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Sukhoi S-32/37 Berkut/Golden Eagle Stealth Fighter

Sukhoi 37

Sukhoi 37

Dimesions (mm): -
-wingspan: 16.7
-lenght overall: 22.6
-heigth overall: 6,4
Maximum speed (km/h): -
-at height: 2500
-at S/L: 1400
Weight (kg): empty: 24'000
Engine: D30F6/AL-31FU
Thrust: 2 x 15'500 kg
Service ceiling: 18000 m
Range (km): 3300
Number of hardpoints: 14: 2 wingtip; 6-8 underwing; 6-4 conformal underfus. + GSh-301
Air-to-air missiles: KS-172 (AA, range=400km), RVV-AE, R-77; R-77PD; R-73; K-74
Air-to-Surface: X-29T; X-29L; X-59M; X-31P/A; KAB-500/1500

THE S-37 IS A BREAKTHROUGH TO PERFECTION

     The local and foreign press have published articles reporting that in the S-37 Russia has created a "multi-purpose fighter of the fifth generation, combining features of a supersonic super maneuverable aircraft undetectable by radar and infra-red surveillance devices." 

S-37

  Current economic hardships in Russia hamper development of its industry, primarily the hi-tech sectors. However, despite these hardships, Russia retains its posture among the world's leading aircraft manufacturers, owing to the vast potential of the aircraft building industry gained in recent decades. A shining example of this potential was the development by the Sukhoi Experimental Design Bureau (leader of Russia's aircraft building industry) of the S-37, an essentially new aircraft that made its maiden flight on September 25, 1997.

The S-37 is a demonstration-experimental aircraft intended to try out new key technological solutions in aerodynamics, flight control systems, and aircraft flight dynamics. The salient feature of this aircraft is its forward-swept wing (FSW) configuration. The choice of this configuration is the result of the Bureau’s efforts to find new approaches to enhancing aircraft aerodynamics, primarily maneuverability.

The concept of the forward-swept wing configuration has been known since the early 1940s. The JU-287 bomber prototype built in Germany in 1944 made its maiden flight in February 1945. Two fighters, dubbed North American RD-1410 (1946) and Conver XB-53 (1948), were developed in the USA.
   
The HFB-300, dubbed Hansa, administrative airplane (1963) and RFB, dubbed Dentreiner, were created in Western Germany.

The best theoretical research results regarding aircraft with a FSW configuration were obtained in the USA during development and flight tests of the X-29A experimental aircraft created by the Grumman company. 

During the tests held from 1984 to 1989, two X-29A experimental aircraft made several hundred flights, attained a speed of 1.6 Mach, altitude of over 15,000 meters and g-load of 6.4. However, the tests were abandoned because, as some foreign experts maintain, at that time the scientific and engineering foundation to solve the problems of divergence or wing instability that were inherent to aircraft with FSW were not available. The wing's instability can cause its mechanical deformation at high flight speeds and result in its disintegration.

The creation of the experimental S-37 aircraft was based on the creative use of experience gained by the world's aircraft building industries to develop aircraft with a forward-swept wing and effective introduction of advanced technologies in the field of aerodynamics, flight control systems, and construction materials. The potential superiorities of the S-37 aircraft compared to that of aircraft with a straight-wing configuration were provided by higher lifting capability of forward-swept wing due to more favorable flow-around and lower aerodynamic drag, especially at supersonic flight speeds. This provides for better aircraft controllability at low flight speeds, good anti-spin characteristics, reduced stall and landing speeds, and an increased flight range. 

