since su27 is a fly-by-wire airplane why do I have to keep trimming. There should be an autotrim feature, not like the H key. Am I right?

I will try to explain this the best i can:

The base Su-27 is FBW. It is analoge not digital. This merely means that command controls from the stick are taken as analoge commands (just like your games joystick) and sent to a central computer processing unit. There is no physical link between the pilot and the control surface (as in the WWII fashion). What this computer does is take in information all of the sensors (speed, alt, etc.) assess the demand from the control stick and 'thinks' what position the control surfaces need to be in to comply. (its not really thinking, computers cannot improvise..).
This is where the fun (confusion) begins; the channels in the Su-27 are triple-redundant, with mechanincal backup. What this means is that there are three wires/lines to the control surface (general rule) which back each other up.
The mechanical, works like the WWII era controls and can only deflect to 50% any control surface.
On top of this it is only FBW in the longitudinal channnel (pitch) and not in roll or yaw...

So why do this.....it to cure two things, with a third positive effect. The problems are first the design of 'dynamic/static instability' ('static' if important to fighter jocks)and the other is fuel weight ( the reason its on the Airbus series....love those ).

This is where it goes complex...so if you want more info...well...ask

Zed