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F 15 vs su-27


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F 15 vs su-27

  1. 1. 1Conflicts in Vietnam and the Middle East revealed a number of weaknessesand conceptual faults in 2ndand 3rdgeneration Mach 2 fighter- interceptors.Fighters of so the called 4thgeneration (F-15, Su-27 etc.) besides agility,which can cope with late WW2 fighters, have the ability to detect targetsbelow the horizon, at a very low altitude.It seemed that until the appearance of the next generation fighters, no planewould have a better overall capability than the F-15.Ten years newer, the Su-27 has an internal fuel range comparable to rivalswith additional external tanks, better subsonic agility and an innovativeweapon concept.CLASH OF THE TITANSCLASH OF THE TITANSSu-27Su-27 vsvs F-15F-15Predrag Pavlović, dipl.inPredrag Pavlović, dipl.ingg..
  2. 2. 2• The primary requirement in the design of thelate 50s fighters was the speed needed tointercept supersonic fighters / bombers. Toreach speeds greater than Mach 2 withavailable engine power at that time, mostmanufacturers considered it was necessary tomake a number of compromises.• In order to reduce drag, wings suffered andwere dimensioned for max. acceptable landingspeed of 270-315 km/h. If a configurationallowed, 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 attentionwas focused on Mach 2 and not on that flightdomain. These planes (F-106, MiG-21 forexample) did not have the necessary thrust orrelative wing span to sustain suchmaneuverability in continuous turns.• The need for wave drag reduction madecanopy flush into fuselage and the pilot wassupposed to solve the interception flight-pathproblem by ‘chasing the dot’ in the radardisplay, so the field of view from the cockpitwas minimal.• Rolling at the g-load or noticeable α was suchthat aircraft often responded opposite to pilotinputs or went out of control (departed).• Range was less than desired, it was necessaryto defend the homeland far away from home.
  3. 3. 3• On the so called 4thgeneration fighters,these flaws were corrected. Confirmedwere the importance of a large radar,medium-range AA missiles and surfaceradar / AWACS support. Planes andpilots brought back close air combatcapabilities so situations where old,subsonic fighters outclassed Mach 2interceptors (as earlier when Gnat andHunter succeeded vs. Mirage 3 and F-104, and MiG-17 vs. F-4 / 8) would notbe repeated.• The first 4thgeneration fighters were theF-14 and F-15. Tomcat was lessconvincing because it did not have thethrust required. F-15 configuration -wings, tail, fuselage and engine intakes(of type that at supersonic speedsunloads tail, similarly to canards) isinspired by MiG-25. More camberedairfoil, more proverse relation ofmoments of inertia (i.e. relatively largerwings) and later mentioned factors giveit a more docile handling. Thedesigners thought that big wingseliminated the need for LE slats / flaps,reduced cost and simplifiedmaintenance.Impressed with the MiG-25, planners inthe U.S. initially requested Mach 2.7speed.
  4. 4. 4• The US knew the rough dimensions of the MiG-25 and demonstrated performance records(people at McDonnell Douglas thought somethings couldn’t be done without additionalrocket motor) but the weight of a MiG-25 wasunknown at that time. Only after defection toJapan in 76 it was found that subsonically it isin the F-4 class because of the engine cycle(turbine inlet temperature and pressure ratio)required for high-speed flight and heavierweight of the conservative materials in thestructure of the aircraft. Later, the US quit highMach requirement because of the huge fuelconsumption of TF engine at that speed (untilthe revolutionary solutions in the compressor)while available fuel was modest. Also, thecockpit transparency area would be limited,much like of F-4. It was impossible to merge theperformance of a MiG-25 with otherrequirements based on experiences gained inVietnam.• The 4thgeneration fighters caught Soviets mid-step because they had just deployed inter-generation fighter / interceptors MiG-23 andMiG-25. The first followed the trend of that time- variable geometry (VG) wings with all theadvantages and disadvantages that this brings,and the other went on the road less traveled –its flight domain practically starts where thespeed / ceiling of other aircraft end.• Other types of that inter-generation were theFrench Mirage F1 (with unsuccessful VG MirageG8), the Israeli Kfir and Swedish Viggen.• The US fighter of the time was theslatted F-4 Phantom. Soon after,USAF abandoned Mach 3interceptors XF-108, YF-12 andlater also Navy F-14 and 3-enginedVigilante, interceptors consideredby USAF.
