Fig. 4. Instantaneous drag traces. The regions where the stroke position of wing is between –90° and 90° are highlighted in gray and roughly approximate the phase of an upstroke or downstroke between wing rotations. Angle of attack varied from –10° to 100° in steps of 10° for each advance ratio. (Ai–Di) =72 deg. s^–1, advance ratio equal to 1/8, 1/4, 3/8 and 1/2, respectively. (Aii–Dii) =–72 deg. s^–1, advance ratio equal to 1/8, 1/4, 3/8 and 1/2, respectively.