The objective of the flight tests of the S-37 aircraft is to prove in practice its anticipated superiorities with a FSW in order to employ them in a new combat aircraft. If the test results are a success, then the aforementioned superiorities, in conjunction with the engineering innovations previously employed by the Sukhoi Bureau in aircraft of Su-27 type (thrust-vectoring engine, integrated system of aircraft and engine control, etc.), will considerably expand the spatial and time range of maneuverability and simplify piloting the aircraft. As a result, the currently "exotic" aerobatic stunts like "Pugachev's cobra," "Frolov's chuckra" and other aerobatic maneuvers may become important elements of pilot training in air force combat units. The attained maneuvering capability of the S-37 aircraft can also demonstrate heavy-duty modes of flight of aircraft that ensure effective performance of the onboard equipment and armaments of future aircraft. In addition, the very creation of this experimental aircraft may give impetus to efforts to create promising high-strength materials to manufacture the forward-swept wing to enhance its strength and rigidity with minimum weights that can be later on borrowed for aircraft of different types.
 

S-37

 
It should be noted here that structurally this aircraft's design incorporated stealth-technology elements. The forward-swept wing has a lower radar signature from the front hemisphere. The extensive use of composite materials and installation of air intakes with curved air ducts, and in the future "flat" nozzles, is to contribute to reduction of the aircraft's radar signature. Besides, the aircraft weapon system is arranged in internal compartments, however, the air weapons can be attached to the under-wing pylons, if the need arises.

Currently the S-37 aircraft is powered by two D-30F6 turbofans. It is planned to substitute them with new-generation engines.

Naturally, the Sukhoi Bureau should do a lot to fulfill the fly tests of the S-37 experimental aircraft to meet the requirements of the Air Force.

Taking into consideration the available research and engineering gains and foreign developers’ experience in creating aircraft of similar aerodynamic configurations, given the current level of financing of military orders and the technical and economical risks, it is unlikely that a development program will be implemented rapidly.

However, its clear even today that construction of the S-37 aircraft, with its extensive potential for further development, has huge technological, military, and political significance in competing for primacy in the aircraft building against Western manufacturers of combat aviation materiel in order to enhance Russia's posture on the international arms market.

      After stealing dozens air shows and breaking thousands hearts, Sukhoi had established as a world known aircraft design bureau, beating a rival Mikoyan after decades of bad luck and political opposition. Sukhoi's workhorse, basic Su-27 had been rebuild as the Su-30 interceptor, Su-33 carrier born fighter, Su-34 tactical bomber, Su-32FN ASW and coastal defence platform, Su-35 and Su-37 air-superiority fighters. However, busy with development of the Su-27, Sukhoi is working on at least two fighter-sized aircraft, one of which is intended to replace Su-27, Su-33, Su-35 and Su-37. (Sergei Skrynnikov, Air Fleet Herald)
     The final configuration of the new generation fighter was revealed at enlarged meeting of the Russian air force Military Council (RusAF MC) which was held on 31 January and 1 February of 1996. The photo, showing RusAF top brass and Russia's top designers participated in the meeting, appeared in the 1996 March-April issue of "Vestnik Vozdushnogo Flota" (Air Fleet Herald formerly known as "Aviatsiya i Kosmonavtika" and recently reincarnated as "Vesnik Aviatsii i Kosmonavtiki"). It is hard to say if chief editor - Sergei Skrynnikov - was aware of the healthy curiosity of western aircraft enthusiasts to fifth-generation Russian fighters, whose focus was mainly attracted to the scale model sitting at the desk in front of Glavcom VVS (RusAF commander) Piotr Deinekin (front row, center) and Sukhoi constructor general Mikhail Simonov (front row, second from right). The type is believed to be new air-superiority fighter referred by west as S-32 (S-37). (Gareth Burgess, Flight International)

Filling MFI Requirement

The Sukhoi's candidate for the Russian air force requirement for a Mnogo-funktsional'ny Frontovoy Istrebitel' (MFI - multifunctional frontal fighter) is less known than its rival Mikoyan article 1.42. Vladimir Ilyushin, Sukhoi's veteran test pilot, revealed in mid 1997 that the aircraft was "close to completion", adding that it will be a "worldwide sensation" when it is unveiled. The scarce information on Simonov's new fighter indicate that it had already underwent high-speed taxi tests by the end of the summer and made its maiden flight at Zhukovsky at September 25th, 1997, in hands of Sukhoi's test pilot Igor Votintsev.

