Green’s Dictionary of Slang

a short trip, orig. in an aeroplane, but also in other forms of conveyance, e.g. an automobile.

1919		W.H. Downing Digger Dialects 23: flip — An aeroplane flight.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: flip. An aeroplane flight.
1929		‘Josphine Tey’ (as ‘Gordon Daviot’) Man in the Queue 74: [H]e was collecting his car preparatory to having a little flip of three or four hundred miles as a slight Sunday diversion.