This has been the subject if many threads is the past . The most logical if i recall correctly is to do with the direction of rotation of the Engine. One of the most interesting was the story that after the war the allies took bits of the twin rotor German helicopter and the French got the blades that went the opposite way to the ones the US got.
Sorry if the question was directly related to the EC135 , it is German helicopter with a French tail , started out as the Bo108 and gained a fenestron after the merger.
[ 21 January 2002: Message edited by: widgeon ]</p>