Although the S-37 was expected to be unveiled at Moscow Aerospace salon (MAKS'97) along with Mikoyan's 1.42, both remained wrapped in veils of secrecy due to decisions made by Russian military. Both MFI contenders were shown to Prime Minister Chernomyrdin at closing days of the air show.

The Sukhoi's vision of fifth-generation fighter is considered a lower cost solution for the MFI requirement than officially cancelled article 1.42. The savings from this slightly smaller, but equally sophisticated aircraft are believed to be due to the less radical and yet very capable design, demonstrating a mix of the fourth-and-a-half (4++) generation technologies and revolutionary new developments.

The S-37 might well be the latest and the last of Russia's aerospace industry, owning its concept to the very final iterations of fundamental aircraft research of former Soviet Union. The exact reasoning behind Sukhoi's decision to pursue heavy fifth-generation fighter is not clear. As recently stated by Russia's Defence Minister Igor Sergeyev, currently Russia develops six types of fighter aircraft. The funding from RusAF remains scarce at best and the competition between ANTK Sukhoi and MAPO MIG for this money is fierce. Clearly, the investment of the capital gained from export sales of Su-27 to China and Su-30MKI to India in the S-37 project can serve as a final blow to the MAPO MIG fighter business. If the S-37 will indeed turn out a cheaper MFI, Simonov can count on possible orders from RusAF in very distant future. The S-37 can also have a great export potential as the Su-27 replacement and compete with F-22 exports. (S-37 Berkut in flight, Kommersant Daily)

What's in the Name?

The S-32 (do not mix with Su-32!) is an internal Sukhoi OKB designation which is rationalized in terms of commonly used yet controversial indexing originated with Sukhoi Su-7 and Su-9 prototypes. These were designated S-1 and T-1 respectively, with "S" being a first letter of swept wing in Russian "Strelovidnoe krylo" and "T" from the Russian for delta wing "Treugol'noe krylo". Clearly, the "S" in S-32 implies that new Sukhoi has a swept wing but the index conflicts with another S-32 taken by Sukhoi Su-17 prototypes few decades ago. There is a great deal of hints that S-32 is a phony designation and presently a different designation is used in conjunction with new Sukhoi fighter -- S-37 (do not mix with Su-37!). The S-37 index was formerly allocated to a single-engined lightweight multirole combat aircraft broadly similar to French Rafale which was cancelled in 1994. In any event, both S-32 and S-37 are internal bureau designation, and could become Su- anything. Reported name of S-37 is Berkut (Ber-koot) which means golden eagle in Russian.

 

From Tailless Canard to Tandem Triplane

The fifth-generation Sukhoi fighter features forward-swept wings (FSW), canards and twin outward-canted vertical stabilisers and incorporates low-observable and thrust-vectoring technologies. Comparing blown up photograph of the scale model and early speculative sketches and artist renderings, which appeared in western aviation press, it is clear that S-37's forward-swept wing is closely coupled to canards. Nonetheless, the aircraft retains the horizontal stabilisers, evolving from pure canard to a tandem triplane layout. The first S-37 photographs show that the stabilizer are highly swept (ca 70 deg) and their leading edges appear to extend aft from the wing roots of FSW. This is very different from X-29A strakes which were extensions of the wing roots themselfs ending with a trailing edge flaps.

The tandem triplane configuration was test flown in 1985 on T-10-24 which served as one of the naval Flanker prototypes. The addition of the canards, referred PGO in Russian (Perednee Gorizontal'noe Operenie - Forward Horizontal Stabilizers), solved the control problems encountered at high angle-of-attack (AOA) flight regimes when the tailerons lost their efficiency in the wake of the wing. The PGO's seemed to be a favourite choice for forth-and-a-half generation of Sukhoi's Su-34, -32FN, -35 and Su-37 and fifth-generation S-37 and S-54.

