Su-47 Firkin / S-37 Berkut
The Su-47 [initially known as the S-37] Berkut [Golden Eagle] is a testbed for developing technologies for the next generation of aircraft. The basic dimensions and weight of the Su-47 Berkut are similar to those of Su-37, although they are different aircraft, and the tail, nose and canopy are similar to those of the Su-35. The first two prototypes of this aircraft were evidently designated the S-32, and the S-37 designation was previously applied to an unrelated fighter project for a smaller delta wing single aircraft that was cancelled due to lack of funding.
The NATO reporting name for this aircraft is "Firkin". A firkin is a small wooden barrel, vessel, small wooden covered vessel or cask of indeterminate size, used for butter, lard, etc. It is also any of several British units of capacity, usually equal to about one-fourth of a barrel [9 gallons or 34 liters). Thus a firkin would be the smallest keg of beer in a tavern, and is a popular name for establishments that serve beer. The Firkin Brewery was a chain of UK brewpubs initially launched in 1979. Beer was often badged as coming from Bruce's Brewery, after the founder David Bruce. They changed hands a number of times until taken over in 1991 by Allied Brewery. Following this takeover there was a veritable explosion of Firkin pubs, many, however, did not brew but received their beer from another nearby Firkin. All breweries were closed during October 1999 following the take-over of Allied Domecq tied estate by Punch Taverns. The word firkin is derived from the Middle English ferken, ferdekin, probably from Middle Dutch *verdelkijn, diminutive of veerdel, one-fourth : veerde, fourth. Another analysis of the origin of the word derives from the Anglo-Saxon word feower, meaning four (or an allied word, perh, in Dutch or Danish).
To designate the Su-47 as Firkin is an elaborate jape at Russian pretentions as to the sophistication of this aircraft. Russians claim that the Su-47 is a "fifth generation" aircraft in the same class as the American F-22 and F-35, but the Firkin [ie, fourth] NATO reporting name disputes this claim, asserting that the Su-47 is merely another inferior "fourth generation" fighter.
The Su-47 features forward-swept wings, which promises a range of benefits in aerodynamics at subsonic speeds and at high angles of attack. The forward-swept wing, which enables the aircraft to increase its range and its manoeuvrability at high altitude, makes extensive use of composite materials. The aircraft has large canards mounted on the intake side, close to the leading edge of the wing. The vertical stabilizers are canted slightly outward [not inward, as previously believed], and two large auxiliary intake doors are visible on the center fuselage section. It is unclear which engines are used on this aircraft. The two powerplants were initially the t D-30F6 turbojets which are normaly used at the MiG-31M, while the second prototype used the Ljulka AL-37FU turbojet with thrust vectoring.
In 1983 the specialists of OKB imeni P.O. Sukhoi began the design of a 5th generation fighter. They took up the task of developing an aerodynamic layout that would provide a qualitative improvement in the maneuverability characteristics of a fighter, a reduction in its radar signature, the possibility of the realization of prolonged cruising supersonic flight. In this case the aircraft had to become the multipurpose aviation combat complex, capable effectively of air battle with the existing and future enemy fighters at any distances, to achieve an interception of the aerial targets of different types across the entire altitude range of flight. It would also be required to strike ground-based and waterborne targets, including small size and mobile targets. For this it it was required to equip the aircraft with the integrated system for control of armament, which included multimode onboard RLS of the long range of action, optical-electronic aiming system and the helmet system of aim designation, and by the diverse controlled weapons of destruction of air and ground targets.
By 1988 the basic studies on the search for the rational layouts of promising fighters were completed. Within this framework which was confirmed the expediency of use on the aircraft of an original configuration "integral tandem-triplane" with the forwardswept wing, the traditional tailed and additional front horizontal tail assembly. While the layout of the "tandem-triplane" had already been tested in OKB imeni P.O. Sukhoi on the experimental version Su-27 ([T]10-24) and the aircraft Su-27[K] and Su-35, the sweptforward wing was a genuine novelty on a fighter. In the opinion developers, it had a number of serious advantages, connected with its higher lift effectiveness, which ensure an improvement in the maneuverability, especially at subsonic speeds, an increase in the flying range and an increase in the takeoff and landing characteristics. Furthermore, the forwardswept wing was considerably less noticeable to enemy radars during illumination of the aircraft from the forward hemisphere, since the reflection from the leading wing edge was screened by the fuselage.
Forward Swept Wing (FSW)
Though similar in overall concept to the American X-29 research aircraft that first flew in 1984, the Soviet Sukhoi Su-47 that first flew in 1997 was about twice the size and far closer to an actual combat aircraft.
Forward-swept wing designs appear to offer selected aerodynamic performance improvements over conventional aft-swept wings, such as higher lift-drag ratios, lower trim drag, and better stall/spin characteristics. In addition, these designs may allow for improved fuselage-volume arrangements, by having the wing box located more rearward.
