flapping (of a flag, fan, etc.); fluttering; whack-whack (e.g. beating dust out of a rug); whap-whap
pitter-patter (of footsteps)
quickly (making progress); in quick succession
旗がぱたぱたと揺れている。
The flag is flapping.
扇子をぱたぱたあおぐ。
Fan oneself with a folding fan.
鳥がぱたぱた羽ばたいた。
The bird flapped its wings.