Problems with add on aircraft

I fly with a Satiek Evo flight stick.
The basic game native aircraft and the WWII Wings of Power planes all fly well with no problems.
Some of the add on planes from this site i'm having problems with.
Some are very difficult to impossible to trim out. Others everything works except fore and aft on the stick the nose only moves about 5 degrees either way and again trim problems. I can switch to one of the native planes like th 747, Piper Cub etc and everything is fine.
This is most frustrating.
The basic game native aircraft and the WWII Wings of Power planes all fly well with no problems.
Some of the add on planes from this site i'm having problems with.
Some are very difficult to impossible to trim out. Others everything works except fore and aft on the stick the nose only moves about 5 degrees either way and again trim problems. I can switch to one of the native planes like th 747, Piper Cub etc and everything is fine.
This is most frustrating.