| Themes > Science > Physics > Fluid Dynamics > Flying the flag for fluid dynamics > Aerodynamics > Hydro- and Aerodynamics of Animal Swimming and Flight > High-lift mechanisms |
The study of very small insects with wingspan around 2mm revealed in 1973 a completely new inviscid mechanism of lift generation, where two flat surfaces are peeled apart by rotation about a common edge. This clap and fling mechanism can generate lift coefficients up to 6-8 times that of a flat plate in an equivalent steady flow. Reviews and further research on this mechanism can be found in [Ma79], [Ma81] and [SM86]. Follow up projects to this work included investigations of the effect of hinged flaps on the leading edge of delta wings for super-manoeuvrable aircraft [SMR89, KMS89]. A further example of novel aerodynamic mechanisms inspired by nature concerns the peculiar shape of the dragonfly wing, which is characterised by having very noticeable corrugations over the first quarter-chord. Dragonflies are active hunters and appear to be able to accelerate and outperform many fellow insects (a serious issue if you happen to be potential dragonfly food), and some well-known, but never repeated, results in the literature claimed very bizarre shapes in the lift-drag polars of 2D wing sections of similar shape in the wind tunnel. An undergraduate student project is currently in progress to carefully investigate this phenomenon at different Reynolds numbers, and for different section geometries. The initial finding is that no such spectacular result can be found at 0.7 x 10^5 < Re 1.5 x 10^5. We are currently repeating the measurements. One might also include drag reduction mechanisms in this section. This includes not only individual wings but also the interaction of wing pairs -- even when they do not belong to the same individual. The potential drag reduction from flying in formation has been investigated [PL70] for arrangements of fixed wings. Presumably the VSCC model could be used to predict phase relationships and inter-bird spacings for flapping flight, but this has not yet been done. Many features of the natural world have, at one time or another, been postulated as having novel and/or superior performance characteristics. It is important to realise that the natural world does not necessarily converge on an optimum solution, even if it were possible to do so given the constraints such as the available materials and current form as a starting point from which the new gizmo must evolve. The interests of the applied aero- and hydrodynamicists embrace also the principles of the design and contruction of flying machines that have no animal counterpart, some of which will be mentioned in the following section. |
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