You can either use FSEdit by Microsoft, but I don't know if it works with helis, and it likes giving you many errors....
there are also lots of other progs for it, but I donÄ't know them.
You can also handedit the entrys with any text editor.
To know which entry defines what, you will have to download the FS9 SDK called "Aircraft Container".
You will find it on
http://support.microsoft.com/kb/555857But don't say I haven't warned you before!!!! ALWAYS MAKE A BACKUP COPY OF YOUR AIRCRAFT.CFGs!!!!!!!!!!!!!!!!!