Although the genesis of the S-37 remains unclear, some sources suggested that original layout was much closer to X-29A tailless scheme and that aerodynamic of early S-37 directly benefited from Central Aerohydrodynamics Institute (TsAGI) wind-tunnel tests with X-29A scale models. It is possible that S-32 may be a technology demonstrator, built to examine FSW aerodynamics and composite wing structures or may have started its life as one, but realities of 90's urged Simonov to take this project one step further in attempt to present the S-32 as a genuine contender for a fifth-generation fighter seeked by the Russian air force. This might explain the fact that the S-32 seems to be much too heavy for a research testbed, being a considerably larger aircraft than Northrop F-5 sized X-29A.

In fact, the S-37 is in the class of Su-27 as seen from comparison of its scale model to the advanced Su-27 Flanker model presented at the same meeting. Moscow Aerospace (MAKS 97) provided additional data on S-37 and confirmed that dimensions, performance and tandem triplane layout of the S-37 are similar to that of Su-37.

First public photographs of the S-37 suggested that the front part of the fuselage including the "hooded cobra" LERX could have come from the original S-37 canard-delta. If true, this could possibly clear up the origins of the S-37 index.

Forward Swept Wing (Tsybin's LL-3)

The early Soviet designs to feature moderately forward swept wing were Belyaev's DB-LK and Babochka aircraft and Mikoyan Gurevitch PBSh-2 (MiG-6) biplane. Captured at the end of WWII, German FSW Junkers Ju-287 was test flown by German and Russian crews. A six engined EF-131 was build and underwent extensive structural and flight testing until 1947, when theme was closed. At about the same time Pavel Tsybin build several testbeds LL (Letauchaya Laboratoriya) -1, -2 and -3 with stright, swept back and forward swept wings respectively (40 degrees). The LL-1 and LL-3 rocket powered gliders performed number of powered flights and provided TsAGI with much needed FSW data. In one of the flights LL-3 reached Mach 0.97 in dive.

The FSW had an edge in the trans- and subsonic performance but because the aluminum alloys commonly used in aircraft design fail to withstand the higher structural loading of the wing, the supersonic FSW concept was kept on the ground until introduction of the composites. A titanium-composite winged flight-by-wire Grumman X-29A had proved the feasibility of supersonic FSW concept. However, due to its poor performance at supersonic speeds, FSW was nowhere to be found in United States Air Force next-generation air superiority fighter.

Sukhoi Fifth-generation Fighter Philosophy

The FSW is a better performer at high angles of attack in post-stall manoeuvring much needed in close-in dogfight. The fact that Simonov had chosen FSW for his fifth-generation fighter once again confirms Sukhoi's commitment to the superagility as a crucial requirement for the next generation air-superiority fighter. This approach, so much different from western concepts of stealth, supercruise and BVR engagements, was taken to the limits in Su-37. The FSW S-32 fitted with TVC expected to outperform its stalemate in close-in dogfight involving post-stall flight regimes. Having the edge in manoeuvring, the S-32 is clearly catching up in stealth with US and European new-generation fighters. However even with its internal weapon bay and RAM coating, the new Sukhoi is a very different concept than F-22. The heavy accent on RAM rather than radar absorbing structures (RAS) is obvious.

The reason for such attitude is not clear, although a combination of the technology limitations and operational doctrine is most likely candidate. The major components of radar stealth -- RAM coatings and surface quality -- are subject to the production and maintenance tolerance as it was shown by USAF F-117 and B-2 operational experience. Untightened screws, scratches or unfastened access panels were known to greatly deteriorate the RCS of the aircraft, reducing the engineering efforts put into aircraft design. It remains to be seen how Sukhoi will overcome the looser production standards of the Russian aircraft plans.

