The Su-27 was designed by Sukhoi OKB as a heavy fighter for the Soviet Air Force and National Air
Defense Forces to regain air superiority over the F-15 Eagle operated by the US Air Force.
In fact, the requirements were based on the performance
of the F-15 adding ten percent. The Sukhoi design fulfilled the requirements and beyond.
The Su-27 is often proclaimed the best and most successful Russian fighter of the Cold War era.
After the end of the Cold War and the USSR, the Sukhoi OKB (often in cooperation with
the KnAAPO plant) developed various advanced variants aimed at prospective foreign customers.
The aircraft was marketed at international air shows, putting up superb aerobatic displays.
The aircraft performance both on paper and in aerobatic displays has stunned many enthusiasts
and experts alike all over the world. Also, the Flanker has proven its air superiority
in combat during several African wars. The Su-27 and its derivatives are today
some of the most popular fighters to be discussed by both aviation enthusiasts and experts.
Designs
The main feature for the success of the Su-27 design is its aerodynamic configuration,
known as the 'integrated aerodynamic concept' by its designers. This configuration is one
with an extremely blended wing and fuselage. The low-aspect-ratio trapezoidal mid-wing is fitted
with large leading-edge root extensions (LERX) and blends into the fuselage creating a single
lifting body. The aircraft has near-zero static stability and thus requires a fly-by-wire system.
The SDU-10 pitch-only fly-by-wire system controls the pitch of the aircraft to
ensure stability and controllability for the pilot, increase aerodynamic performance,
limit overload and angle of attack when needed, and decrease the airframe aerodynamic load.
Two AL-31F after-burning turbofans are placed in separate, widely spaced engine nacelles
that are mounted under the lifting body. The air intakes are fitted with variable ramps.
The Su-27 has twin vertical fins fitted on the outer sides of the fuselage and twin central
fins underneath. The airbrake is placed in the center of the midsection of the aircraft behind
the cockpit. The tricycle landing gear of Su-27 and Su-27UB has a single wheel on each strut.
The nose wheel is fitted with a mudguard to protect against foreign object damage (FOD).
Systems & Avionics
The basic Su-27 is fitted with the SUV-27 fire control system,
which incorporates the RLPK-27 radar sighting system, OEPS-27 electro-optical sighting system,
SEI-31 integrated indication system, IFF interrogator, and built-in test system.
The fire control system is integrated with the PNK-10 flight navigation system,
radio command link, IFF system, data transmission equipment, and EW self-defense system.
The RLPK-27 system is controlled by the Ts-100 digital computer and includes the N001
pulse-Doppler lookdown-capable radar with a range of 80–100 km in the front hemisphere and 30–40
km in the rear hemisphere for a fighter-sized target. It can simultaneously track up to ten
aerial targets in track-while-scan mode and provide interception of the top priority target.
The OEPS-27 electro-optical sighting system consists of the OLS-27 infrared/laser
search-and-track system (IRST) and the Shchel-3UM helmet-mounted target designator and is controlled
by the Ts-100 digital computer. The OLS-27 sensor is placed forward of the cockpit canopy
in the center. The system acquires and tracks aerial targets by their thermal signatures. The
helmet-mounted sight and the laser range finder of the IRST can also be used to visually acquire
and determine coordinates of air and surface targets. The SEI-31 integrated indication system
provides flight, navigation, and sighting data on the ILS-31 head-up display (HUD) and CRT. The EW
self-defense systems provide a warning to the crew when illuminated by enemy radar and employ both
passive and active countermeasures. The aircraft is equipped with the SPO-15 Beryoza RWR and APP-50
IR decoy dispenser. Chaff dispensers are placed in the tail section between the engine nozzles.
In addition, the aircraft can carry the Sorbtsiya active ECM pods on its wingtips.
Cockpit
The cockpit is fitted with the K-36DM Series 2 ejection seat. The seat-back is being inclined
at an angle of 17 degrees. In the two-seat Su-27UB version, the seats are placed in tandem with the
rear seat being elevated to ensure good forward vision. The basic Su-27 cockpit layout consists
of analog instruments, HUD, and CRT display to display data from radar and electro-optical sight
(IRST). On both sides of the HUD control panel, there are sensors for the helmet-mounted target
designator system. On the right side below the CRT display, the RWR indicator is placed.
Weapons
The Su-27 is fitted with one GSh-301 automatic single-barrel 30mm cannon
fitted inside the starboard wing LERX. It can be armed with up to 150 high explosive incendiary
or armor-piercing tracer rounds. The basic Su-27's primary armament consists of up to six R-27R/ER
semi-active radar homers or R-27T/ET heat-seeking homer medium-range air-to-air missiles,
as well as four R-73 IR agile all-aspect short-range air-to-air missiles. The basic Su-27
has only a limited air-to-surface capability consisting of only unguided bombs and rockets.
Upgrading the Russian Air Force SU-27 Fleet
The Russian Air Force received its first batch of upgraded Su-27s in 2006. The air force seems to
have settled for the mid-life upgrade offered by KnAAPO based on the Su-30MK2, which brings
the aircraft up to Su-27SM standard. The Su-27SM is equipped with an upgraded fire control system
including the improved N001V radar with phased array antenna, which offers improved performance
and air-to-surface mode. The new system enables the use of the RVV-AE (R-77) medium-range
air-to-air missile and a wide selection of guided air-to-surface bombs and missiles. Another heavily
updated feature is the cockpit, which is upgraded with three MFD, a new HUD, a satellite receiver,
and a new communications set. The aircraft's self-defense suite has also been upgraded.
The Russian Air Force plans to upgrade its entire fleet to Su-27SM standard,
but the exact number of aircraft involved remains unclear.
The Su-27SM is based on earlier proposed upgrades for the Su-27SK export version. The Su-27SMK as it
is designated has seen two attempts, with at the basis a different radar system (N001M and N001VEP
respectively). China was seen as the premier customer for an upgrade package.
However, China opted to expand its Flanker fleet with multi-role Su-30MKK and Su-30MKK2
instead of upgrading its Su-27SK and J-11 single-seaters. Instead,
China planned an indigenous upgrade for its J-11s. Other clients also preferred two-seat Su-30MK/MK2.
From 2002 onwards, Sukhoi and KnAAPO developed a new deeply modernized single-seat Su-27 derivative
known as Su-27BM. Designated Su-35, it will be offered for new export orders,
replacing the previously offered Su-35, which was based on the Su-27M and offered in the 1990s.
Based on the Su-35, the Su-27SM2 upgrade is on offer to the Russian
Air Force for the second phase of its Su-27 mid-life upgrade program.
The Su-27SM2 upgrade will give Russia's existing Su-27s a similar avionics and weapons
suite as offered on the Su-35. The Russian Air Force has expressed interest in the Su-35, but it
remains to be seen whether this will include new airframes or be limited to the Su-27SM2 upgrade.