Magnitude Of Drag Research Articles

The evolution of hymenopteran wings: the importance of size

The allometric relationships between body size and several aspects of wing morphology in the insect order Hymenoptera were investigated using multivariate morphometric techniques. The study focused primarily on wing allometry in five monophyletic genera of bees (Perdila, Halictus, Ceratina, Trigona and Apis), but the patterns of size‐related evolutionary change found within each of these genera are also found to exist in numerous other hymenopteran taxa. Increased body size in hymenopteran lineages is correlated with the following changes in wing morphology: (1) decreased relative stigma area, (2) distal extension of wing vein elements, (3) increased aspect ratio and (4) proximal shift in the centroid of wing area. The reverse is true for decreased size. The widespread allometric trends most likely result from adaptive change in wing morphology due to size‐related changes in the physical properties impinging on the organism–principally the quality and magnitude of drag. The fact that similar wing morphologies among distantly related species can result from similarity in body size has important implications for the study of hymenopteran phylogeny, especially at lower taxonomic levels and when a high proportion of wing characters are employed.

Comparison of quasi-static and dynamic wind tunnel measurements on simplified tractor-trailer models

The results from a series of wind tunnel experiments are presented, intended to measure dynamic forces and moments on simplified commercial vehicle type models rotating about their vertical centre line axis in smooth, uniform flow. These results are compared with quasi-static measurements on the same models over a range of fixed yaw angles (the conventional technique for wind tunnel test on this type of vehicle) in order to assess the significance of attempting to simulate the essentially dynamic nature of the full scale flowfield in a wind tunnel. It is shown that the magnitude of drag and yawing moment coefficients do not change significantly even at rotational rates as high as 64° s −1. However the dynamic coefficient versus yaw angle curves appear displaced, relative to the yaw angle axis, compared to the static data. The magnitude and sign of this “phase shift” are seen to be dependent on both yaw rate and model geometry and are evident at rotational rates as low as 0.25° s −1.