Fig. 4. Thrust and efficiency versus average chord length for theoretical wings with different shape, but the same proportion of area in the outer one-fifth of the wing. Wings were generated with three different shape equations: a beta distribution, a first-degree polynomial and a third-degree polynomial. All wings have 9% of area in the outer one-fifth of the wing. Chord length distributions are also shown. S_p=0.0069m², U=0.15ms^-1, c=0.3ms^-1, H=0.058m and f=2.27s^-1. S_p, total area of one pectoral fin; U, velocity; c, wave speed; H, fin tip amplitude; f, flapping frequency.