Su-27vsF-15 - MilitaryRussia.Ru

CLASH OF THE TITANS
Su-27 vs F-15
Predrag Pavlović, dipl.ing.
Conflicts in Vietnam and the Middle East revealed a number of weaknesses
and conceptual faults in 2nd and 3rd generation Mach 2 fighter- interceptors.
Fighters of so the called 4th generation (F-15, Su-27 etc.) besides agility,
which can cope with late WW2 fighters, have the ability to detect targets
below the horizon, at a very low altitude.
It seemed that until the appearance of the next generation fighters, no plane
would have a better overall capability than the F-15.
Ten years newer, the Su-27 has an internal fuel range comparable to rivals
with additional external tanks, better subsonic agility and an innovative
weapon concept.
1
•
•
•
•
•
The primary requirement in the design of the
late 50's fighters was the speed needed to
intercept supersonic fighters / bombers. To
reach speeds greater than Mach 2 with
available engine power at that time, most
manufacturers considered it was necessary to
make a number of compromises.
In order to reduce drag, wings suffered and
were dimensioned for max. acceptable landing
speed of 270-315 km/h. If a configuration
allowed, by the way, a slow minimum speed /
good maneuverability (at angles of attack
[hereinafter α] 2-3 times higher than landing α),
it was not taken seriously because attention
was focused on Mach 2 and not on that flight
domain. These planes (F-106, MiG-21 for
example) did not have the necessary thrust or
relative wing span to sustain such
maneuverability in continuous turns.
The need for wave drag reduction made
canopy flush into fuselage and the pilot was
supposed to solve the interception flight-path
problem by ‘chasing the dot’ in the radar
display, so the field of view from the cockpit
was minimal.
Rolling at the g-load or noticeable α was such
that aircraft often responded opposite to pilot
inputs or went out of control (departed).
Range was less than desired, it was necessary
to defend the homeland far away from home.
2
•
•
On the so called 4th generation
fighters, these flaws were
corrected. Confirmed were the
importance of a large radar, mediumrange AA missiles and surface radar /
AWACS support. Planes and pilots
brought back close air combat
capabilities so situations where old,
subsonic fighters outclassed Mach 2
interceptors (as earlier when Gnat and
Hunter succeeded vs. Mirage 3 and F104, and MiG-17 vs. F-4 / 8) would not
be repeated.
The first 4th generation fighters were
the F-14 and F-15. Tomcat was less
convincing because it did not have the
thrust required. F-15 configuration wings, tail, fuselage and engine intakes
(of type that at supersonic speeds
unloads tail, similarly to canards) is
inspired by MiG-25. More cambered
airfoil, more proverse relation of
moments of inertia (i.e. relatively larger
wings) and later mentioned factors
give it a more docile handling. The
designers thought that big wings
eliminated the need for LE slats / flaps,
reduced cost and simplified
maintenance.
Impressed with the MiG-25, planners in
the U.S. initially requested Mach 2.7
speed.
3
•
•
•
The US knew the rough dimensions of the MiG25 and demonstrated performance records
(people at McDonnell Douglas thought some
things couldn’t be done without additional
rocket motor) but the weight of a MiG-25 was
unknown at that time. Only after defection to
Japan in '76 it was found that subsonically it is
in the F-4 class because of the engine cycle
(turbine inlet temperature and pressure ratio)
required for high-speed flight and heavier
weight of the conservative materials in the
structure of the aircraft. Later, the US quit high
Mach requirement because of the huge fuel
consumption of TF engine at that speed (until
the revolutionary solutions in the compressor)
while available fuel was modest. Also, the
cockpit transparency area would be limited,
much like of F-4. It was impossible to merge the
performance of a MiG-25 with other
requirements based on experiences gained in
Vietnam.
The 4th generation fighters caught Soviets midstep because they had just deployed intergeneration fighter / interceptors MiG-23 and
MiG-25. The first followed the trend of that time
- variable geometry (VG) wings with all the
advantages and disadvantages that this brings,
and the other went on the road less traveled –
its flight domain practically starts where the
speed / ceiling of other aircraft end.
Other types of that inter-generation were the
French Mirage F1 (with unsuccessful VG Mirage
G8), the Israeli Kfir and Swedish Viggen.