  5. 5. 5The main features of 4thgeneration fighters, besides agility and wide field of view that cockpittransprency allows (the pilot in an F-15, sits more ‘outside than inside the cockpit), is theability to detect and engage targets below the horizon, at a very low altitude - in thepresence of ground clutter.Increased maneuverability of 4thgen. 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 turnradius. A side benefit is slower landing speed of 225-250 km/h, at lower α, which meansthat fleet will not be spent in peacetime accidents on landing.• More engine power (all relative to the weight of the aircraft) which allows sustaining a40% higher g-load without losing speed and the maximum rate of climb increased fromabout 150-220 to 230-330 m/s.Max thrust without afterburner for a given air flow, depends on the temperature thatturbine can withstand, without burning. A significant increase in thrust of that enginegeneration 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 usedthat metallurgy in the West was J58 that powered the SR-71, a 1st fighter engine, F100-PW-100 which powers F-15 and TF30-P-100 for F-111F bomber. Combined with aircooling for the turbine (hot compressor air), an increase of about 300ºC (from about 1100to 1400) was achieved, compared to the previous generation.Further development in turbine metallurgy were singlecrystal blades (whole turbine blade in one crystal)applied after 1986 with much fanfare on the F100-PW-220.L-julka AL-31F, the Sukhoi 27 engine, has a singlecrystal turbine blades cooled by compressor airpreviously cooled in the heat exchanger.
  6. 6. 6The last of the Soviet fighters designed before the collapse of their ideologicalsystem. Their leaders failed in promotion of ethics and social justice, so the peopleopted for consumer freedom, vice and justice for corporations.
  7. 7. 7The F-15 Eagle is an all-weather, tactical fighter of extreme performance andmaneuverability, designed to gain and maintain air supremacy over friendly or enemy-controlled airspace. It is the fastest conventional fighter with agility and avionicsunmatched until MiG-29, Typhoon and Rafale, fighters that entered inventory 10 (MiG)to 27 years later (Typhon).
  8. 8. 8L-julka AL-31F, Sukhoi 27 engine, has a single crystal turbine blades cooled bycompressor air previously chilled in the heat exchanger.The second, less well-known contributor for thrust increase and weight reduction is inthe turbofan concept itself. It has lighter turbo-machinery weight (about 200-300 kg inthis class) and higher afterburner thrust increase (more unused oxygen in the bypasschannel. The compressor diameter (weight) is much smaller than that of turbojet (seeGE129 scheme). That’s why only 60% of the air is compressed to 23 atmospheres, andthe remaining 40% to 3 atm only, for example. Specific fuel consumption is 25% lowerthan the in previous generation fighter engines, partly because of the highercompression ratio (about 24 vs.14) and partly because thrust of bypass air has slowerexhaust velocity.AL-31F has active compressor stall protection measures (e.g. when flying behind anotheraircraft or when missiles are launched) for stable operation of the engine, which is thestandard previously applied even in the MiG-21.
  9. 9. 9• Better structural and volumetric (for fuel and systems) efficiency due to wing-fuselageblending. Wing-body fairings give the wing root rib more height increasing structuralrigidity and strength, or vice versa, for required strength weight of the structure could belighter. F-15 and Su-27 both contain a high percentage (25-30%) of titanium alloys forbetter strength / weight ratio than steel or aluminum, resulting in a weight reduction of20% of those structural parts. Less known is another feature of newer materials, given inthe table:Material Cost in the U.S, late 80sMaterial price ($/kg)Aluminum AL 2024-T4 3.3Aluminum AL 7075-T6 11.8Carbon epoxy composite 357.5Steel D6AC 4.4Titanium alloy Ti-6Al-4V 502.5• Improved controllability and stability: Adversecharacteristics such as pitch-up and wing-rock,yaw divergence, adverse yaw due to roll andspin tendency are reduced or eliminated. Toimprove handling – i.e. to ‘fix’ pilot commands,Command Augmentation System (CAS) hasbeen added to Flight Control System.CAS has a 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-gand departure (yaw-rate) warning tone.
