Thomas Coupling #1128
"In answer to a previous enquiry about Gazelle fenestron stall: The EC135 [it being a mix of the German BO105 and the French Aerospatialle]. The phenomenon experienced by some Gazelle drivers was machined out when it came to the 135 by champfering the edge of the fenestron ring thus widening the "acceptance angle" of the fenestron and reducing (not fully eliminating) the risk of 'fenestron stall'. "
TC, many thanks for clearing up that question - glad the designers made some progress to eliminate FS in subsequent designs. I remember the occasional white faces of Gazelle drivers, who had fallen out of high hovers over Belfast in the small hours back in the 80s. One chap said he had just input some yaw and was adamant that he wasn't going backwards (very difficult to judge at 6000ft and inadvertently going backwards was the common reason for them ending up looking at the city through their roof Perspex!!) He regained control after gyrating back to positive airspeed but he thought he had lost yaw control. We had some serious respect for those guys trying to do that job without any auto stab control.
Kbc