Sukhoi Su-27 real story

Sukhoi Su-27 : the real story

Text by Marcin Ladra (ladra@zeus.polsl.gliwice.pl)

The history of Su-27 has started in the late sixties. Under the influence of intelligence informations about newest russians fighters (e.g. advanced versions of MiG-21 and first prototypes of MiG-23) Americans have held competition for an entirely new generation of fighters which should be an answer to Russian counterpartners.

Three different planes were born from this competition : two light fighters: the F-16 "Fighting Falcon" and the F-18 "Hornet" and one heavy fighter-interceptor the F-15 "Eagle". All these constructions did have very good maneuvering abilities and had excellent dogfight capabilities. Introducing of these features were caused by the experiences from the previous conflict, and according to these experiences combat fighter must be able to fight at short distances ( former fighters like MiG-21 and F-104 were rather „piloted rockets with missiles” and were not much capable as dogfighters). In answer to the Americans competition Russians (in 1969) have also held their own contest for development of new fighters. Officially the program was called PFI (Perspektywnyi Frontowoy Istryebytyel - in English: Perspective Front-line Fighter), unofficially it was called „anti-F-15”. Russian have planned to create plane which should be better than F-15 in most aspects. In the competition participated all significant designs bureaus: Yakovlev with Yak-45, Mikoyan with the first project of MiG-29 and Sukhoi with the prototype of Su-27 - T-10. Somewhat later it was decided that two planes should be developed: one light counterpartner of F-16 (MiG-29) and one heavy-interceptor as the counterpartner of F-15 (Su-27).

Tactical foundations of the heavy fighter-interceptor were following:

maximal velocity : 2500 km/h (1500 km/h at sea level) and ceiling up to 18.5 km, range of 2500 kms
ability to destroy enemy planes flying as fast as 2400 km/h (1400 km/h at sea level) at an altitude between 30 m and 18 kms

Constructors also decided that the plane should be able to take-off from a 1200m runway. Very important in the later development of Su-27 was Russian mastery in advanced materials technology (titanium) and also knowledge of the fly-by-wire systems which had been tested on earlier Sukhoi’s T-4 (S-100).

It is rumoured that Pavel Sukhoi was thinking that it was impossible to create such (better than F-15) plane in the actual state of Russian technology, especially in the area of avionics, but finally he convinced himself to this project. Unfortunately he was not able to finish development of Su-27 since he died in 1975. In this situation Mikhail Simonov became general constructor of Su-27 project.

Su-27 cockpit detail

Birth of a sky master

Two main foundations of future Su-27 were : integral fuselage with strand wings and twin tail-plane and fly-by-wire system in longitudinal canal (plane could be statical unstable).

The first project of T-10 had ogival wing and one-trace undercarriage, the second was a continuation of MiG-25 series. Finally the first project was choosen, but its main problem was difficult technology of making ogival wing.

T-10 prototype

Thanks to the integral aerodynamical arrangement the constructors were able to put a huge amount of fuel into the fuselage. It was shown that the requested range of 2500 km plane could be achieved with only 5350kg of fuel (the complete amount was 9000kg). Since it was excellent score there was only a little problem : according to an endurance industrial standard the plane should be able to stand 8g congestion with 80% of fuel in reservoirs, but the plane endurance was adjusted to 5350 kg of fuel ! Fitting the plane to the standart was impossible because it could cause a serious growth of the mass, in the final oddity solution constructors have declared that capacity of fuel tanks is 5350kg and the rest of 9000kg fuel is the „internal additional fuel tank”. According to these facts plane’s range with full fuel tanks was 4000 kms instead of planned 2500 kms.

The next problem was to choose appropriate engines for new plane. At the initial stage it was intented to use Al-21F but these engines were not able to achieve the demands of thrust and economy. In this case new engine AL-31 was ordered at Lyulka design bureau. According to technical foundations this engine should have thrust of 122.5 kN and singular consumption of fuel smaller than 0.061 kg/Nh. Because the Russians was not able to introduce the technology of monocrystal shovels (although some sources saying that the monocrystal shovels was used in the construction of engine) the final achievements of Al-31 were slightly worse (i.e. singular consumption at the level of 0.068 kg/Nh). Since the development of AL-31 took a couple of years, the first prototypes of Su-27 were flying with older Al-21F3. In Su-27 plane, for the first time in Soviet Union the high pressure hydraulical installation was used, thanks to this solution the mass of installation was significantly smaller.

Another great problem for the constructors of Su-27 was the avionics, especially the radar system. It was intented to use the radar with the slit antenna but once again this technology was too advanced for Russian industry. In replacement the ordinary parabolical antenna was used. According to russian sources the ranges of the new radar are : 240 km detect range and 185 km tracking range. Some sources says that the Su-27 radar uses some technology of Americans constructions: APG-65 and AN/AWG-9 from Hughes company although the Flanker radar has greater range. Curious detail is that it was intented to arm the Flanker with R-33 missiles (well known from MiG-31) but these missiles, normally used by the air defence forces, were using other control frequencies than normal missiles and this project was finally abandonned.

The first prototype of Su-27, T-10-1 has made his first flight on 20 May 1977 from runway of Institute of Flight Test in Zhukovski. Not long after that, the plane was photographed for the first time by an American satellite and received the codename RAM-K (RAM from Ramienskoje site). Later the plane also received the NATO code-name Flanker-A. Analysis of the capabilities of the first prototype and their comparisons with the capabilities of F-15 (which data was supplied by the polish spy Marian Zacharski) has showed that the Su-27 was inferior to his counterpartner.

A new prototype

In this situation, despite the decision about starting the industry production of T-10, constructors had decided to thoroughly rebuild the plane, and have developed the almost new plane T-10S.

The main changes were in following areas:

the wing has no longer ogival edge, also the mechanization of the wing edge was introduced, ailerons were moved toward the fuselage and wing has received full adaptative mechanisation (later also automatic), the area of transversal cut was decreased to about 80% of previous. This last change was achieved by the reconstruction of engines mount, in the new design the gears boxes were on the top of both engines, it was also necessary to move vertical tail planes into another place. Finally the aerodynamic hackles were removed from the wings.
aerodynamic brake was removed from the under-fuselage position, and in the new design it became similar to the F-15 aerodynamic break: a big hatch on the top of fuselage.
in order to protect the engines from the dirt on runway the front undercarriage was moved to the rear, and the additional protecting nets were implemented in the air intakes of the engines.
the canopy was fully redesigned.
one of the most significant changes was the introduction of the new engines Al-31F (the new engines were used also in previous T-10 prototypes, starting from the number T-10-3). Two T-10S were build : T-10S-1 (T-10-7) and T-10S-2 (T-10-12) both in Sukhoi’s construction factory.

Thanks to all those changes the odds between F-15 and Su-27 have changed and the final ratio was 1.35:1 for Su-27 (according to Russian sources).

There were a lot of disaster during the development of Su-27, for example two prototypes were destroyed : T-10-2 (pilot Yevgenyi Soloviov died, probably from a fly-by-wire software failure), T-10S-1 and T-10S-2 (pilot Aleksander Komarov also died).

Serial production of Su-27 Flanker-B started in 1982, but the goverment tests were finished in 1985 and in this year the plane officialy entered service in army (first operational unit received Su-27 in december 1984).

Sources:

Note from the WebMaster : neither me nor the author of this text are from an english langage country. So this text could be sometimes odd or badly worded. If anyone reading it was willing to spare some time to correct it, I would gladly appreciate it.