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  12. 12. 12• 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 oreliminated. To improve handling – i.e. to ‘fix’ pilot commands, Command AugmentationSystem (CAS) has been added to Flight Control System. CAS has subsystem to reduceyaw during roll at high α (ARI Aileron-Rudder-Interconnect). Su-27 has α and g-loadslimiter, 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 planeshould have positive directional stability, favorable dihedral effect, efficient rudder andailerons and proverse aileron yaw.The maximum usable αdepends on the combination ofthese factors. It is crucial thatdynamic directional stabilityalong flight-path and factorcalled lateral control departureparameter’ (LCDP) i.e. rollresponse to roll command arepositive to the highest α. It wasfound that if the LCDP isnegative (opposite rollresponse), it will cause yawdivergence and if dynamicstability along the flight path isalso negative, the plane will gointo spin. Radome shape -depth / width ratio andcurvature of the lower part ofthe nose cross section areconsidered factors whichcontribute significantly to thespin resistance.
  13. 13. 13Minimizing the coupling between roll and yaw axis is crucial for improved handling ofthe 4th and newer generation fighters. In fact, depending on the Mach and α, along thepilot commanded deflection of ailerons, the system adds rudder which reduces sideslipangle and provides an appropriate response to the rolling inputs. Similar controlfeedback (loop) helps aircraft to roll along the flight path axis and not about thelongitudinal axis of the aircraft.Loss of control in the F-15 is not possible when α is less than 20º. At higher α, if thereis any significant asymmetry of fuel, external payload or asymmetrical flow emanatingfrom the nose (due to geometry erosion caused by years of service) increasessusceptibility to loss of control / departure.ARI reduces pilot aileron inputs and thereforethe aircraft is slower in roll response at higher α,but the aircraft is safer. Rudder inputs can makerolling faster - creating a sideslip angle, butthere is a thin line to spin. At Mach numbersbetween 0.5 and 0.76 and 30-35º α, F-15 isdirectionaly dynamically unstable (along theflight-path), like many modern aircraft. In thisdomain, spin resistance is reduced. Otherwise,if the commands are placed in a neutral positionat the first sign of loss of control(uncommanded roll or yaw) the plane will beback under control.Good controllability at high α comes fromeffective roll and yaw controls (high-qualityairflow around them, influence of LERX, rudderposition out of disturbed airflow that comesfrom h. tail and body) and aileron proverse yaw.
  14. 14. 14Su-27 is a newer airplane and therefore aerodynamically more refined. Wing profile withleading edge flap (LEF), at high α has more curvature providing more lift and lateral-directional stability. Ratio of flap chord over the wing chord length is higher at the wingtip than at the wing root, so when flap is deflected wing tip profile has more camber thanroot profile, resulting in proverse increment of pitching moment at high α.- Leading edge wing root extensions (LERX) / strakes large sweep angle generatesvortices on the inner wings and Sukhoi fuselage, delaying stall. Same mechanismimproves the static directional and lateral stability and significantly reduces buffet athigher α. These two innovations combined significantly reduce buffet, increase lift andlift-to-drag ratio in turn.- Wide fuselage, LEX and blended wing-body together form low aspect lifting area thatcontinues to generate lift at high α, when the wing stalls. Attention is paid to thedistribution of masses and side-area to obtain a combination which as sideslip angleincrease gives a negative increment (nose down) of pitching moment, so that spin wouldbe oscillatory rather than stable.- Sukhoi saw benefits of reduced trim drag by relaxing longitudinal static stability andincorporation of electronic commands. Su-27 is up to 5% mac unstable. Spin preventionsystem limits α to 24º at low Mach, but the system can be overridden as seen in Cobramaneuver.
