Mikoyan-Gurevich SM-12

The Mikoyan-Gurevich SM-12 was the internal denomination that Mikoyan-Gurevich OKB (Mikoyan-Gurevich Design Bureau) gave to a series of four new prototypes for a new fighter that would replace the MiG-19. All of them were built at the Moscow's Aircraft Factory No.155. 

This new fighter design was an evolution of the basic MiG-19 which evolved, by a process of incremental modification as a point-defence interceptor with a mixed-power plant.

When the MiG-19 entered officially service with the VVS (Soviet Air Force), Mikoyan-Gurevich OKB kept on refining their SM-1 (I-340) design which dated back to 1951. The SM-12 was initially an exercise in drag reduction by using new air intake configurations. The first three prototypes (SM-12/1 to SM-12/3) were basically MiG-19S with an extended and straight-tapered nose with a sharp-lipped orifice and a pointed, two-position shock cone in the intake splitter. 

The third prototype differed from the rest in having a different engine. The previous two ones were powered by a pair of Tumansky RD-9B with 2.600 kg (5.732 lb) of thrust power. The third was, however, powered by a Sorokin R3-26 which offered the same amount of theoretical thrust power, but had more afterburning power. Thanks to this extra power, the SM-12/3 could achieve speeds of 1.430 km/h (888,56 mph - mach 1,16) at sea level and 1.930 km/h (1.199 mph - mach 1,56) at 12.000 m (39.370 ft) high. In some tests it even achieved a mach of 1.8 (2.222 km/h - 1381 mph) at an altitude between 17.500 m (57.415 ft) and 18.000 m (59.055 ft) high. Those impressive numbers prompted for the creation of a new point defence interceptor and was even tested with armament.

In a similar way, powered by the R3-26 engine, embodying a nose redesign with a larger orifice which allowed for the installation of a TsD-30 radar in a two-position conical centrebody, another prototype was produced under the name of SM-12PM. This one, unlike its predecessors, discarded the NR-30 cannons at the wing roots and was armed with two beam-riding K-5M air-to-air missile. It entered flight testing in 1957 and, in the end of 1958 it was joined by another prototype, this time called SM-12PMU. This PMU had its R3M-26 engines uprated to 3.800 kg (8.377 lbs) of thrust power with afterburning and augmented by a U-19D accelerator which, just like in the case of the of the MiG-19PU, took the form of a permanent ventral pack containing an RU-013 rocket motor with its propeller tanks. It was developed by D.D. Sevruk and the RU-013 could develop an additional thrust power of 3000 kg (6.614 lbs) of thrust power. With the aid of this ventral pack the SM-12PMU achieved an altitude of 24.000 m (78.740 ft) and a speed of mach 1,69 (2.086 km/h - 1296 mph). However, by the time this test was performed, the decision of manufacturing the Ye-7 (the prototype of the MiG-21) was already taken and the SM-12 was therefore, discontinued.

Anyway, many aspects of the SM-12 were carried over to the MiG-21 and its many variants.

Sources:

1. http://www.aviastar.org/air/russia/mig_sm-12.php

2. https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-19

3. https://www.valka.cz/Mikojan-Gurevic-SM-12-t826

4. Midland Publishing - Mikoyan-Gurevich MiG-19. The Soviet Union's First Production Supersonic Fighter