ICAS2002 CONGRESS GENERATION OF SU-27 FIGHTER. Mickhail A. Pogossyan, Mickhail P. Simonov, German I. Zagainov, Alexy Z. Tarasov Sukhoi Aircraft Design Bureau, Russia Keywords: fighter, aerodynamics, aerodynamic scheme, negative longitudinal stability, closed loop system, fly-by-wire, thrust vectoring, combat, high angle of attack, supermaneuverability. Abstract completely because of one reason: mechanical control system. The outstanding project of The history of design and development of Sukhoi superlight fighter of Swedish designers had Su-27 fighter family including more than 10 realized in "Grippen" program: modern modifications is presented. aerodynamic scheme, fly by wire control system and other achievements had placed this aircraft 1 Introduction. Prehistory. in the row of outstanding fighters of the world. Prehistory of this paper had started from the As to USA and former Soviet Union in beginning of 70th. their history of design of fighters during last 50 During some decades after Second World years, there were some outstanding War only two countries - USA and former achievements and mistakes. For example, USSR were and continue to be real competitors historical lessons have been received from in development of fighters. In Europe only aircrafts with variable sweep wing (F-111, and France had active position in development and MiG-23) and others: F-104, F-4E, F-117, and production of fighters (Mirage family). Russian T-58D2. However, at the same time However, comparison between Mirage-family two countries had some unique aircraft: F-5E, and 4th generations of US and Russian fighters: MiG-25 and others. has evident result: superiority belongs F-15, F- At the beginning of 70th on the base of 16, F-18, Su-fighters generation (from Su-27 up experience of local wars USA started to develop to Su-37) and MiG-29. the new generation of fighters and multipurpose Three decades ago Great Britain, crafts such as F-15, F-16 and F-18 with new Germany, Italy decided to joint its efforts in approaches, using in projects: development of military crafts, but with • New aerodynamic scheme, a little contradictory requirements to aircraft. As a bit resembling MiG-25, for result of their joint efforts "Tornado" had been achievement of new level of developed and produced (no comments about manoeuverability with α≥25°, this plane). CL≥1,35 (previous generation of During last years Germany, Great Britain, fighters had α<20°, CL<1.0); France, Italy, Spain elaborated "Eurofighter" • Fly-by-wire control system; with an aerodynamic scheme resembling • New generation of avionics. "Mirage" with small canard. It is typical At that time Russian Ministry of Defense representative of 4th generation of fighters with gave out the official order to design new modern airborne systems and equipment. generation of fighters with better characteristics An original way of design of fighters had in comparison with mentioned above USA been selected by Sweden many years ago. The projects, but with lag about 3-4 years. known aircraft "Viggen", canard, was very Sukhoi Aircraft Design Bureau (Su-ADB) impressive, but potential possibilities of its together with other aviation enterprises and aerodynamic scheme had not realized 165.1 M. Pogosyan, M. Simonov et al aviation research centers (Central Aero- Approximately in the middle of 70th in Su-ADB Hydrodynamic Institute TsAGI and Sibirian and Russian research centers there were Aviation Research Institute SibNIA) had carrying out wind tunnel investigations of developed new aerodynamic scheme (so called aerodynamics of fighter with thrust vectoring "integral scheme") with optimal longitudinal and impressive data were received and we relied unstability 3%...5% of mean aerodynamic chord for the achievement of CL∼2,5 with using thrust (at subsonic speeds) and fly-by-wire flight vectoring and increasing of aircraft negative control system for future heavy fighters. The stability margin. project was called T-10. But what about angles of attacks? What Su-ADB, step by step, developed the ° project and as the result of extensive work and angles of attack after 30 will be useful for closed cooperation of Sukhoi, research centers fighters, especially in closed combat? and many aviation enterprises the maiden flight of Su-27 prototype T-10-1 have been in May 2.1 Simulation of combat at high angles of 1977, Fig. 1. attack. At first stage of aircraft design: In 1980 research teams in Su-ADB and TsAGI Some problems of stability have been have started to investigate the closed combat of solved. For example, there was guarantee the two fighters; one of them had possibility to stability of "aircraft+FBW" closed loop system realize maneuvers with achievement of α~60°, under great disturbances (so called "stability in or so-called supermaneuverability. The results large") with simultaneous minimization of of simulations were very impressive [1]. These hydraulic systems power. As we know, this results were obtained before the well-known problem has led to flight accidents with