  15. 15. 15When F-15 set the standards, other manufacturers such as Dassault-Breguet could laterproduce fighters better in one aspect, e.g. M2000 has more wing, relatively, for betterinstantaneous turns (but with greater speed loss) for faster target IR missile acquisitionbut overall, as U.S. military claims, none of the newer fighters, except for Stealth hassignificant (>10%) better performance. It seemed that until the emergence of the nextgeneration fighters, no aircraft would have better overall capability. F-15 has beenoperational for 35 years.Then came the Su-27, the Russian answer to the F-15. It was intended to be a superioraircraft 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 enemyterritory. It looks like a combination of F-16 and F-14. The initial configuration of theaircraft did not have an appropriate position of the vertical fins which caused bad stallbehavior. Also, wing geometry with double curvature leading edge, along with twist andcamber in profile, was technologically difficult to produce.In the design of Sukhoi, special care was taken to the optimization of the cross-sectionarea and distribution (see picture of nose to nose Su-27 / F-15). Relative size of cross-section area was about ¼ less than in competitors, which gives max. trimmed L/D of 11.6compared 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 amountof internal fuel ratio relative to aircraft weight, whichprovides range as competition with additionalexternal tanks. To keep the weight of the aircraftunder control, structure weight had to be reduced atthe expense of lower allowable g-load, 8 versus 9gstandard, and 50-100 km/h less allowed airspeed (q).
  16. 16. 16When Su-27 appeared, it was a difficult tactical problem for adversaries. Range withinternal fuel was 2 times greater than of the F-15A, turn performance and controllabilitybetter, radar had similar range, radar missiles had greater range because of inertialmid-guidance phase, large off-boresight angle, helmet cued IR missiles - 20 yearsbefore the West, were considered fatal.Thats not all, because the Soviets were practised in smart attack tactics, where a pairof fighters would approach the opponent with crossing paths, together making ahorizontal 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 (reflectsfalse target position) which takes the radar centroid off the target, until the break oflock-on (like Sorbcija jammer).
  17. 17. 17Climb record breakersTo break climb records to the tropopause (about 11 km altitude) an aircraft needs best thrustto 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 greaterheights, the aircraft must be particularly fast (MiG-25). These planes are also weightstripping champions. At the start of the attempt to the first height step (H=3 km) F-15s take-off weight was 12700 kg and the Su-27’s was 14100 kg. Stripped down F-15 had no flap andair brake actuators, cannon, radar and electronics, displays, generator, backup hydro-system and even landing lights and paint were missing. Sukhoi has gone even further andremoved the ventral fins, tip of vertical stabilizers and an engine inlet VG ramp and aileronactuators. The F-15 took about 1 minute to 12 km altitude, from the start of take-off. It heldthe records to 3, 6, 9, 12, 15, 20, 25 and 30 km. The F-15 still holds the record to 20 km. TheP-42 (Su-27) climbed about 10% faster all the way up to 15 km and the MiG-25 has re-takenthe records to 25, 30 and 35 km.
  18. 18. 18Their engines were tweaked to increase thrust 5-10%, which gives them the thrust toweight 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 itcould climb vertically and at the same time accelerate at 0.3 g (3 m/s2) or accelerate inlevel flight at 1.3 g i.e. to increase speed 450 km/h in 10 seconds. TO ground run was120 meters in 4 seconds after the release of the brakes. It was supersonic after the next19 seconds.
  19. 19. 19Not to mention figures that MiG-29 did at Farnborough 1988, the loop immediately aftertakeoff, with leveling off at the top (the most challenging stability and control ‘test’ wherehigh α transitions to β and again to α at top of the loop and the lowest airspeed, thedomain where half the Phantoms in Vietnam were lost, the figure that even F-18 does notdare to replicate). It was followed with another loop at the top of the first one – S figure. Ortailslide / bell, the vertical climb until running out of speed until the plane starts to gobackwards (0g). With forward stick nose was pitched down, retaining throughout the fulllongitudinal and lateral stability. The aircraft needed 10 times less airspace to completethe figure than the best previous fighters whose behavior was not always predictable! Thereason why MiG-29 needed such a small altitude for tailslide was simultaneous AB light-on on both engines (otherwise it would yaw and roll, the aero-surfaces would not be ableto compensate at that airspeed). No Western engine would have a satisfactory responseunder those conditions (GE, PW, RR, MTU, IHI, FIAT).CobraUntil 1988 Soviet military aircraft were missingat Western airshows, a fact that made room forunderestimation. E.g. the notorious spy-airlinerinterceptor - Su-15, was praised as theinterceptor with the best performance byBelenko, the pilot who escaped in the MiG-25. Itspredecessors, Su-9 and 11 held the world recordfor sustained altitude, 1 kilometer more thanPhantom and that is an indicator of overallperformance.
