Powered, flapping flight has evolved at least four times in the Animal Kingdom: in insects, birds, pterosaurs, and bats. Although some aspects of flight mechanics are probably common to all of these lineages, each of the four represents a unique solution to the challenges of maneuverable flapping flight at animal length scales. Flight is less well documented and understood for bats than birds and insects, and may provide novel inspiration for vehicle design. In particular, bat wings are made of quite flexible bones supporting very compliant and anisotropic wing membranes, and possess many more independently controllable joints than those of other animals. We show that the mechanical characteristics of wing skin play an important role in determining aerodynamic characteristics of the wing, and that motions at the many hand joints are integrated to produce complex and functionally versatile dynamic wing conformations.

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The possible existence of slip of liquids in close proximity to a smooth surface is studied experimentally via the dynamics of small particles suspended in a shear flow. Sub-micron fluorescent particles suspended in water are imaged and analyzed using Total Internal Reflection Velocimetry (TIRV). For water flowing over a hydrophilic surface, the measurements are in agreement with previous experiments and indicate that slip, if present, is minimal at low shear rates, but increases slightly as the shear rate increases. Furthermore, surface hydrophobicity can be attributed for additional shear-rate dependent boundary slip. Issues associated with the experimental technique and the interpretation of results are also discussed.

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