Fig. 12. Composite colour-coded spanwise vorticity with superimposed velocity field vectors for flight speeds U=5, 8 and 11 m s^–1. Data are from the vertical centreplane. Velocity vectors are shown at half resolution. The vorticity is mapped symmetrically about a 10-step colour bar. The resolution of the colour bar matches the worst-case uncertainty in the measurement, so all visible features exist. The colour bar is rescaled to local absolute maxima at each different flight speed; these are ±700, 280 and 200 s^–1, respectively. The regions corresponding to a starting and stopping vortex are indicated by a (+) and (–) arrow, respectively. The stroke wavelength is shown as a black bar and the wingspan, 2b, and mean chord, c, is shown for reference. For more details and examples of wakes at other speeds (4, 7 and 10 m s^–1; see Spedding et al., 2003a).