•
The US fighter of the time was the
slatted F-4 Phantom. Soon after,
USAF abandoned Mach 3
interceptors XF-108, YF-12 and
later also Navy F-14 and 3-engined
Vigilante, interceptors considered
by USAF.
4
The main features of 4th generation fighters, besides agility and wide field of view that
cockpit transprency allows (the pilot in an F-15, sits more ‘outside' than inside the
cockpit), is the ability to detect and engage targets below the horizon, at a very low
altitude - in the presence of ground clutter.
Increased maneuverability of 4th gen. fighters is achieved through:
• Large wings (in span & area) that brought back the minimum speeds of early jet fighters
(such as F-86) of 200 instead of 270-300 km/h. This allowed a two times tighter turn
radius. A side benefit is slower landing speed of 225-250 km/h, at lower α, which means
that fleet will not be spent in peacetime accidents on landing.
• More engine power (all relative to the weight of the aircraft) which allows sustaining a
40% higher g-load without losing speed and the maximum rate of climb increased from
about 150-220 to 230-330 m/s.
Max thrust without afterburner for a given air flow, depends on the temperature that
turbine can withstand, without burning. A significant increase in thrust of that engine
generation is achieved with the use of directional solidification of nickel superalloys,
similar to choosing the direction of graphite fibers in epoxy resin (polymer composites)
gets greater strength of the composites in a stress direction. The first engine that used
that metallurgy in the West was J58 that powered the SR-71, a 1st fighter engine, F100PW-100 which powers F-15 and TF30-P-100 for F-111F bomber. Combined with air
cooling for the turbine (hot compressor air), an increase of about 300ºC (from about 1100
to 1400) was achieved, compared to the previous generation.
Further development in turbine metallurgy were single
crystal blades (whole turbine blade in one crystal)
applied after 1986 with much fanfare on the F100-PW220.
L-julka AL-31F, the Sukhoi 27 engine, has a single
crystal turbine blades cooled by compressor air
previously cooled in the heat exchanger.
5
The last of the Soviet fighters designed before the collapse of their ideological
system. Their leaders failed in promotion of ethics and social justice, so the people 6
opted for consumer freedom, vice and justice for corporations.
The F-15 Eagle is an all-weather, tactical fighter of extreme performance and
maneuverability, designed to gain and maintain air supremacy over friendly or
enemy-controlled airspace. It is the fastest conventional fighter with agility and
7
avionics unmatched until MiG-29, Typhoon and Rafale, fighters that entered inventory
10 (MiG) to 27 years later (Typhon).
L-julka AL-31F, Sukhoi 27 engine, has a single crystal turbine blades cooled by
compressor air previously chilled in the heat exchanger.
The second, less well-known contributor for thrust increase and weight reduction is in
the turbofan concept itself. It has lighter turbo-machinery weight (about 200-300 kg in
this class) and higher afterburner thrust increase (more unused oxygen in the bypass
channel. The compressor diameter (weight) is much smaller than that of turbojet (see
GE129 scheme). That’s why only 60% of the air is compressed to 23 atmospheres, and
the remaining 40% to 3 atm only, for example. Specific fuel consumption is 25% lower
than the in previous generation fighter engines, partly because of the higher
compression ratio (about 24 vs.14) and partly because thrust of bypass air has slower
exhaust velocity.
AL-31F has active compressor stall protection measures (e.g. when flying behind
another aircraft or when missiles are launched) for stable operation of the engine, which
is the standard previously applied even in the MiG-21.
8
•
Better structural and volumetric (for fuel and systems) efficiency due to wing-fuselage
blending. Wing-body fairings give the wing root rib more height increasing structural
rigidity and strength, or vice versa, for required strength weight of the structure could be
lighter. F-15 and Su-27 both contain a high percentage (25-30%) of titanium alloys for
better strength / weight ratio than steel or aluminum, resulting in a weight reduction of
20% of those structural parts. Less known is another feature of newer materials, given in
the table:
Material Cost in the U.S, late '80s
Material
Aluminum AL 2024-T4
3.3
Aluminum AL 7075-T6
11.8
Carbon epoxy composite
Steel D6AC
Titanium alloy Ti-6Al-4V
•
price ($/kg)
357.5
4.4
502.5
Improved controllability and stability: Adverse
characteristics such as pitch-up and wing-rock,
yaw divergence, adverse yaw due to roll and
spin tendency are reduced or eliminated. To
improve handling – i.e. to ‘fix’ pilot commands,
Command Augmentation System (CAS) has
been added to Flight Control System.
