excessive weight comprised
a few hundred kilograms, which, naturally, led to the aircraft's overall
weight increase, hampered its manoeuvrability and reduced the range.
Secondly, the engine's specific fuel consumption ordered in the performance
specifications had not been achieved by the developer either. Truth be told,
the issue was settled later when the requirements to the engine's specific
fuel consumption were found to be a tall order which could not be met then.
In spite of the T-10's considerable deficiencies revealed during the
research and flight tests, Designer General Yevgeny Ivanov hoped,
nonetheless, for possibility to gradually hone that configuration through
minor design modifications, fuel capacity increase, etc. Otherwise, Mikhail
Simonov was pushing hard for radical aircraft reworking, since as early as
in 1976-77 a team of his subordinates in cooperation with the SibNIA
scientists developed on their own and later tested in the wind tunnel a new
configuration of the airframe devoid of the deficiencies which the previous
configuration had in abundance. Justice should be done to M.P. Simonov (who
went to work for the Aviation Industry Ministry in 1979 to return to Sukhoi
as Designer General in 1983) who managed to persuade the leadership to risk
radical change in the configuration of the fighter that had been already
undergoing tests by then. With the passage of time, this decision proved to
be right and led no matter what to building the aircraft that still - almost
two decades later - has been regarded as one of the best warplanes in the
world. Having commenced production of the Su-27 in its final configuration,
Sukhoi confirmed its reputation of a world leader of aviation industry in
line with its old tradition of never fielding mediocre aircraft.

From T-10 to T-10S

The fighter's version featuring the new configuration was designated T-10S
in the Sukhoi design bureau with its full-scale design work starting in
1979. Preliminary attempts to do away with the first T-10 version's glitches
and meet the performance specifications' requirements, conducted by the
design bureau and SibNIA (in the SibNIA the work was headed by Stanislav
Kashafutdinov, candidate of technical sciences) ensured setting the
guidelines for modifying the initial configuration. With the developing of
those guidelines, differences in design between the T-10S and T-10 became
even more obvious. In the end, it became clear that the designers would have
to develop an utterly different aircraft. According to Mikhail Simonov, the
only things the T-10S inherited from its T-10 predecessor were the main
landing gear's wheels and ejection seat. Only general principles set up for
the Su-27 by P.O. Sukhoi himself, such as the integrated airframe
configuration, statically unstable design with the aft centre of gravity,
fly-by-wire control system, mounting the engines in isolated engine nacelles
with belly-mounted air intakes, etc., were retained.
The T-10S had a new wing featuring a straight leading edge, aerodynamic
twist and reconfigured sharp leading edge extension. Ogyval wing tips lost
the ground to traditional permanent leading edge sweepback angle ones
featuring pylons for air-to-air missiles, which resulted, firstly, in
discarding flutter-preventing weights carried by the T-10 and, secondly, in
beefing up the number of missiles from eight to 10. The wing area grew from
59.4 sq.m to 62 sq.m with the wing high-lift devices changing drastically.
Ailerons and flaps were replaced with unified control devices - flaperons,
wing leading edges were fitted with flaps (the T-10 had no leading edge
high-lift devices), the automatic adaptive deflection mode for the flaperons
and leading edge flaps was ensured providing for the fighter's "polar curve
envelope" flight concept. The airframe's lifting characteristics were
enhanced through the use of the new wings and leading edge extensions while
maintaining the negative pitching moment at positive angles of attack and
extending significantly the range of operational angles of attack which
ensured satisfactory lateral stability and prevents buffeting.
To reduce drag, the fore part of the airframe was reworked: the airframe
cross section in front of and around the cockpit was decreased, canopy's
midsection was reduced while its rearward movement was enhanced, the
airframe's fore part cross section in the first fuel tanks area was
increased. Besides, airframe and spine fairing couplings were introduced
along its whole length, spine fairing's lateral cross section in the
aircrfame's midsection was reduced, central tail boom arrangement was
altered through addition of a cylindrical tip being an extension of the rear
integral tank. At the same time, the total internal fuel capacity increased
making up 9.4 tonnes. Making the shape of the engine nacelles more graceful
while reducing their weight was achieved through fitting the T-10 aircraft
with AL-31F engines featuring top-mounted aircraft and engine accessory
gearbox (the T10-3 and T-10-4 were powered by the AL-31F engines featuring
bottom-mounted accessory gearboxes). While preserving the general
arrangement of air intakes, the new aircraft had a new foreign-object damage
(FOD) system introduced for preventing FOD during taxiing, run and take-off
trough the use of extendable screens in the air intakes' ducts.
Supplementary air inlet ramps were added to the lower surface of the air
intakes.
To enhance directional and lateral stability through raising efficiency of
the corresponding control surfaces, the empennage underwent substantial
redesign. The two vertical stabilisers were set wide apart at the reinforced
booms on both sides of the engine nacelles with an optimum position for the
stabilisers chosen in the vortex system generated by the leading edge
extensions and wing panels. This resulted in considerable increase in
directional stability and controllability of the fighter at high angles of
attack and slipping. Also, the T-10S was fitted with ventral fins increasing
its directional stability and anti-spin performances. The air brakes - the
main landing gear doors featured by the earlier version and discarded due to
horizontal control surface flutter caused by their extending - were ousted
by the large air brake mounted behind the cockpit.
The landing gear was reworked too: main struts were provided with "slant"
main pivot, which made it possible to retract the gear into the wing centre
section thus requiring no folding struts to be installed. This also allowed
to reduce the lifting body's cross section in the area of the landing gear
wells. The nose gear strut was reinforced and moved aft, which enabled
better taxiing and decrease a chance of foreign object damage during
taxiing, run and take-off. In general, the fighter's configuration
modification provided the lifting body midsection reduction by 15 percent,
which led to reduction of drag by 18-20 percent in the subsonic and
supersonic speed range. This combined with an increase in the airframe's
lifting characteristics and lateral and directional stability and
controllability in all three planes in all flight modes provided the
aircraft with superior manoeuvrability with special emphasis put on high
angles of attack and meet the requirements set for the fighter's range.

