Rosevidney1 ... During the Summer of 1949 the Chipmunk experienced a number of issues with cracked spinners and backplates while the initial production batch was being constructed for the RAF. In fact spinner problems plagued the RAF Chipmunk until late 1950 when it was removed permanently (but retained the backplate) until a completely revised spinner was then fitted (which required a slight additional mod to the cowling).
Mod H231 in Aug 1958 saw the fitting of the spinning strakes.
Cheers ...
Coff.