Low Observable

One of the early Sukhoi exposures to the low visibility technologies were tests with Sukhoi Su-25 Frogfoot prototypes T8-11 and T8-12. First trial, code named "Astra", involved T8-11 which is now displayed in Monino Air Force museum. A graphite based filler was applied to the basic T8-11 airframe for reduction of the aircraft radar cross section (RCS). Additional tests involved the first series production T8-12, which became a testbed for radar absorbing material (RAM) coatings and special camouflage schemes, intended to lower radar and visible signatures of the aircraft. This low visibility paint tests were similar to those carried out for USAF A-10 in early 1990s. The cannon port was faired-over and forward fuselage of the stealthy Frogfoot was painted with rubber like material. For a brief period this RAM coated T8-12 joined T8-16 at Khodynka, but its prompt removal suggested that the hightech and state secrets were at stake and it was put on display by a mistake or ignorance in a first place.

The Afghanistan experience where Sukhoi's encountered a thread of the shoulder launched infrared homing surface-to-air missiles such as Redeye, Stinger and SA-7, forced Sukhoi team to work on the reduction of the infrared signature of the Su-25. The results materialized in the Su-25T development -- Su-25TM (Su-39 in Sukhoi's nomenclature). The installation of the intake cones hiding the turbine blades and efficient mixing of the exhaust with cold air reduced the IR signature of the Frogfoot from front and rear aspects. This fourfold reduction at expense of 2% lower SFC is indeed an impressive achievement.

Further experiments with low visibility involved the advanced Flanker development prototypes, aircraft of 700 (Su-35,-37) and 600 (Su-30) series. These fighters wear eye catchy new camouflage schemes designed to reduce the visual signature of the aircraft on the ground and in the sky. One of the most interesting examples of Sukhoi experiments was a scheme applied to 701, designed to deceive space based optical systems.

Some effort was directed in reduction of the radar cross sections of advanced Flankers as well. The Su-34,-32FN have optimized radar random shape, lack variable geometry intakes and were reported to have partial RAM coating. Recently Sukhoi stated that basic export models of Su-30MK can be treated with RAM to fulfill customer requirement for a lower RCS aircraft.

Clearly benefitting from previous research, the S-37 prototype relies heavily on the Sukhoi's state of the art low observable technology. The forward swept wing, a conformal underfuselage weapon station(s), use of RAM and the inward-canted tailfins, suggest a further reduction of the aircraft radar signature down from similarly sized Flanker's 3-5 sq m. The extend of the reduction of the IR signature of the S-37 exhausts will depend on the choice of the trust vectoring nozzle. The F-22 type flat 2D nozzle can give a better results while 2D nozzle might contradict to Simonov's superagility ideas favouring 3D exhaust. The Saturn-Lulka was reported to work on reduction of the IR signature of the axi-symmetric trust vector controlled (TVC) Al-37FU power plant on non-afterburning regimes.

Powerplant

The scarce availability of trust vectoring Saturn-Lulka Al-41F engineered for the Mikoyan's article 1.42 forced Sukhoi to seek a replacement for the originally planned powerplant. According to MAPO MIG sources, the limited number of Al-41F are involved in Mikoyan's Article 1.42 tests and not available to Sukhoi's competitor. Reluctance of MAPO MIG made a trust-vectoring control (TVC) Al-37FU (sometime referred as Al-31FU where FU stands for Forsazh, Upravlaemoye soplo - afterburning, articulated nozzle) powerplant used in Sukhoi's Su-37 a natural choice for fifth-generation fighter, but would have been premature for the first S-32 airframe. Additionally, the availability of the Al-37FU could be a problem since all prototypes are involved in flight tests on the Su-37 and in the bench endurance tests. At the time of the Su-37 first flight only three Al-37FU were built.