CAS has a subsystem to reduce yaw during roll at high α (ARI Aileron-RudderInterconnect). Su-27 has α and g-loads limiter, while F-15 has subsystems for α, overg and departure (yaw-rate) warning tone.
9
10
11
•
Improved controllability and stability: Adverse characteristics such as pitch-up and
wing-rock, yaw divergence, adverse yaw due to roll and spin tendency are reduced or
eliminated. To improve handling – i.e. to ‘fix’ pilot commands, Command Augmentation
System (CAS) has been added to Flight Control System. CAS has subsystem to reduce
yaw during roll at high α (ARI Aileron-Rudder-Interconnect). Su-27 has α and g-loads
limiter, while F-15 has subsystems for α, over-g and departure (yaw-rate) warning tone.
To be docile i.e. not to have spin and loss of control / departure tendencies, a plane
should have positive directional stability, favorable dihedral effect, efficient rudder and
ailerons and proverse aileron yaw.
The maximum usable α
depends on the combination of
these factors. It is crucial that
dynamic directional stability
along flight-path and factor
called 'lateral control departure
parameter’ (LCDP) i.e. roll
response to roll command are
positive to the highest α. It was
found that if the LCDP is
negative (opposite roll
response), it will cause yaw
divergence and if dynamic
stability along the flight path is
also negative, the plane will go
into spin. Radome shape depth / width ratio and
curvature of the lower part of
the nose cross section are
considered factors which
contribute significantly to the
spin resistance.
12
Minimizing the coupling between roll and yaw axis is crucial for improved handling of
the 4th and newer generation fighters. In fact, depending on the Mach and α, along the
pilot commanded deflection of ailerons, the system adds rudder which reduces
sideslip angle and provides an appropriate response to the rolling inputs. Similar
control feedback (loop) helps aircraft to roll along the flight path axis and not about the
longitudinal axis of the aircraft.
Loss of control in the F-15 is not possible when α is less than 20º. At higher α, if there
is any significant asymmetry of fuel, external payload or asymmetrical flow emanating
from the nose (due to geometry erosion caused by years of service) increases
susceptibility to loss of control / departure.
ARI reduces pilot aileron inputs and therefore
the aircraft is slower in roll response at higher
α, but the aircraft is safer. Rudder inputs can
make rolling faster - creating a sideslip angle,
but there is a thin line to spin. At Mach numbers
between 0.5 and 0.76 and 30-35º α, F-15 is
directionaly dynamically unstable (along the
flight-path), like many modern aircraft. In this
domain, spin resistance is reduced. Otherwise,
if the commands are placed in a neutral position
at the first sign of loss of control
(uncommanded roll or yaw) the plane will be
'back' under control.
Good controllability at high α comes from
effective roll and yaw controls (high-quality
airflow around them, influence of LERX, rudder
position out of disturbed airflow that comes
from h. tail and body) and aileron proverse yaw.
13
Su-27 is a newer airplane and therefore aerodynamically more refined. Wing profile with
leading edge flap (LEF), at high α has more curvature providing more lift and lateraldirectional stability. Ratio of flap chord over the wing chord length is higher at the wing
tip than at the wing root, so when flap is deflected wing tip profile has more camber than
root profile, resulting in proverse increment of pitching moment at high α.
- Leading edge wing root extensions (LERX) / strakes large sweep angle generates
vortices on the inner wings and Sukhoi fuselage, delaying stall. Same mechanism
improves the static directional and lateral stability and significantly reduces buffet at
higher α. These two innovations combined significantly reduce buffet, increase lift and
lift-to-drag ratio in turn.
- Wide fuselage, LEX and blended wing-body together form low aspect lifting area that
continues to generate lift at high α, when the wing stalls. Attention is paid to the
distribution of masses and side-area to obtain a combination which as sideslip angle
increase gives a negative increment (nose down) of pitching moment, so that spin would
be oscillatory rather than stable.
- Sukhoi saw benefits of reduced trim drag by relaxing longitudinal static stability and
incorporation of electronic commands. Su-27 is up to 5% mac unstable. Spin prevention
system limits α to 24º at low Mach, but the system can be overridden as seen in Cobra
maneuver.
