S!
First of all it would help to see your system specs
For example put them as your signature or something. Then what graphical settings are you using in game and in the GPU control panel.
CoD can be picky on programs running in the background like TeamSpeak Overlay, GameBooster etc. Make sure to have all unnecessary programs closed before playing. IT is also worth checking drivers if they are up to date.
One thing to check is also to go to the X:\Steam\steamapps\common\il-2 sturmovik cliffs of dover\redist folder and install DotNetFX40. Some say it has helped running these installation packages and then running the game.
Also make sure to clean the cache BEFORE using the beta patch. It is located in the folder like this..C:\Users\Your username here\Documents\1C SoftClub\il-2 sturmovik cliffs of dover\cache It is safe to delete cache-folder as it regenerates when you launch the game.
Try these tips