Fig. 7. Graphs of relative thrust—drag T_r against _b for the unpaired (A—C) and paired (D—F) analyses of the angle series data, and against U (G—I) for the speed series data. For further explanation, see legend to Fig. 6. Individual regressions of T_r against U² (G—I) are shown as black dotted lines where the individual regression and the corresponding GLM treating U² as the covariate were both significant; it is clear that the deviation from linearity is small over the range of speeds used.