Aviapedia

Su-27 family visual differences table

How visually to identify Su-27 modification? I would like to talk now only about visual differences, no any avionics or something. This information only to help identify the Su modification on the photo, in video or in the air etc.

First of all, about letters in designations.

The K letter - if it goes after the letter of main modification, it means “Kommercheskiy” - Commercial. These fighters go for export. If K letter goes straight after the series number, it means “Korabelniy” - Naval.
Examples:
Su-27KUB - Korabelniy Uchebno-Boevoy - Naval Combat Trainer
Su-27UBK - Uchebno-Boevoy Kommercheskiy - Commercial Combat Trainer

Su-27SM - “Seriyniy Modernizirovanniy” - Serial Modernized

Su-27MK - “Modernizirovanniy Kommercheskiy” - Commercial, Modernized. Base modification.

If purchasing country wants some special features, like custom avionics or weapon systems etc, after designation goes the letter of country:
Su-30MKI - “Modernizirovanniy Kommercheskiy Indiyskiy” - Indian Commercial, Modernized
Su-30MKK - “Modernizirovanniy Kommercheskiy Kitayskiy” - Chinese Commercial, Modernized

Su-27KUB (Su-33UB) - Korabelniy Uchebno-Boevoy - Naval Combat Trainer. Looks very much like Su-34, but there are differences:
- tailplane are less high
- tail boom is shorter and less massive, then Su-34
- main landing gear (MLG) has two wheels and nose landing gear (NLG) has one wheel
- Tail hook, of course

Su-27SM(K) - has bigger ‘hump’ then basic Su-27

Su-34 evolution:
T-10V -> Su-27IB -> Su-32 -> Su-32FN -> Su-34 (when got into series production)

Su-35 evolution:
Su-27M (also known as Su-35 old) -> Su-37 Terminator tail No.711 (short TVC engines test period) -> Su-27BM tail No. 711 (also known as Su-35BM), program freezed after tail. 711 crashed 19.12.2002 -> Su-35 new (shape still not finalized)

* - according the information from KNAAPO site