When the Su-27 “Flanker” and MiG-29 “Fulcrum” came onto the scene in the 1980s, they represented a significant generational leap in technology compared to earlier Soviet fighters. The missiles they carried also represented a generational leap in their own way.
Indeed, both the R-73 short-range air-to-air missile and R-27 medium range air-to-air missile which were first fielded on those aircraft serve on to this day. But the R-27 design in particular has proven to be particularly adaptable and resistant to replacement by more modern designs. But why has the design proven to be so long lived?
In 1974, the Central Committee of the CPSU approved for work to begin on the 4th generation of fighters—the MiG-29 and Su-27. As a result of this, the Vympel missile design bureau began work on the R-27 (referred to as the K-27 during prototyping and testing) missile.
It was first envisioned that there would be two different variants of the R-27 in service, a lighter K-27A for the MiG-29 with shorter range and a heavier K-27B for the Su-27 with longer range. As a result, the propulsion system for the missile was designed to be modular.
Due to the Soviet trend of creating both radar and IR-seeking versions of missiles, the R-27 was also designed with a modular seeker. This would come in handy later as many different variations of the R-27 were made with different seekers.
Another interesting design decision was the selection of the “butterfly” shaped control surfaces in the center of the missile. This was not uncontroversial. Some designers wanted a scheme similar to the earlier R-23 missile where control surfaces were mounted on the tail of the missile, as it afforded less air resistance at low angles of attack and was considered to be generally aerodynamically superior. However the need for the missile to be modular took priority and that design was rejected, as mounting control surfaces on the rear would compromise the modularity of the propulsion system.
Also interesting is that the designers of the R-27 thought that even with advancements in Soviet technology the possible radar power and radar seeker sensitivity of the R-27 and its launching aircraft would be inferior in power and sensitivity to Western aircraft. To counter this, Soviet designers improved the lock on after launch (LOAL) capabilities of the missile.