Mikoyan-Gurevich MiG-19. Soviet experiments and prototypes

During its career with the VVS (Soviet Air Force), the MiG-19 was used as a testbed for various projects and prototypes. Some of them ended up being mass-produced, while others didn't go beyond the prototype stage.

The ones we're dealing with on this post are the following:

• Mikoyan-Gurevich SM-9/2: This, together with the SM-9/1, was the initial prototype for the MiG-19 (sans suffixe) and MiG-19S series. A single prototype was produced by Moscow's Aircraft Factory No.155. Work on it started in 1953 but it wasn't finished until 5th February 1954 when it flew for the first time. 
  It was powered by two Tumansky RD-9B which offered 5.732 lb of thrust power.Although initially unarmed, later it was armed with a single 23 mm NR-23 cannon in the nose plus another two NR-23 cannons placed in the wing roots. It also had hardpoints for two ORO-57K rockets, two bombs or additional fuel tanks.
• Mikoyan-Gurevich SM-9/3: This aircraft was the prototype for the MiG-19S version. It flew for the first time on 27th November 1955 though its production was started one year earlier. It was powered by the same engine as the SM-9/2 but it was armed with more powerful 30 mm NR-30 cannons. One in the nose and two in the wing roots. It also was equipped with a Svod long-range navigation receiver and served as the basis for the MiG-19S which was produced from 1956 onwards with some additional improvements. It could carry the same payload as the SM-9/2.
• Mikoyan-Gurevich SM-7: This designation was used for the three prototypes of the MiG-19P all-weather interceptor. They were produced concurrently with the SM-9 in 1954 andthe first machine, SM-7/1, flew for the first time on 28th August 1954. It was powered by the same engine as the SM-9 machines and was armed with the same NR-23 cannons placed also in the nose and the wing roots with hardpoints adapted for the same payloads. It was equipped with an RP-1 Izumrud radar in the nose which gave its characteristic 'flat' looking nose.
• Mikoyan-Gurevich MiG-19SU: AKA Mikoyan-Gurevich SM-50/SM-51. This was a high-altitude interceptor intended to reach the American Lockheed U-2 recon plane. It was equipped with a self-contained liquid booster rocket pack. A total of six machines were converted from MiG-19S fighters in late 1956 (the first prototype took off to the skies on 30th November 1956) and it was armed with just two NR-30 placed at the wing roots. 
  It seems that the project was abandoned due to the inability to control the aircraft at very high altitudes and its tendency to enter supersonic spins.
• Mikoyan-Gurevich MiG-19PU: AKA Mikoyan-Gurevich SM-52. These were a small series of three MiG-19P fitted with a Sevrook re-usable rocket booster pack in the same fashion as the MiG-19SU. It was also intended to be a high-altitude interceptor and the first prototype took off for the first time on June 1958. It was armed with the same weaponry as the MiG-19SU and, considering it was a converted MiG-19P, it was also equipped with an RP-1 Izumrud radar.

Sources:

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

2. https://www.valka.cz/Mikojan-Gurevic-SM-9-t824

3. https://www.valka.cz/Mikojan-Gurevic-SM-7-t823

4. https://www.armedconflicts.com/Mikoyan-Gurevich-MiG-19SU-t828

5. https://www.armedconflicts.com/Mikoyan-Gurevich-MiG-19PU-t829

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

7. Salamander Books - The Complete Book of Fighters