14
When F-15 set the standards, other manufacturers such as Dassault-Breguet could later
produce fighters better in one aspect, e.g. M2000 has more wing, relatively, for better
instantaneous turns (but with greater speed loss) for faster target IR missile acquisition
but overall, as U.S. military claims, none of the newer fighters, except for 'Stealth' has
significant (>10%) better performance. It seemed that until the emergence of the next
generation fighters, no aircraft would have better overall capability. F-15 has been
operational for 35 years.
Then came the Su-27, the Russian answer to the F-15. It was intended to be a superior
aircraft so everything was designed 10% larger – from radar antenna diameter (by the
way, radar is 2/3 heavier) to engine air flow i.e. thrust, aircraft dimensions...Unlike earlier
short-range air-defense interceptors, Su-27 was intended primarily for combat over enemy
territory. It looks like a combination of F-16 and F-14. The initial configuration of the
aircraft did not have an appropriate position of the vertical fins which caused bad stall
behavior. Also, wing geometry with double curvature leading edge, along with twist and
camber in profile, was technologically difficult to produce.
In the design of Sukhoi, special care was taken to the optimization of the cross-section
area and distribution (see picture of nose to nose Su-27 / F-15). Relative size of crosssection area was about ¼ less than in competitors, which gives max. trimmed L/D of 11.6
compared to 10 of the F-15, which is equivalent to the addition of 15% of the engine
power. The difference is noticeable in turns and range. Su-27 has the largest amount
of internal fuel ratio relative to aircraft weight, which
provides range as competition with additional
external tanks. To keep the weight of the aircraft
under control, structure weight had to be reduced at
the expense of lower allowable g-load, 8 versus 9g
15
standard, and 50-100 km/h less allowed airspeed (q).
When Su-27 appeared, it was a difficult tactical problem for adversaries. Range with
internal fuel was 2 times greater than of the F-15A, turn performance and controllability
better, radar had similar range, radar missiles had greater range because of inertial
mid-guidance phase, large off-boresight angle, helmet cued IR missiles - 20 years
before the West, were considered fatal.
That's not all, because the Soviets were practised in smart attack tactics, where a pair
of fighters would approach the opponent with crossing paths, together making a
horizontal 8, which creates a tracking problem for the radar and radar-guided missile,
similar to that of a deception jammer that transmits a phase-shifted signal (reflects
false target position) which takes the radar centroid off the target, until the break of
lock-on (like Sorbcija jammer).
16
Climb record breakers
To break climb records to the tropopause (about 11 km altitude) an aircraft needs best
thrust to weight ratio. The operational F-15 is still unsurpassed in that respect. Up to 20 km
altitude, it is important that the plane also has great acceleration to Mach 2 +. To even
greater heights, the aircraft must be particularly fast (MiG-25). These planes are also weight
stripping champions. At the start of the attempt to the first height step (H=3 km) F-15's takeoff weight was 12700 kg and the Su-27’s was 14100 kg. Stripped down F-15 had no flap and
air brake actuators, cannon, radar and electronics, displays, generator, backup hydrosystem and even landing lights and paint were missing. Sukhoi has gone even further and
removed the ventral fins, tip of vertical stabilizers and an engine inlet VG ramp and aileron
actuators. The F-15 took about 1 minute to 12 km altitude, from the start of take-off. It held
the records to 3, 6, 9, 12, 15, 20, 25 and 30 km. The F-15 still holds the record to 20 km. The
P-42 (Su-27) climbed about 10% faster all the way up to 15 km and the MiG-25 has re-taken
the records to 25, 30 and 35 km.
17
Their engines were tweaked to increase thrust 5-10%, which gives them the thrust to
weight ratio of 1.7 and 1.9 respectively (to H=3km).
F-15 had the highest 'spec. excess power' about 420 m/s at 0.95 Mach, SL. That means
it could climb vertically and at the same time accelerate at 0.3 g (3 m/s2) or accelerate
in level flight at 1.3 g i.e. to increase speed 450 km/h in 10 seconds. TO ground run was
120 meters in 4 seconds after the release of the brakes. It was supersonic after the next
19 seconds.
18
Cobra
Until 1988 Soviet military aircraft were missing
at Western airshows, a fact that made room for
underestimation. E.g. the notorious spy-airliner
interceptor - Su-15, was praised as the
interceptor with the best performance by
Belenko, the pilot who escaped in the MiG-25.
