One 500 I flew in the 1990’s had a 4 bladed TR. At the time it was called the low noise tail, and had the reputation of less authority (might have turned slower?). It was an Ex Law Enforcement machine from the US, with a bizarrely high Total Time (like 4+hrs every day since it was made). Like the fenestron on the EC120 the blades weren’t equally spaced: to reduce “howling”. ie more like an X than a cross - looks the same on the 564. All from distant memory, with the usual caveats.
