In 1973 SA decided to install and test a fenestron on the S-67. Part of that preparation included a short evaluation of a Gazelle arranged thru a private owner. What was ironic was that we noticed the 341 was happy with any pedal position with 3 degrees of sideslip in forward flight, and voila, so was the S-67 version. We added a rudder to the design, but the original tail rotor was reinstalled after the fenestron test program and the whole subject became OBE.
Until Comanche came along, anyway.
If one looks into the SA Archives site and notices that max speed number for the 67, it was recorded with the fenestron. We simply were doing the full envelope and on the day, we needed a 200KIAS data point, which was the standard 67 number. It was a clear, cold windy day but at least was smoother above 3-4 thousand feet, and quite frankly, we were watching the main rotor for mach related instability ( arising from a prior experience with the S-61F, where the rotor went unstable at a free stream mach of 0.94 ). Anyhow at 200 KIAS the rotor was ok-fuzzy tip path but only n/rev vibration. Tip mach was 0.96 at this data point.