You can download the latest betapatch here, just avoid the oron.com download link as it sucks :
http://forum.1cpublishing.eu/showthread.php?t=32916
How to install the beta :
1) Have Steam verify integrity of local files (to get back to last official version)
2) Go to your documents\1c softclub\IL-2 sturmovik cliffs of dover folder and go into the cache folder. Delete everything in there (the game will rebuild it based on the new version next time you run the sim).
3) Extract the beta patch in the game folder (c:\whatever_you_named_it\steam\steamapps\common\I L-2 sturmovik cliffs of dover) and let it overwrite anything it wants to overwrite
4) Run the sim and load a quickmission to force it to rebuild the cache.
5) Restart the game
(yes this how-to was stolen from Septic who, i think, stole it from Blackdog ;p )
Just remember it is a beta and as such has some known bugs, most notably with trees only being drawn for a short distance and the 100oct planes being difficult to start online.
If it messes something up for you, just repeat step 1 to get back to the last official version.