  20. 20. 20The F-15 does not test odds against mishaps and does tailslide at high altitude, fromwhich 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 worldaudience with a figure that showed a remarkable degree of the aircraft’s pitch agility. Inlevel flight, at about 400 km/h, the pilot suddenly pitched the plane to about 120º (withapproximate α) while continuing to fly forward. The whole time there were no signs ofrolloff or yawoff. The figure was reminiscent of a cobra that takes momentum before theattack.Before the performance, the Soviets had problems logging a flight program. Accordingto Pugachev, the French had taken the position that they invented aviation and thatsuch a figure should not be performed because it was dangerous. Pugachev showeddocumentation, 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. Therewere similar, poor-man Cobras, demonstrated earlier at high altitudes. For example, thefamous pilot-strategist Boyd used to bet with colleagues that within 40 seconds he’doutmaneuver 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 managednot to lose the bet. But sometimes the aircraft would be lost, brining him before a CourtMartial, where he defended himself by saying that in the Flight Manual nothing said thatthis should not be done. Other famous performers of a modest Cobra (up to 80°) areDraken and F-14. Many 4th generation fighters have been tested to 90º α but at highaltitudes (during Tailslide), where there was enough airspace to restore control, afterpossible engine flame-out, departure or spin.
  21. 21. 21Pugachev 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 helpof LEX vortex lift mechanism and longitudinal instability allows dynamic pitch angles and αin 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 unstabledirectionally at α of about 20-40º, where the airflow begins to separate. Su-27 rolls-off here at40° α. The essence of the Cobra figure is to quickly pass unstable α region (while the largeinertia of the aircraft prevents the potential roll/yaw-off) and come into benign region ofcompletely separated airflow;​- Longitudinal stability at 100°+ α: because of the high pitch rate, the aircraft passes thepoint of max trimmed α (that is about 50-60º α), but the tailplane size and deflection pitchaircraft back to the initial α. The author believes that the aircraft was designed with over-dimensioned tailplane (as a backup) because the static longitudinal instability was stillunproved. F-16/18 fighters have large LEX compared to tail ‘volume’ so planes have difficultyreturning 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 notresult in pitch down motion.- Stable engine operation at 100° α / less than 200 km/h IAS (earlier generation turbofans hasabout 20º α limit);Su-27 set new standards in fighter design and paved the way for super and hyper (up to120º α) maneuverability (dynamic entrance into supercritical α - flight mode that permits adecrease of airspace needed for turn by 2 times).
  22. 22. 22RadarF-15 has always had the most modern radar. The planar antenna, combined with the highand medium-pulse repetition frequency (prf) transmitter gave the Hughes APG-63 radar10 years advantage over other radars with a mechanical antenna. European radars onTornado, M2000, and JA-37 Vigen (the latter had a modest Hughes license) had the oldertype of antenna with inferior sidelobe characteristics - reverse cassegrain, while bothhigh and medium prf (the first provides greater look-down range and the latter is moresuitable for the detection tail-on, low-altitude targets) was far away. So Viggen has twotimes less range while Tornado chases nose-on targets. Neither did the F-14 havemedium prf. The French M2000 RDM radar had a low prf, unsuitable for target detectionbelow the horizon.Sukhoi -27 radar N001 has both prf, but because of the technology gap, it kept thereverse 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 againstfighter sized targets, the USAF confirmed that they had the same range.
  23. 23. 23Electronic warfareF-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 ownposition) that can be stored internally. Its operational status, like of some other systems ofthe U.S. Military, is often accompanied by criticism that it has serious flaws and thereforelimited operational capability (to protect the carrier-aircraft in this case). The GAO (GeneralAccounting Office), was established by the U.S. Congress to prevent deception by Militaryand big corporations. According to GAO, system ALQ-135 had been purchased although it dinot show an acceptable operating performance (they were not published in the media in ordenot to spoil the mood of the possible opponents for surrender). The Sukhoi jammer - SorbciaS is bulkier but uses innovative methods of deception jamming. Located in the containers atthe tip of wings, with front and rear wideband phase-steered antennas. For effective noisejamming, a very high transmitter power is required, which only specialized planes have. Thesecond method - deception jamming is not effective against monopulse antennas. But if thejammer antennas are spaced (15 m in Su-27 wingtip case or better if the plane tows jammeron a long wire) the cross eye technique gives good results, especially with phasecontrollable beams that rationally use available power, as in Sorbcia. It allows simultaneousjamming up to 10 threat radars.
