Science Literature

Wing morphology has a profound effect on aerodynamic performance. Gliding birds such as swifts exploit their ability to morph their wings: "Extended wings are superior for slow glides and turns; swept wings are superior for fast glides and turns. This superiority is due to better aerodynamic performance - with the exception of fast turns. Swept wings are less effective at generating lift while turning at high speeds, but can bear the extreme loads."
New research has led to a more refined aerodynamicmodel, enhancing understanding and stimulating ideas for future developments in aircraft design. "Lentink says that these aircraft designs are crude compared with what the swifts can do, thanks to the engineering challenges involved. "The swifts are just better at it," he says, "The amount of feathers and muscle involved is challenging for us [to imitate].""
One might anticipate that research like this might stimulate thoughts about intelligent design. That is certainly the way engineers have to approach their work. The glide speeds at which the birds minimize energy expenditure have been determined. But one of the co-authors is quoted as saying: "They [swifts] have evolved an aerodynamic design for cheap flight". However, there is nothing in this research that suggests that these capabilities are evolved rather than intelligently designed. This comment linking design to an evolutionary origin is theory-laden and is actually a pointer to a socially-constructed 'reality' adopted by the researcher.

How swifts control their glide performance with morphing wings
D. Lentink, U. K. Muller, E. J. Stamhuis, R. de Kat, W. van Gestel, L. L. M. Veldhuis, P. Henningsson, A. Hedenstrom, J. J. Videler and J. L. van Leeuwen.
Nature 446, 1082-1085 (26 April 2007) | doi:10.1038/nature05733

Gliding birds continually change the shape and size of their wings1, 2, 3, 4, 5, 6, presumably to exploit the profound effect of wing morphology on aerodynamic performance7, 8, 9. That birds should adjust wing sweep to suit glide speed has been predicted qualitatively by analytical glide models2, 10, which extrapolated the wing's performance envelope from aerodynamic theory. Here we describe the aerodynamic and structural performance of actual swift wings, as measured in a wind tunnel, and on this basis build a semi-empirical glide model. By measuring inside and outside swifts' behavioural envelope, we show that choosing the most suitable sweep can halve sink speed or triple turning rate. Extended wings are superior for slow glides and turns; swept wings are superior for fast glides and turns. This superiority is due to better aerodynamic performance - with the exception of fast turns. Swept wings are less effective at generating lift while turning at high speeds, but can bear the extreme loads. Finally, our glide model predicts that cost-effective gliding occurs at speeds of 8-10 m s-1, whereas agility-related figures of merit peak at 15-25 m s-1. In fact, swifts spend the night ('roost') in flight at 8-10 m s-1 (ref. 11), thus our model can explain this choice for a resting behaviour11, 12. Morphing not only adjusts birds' wing performance to the task at hand, but could also control the flight of future aircraft7.

See also:
Ledford, H. Wings in a wind tunnel show secrets of flight. Study of swifts could improve airplane designs.
news@nature.com, 25 April 2007 | doi:10.1038/news070423-7