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The Birth of the Su-27 Flanker Family

Issue 102

In 1968, the United States started a new aircraft project called the F-X (Fighter Experimental). The requirements of the F-X project were 40,000 lb. MTOW, a maximum speed of 2.5 Mach, and a high thrust-to-weight ratio. In 1969, McDonnell-Douglas's F-15 was selected. The same year, the Soviet Ministry of Defense prepared the General Operational Requirement for a new aircraft initiating the project, which would be the Soviet's response to the F-15. The new fighter would be single-seated, highly maneuverable (+9.0 max G-load), and has a power-to-weight ratio of 1.1 or better. It would carry medium and short-range air-to-air missiles, a powerful fire control radar, and a 30mm autocannon for close-air combat. Another requirement of the project was for the new aircraft to be the standard fighter of both the Soviet Air Force (Voenno-Vozdushnye Sily–VVS) and Air Defense Forces (Voyska Protivovozdushnaya Oborona–PVO). While the VVS wanted a tactical fighter, the PVO needed an interceptor aircraft. VVS wanted the aircraft to perform Combat Air Patrols away from its home base for an extended time, while PVO wanted it to reach the required altitude and interception zone in the required time. To meet these needs, Sukhoi OKB (Opytnoye Konstruktorskoye Buro - Experimental Design Bureau) launched the T-10 project. 

The T-10 prototype had the following central design features:

A blended wing body (BWB) to form a single lifting body with no clear dividing line,

Wings with LERX (Leading-edge root extension),

Low-mounted stabilators,

Twin vertical stabilizers,

Widely spaced engine nacelles to provide additional lifting surface. 

As a result of these design features, the aircraft's fuselage grew larger, gaining more space for fuel and avionics, its structural strength and stiffness were increased thanks to LERX, and it achieved increased lift and significantly reduced drag thanks to the BWB, and better airflow was provided to the engines due to the location of the intakes. 

Production of the first prototype (T10-1) started on December 26, 1976 and made its maiden flight on May 20, 1977. T10-1 was powered by a pair of AL-21F-2AI turbojet engines. The Su-27 program experienced its first serious problem on July 7, 1978, when the second prototype (T10-2) crashed on its 13th flight. After an unintentional high positive G maneuver during the flight due to shortcomings in the FBW (Fly-By-Wire) system, the pilot tried to correct the situation by pushing the stick forward, causing the aircraft to pull a high negative G. However, when he pulled the lever back, the plane could not withstand the high G and broke-up in mid-air, killing the test pilot Yevgeny Solovyov. As the first prototype (T10-1) had also experienced a similar problem the day before the accident, the FBW (Fly-By-Wire) system was later upgraded, and corrections were made. As a result of the tests performed with more than ten prototypes, Sukhoi found it impossible to meet the initially required criteria. In their current state, the prototype aircraft started to flutter when the angle-of-attack exceeded 10°, and vibrations doubled when it exceeded 14°, making it impossible to fly. The newly developed AL-31F turbofan engine was very powerful, but its fuel consumption rate was higher than planned, requiring the aircraft's redesign to carry more fuel. Also, anti-flutter weights had to be added to solve the high AOA vibration problem. However, the T10 was also unable to meet the desired power-to-weight ratio, and the aircraft had to be lightened. Thus, the designers then went back to the drawing board. After the necessary changes and thousands of hours in the wind tunnel, the T10/13 (later named T-10S) emerged. Now the plane had those beautiful Su-27 lines that we know and love visually. Its wingspan was increased, and pylons were attached to the wingtips, which replaced the anti-flutter weights. Furthermore, the plane was equipped with a single air brake on top instead of two air brakes under the fuselage. 

The Su-27 achieved Initial Operational Capability (IOC) in the summer of 1985 and began to be called Flanker-B by NATO. Later, the tandem-seat trainer model, Su-27UB, and the two-seat supermaneuverable multi-role fighter, Su-30 series, also started to be produced.

 

The New Generation of the Family

 Su-35S “Flanker-E”

Having started its 5th generation fighter development studies in the 1990s, Sukhoi OKB introduced the experimental S-37 (Su-47 Berkut) technology demonstrator prototype, which is considered the predecessor of the PAK FA program (Perspektivny Aviatsionny Kompleks Frontovoy Aviatsii - Future Tactical Aviation Aircraft System). The Russian Air Force issued a request for proposal (RFP) in 1998 and later selected the Sukhoi Design Bureau in 2002 to develop the full-size twin-engine T-50 prototype. The development of the T-50 (now Su-57) was started under the PAK FA program in 2005. On the other hand, to upgrade Russia's aging fleet of Su-27 aircraft and bridge the gap between the newer and older previous generation fighters, in 2002 Sukhoi and KnAAPO revealed the modified Su-27SM aircraft with integrated glass cockpits and improved weapons-control systems. Following this project, Sukhoi proceeded with a second modernization program, known as T-10BM, in December 2003 to serve as an interim solution until the introduction of the Su-57 fifth-generation fighter. Sukhoi presented the new plane as a 4++ generation aircraft. Actually, the studies on the first generation Su-35 (Su-27M/T-10M) were started in the 1990s by the KnAAPO (Komsomolsk-on-Amur Aircraft Production Association) plant; however, it did not receive any orders and remained as a technology demonstrator. Sukhoi initially named the new aircraft Su-35BM but later renamed to only Su-35. The aircraft made its first flight in February 2008. Although it was designed for export, the Russian Air Force became the launch customer in 2009, with the production version designated Su-35S. The most important structural difference between the new Su-35 is that it does not have an air brake on top of the fuselage like the Su-27. Instead, the rudders provide this feature; both rudders open outwards at the same time and create air resistance. With the elimination of the air brake, the hydraulic system was simplified, and the capacity of the internal fuel tank (number 1) was increased. With the redesigned body, its service life was extended to 6,000 hours/30 years. To reduce the radar cross-section of ​​the aircraft, radar absorbing material was used at the leading edges of wings, tails, and air inlets. For the same purpose, the canopy was covered with a special coating. Another important addition was the thrust-vectoring AL-41F1S (117S) turbofan engine. The new engine produces 16% more power than the AL-31F, and its service life also increased from 2,000 hours to 4,000 hours. The AL-41F1S has the AL-100 nozzle with 3D thrust vectoring capability, which can move +/- 20° in all directions. Thanks to this engine, the Su-35 also gained super cruise capability (achieving supersonic speed without engaging afterburners), becoming the first Russian aircraft with this feature. Furthermore, the Aerosila TA14-130-35 gas-turbine auxiliary power unit (APU) was used for the first time in a single-seat Flanker.