  24. 24. 24WeaponsDensity of missile guidanceelectronics was always on the Westside. As it turned out in conflicts (i.e.SAM systems of the 60s and F-117/16), fighters fall down evenwhen they are hit with missiles withless densely packed electronics. It ismore important to design i.e.monopulse antenna seeker for moreaccurate guidance and resistance tojamming or to add an inertialsubsystem for guidance at rangeswhere the missile seeker/radarantenna is too small to acquire thetarget.Missiles AIM-7F / M and R-27R havealmost the same max range of about40 km. However, the R-27R has anadvantage when launched atsupersonic speeds. In that case,because of the additional inertialmid-guidance phase, it can belaunched from 60 km and missileguidance radar seeker canacquire target in the second phase of the flight,when it gets close to 30-40 km.Western missile guidance system improvementswere evolutionary, based mainly on improving thecomponents and the packing density of electronics.The launching of AIM-7M missiles at a speed ofMach 2 would not increase launch distance, justthe limits of target’s max speed and g-load. A largeamount of fuel allows Sukhoi to fly generously atsupersonic speeds providing the missile launchspeed and kinematic advantage.Regarding speed and altitude, both missiles canshoot targets in the SR-71 aircraft class.
  25. 25. 25Turn performanceSu-27 has 5-10% advantage in lift limited turns i.e. instantaneousturns at subsonic speeds. As directional stability decreases withMach number, α limiter of the Su-27 (as in F-16) cuts allowed α andso min airspeed (with 4 AAMs and half fuel) increases from 203 to230 km/h at M 0.9. This is visible at high altitudes where cornervelocity migrates to transonic speeds.The F-15’s FCS does not limit α but buffeting at higher subsonicMach numbers does. At Mach 0.9, F-15 experiences heavy buffet atabove 10º α so it is physically impossible to sustain cited α morethan a couple of seconds. At trans/supersonic speeds, structural g-limit advantage is on F-15’s side, but no one will look at the limitsduring a dogfight. However, as at high altitudes, at trans /supersonioc speeds, turn radius exceeds the target practical visualrange limit (about 2000 m) and dogfights do not normally occur here.The situation is similar with the thrust limited (sustained) turns. Atsubsonic speeds the advantage is on the side of the Su-27, between0.9 and 1.3 M there are no noticeable differences, and above that, theadvantage is on the side of the F-15. The latter is possible thanks toPW220’s digital engine controls, which can more flexibly supportsupersonic 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 suppresspossible departure and spin, analog flight control systems limitaileron / tailplane deflection and so roll rate with α decreases, whereat about 30º it is close to zero.
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  28. 28. 28Against each otherThe author’s intention is not to present anybody’s propaganda nor to be involved inmarketing. We’ll just look at the validity of some allegations about the kill ratios mentioned inthe media. Regarding the F-15, the reported figure is about 100:0, achieved by US and IsraeliAF.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 toone scenario. In close combat, according to Rand studies, with the same generationweapons "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 ofspecial 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 hadonly to approach, fire AMRAAMs and immediately withdrew. The number of hours of flightcrew training and reality were additional factors.Ethiopian Sukhoi 27 shot down the Eritrean MiG-29, supposedly only because of Russiansupport. Alleged results of so called simulated combat between Su-27 and F-15 during theSu-27’s visit to U.S. were not serious because the Sukhoi even without afterburner, notexceeding 18 º α, succeeded to outmaneuver F-15.
  29. 29. 29After Vietnam, the U.S. military learned a lesson about the public and the media, and now allinformation 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 theAmerican pilot of B-52, Dana Drenkowski, a decorated Vietnam vet, whose personal life wasruined because of his endeavors. He wrote about the long tradition of concealing losses ofUS aircraft, from Korea and after. He touches on losses in Operation Linebacker II, in 72, inwhich 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 personallycounted 22 planes (+5 which landed with damage beyond repair). He thought thatVietnamese claims of 25 planes should also be noted.Israeli historian Shlomo Aloni in his works on the 67 war touches on air combat. He writesthat IAF/DF’s (Israeli Air Force/Defence Force) two downed Israeli Mirage IIICJ officiallyattributed to the Syrian air defense, according to Israeli intelligence agency were in fact shotdown by the Egyptian pilot Nabil Shoukry flying the MiG-21. Of course, in the so-called “freeworld” 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 thetwo-seater MiG-21 demonstrated handling and maneuverability at low and zero airspeed.
