C# 1256 file encoding

Hello
I am facing an encoding problem.
I want to write information to a file ( Arabic Letters ( windows-1256 ) ), but the letters are written in UTF-8 , here is the code :

FileStream afile = new FileStream ("school_db.sql", FileMode .OpenOrCreate);
StreamWriter sw = new StreamWriter (afile);
string test = "شكرا على المساعدة ";
sw.WriteLine(test);
sw.Close ();


So I want to convert the variable :' test' to windows-1265 befor writing it to the file.
Thank you for your help
Regards