Its predecessors, Su-9 and 11 held the world
record for sustained altitude, 1 kilometer more
than Phantom and that is an indicator of overall
performance.
Not to mention figures that MiG-29 did at Farnborough 1988, the loop immediately after
takeoff, with leveling off at the top (the most challenging stability and control ‘test’ where
high α transitions to β and again to α at top of the loop and the lowest airspeed, the
domain where half the Phantoms in Vietnam were lost, the figure that even F-18 does not
dare to replicate). It was followed with another loop at the top of the first one – S figure.
Or tailslide / 'bell', the vertical climb until running out of speed until the plane starts to go
backwards (0g). With forward stick nose was pitched down, retaining throughout the full
longitudinal and lateral stability. The aircraft needed 10 times less airspace to complete
the figure than the best previous fighters whose behavior was not always predictable! The
reason why MiG-29 needed such a small altitude for tailslide was simultaneous AB lighton on both engines (otherwise it would yaw and roll, the aero-surfaces would not be able
to compensate at that airspeed). No Western engine would have a satisfactory response
under those conditions (GE, PW, RR, MTU, IHI, FIAT).
19
The F-15 does not test odds against mishaps and does tailslide at high altitude, from
which an aircraft would have the time to recover from unwanted situations.
At the Paris Airshow 1989. the pilot Viktor Pugachev in Su-27 stunned the world
audience with a figure that showed a remarkable degree of the aircraft’s pitch agility. In
level flight, at about 400 km/h, the pilot suddenly pitched the plane to about 120º (with
approximate α) while continuing to fly forward. The whole time there were no signs of
rolloff or yawoff. The figure was reminiscent of a cobra that takes momentum before
the attack.
Before the performance, the Soviets had problems logging a flight program. According
to Pugachev, the French had taken the position that they invented aviation and that
such a figure should not be performed because it was dangerous. Pugachev showed
documentation, convincing them that he had performed the figure a thousand times.
Before the show, he had to demonstrate the figure a few times for the organizer. There
were similar, poor-man Cobras, demonstrated earlier at high altitudes. For example, the
famous pilot-strategist Boyd used to bet with colleagues that within 40 seconds he’d
outmaneuver them even if they were at his back. He used to pull stick full back,
'stopping' in the air (probably achieving α of about 50°) and with a rudder rolls managed
not to lose the bet. But sometimes the aircraft would be lost, brining him before a Court
Martial, where he defended himself by saying that in the Flight Manual nothing said that
this should not be done. Other famous performers of a modest 'Cobra' (up to 80°) are
Draken and F-14. Many 4th generation fighters have been tested to 90º α but at high
altitudes (during Tailslide), where there was enough airspace to restore control, after
20
possible engine flame-out, departure or spin.
Pugachev performed the Cobra in front of audiences every day at an altitude of 300 meters.
Needless to say, Su-27 (like the F-22 e.g.) does stall/roll off at about 40º (Mach 0.3) and 33° α
(Mach 0.9).
The key to the Cobra maneuver are four characteristics of the aircraft:
- High pitch agility: A huge so called tailplane 'volume' (relative area and arm), with the help
of LEX vortex lift mechanism and longitudinal instability allows dynamic pitch angles and α
in excess of 100°. F-14/15/18/M2000 planes cannot reach these angles;
- Lateral stability: every plane is to a lesser or greater extent dynamically unstable
directionally at α of about 20-40º, where the airflow begins to separate. Su-27 rolls-off here
at 40° α. The essence of the Cobra figure is to quickly pass unstable α region (while the
large inertia of the aircraft prevents the potential roll/yaw-off) and come into benign region
of completely separated air​flow;
- Longitudinal stability at 100°+ α: because of the high pitch rate, the aircraft passes the
point of max trimmed α (that is about 50-60º α), but the tailplane size and deflection pitch
aircraft back to the initial α. The author believes that the aircraft was designed with overdimensioned tailplane (as a backup) because the static longitudinal instability was still
unproved. F-16/18 fighters have large LEX compared to tail ‘volume’ so planes have
difficulty returning from about 60° α. The pilot of an F-16 needs to move stick in phase with
falling leaf - rocking motion of aircraft, trying to get out of the α region where full forward
stick does not result in pitch down motion.