The ultimate S-32 powerplant -- Al-37FU -- operates in automatic and manual modes. In manual mode the nozzle deflection angle is set by the pilot, and in automatic mode the axi-symmetric nozzles are controlled by the MNPK Avionika full-authority, digital fly-by-wire flight control system (FCS). The movable in pitch axis nozzle deflects 15 degree at 30 deg/s by a pair of hydraulic jacks. The production Al-37FU will use jet fuel instead of hydraulic liquid to drive the nozzles.

Surprisingly, as a temporal solution, instead of similar and widely available Su-27 Flanker's Al-31F powerplants, the S-32 prototype received a pair of Perm Aviadvigatel D-30F6 engines used on MiG-31 Foxhound interceptors. Designed by the 1980, this full authority digital engine control (FADEC) engine comprises six interchangeable modules and a core module. Although powerplant accumulated several thousand flight hours and experienced no operational drawbacks, it has estimated 300 hrs life between overhauls (Russian engine maintenance is very different from western philosophy and term "overhauls" has a different meaning). There were no reports on TVC versions of D-30F6.

The photographs of S-37 Berkut, show two details: the starboard tail sting is slightly longer than the port one and the two auxiliary intakes on the top of the fuselage. There are three reasonable explanations to the sting asymmetry:
a) it houses a breaking or a spin recovery shute
b) it is due to the asymmetric engine installation typical for prototypes. The port engine will be used to test a 3D TVC nozzle which will require adequate space for the yaw vectoring
c) Sukhoi used two 2D nozzles oriented perpendicular to each other to control pitch and yaw separately. Combined action give a pseudo 3D effect. This last explanation is least likely since Lulka reported to have 3D TVC nozzle "in the pocket" at the time of Farnborough 96.

Auxiliary intakes could be used during take offs for increased air flow to the engines. These could have been repositioned from the underside of the aircraft due to the reduces radar cross section considerations or/and lack of the space taken by internal missile bay(s).

Avionics

In early September, defence-ministry acquisition chief Col Gen Anatoly Sitnov noted: "What is the use of developing the Sukhoi fifth-generation fighter, if the aircraft's cockpit dates back to a second- or third-generation design?" While Sitnov statement clearly implying the state of the art of the S-32, one can hardly expect that a first test airframe will incorporate all innovations planned for the series production. Similarly, the sole Su-37 demonstrator flies with a counterweight instead of the advanced radar hence the aircraft is intended to explore among other things the trust vectoring modes of the new powerplant. However, the Su-37 fighter will have the top notch avionics suit which is tested on other 700 series airframes -- Sukhoi Su-35s.

It is expected that the sophistication of S-32 cockpit and avionics suit should at least match that of forth-and-a-half generation Su-35 and Su-37 aircraft. The cockpit of the S-32 does most certainly feature the color liquid crystal MFDs and wide angle HUD. The test proven in Su-37 demonstrator inclined pilot seat, a fixed pressure sensitive throttle and side-stick controller will also find its way to the cockpit of new fighter expected to impose even greater G-loads on pilot than superagile Su-37.

The type of the radar intended for S-32 is not known. The size of the random seems to be somewhat smaller than that of Su-27 family, possibly implying the smaller diameter antenna. Since the S-32 lacks the Flanker's sting, the placement of the rearward facing radar will be challenging at best.

Armament

The armament of the S-32 will most likely never get close to the air-to-air arsenal of Mikoyan's article 1.42, enjoying super long range K-37. However the ram jet version of AA-12 Adder, R-77PD (RVV-AE-PD), seems to be the most appropriate long stick for the new fighter. The missile's collapsible lattice stabilizers give R-77 family the compactness well suited for the internal weapon bay(s) of the stealth S-32. However, the aerodynamically superior lattice stabilizers have reportedly a much greater RCS than conventional surfaces, thus potentially revealing the position of the aircraft at the moment of the missile launch.

The exact number of weapon bays is not known, although the total number of the hardpoints will be fourteen. The use of the internal/external weapon loads will depend on the mission.


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