Haraka ...
Thanks for that ...
More on that mod, it would appear that the mod 'embodiment' required all RAF Chipmunks to be fitted not later than three months AFTER receipt of parts (time for embodiment was estimated at six hours for the engineers). I guess it's quite possible that there might have been supply difficulties given the size of the fleet back then. I understand that RAF Chipmunks were NOT cleared for aerobatic manoeuvres (including spinning) unless strakes were fitted post the Aug 1958 mod date.
Sorry ... I never need an excuse to 'enthuse' about the Chipmunk
You might be interested to know that WP804, with the extended Rudder Chord mod, was used in March 1958 to undertake pre mod spinning trials with the then proposed strakes ... and was equipped with a GQ anti-spin parachute fitted in to a modified tail cone (activation via a lever in the front cockpit). Post the trials with WP804 ... further trials were conducted with WD292, WK517, WK618, WP803 and WG403 with the strakes mod. The H231 mod appeared shortly after these final trials.
Best regards ...
Coff.
Reference : Chipmunk 'The Poor Man's Spitfire' : Rod Brown