- Stable engine operation at 100° α / less than 200 km/h IAS (earlier generation turbofans has
about 20º α limit);
Su-27 set new standards in fighter design and paved the way for super and hyper (up to
120º α) maneuverability (dynamic entrance into supercritical α - flight mode that permits a
21
decrease of airspace needed for turn by 2 times).
Radar
F-15 has always had the most modern radar. The planar antenna, combined with the
high and medium-pulse repetition frequency (prf) transmitter gave the Hughes APG-63
radar 10 years advantage over other radars with a mechanical antenna. European radars
on Tornado, M2000, and JA-37 Vigen (the latter had a modest Hughes license) had the
older type of antenna with inferior sidelobe characteristics - reverse cassegrain, while
both high and medium prf (the first provides greater look-down range and the latter is
more suitable for the detection tail-on, low-altitude targets) was far away. So Viggen has
two times less range while Tornado chases nose-on targets. Neither did the F-14 have
medium prf. The French M2000 RDM radar had a low prf, unsuitable for target detection
below the horizon.
Sukhoi -27 radar N001 has both prf, but because of the technology gap, it kept the
reverse cassegrain antenna on previous fighters.
Before Su-27 appeared, the F- 15’s radar range data that circulated in the media, was 100
(nautical) miles. When the Sukhoi revealed a figure for their radar - 100 km against
fighter sized targets, the USAF confirmed that they had the same range.
22
Electronic warfare
F-15 has always had the most advanced and capable automatic active jammer, ALQ-135
(jamming by shortening threat radar range, by emitting ‘noise’ or by deception of own
position) that can be stored internally. Its operational status, like of some other systems of
the U.S. Military, is often accompanied by criticism that it has serious flaws and therefore
limited operational capability (to protect the carrier-aircraft in this case). The GAO (General
Accounting Office), was established by the U.S. Congress to prevent 'deception' by Military
and big corporations. According to GAO, system ALQ-135 had been purchased although it
did not show an acceptable operating performance (they were not published in the media in
order not to spoil the mood of the possible opponents for surrender). The Sukhoi jammer Sorbcia-S is bulkier but uses innovative methods of deception jamming. Located in the
containers at the tip of wings, with front and rear wideband phase-steered antennas. For
effective noise jamming, a very high transmitter power is required, which only specialized
planes have. The second method - deception jamming is not effective against monopulse
antennas. But if the jammer antennas are spaced (15 m in Su-27 wingtip case or better if the
plane tows jammer on a long wire) the 'cross eye' technique gives good results, especially
with phase controllable beams that rationally use available power, as in Sorbcia. It allows
simultaneous jamming up to 10 threat radars.
23
Weapons
Density of missile guidance
electronics was always on the West
side. As it turned out in conflicts
(i.e. SAM systems of the '60s and F117/16), fighters fall down even
when they are hit with missiles with
less densely packed electronics. It
is more important to design i.e.
monopulse antenna seeker for more
accurate guidance and resistance to
jamming or to add an inertial
subsystem for guidance at ranges
where the missile seeker/radar
antenna is too small to acquire the
target.
Missiles AIM-7F / M and R-27R have
almost the same max range of about
40 km. However, the R-27R has an
advantage when launched at
supersonic speeds. In that case,
because of the additional inertial
mid-guidance phase, it can be
launched from 60 km and missile
guidance radar seeker can
acquire target in the second phase of the flight,
when it gets close to 30-40 km.
Western missile guidance system improvements
were evolutionary, based mainly on improving the
components and the packing density of
electronics.
The launching of AIM-7M missiles at a speed of
Mach 2 would not increase launch distance, just
the limits of target’s max speed and g-load. A large
amount of fuel allows Sukhoi to fly generously at
supersonic speeds providing the missile launch
speed and kinematic advantage.
Regarding speed and altitude, both missiles can
shoot targets in the SR-71 aircraft class.
24
Turn performance
Su-27 has 5-10% advantage in lift limited turns i.e. instantaneous
turns at subsonic speeds. As directional stability decreases with
Mach number, α limiter of the Su-27 (as in F-16) cuts allowed α and
so min airspeed (with 4 AAMs and half fuel) increases from 203 to
230 km/h at M 0.9. This is visible at high altitudes where corner
velocity migrates to transonic speeds.
