The reality of Sukhoi Su-21

[hesham]

Hi,

Some Western reports indicate that the Su-15TM was also
designated Su-21 and the Su-15UM or Su-21U. These reports
are apparently incorrect. Designation Su-21 was reserved for
Su-17M4 but never used.

http://en.wikipedia.org/wiki/Sukhoi_Su-15

 

[fightingirish]

I presume, that the "Su-21" designation was not used either for the Su-15TM, the Su-17M4 or any Sukhoi aircraft in general , because nobody wanted it mixed up with - or compared to - the better known Mikoyan-Gurevich MiG-21.

 

[frank]

Kinda like Su-15, Su-17, Su-25 & Su-27 not getting confused with the respective MiGs? ???

I presume, that the "Su-21" designation was not used either for the Su-15TM, the Su-17M4 or any Sukhoi aircraft in general , because nobody wanted it mixed up with - or compared to - the better known Mikoyan-Gurevich MiG-21.

 

[redstar72]

According to http://www.sukhoi.org/planes/museum/su17/, "Su-21" was provisional interim designation of what we know as Su-17M (the whole M-series, not only M4!). When the technical offer was submitted in April 1970, the proposed name was Su-21. It was logical enough, because the aircraft was much different from existing Su-17 (which was, in general, no more than swing-wing Su-7): new generation AL-21 engine instead of AL-7F and many other improvements. Moreover, it was planned to implant new avionics to match the rival - MiG-23B. But the avionics designers delayed with new equipment supply, so this upgrade was postponed. In June 1970, Sukhoi propositions were confirmed by joint resolution of the Air Ministry and the VVS - but under official designation "Su-17M" (internal S-32M).

Next time Su-21 designation appeared in 1975, again as provisional, for the next stage Su-17M modernization. It was planned to implant AL-31F turbofan engine, new TKB-687 built-in cannons instead of NR-30, all-new sighting/navigation complex (based on that used on MiG-27K), etc. But during the study, amount of changes permanently diminished - and, as a result, we got Su-17M4.

Any Su-15 version was never designated "Su-21"! As I understood, that's NATO experts "identified" the Su-15TM (Flagon E) with double-delta wings in this way, and then Turkish "Pioneer 2" company released a scale model under this name. But this "designation" has no common with reality.

P.S. Maybe Su-15 could obtain Su-21 designation if it would be exported (like Su-17 turned into Su-20 and -22). But Su-15 was never exported...