YF-22 publication of Herbst [2] but the publication was and "Grippen". This problem was solved at the impossible because of secrecy reasons. design stage with less tail deflection rate in These data convinced us to continue our comparison with two mentioned planes. investigations and the second topic of our Very effective (from pilots opinion) researches was the investigation of fighter limitation of normal load factor nz and angle of aerodynamics at high angles of attack and attack α was realized for usual exploitation. development of its mathematical model. However, we did not avoid an accident with PIO because of methodological mistake during 2.2 Fighter aerodynamics at aigh angles of flight tests and crash (destruction) of craft for attack the same reason. Very soon, we understood, that our In order to realize supermaneuverability in prospects and expectations had confirmed by flight and before training of pilots, it needs to flight tests; moreover, concrete data surpass our have mathematical model of aerodynamics at expectation. Aircraft achieved angles of attacks high angles of attack and solve the problem of (in maneuver) more then 25° and CL>1,6. After stall and spin (these regimes have to be some improvements in aerodynamics of Su- excluded). During many years joint Su-ADB family fighters the lift coefficient CL~2,0 have and TsAGI team investigated the aerodynamic been achieved in stable turn. peculiarities at high angle of attack and Therefore, we received in 1977-1978 the elaborated the mathematical model of confirmation that the task of creation of fighter aerodynamics with description of some effects succeeding in maneuverability the fighter- [1][3][4]: competitor F-15 has been solved. • Nonsymmetrical flow including nonsymmetrical breakdown of 2 High maneuverability, theory and practice. vortexes at high angles of attack, and nonsymmetrical yaw and roll moments as a result; 165.2 GENERATION OF SU-27 FIGHTER • Dynamic lag, static and dynamics coating, expansion of the set of weapon, new hysteresis in lift, pitch, yaw, roll airborne avionics and FBW control system, new moment, side force at high angle of materials etc.) and to extend the sphere of attack. application (closed combat and interception On the base of systematical wind tunnel individually and in group, ground attack, investigations, flight tests in Su-ADB and Flight reconnaissance, medium range bomber, navy Research Institute (LII), the mathematical aviation with take off and landing to aircraft model was developed with using additional carrier). differential equations for parameters, which In this paper only basic modification of determine the scale of phenomena: local on Su-27 of plane will be mentioned, see Fig. 1: profile, wing, or global, including whole plane • Su-27S/SK basic single seat from nose up to tail. configuration (typical role is On the base of this investigations more interception) with neutral and small detailed studying of stall and spin, requirements negative margin of longitudinal to effectiveness of aerodynamics and thrust- stability, maximal Mach number up vectoring control, requirements to pitch control to 2.3 and airspeed up to 1350 km/h. of airplane and requirements to characteristics On this plane pilot Victor Pugachev of inlets and nozzles were fulfilled. realized maneuver "Cobra" with At that time, Su-ADB continued the flight angle of attack up to 110°; tests of first copies of Su-27 fighter and • Su-30MK – two seats multirole discovered the possibility to fulfill maneuver fighter, aerodynamicaly is identical with achievement angles of attack more then to Su-27, with new airborne 60°. avionics and wide air-to-ground Joint efforts of specialists and pilots from attack possibilities, Fig. 3; Sukhoi ADB, FBW control system deliver • Su-30MKI – two seats multirole MNPK "Avionika" and TsAGI provided the fighter with small canard and modification of control system and unstable aerodynamic configuration methodology of flight tests. Intensive training of (up to 8…12% of longitudinal pilots was carrying out using TsAGI moving- unstability is permissible), with based simulator. It has opened the "door" for in three axes thrust vectoring, Fig. 4. flight realization of maneuver, later called On this aircraft CL∼2.0 is achieved "Pugachev Cobra", Fig. 2. and angle of attack limitation is absent. 3 Sukhoi Su-27 family of fighters • Su-34/32MF – two seats middle Role of personality in history is tremendous, not range bomber with maneuverability only in politics but in technology, science and typical to fighter, with original engineering too. scheme of pilots disposition similar Pavel O. Sukhoi, the first General to one at civil crafts (side by side), Designer of Sukhoi ADB, was initiator of Su-27 with flat and sharp-pointed nose, project. After him, E.A. Ivanov made Fig. 5,6; • outstanding contribution in design of this plane Su-33K – single seat navy fighter, and its modifications. unstable aerodynamic configuration Totally, Su-ADB elaborated more than 10 with small canard, Fig.