Before World War II, there were some gliders with forward-swept wings, and the NACA Langley Memorial Aeronautical Laboratory, Hampton, Va., did some wind-tunnel work on the concept in 1931. Germany developed a jet-propelled aircraft with forward-swept wings during the war known as the Ju-287. The concept, however, was not successful because the technology and materials did not exist then to construct the wing rigid enough to overcome bending and twisting forces without making the aircraft too heavy.
It may be of interest, especially to persons aware of the earliest flights to supersonic speeds, that the fuselage and empennage of the quarter scale X-1 model were tested with both swept-back and swept-forward wings. Other interest in FSW configurations during World War II came from the American Cornelius Aircraft Company, which worked on several configurations, including the XFG-1, a piloted towable glider used to transport fuel. In the late 1940s the Swiss performed wind tunnel tests of 25- and, later, 13-degree forward-swept wing aircraft under their P-25 project. Following World War II, the only significant FSW aircraft built was the German Hansajet business jet, which was designed by the same chief engineer who designed the Ju-287. The aircraft never enjoyed a large market.
Because of warnings published in 1948, concerning aeroelastic structural divergence for forward-swept wings, designers of high-speed aircraft were reluctant to employ forward sweep for more than two decades.
Until the late 1970s, the region beyond stall was considered an unacceptable flight regime frequently characterized by uncontrollable flight in spins and by undesirable deep stalls. Any deep stall condition is characterized by a stable trimmed flight but at a high angle of attack from which return to normal flight may be difficult or impossible. A deep stall may be defined as an out-of-control condition at an angle of attack greater than the angle of attack for maximum lift with no significant motion other than a high rate of descent. Conventional airplanes usually stall and lose control effectiveness at angles of attack in the range of 18° to 20°. Because movement other than a high rate of descent can be controlled by varying thrust levels and all moveable control surfaces with large deflections, the safety and usefulness of flight at extremely high angles of attack were re-examined and redefined.
Present day efforts in the aircraft industry are directed to developing aircraft that can operate at very high or supersonic speeds. Such supersonic aircraft, particularly when used as combat fighter planes, should be highly maneuverable to allow rapid turns, rolls, dives and ascents without danger of stalling or loss of control. Some aircraft may need to cruise long distances at supersonic speeds requiring the most efficient integration of the engine-propulsion system and the external airframe aerodynamics. Also, it is desirable that the aircraft should be capable of performing landings and takeoffs at low subsonic speeds, using a minimum length runway or, for some missions, landing or taking off vertically. To realize these goals for high speed aircraft, it is necessary to have optimum control of powered lift and air flow.
Recent investigations of aircraft configurations indicates that a significant number of benefits may be achieved by utilizing a forward swept wing (FSW) planform. When an FSW is used in combination with a canard at transonic and low supersonic maneuvering flight, favorable interference is provided over the inboard portion of the wing where the shock is strongest. This leads to higher aerodynamic efficiency than with the use of aft swept wings. In an aft-swept wing configuration the spanwise flow normally thickens the boundary layer at the tips. The flow on an FSW tends to separate first at the inboard section while good flow conditions can be maintained at the tip because of low induced angles of attack of the outer wing sections and because the air tends to flow toward the root rather than to the tip as it does on a sweptback wing. These flow conditions result in stall characteristics which allow the ailerons to remain effective at high angles of attack, even after most of the wing has stalled. Thus the FSW aircraft is more controllable at higher lift coefficients.
Extensive investigation of various aircraft configurations indicates that significant benefits may be achieved by utilizing the forward swept wing configuration. Forward swept wings have some potentially attractive aerodynamic features including a higher geometric sweep at the shock position, `good` stalling characteristics due to the more highly loaded inner wing, and lower wing root bending moments leading to a lighter wing structure than the equivalent aft swept wing.
In an aft-swept wing configuration, spanwise air flow normally thickens the boundary layer at the wingtips. In a forward swept wing configuration, air flow tends to separate first at the inboard section of the wing while good flow conditions are maintained at the wingtips. Thus, higher aerodynamic efficiency is exhibited with forward swept wings than with aft swept wings. Such flow conditions result in stall characteristics which render the ailerons effective at high angles of attack after most of the wing has stalled, making the aircraft controllable at relatively high lift coefficients. Since a forward swept wing tends to stall first on the inboard wing sections rather than on the outboard sections, air flow control over the fuselage must be carefully controlled to insure stability in low speed flight, at high angles of attack, and at high subsonic speeds.
They do have some disadvantages, not the least of which is the aerodynamic design of the inner wing region. The outer wing design is fairly straight forward and it is not difficult to maintain well swept isobars. Over the inner wing, however, there is a tendency for a very strong, unswept shock to form at high subsonic Mach numbers and at high lift coefficients.
