when did he join the air force?
January 1923.
Frank Bladin
 He transferred to the recently established Royal Australian Air Force as a flying officer in January 1923. 
what is frank bladin? A senior commander in the Royal Australian Air Force (RAAF).
wiki:17720232
Frank Bladin [SEP] Early career
He proceeded to change this, deploying the squadron 300 miles away to Cootamundra in rural New South Wales, where he "borrowed a portion of a sheep station from a friend so that the pilots could carry out their bombing practice" over a two-week period commencing in late November 1935. After completing his tenure with No. 1 Squadron in December 1935, Bladin was appointed Officer Commanding Cadet Squadron at No. 1 Flying Training School. He modelled the squadron's training course on that of Duntroon, foreshadowing instruction at the Air Force's own cadet institute, RAAF College, which would be established in 1947.