A new quadruplex fly-by-wire control system called KSU-35 has been developed for the Su-35S. Thanks to this system and 3D thrust-vectoring nozzles, the aircraft achieved supermaneuvrability. With the upgraded fuel system, the fuel capacity increased from 9,400 kg to 11,500 kg. The aircraft also incorporates an L-shaped retractable inflight refueling probe on the left side of the nose.

The aircraft is equipped with a completely new avionics suite. Su-35S uses an N035 Irbis-E X-Band Passive Electronically Scanned Array (PESA) fire control radar. The new radar has more than twice the bandwidth size of the older generation N011M BARS, and its scanning angle was increased from 70° to 120°. The radar can track 30 targets in Track While Scan (TWS) mode and engage two of them simultaneously with semi-active radar homing (R27 Series) and eight of them with active radar homing (R77 Series) air-to-air missiles. The Irbis-E can detect targets with a 3 m2 radar cross-section from 400 km and targets with ​​a 0.01 m2 radar cross-section such as cruise missiles from 90 km. In air-to-ground mode, it can track four targets and engage two of them with guide missiles. Thanks to synthetic aperture mode, the radar can also be used for radar mapping. N035 can track air targets with the TWS feature while tracking a ground target. Another feature of the Su-35S is the N036B-1-01 L-Band AESA antennas embedded in the wing’s leading-edge extensions for increased angular coverage. These allow the S-35S to detect low observable (LO/Stealth) targets and are also used for identification of friend-or-foe (IFF) and electronic warfare purposes.

The Su-35S uses the OLS-35 IRST/LR (Infrared Search and Track/Laser Rangefinder) system to identify and track targets passively. It can detect large air targets from 35 km from the front and 90 km from the rear. The laser range finder can track/measure air targets from 20 km and ground targets from 30 km.

The cockpit features two 15-inch MFI-35 full-color liquid crystal MFDs and IKSh-1 wide-angle holographic HUD (Head-Up Display). It is considered the most ergonomic Russian cockpit ever made. The symbology used with the cockpit design is the same as that of the Su-57. In this way, it will be easier for pilots to switch from Su-35 to Su-57. Su-35S uses S-103 radio link for communication and S-108 for data-link connection.

Su-35S's ECM/ESM (Electronic Counter Measures/Electronic Support Measures) capability consists of two main elements; L150-35 RHAWS (Radar Homing and Warning System) and SAP-518 (L175M) ECM pods mounted on the wingtips. RHAWS antennas are located on the wing leading edge flaps and on both sides of the drag chute housing in the tail cone. Operating in the 5 GHz to 18 GHz frequency bands, the SAP-518 ECM Pod can be used against the search and engagement radars of air defense systems, as well as the fire control radars of hostile aircraft and radar-guided missiles. Other elements of the self-protection system are MAWS (Missile Attack Warning System) and LWR (Laser Warning Receiver) systems which allow the Su-35S to detect incoming missiles from long distances and take measures (Chaff/Flare) against them.

It can carry a total of 8,000 kg of munitions in 12 hardpoints, including medium-range R-27ER/ER1, R-27ET/ET1, R-77, and short-range R-73E air-to-air missiles, Kh-27, Kh-29, Kh-31, Kh-35, Kh-38, and Kh-59 air-to-ground/cruise missiles, as well as KAB-500 and KAB-1500 series smart bombs, unguided bombs (AB-100, 250, and 500) and unguided rockets (S-8 and S-13).

The Su-35 achieved Initial Operational Capability (IOC) in January 2014. When a Russian Air Force Su-24M was shot down by the Turkish Air Force for violating Turkish airspace on November 24, 2015, four Su-35S were sent to Syria on January 30, 2016, following the tension between the two countries. These planes started escorting the other aircraft that were conducting bombing runs. During these missions, the most surprising element was that the Su-35s flew with the older R-27s instead of the newer R-77s. It is believed that the Russians could not fully solve all the problems with the R-77 and preferred to fly with the older missiles to not take risks in a possible conflict. As Syria became the ideal testing ground for Russia, the Operational Test and Evaluation of new equipment (Su-30SM, Su-34, and Su-35S) and munitions started to be carried out in Syria.

Russia proposed the Su-35S, which was also purchased by China and Egypt, to Turkey as a new generation fighter after Turkey's suspension from the F-35 project. In this context, a Su-35S aircraft participated in Teknofest 2019 and performed an aerobatic show in Istanbul.

The Su-35S is a highly maneuverable aircraft thanks to its superior aerodynamic shape and powerful engines. Thus, it is considered an extremely deadly opponent against all aircraft types in air combat, especially at close range. With its super cruise capability, powerful radar, electronic warfare systems, and long-range missiles, the Su-35S has serious BVR (Beyond-Visual-Range) capability. With these features, it can easily surpass all existing 4th generation aircraft.