RAF never had them Onan! Irish AC, Indian AF did - any others? All converted post-war from MkVIII and IX. Still, looks nice, and gives lucky b*****s a chance for a ride/pole... (ie I'd like a ride please!!)
The aircraft in the background is a Pilatus P2 - the vanes control the prop pitch I believe, faster it goes presumably the prop fines off and reverts to coarse pitch for as it slows to approach speeds. Did I get that the right way round, vp props confoose me!