Green’s Dictionary of Slang

(US) a helicopter.

1951		Newsweek 5 Nov. 35: To those who fly it, the helicopter is a whirlybird or a puddle jumper.
1961		(con. 1950s) C. Barbeau Ikon 54: ‘Wish we had one of those in the last war,’ White nodded at the whirlybird.
1969		C. Sellers Where Have All the Soldiers Gone 46: ‘Tell whirlybird to work over that patch of jungle’.
1989		(con. 1950s) C.S. Crawford Four Deuces 101: Red [...] told me about the ‘whirlybirds,’ the ‘eggbeaters,’ the ‘windmills.’.
1998		P. Cornwell Point of Origin (1999) 6: The whirlybird’s picking us up before dawn.
2004		C. Hiaasen Skinny Dip 248: He kept his eyes on the red-striped helicopter [...] ‘Whirlybirds, I swear to God.’.