Aeroelastic divergence occurs when a forward swept wing bends upwardly due to high angles of attack or gust loads. Because of the forward sweep geometry of the wing, the resultant torsional deflection increases the angle of attack of the wing. The increase in angle of attack of the wing increases aerodynamic load still further causing yet additional increases in the angle of attack. This self-propagating "divergence" can lead to structural damage or failure of the wing. Forward swept wings of metal are limited in their use due to the static stability phenomenon of divergence at high speed flight conditions. Making the wing out of composite materials offers relief from this phenomenon. But a composite material wing can be quite expensive and labor intensive.
Su-47 Program History
Work moved at a rapid rate: it was intended to raise the experimental model of the fighter into air by 1991, and it was planned that within five more years there could appear the first series machines. Thus, the planned periods of creation of the fifth generation fighter did not lag behind its western competitor - the American Advanced Tactical Fighter ATF. Fate was, however, ordered otherwise. The situation of the increasing economic crisis into the USSR by the end of the 1980s, the subsequent disintegration of the Union and the market reforms in Russia led to the significant reduction of the budget allocations on military R&D. This generally proved to be the case with the development of new aircraft, and without the financing the purchases of new combat aviation equipment practically ceased.
However, the management of OKB imeni P.O. Sukhoi, realizing the need of continuing the studies in promising technology, made every efforts for the advancement of the program of the experimental fighter, which was called subsequently S-37 Berkut ["golden eagle"]. To cut costs, elements of the Su-27 were carried over to the new design (forward fuselage, landing gear, and vertical tails), and the design was given an “official” designation of Su-47 in hopes of attracting a customer.
It was possible to complete assembling the fuselage of the first version of the aircraft in the middle of 1996. For accelerating the rate of creation of the new machine under the conditions of scarcity of means, the solution was accepted to conduct static tests with this copy, and then later the first stage of flight tests. For the reduction of expenditures for the experimental fighter it was necessary to equip it with a number of systems already mastered in production systems and aggregates (so, they were used the production Soloviev D-30[F]6 engines used on the MiG-31 interceptor). The additional equipping of aircraft after the static tests was finished by May 1997; and in July 1997 the S-37 was transported to the flying station of the OKB in Zhukovskiy, where the preparation of the machine began for the flight tests.
The first flight was executed on 25 September 1997. The first stage of the tests of the aircraft, in course of which 8 flights were conducated, was completed in November 1997. On the statement of representatives OKB imeni P.O. Sukhoi all the required tasks in this stage of testing were executed. After the analysis of obtained data and of the planned finishing of systems and equipment with the spring of 1998. The OKB continued the flight test program of the experimental S-37 fighter. It was intended to use their results for the development of the future 5th generation fighter, which was to enter into service with the Russian Air Force after the year 2000.
While the S-37 was initially equipped with the D-30F-6 of the MiG-31, it was to receive the Saturn/Ljulka AL-41F later. This 5th Generation engine was tested with the help of Tupolev Tu-16LL and the Mikoyan Gurevitch LL 20-84 (a modified MiG-25PD) and incorporated for the first time into the MiG MFI. With this engine the S-37 without afterburners could reach supersonic speed and supercruise. In 1999 the S-37 was recognized by the state officially as an experimental airplane and prototype and testing is resumed.
The Su-47 would finally took flight in 1997, proving to have the excellent agility it was designed for and validating Sukhoi’s forward-swept wing design. However, the prototype was initially limited to Mach 1.6 due to structural concerns. Even with later examinations and modifications allowing the Su-47 to be rated to Mach 2+ flight, the prototype would never fly faster than Mach 1.65. In the end, no orders would ever materialize for the Su-47, and Sukhoi shifted its efforts to more promising designs.
In the year 2001 the airplane received the official designation Su-47. At MAKS 2001 a lot of things were unveiled, including the Su-27UB and Su-35UB twinseat multirole fighters, Su-24M, Su-25 and Su-39 attack aircraft upgrades, and the Su-47 Berkut experimental aircraft.
In April 2002 the OKB Sukhoi was chosen as the system leader for the development of a new combat aircraft of the 5th Generation, with an internal designation of T-50. MiG and Sukhoi had long been in competition for the state order for the development of a fifth generation fighter jet. MiG specialists chose the 1.44 index aircraft as the prototype of the new jet, whereas Sukhoi decided to base its work on the Su-47 fighter jet. Sukhoi's Su-47 eventually won the contest.