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 reequip
production lines for manufacturing the new-configuration aircraft. The first
aircraft of the pre-production batch designated T10-5 was finished in July
1980 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 maden flight piloted by test pilot V.S.
Ilyushin. Also in 1981, a static version (T10-8, or T10S-0) and the second
flying prototype featuring new configuration were built. From 1981 on, the
Su-27 programme had been headed by Alexei Knyshev who still is the
aircraft's Chief Designer. 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 Komarof, died in the crash.
It proved to be impossible to determine all reasons for that 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 flap 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
another 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 calculation of hinge moment emerging due to
deflection of the adaptive leading edge flap in certain modes of flight.
Urgent measures were taken to rework the design, including airframe and wing
reinforcement as well as developing lesser-area adaptive leading edge flaps.
In 1982, the new fighter's testing programme was joined by first
new-configuration aircraft manufactured in Komsomolsk-on-Amur, namely: the
T10-15 (later converted into the P-42 record-maker), T10-16 and
above-mentioned T10-17. Flying out of the first series-built Su-27 took
place on 2 June, 1982. The next year, Komsomolsk-based plant delivered
another nine fighters with the work on the pre-series batch of the T10-5
being in full swing too. The T10-5 were used to test the weapons control
system. In May 1982, due to the computer's unreliability and the Mech
(Sword) radar antenna's unacceptable characteristics, a decision was taken
to fit the Su-27 with a new computer derived from the Ts100 digital computer
developed by the NIITSEVT institute as well as with a radar antenna to be
derived from the MiG-29's Rubin (Ruby) radar. In spite of another sharp
twist of the fighter's fate, the Su-27 featuring a redesigned weapons
control system began flight testing as early as in late 1982, while in late
1983 it was submitted for official testing.
In 1984, first Su-27s were fielded with the Soviet Air Force followed by
almost a hundred more fighter having been produced by the end of the next
year and Air Force and Air Defence Forces's units mass transition to the new
fighter. The first line unit to receive the Su-27 was a Far East-based AD
fighter regiment. The Komsomolsk-based plant's proximity ensured expeditious
resolution of problems cropping up at the initial stage of transition to the
Su-27. In line with traditions, "breaking in" new aircraft, working out
recommendations on their operation and combat employment as well as
retraining line unit personnel was performed at the Lipetsk-based Combat
Employment and Training Centre (Air Force) and Savasleika-based Combat
Employment and Training Centre (AD Forces).
The Su-27's joint official tests were accomplished in 1985 with their
results testifying to the development of a superb fighter second-to-none in
manoeuvrability, range and combat effectiveness. However, some elements of
the avionics suite, first of all, the ECM system, required additional
testing which was conducted under a special programme upon completion of the
joint official tests. After the whole avionics suite had been fine-tuned,
the Su-27 entered the Soviet Air Force and Air Defence Forces' inventory in
accordance with the USSR Council of Ministers' decree of 23 August, 1990.