The F-15’s FCS does not limit α but buffeting at higher subsonic
Mach numbers does. At Mach 0.9, F-15 experiences heavy buffet at
above 10º α so it is physically impossible to sustain cited α more
than a couple of seconds. At trans/supersonic speeds, structural glimit advantage is on F-15’s side, but no one will look at the limits
during a dogfight. However, as at high altitudes, at trans /
supersonioc speeds, turn radius exceeds the target practical visual
range limit (about 2000 m) and dogfights do not normally occur here.
The situation is similar with the thrust limited (sustained) turns. At
subsonic speeds the advantage is on the side of the Su-27, between
0.9 and 1.3 M there are no noticeable differences, and above that, the
advantage is on the side of the F-15. The latter is possible thanks to
PW220’s digital engine controls, which can more flexibly support
supersonic thrust increase within turbine temperature limits.
According to the US pilots who flew it, Su-27 has a higher roll rate
(max about 270 º/s), something in the F-18 class. To suppress
possible departure and spin, analog flight control systems limit
aileron / tailplane deflection and so roll rate with α decreases, where
at about 30º it is close to zero.
25
26
27
Against each other
The author’s intention is not to present anybody’s propaganda nor to be involved in
marketing. We’ll just look at the validity of some allegations about the kill ratios mentioned
in the media. Regarding the F-15, the reported figure is about 100:0, achieved by US and
Israeli AF.
Clearly the plane, at least when it appeared, had no competition in combat, up to Mach 2.
But circumstances where such combat occured did not always involve an isolated one to
one scenario. In close combat, according to Rand studies, with the same generation
weapons "all die equally“. At medium ranges, the circumstances are crucial. For example,
single Yugoslav AFMiG-29s clashed with a number of F-15s, which had the support of
special aircraft for surveillance and jamming E-3B / C, E-8C, EC-130, RC-135, EA- 6B, P-3C,
while the bombers and cruise missiles attacked MiG bases and ground radars. The F-15 had
only to approach, fire AMRAAMs and immediately withdrew. The number of hours of flight
crew training and reality were additional factors.
Ethiopian Sukhoi 27 shot down the Eritrean MiG-29, supposedly only because of Russian
support. Alleged results of so called simulated combat between Su-27 and F-15 during the
Su-27’s visit to U.S. were not serious because the Sukhoi even without afterburner, not
exceeding 18 º α, succeeded to outmaneuver F-15.
28
After Vietnam, the U.S. military learned a lesson about the public and the media, and now all
information is censored and journalists are not allowed to access war zones uncontrolled.
Even Congress has a problem to know the truth in such media management.
Long before Wiki-leaks, there were individuals – fighters for truth in war. One of them is the
American pilot of B-52, Dana Drenkowski, a decorated Vietnam vet, whose personal life was
ruined because of his endeavors. He wrote about the long tradition of concealing losses of
US aircraft, from Korea and after. He touches on losses in Operation Linebacker II, in '72, in
which he participated. The U.S. Air Force told the media that 17 B-52 planes were shot down,
while Congress was presented with a figure of 13 aircraft. He and other pilots personally
counted 22 planes (+5 which landed with damage beyond repair). He thought that
Vietnamese claims of 25 planes should also be noted.
Israeli historian Shlomo Aloni in his works on the '67 war touches on air combat. He writes
that IAF/DF’s (Israeli Air Force/Defence Force) two downed Israeli Mirage IIICJ officially
attributed to the Syrian air defense, according to Israeli intelligence agency were in fact shot
down by the Egyptian pilot Nabil Shoukry flying the MiG-21. Of course, in the so-called “free
world” nobody ever heard the Egyptian claims. It is interesting that the same Egyptian pilot,
decades after the war, as a general, in the local presentations for Western media, flying the
two-seater MiG-21 demonstrated handling and maneuverability at low and 'zero' airspeed.
29
Su-27 in the US Air Force
According to U.S. aviation authorities (FAA - Federal Aviation Administration) there were
two Su-27s in the United States, privately owned. Using a favorable political situation in
Ukraine in 2008, two Su-27 aircraft were sold to the private company Pride Aircraft, Inc. in
Illinois, US. The company website claims that the planes are no longer in their possession,
that they were sold. Russian news agencies reported that the track leads to U.S. Military.
30
Neither the F-15 nor Su-27 are able to land with both engines-out, because aircraft systems
can not support that.