The seventh MAKS aerospace show ended in Zhukovsky outside Moscow on 21 August 2005. The stars were the aerobatic teams Patrouille de France and Frecce Tricolori (Italy) flying trainers, the Russian Knights and Swifts flying the Su-27 (Flanker) and MiG-29 (Fulcrum) fighters, the Rus team flying L-39 trainers, and the test pilots of Sukhoi and Mikoyan flying the multirole Su-30MKI and Su-27SKM fighters, the Su-47 (Firkin) with forward-swept wings and the thrust vectoring MiG-29OVT (Fulcrum), as well as their colleagues from the Gromov Flight Institute. Only at the MAKS show could one see the entire family of Su fighters, assault aircraft and bombers, including the experimental Berkut Su-47 (Firkin) with wings swept forward, which was said to be the prototype of a fifth-generation fighter.
Sukhoi presented its new plane, the SuperJet-100, previously called the Russian Regional Jet, or RRJ, at the Le Bourget air show in France on June 18-24, 2007. This year, for financial reasons, Sukhoi will not make demonstration flights at Le Bourget. The flight to Le Bourget and back, deployment at the airport there and demonstration flights (up to three per day) cost too much for the company. Instead, there were models of the company's combat aircraft - the Su-30MKI, the multi-role fighter built for India, the Su-30MKK made for China, the Su-30MKM made for Malaysia, the Su-30MK2 made for Algeria, the Su-35 designed for the Russian Air Force, and the experimental Su-47 with forward-swept wings.
The Su-47 plane will serve as a base on which new solutions of the fifth generation plane will be tested. Mikhail Pogosyan, Sukhoi's general director, said in 2005 that the new fighter jet will be a fundamentally new machine, not just a modernized version of the "Berkut."
At about the same time as the American "Sea Master" in Britain, there was also a development of a multipurpose seaplane that could be used as a patrol, bomber and transport. Among other projects, the firm "Saunders-Roe" also developed a plane with a "canard" scheme, with a backward sweep of both the wing and the front horizontal tail. The power plant was 4 turbojet engines in the root part of the wing.
Before World War II, some gliders with forward-swept wings existed. Though most of the aircraft of the 1920s and 1930s did not use wing sweep, some early tailless gliders and airplanes employed sweep. at least four experimenters employed forward sweep over part or all of the span from 1911 to 1928.
The NACA (the National Advisory Committee for Aeronautics) Langley Memorial Aeronautical Laboratory (now Langley Research Center) in Hampton, Virginia, performed wind-tunnel studies on the concept in 1931. Interest in forward-swept wings increased when some wind-tunnel tests in 1931 showed that 20° of forward sweep provided a greater useful angle-of-attack range than did a corresponding amount of aft sweep.
Research results showed that the configuration of forward swept wings, coupled with movable canards, gave pilots excellent control response at up to 45 degrees angle of attack. Later, as airplane wings began to experience the effects of local shock waves, A. Busemann and R.T. Jones independently recommended sweepback as ameans of reducing transonic and supersonic drag
Germany developed a jet-powered aircraft with forward-swept wings, the Junkers Ju 287, during the war. The Junkers prototype bomber, the Ju-287, flew briefly in early 1945. The German-built Ju-287 had about 15° of forward, leading-edge sweep. The concept, however, was not successful because the technology and materials did not exist to construct the wing rigid enough to overcome bending and twisting forces without making the aircraft too heavy.
Subsequently, interest in forward-swept wings increased in the United States during the years following World War II. Hamburger Flugzuebau designed and built the Hansa Jet HFB-320 in the early 1960s; the aircraft first flew in 1964. The company built 45 HFB-320s, the only certified civilian business jet to use a forward-swept-wing.
But by 1948, concerned over aeroelastic structural divergence for forward-swept wings, designers of high-speed aircraft were reluctant to employ forward sweep for more than two decades. To avoid this problem, that is, to achieve sufficient structural stiffness, conventional metal wing construction would have resulted in substantial weight penalties.
The introduction of composite materials in the 1970s opened a new field of aircraft construction, making it possible to design rugged airframes and structures stronger than those made of conventional materials, yet lightweight and able to withstand tremendous aerodynamic forces.
In 1977, the Defense Advanced Research Projects Agency (DARPA) and the U.S. Air Force Flight Dynamics Laboratory (now the Air Force Research Laboratory or AFRL) at Wright-Patterson Air Force Base, Ohio, issued proposals for a research aircraft designed to explore the forward-swept wing concept. The aircraft was also intended to validate studies that predicted better control and lift qualities in extreme maneuvers and possibly reduce aerodynamic drag, as well as fly more efficiently at cruise speeds.
The Grumman Corporation was chosen in December 1981 to receive an $87 million contract to build two X-29 aircraft. They were to become the first new X-series aircraft in more than a decade. First flight of the No. 1 X-29 was Dec. 14, 1984, while the No. 2 aircraft first flew on May 23, 1989. Both first flights were from NASA Ames-Dryden Flight Research Facility.
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