  30. 30. 30Su-27 in the US Air ForceAccording to U.S. aviation authorities (FAA - Federal Aviation Administration) there were twoSu-27s in the United States, privately owned. Using a favorable political situation in Ukrainein 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 theywere sold. Russian news agencies reported that the track leads to U.S. Military.
  31. 31. 31Neither the F-15 nor Su-27 are able to land with both engines-out, because aircraft systemscan not support that.During the decades of operational use of F-15 there were opportunities to see theusefulness 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 lightsubsonic A-4 attack aircraft of the 50s, collided with one another after which the F-15 lostone 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 useselectro-hydraulics and established control. He considered whether to leave the plane andyet no warning light that something is wrong was blinking. He managed to land safely atabout 400 km/h.F-15 has max lift (minimum speed) at about 35° α. Above 20° wings are stalled and fuselagecarries the plane.The advantage of F-15’s early appearance, has now turned into a handicap because theaverage age of operational aircraft is now 25 years.
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  33. 33. 33TECHNICAL DATA*F-15C (PW-220) Su-27SKFirst Flight (initial model) 1972. (F-15A) 1977./1981.Operational from 1976. (F-15A) 1985. (1990.)Length overall, without pitot-tube, m 19,4 21,9Wing span, m 13,05 14,7 (14,95 w tip R-73)Wing area, m256,5 62Wing aspect ratio 3 3,5Height, m 5,63 5,93Tail span, m 8,74 9,8Weight empty equipped, kg 13400 17200Fuel 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 kgMax external payload, kg 6 - 8000 6000Combat weight with 50 % fuel, 4 AAM, kg 17625 22780Thrust/Combat weight ratio 1,21 1,1Max. Take-off Weight, kg 30850 28-33000 =f (wheels)Engine2 x F100-PW-2206,52-10,64 t2 x AL-31F7,77-12,5 t
  34. 34. 34TECHNICAL DATA (cont) *F-15C (PW220) Su-27SKRange (internal fuel), km 2200 3700Range (with external fuel), km 4000 -Limit airspeed / Mach in dive 1470 km/h IAS / 2,5 M 1400 km/h IAS / 2,35MCombat ceiling, 4 AAM, m 17100 18000Max level speed at SL, clean config, Mach 1,15 1,12Max level speed, clean config, Mach 2,4 (2,2 PW100 engine) 2,15Min airspeed, 1/2 fuel, 4 AAM, SL, km/h 230 203Max rate of climb, ‘’ ‘’ SL, m/s 300 290Max instantaneous turn rate, SL, º/s 26,4 (9g) SL 28,0 (8,0g) SLcorresponding inst. turn radius, m 415 330Max sustained ‘g’ in turn, altitude (H)=5km 6,65 6,67Max 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 secAcceleration 1100-1300 km/h, Comb. w, SL 11,5 sec 12 sec
  35. 35. 35* All data are official or computationally derived from official sources* Comparison F-15/Su-27 is done with a proportionally lighter F-15 (relatively lessfuel to a/c weight) and with less missile drag (only AIM-7 with conformal methodof carriage) w/o MRM/SRM combination as in Su-27TECHNICAL DATA (cont) *F-15C (PW220) Su-27SKLimit g-load (subsonic) 9,0 at 17,0 tonnes (M<1) 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 tonnesTake-off ground run, m 380 at 20,7 tonnes 650 at 27,4 tonnesLanding run, m 1300 620 with chuteInternal armament 1/6 x 20 mm 1 x 30 mmExternal AA armament 8 AAMs 10 AAMsNumber built 1200 680Price 1998 year, m$ 30 30Similar, more comprehensive title (at Performance in Practice: Phantom versus MiG-21:How to do split-S in Mig-21 within 3000 ft: Unexploited low speed maneuverability
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