During the decades of operational use of F-15 there were opportunities to see the
usefulness of the dual flight control system (mecha-hydraulic and electro-hydraulic [CAS])
for some aero-surfaces. The Israeli Air force F-15 in simulated close combat with a light
subsonic A-4 attack aircraft of the '50s, collided with one another after which the F-15 lost
one wing. The plane fell into a spiral and the pilot was not immediately aware of damage.
He switched to the electrical FCS because the horizontal tail controls for rolling uses
electro-hydraulics and established control. He considered whether to leave the plane and
yet no warning light that something is wrong was blinking. He managed to land safely at
about 400 km/h.
F-15 has max lift (minimum speed) at about 35° α. Above 20° wings are stalled and
fuselage carries the plane.
The advantage of F-15’s early appearance, has now turned into a handicap because the
average age of operational aircraft is now 25 years.
31
32
TECHNICAL DATA*
F-15C (PW-220)
Su-27SK
First Flight (initial model)
1972. (F-15A)
1977./1981.
Operational from
1976. (F-15A)
1985. (1990.)
Length overall, without pitot-tube, m
19,4
21,9
Wing span, m
13,05
14,7 (14,95 w tip R-73)
Wing area, m2
56,5
62
3
3,5
Height, m
5,63
5,93
Tail span, m
8,74
9,8
13400
17200
Fuel internal, kg
6100 (ρ=0,78)
9220-9400 (ρ=0,785)
Fuel external, kg
3 x 1800 kg
-
Take-off Weight, 4 AAM, 100% int. fuel
20675 kg
27390 kg
Max external payload, kg
6 - 8000
6000
17625
22780
1,21
1,1
30850
28-33000 =f (wheels)
2 x F100-PW-220
6,52-10,64 t
2 x AL-31F
7,77-12,5 t
Wing aspect ratio
Weight empty equipped, kg
Combat weight with 50 % fuel, 4 AAM, kg
Thrust/Combat weight ratio
Max. Take-off Weight, kg
Engine
33
TECHNICAL DATA (cont) *
F-15C (PW220)
Su-27SK
Range (internal fuel), km
2200
3700
Range (with external fuel), km
4000
-
Limit airspeed / Mach in dive
1470 km/h IAS / 2,5 M
1400 km/h IAS / 2,35M
17100
18000
1,15
1,12
2,4 (2,2 PW100 engine)
2,15
Min airspeed, 1/2 fuel, 4 AAM, SL, km/h
230
203
Max rate of climb, ‘’ ‘’
300
290
26,4 (9g) SL
28,0 (8,0g) SL
corresponding inst. turn radius, m
415
330
Max sustained ‘g’ in turn, altitude (H)=5km
6,65
6,67
Max sustained ω in turn, H=SL, º/s
19 (9g)
19,4 (8,0g)
Min sustained turn radius, H=SL, m
450 at 370 km/h, (2,6g)
355 at 350 km/h, (2,9g)
Acceleration 600-1100 km/h, Combat w, SL
14,5 sec
15 sec
Acceleration 1100-1300 km/h, Comb. w, SL
11,5 sec
12 sec
Combat ceiling, 4 AAM, m
Max level speed at SL, clean config, Mach
Max level speed, clean config, Mach
SL, m/s
Max instantaneous turn rate, SL, º/s
34
TECHNICAL DATA (cont) *
F-15C (PW220)
Limit g-load (subsonic)
9,0 at 17,0 tonnes (M<1)
“”
Su-27SK
8,0 at 21,4 t. (M<0,85)
9,0 at 19 t. (M<0,85)
Take-off speed, km/h
265 at 20,7 tonnes
290 at 27,4 tonnes
Take-off ground run, m
380 at 20,7 tonnes
650 at 27,4 tonnes
1300
620 with chute
1/6 x 20 mm
1 x 30 mm
8 AAMs
10 AAMs
1200
680
30
30
Landing run, m
Internal armament
External AA armament
Number built
Price 1998 year, m$
* All data are official or computationally derived from official sources
* Comparison F-15/Su-27 is done with a proportionally lighter F-15 (relatively less
fuel to a/c weight) and with less missile drag (only AIM-7 with conformal method
of carriage) w/o MRM/SRM combination as in Su-27
Similar, more comprehensive title (at marina.biblija@gmail.com):
Fighter Performance in Practice: Phantom versus MiG-21:
How to do split-S in Mig-21 within 3000 ft: Unexploited low speed maneuverability
35
36