Sukhoi Su-47 (formerly known as the S-37 Berkut)
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.
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. The NATO reporting name for this aircraft is "Firkin".
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
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 straight, 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.
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 super agility 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.
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 optimised 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 fulfil customer requirement for a lower RCS aircraft. Clearly benefiting
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.
S-37/S-32 vital statistics
Wingspan: 16.7 m
Length overall: 22.6 m
Height overall 6.40 m
Weight empty, equipped : 24,000 kg (52,910 lb)
Max T-O weight : 34,000 kg (74,960 lb)
Max level speed at height : 2,500 km/h (1,350 knots)
Max level speed at S/L : 1,400 km/h (756 knots)
Service ceiling : 18,000 m (59,050 ft)
Range with max fuel at height : 1,782 nm (3,300 km/2,050 miles)
Number of hardpoints: 14: 2 wingtip, 6-8 under wing, 6-4 conformal under fuselage
Air-to-air : R-77, R-77PD, R-73, K-74
Air-to-surface: X-29T, X-29L, X-59M, X-31P, X-31A, KAB-500, KAB-1500
Text : Alexei Gretchikhine
