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.

While the earlier R-23 missile had inertial LOAL, where the missile’s seeker could home in on a target after being launched and flying without a lock for some time with an inertial navigation system keeping the missile flying straight, the R-27 improved upon this by adding the ability for the aircraft to issue course corrections via a radio datalink to the missile.

Tests were carried out at the end of the 1970s, with K-27s being fired from MiG-23s, although these were simply to test the telemetry of the missile and were not guided shots. The thermal version was also tested from the MiG-23, being shot at parachute targets. Test K-27 missiles were also shot from a prototype MiG-29 in 1980 with the thermal missile, though the prototype MiG-29 didn’t have a radar installed at the time.

Testing continued throughout the 1980s, with state trials concluding in 1984. The K-27 missile was finally adopted in 1987 as the R-27R and R-27T missiles, with R being the semi-active radar homing variant and the T being the heat-seeking variant.

At the same time, the K-27B “heavy” missile originally intended for the Su-27 had its designation changed to the K-27E, with the E indicating it would have more energy (longer range). It went through a longer development cycle than the lighter K-27 missile due to redesigns of the Su-27’s radar system to improve it and make it more competitive. Additional challenges posed by the extended range at which the K-27E was expected to operate at also caused a longer development cycle.

Testing for The K-27E was finally adopted in 1990 as the R-27ER and R-27ET, and the creators of the missile were awarded a state prize in 1991.

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During the long development cycle of the R-27, it was realized that the semi-active radar homing (in which the missile homes in on a radar signal created by the launching aircraft) on which these missiles was based might become obsolete. Studies were made into creating an active radar homing (ARH) version of the missile. ARH missiles have a small radar in the seeker, which allows the missile to self-illuminate the target instead of relying on an external aircraft.

This version was called the R-27EA. Drafted in 1983, it also underwent develop during the 1980s, but difficulties creating the small radar in the seeker delayed development. The fate of the project is uncertain, but most sources say major development was stopped around 1989 in order to focus on the R-77 missile instead, although work may have continued in private.

Overall, the main advantage of the R-27 series of missiles is the range on the ER variants, which is said to be around 130 km. This is far longer than any variant of the AIM-7 Sparrow, the closest NATO equivalent. The primary problem with the R-27 is that long development cycle of the allowed American missiles to surpass it.

One example of this is the mid-course datalink course correction feature of the R-27. While it was originally designed with this feature in the 1970s, the final missile only reached service by 1987. By that time, American engineers had incrementally added updates to their existing AIM-7 missile, including the same capability by the AIM-7P Block II, which was also adopted in 1987.

The compromise nature of the control surfaces probably also contributed to the decision to not further develop the missile. The next-generation ARH missile that was meant to arm the Soviet Air Force, the R-77, featured grid-fins on the rear of the missile for better maneuverability. Since the R-27 would never reach the level of aerodynamic performance of the R-77, it probably was determined to be a waste of further effort to give the missile ARH capability.

In many ways, the R-27ER can be seen as the “last gasp” of the SARH. It was designed to be one of the most advanced missiles of its type with long range and mid-course correction capability, but by the time it entered service, its type of missile was nearing obsolescence. America fielded its first ARH missile in 1991, the AIM-120 AMRAAM, only one year after the R-27ER entered service.

The Russian Air Force probably continues to field them because their long range outclasses most lesser adversaries who are unlikely to utilize ARH missiles. However, as seen in Syria, when a danger is posed by a peer or near-peer air force, the R-27s will come off in favor of the R-77s.

Charlie Gao studied political and computer science at Grinnell College and is a frequent commentator on defense and national-security issues.