Pterosaur wings had variable geometry and that, combined with their slow flight enabled them to land very gently, reducing the chance of damage to their thin bones. This goes a long way to explaining how pterosaurs became the largest flying creatures ever known, with a wingspan up to 10m across.
Colin Palmer said: “Pterosaur wings were adapted to a low-speed flight regime that minimizes sink rate. This regime is unsuited to marine style dynamic soaring adopted by many seabirds which requires high flight speed coupled with high aerodynamic efficiency, but is well suited to thermal/slope soaring. The low sink rate would have allowed pterosaurs to use the relatively weak thermal lift found over the sea.
“Since the bones of pterosaurs were thin-walled and thus highly susceptible to impact damage, the low-speed landing capability would have made an important contribution to avoiding injury and so helped to enable pterosaurs to attain much larger sizes than extant birds. The trade-off would have been an extreme vulnerability to strong winds and turbulence, both in flight and on the ground, like that experienced by modern-day paragliders.”
Palmer constructed models of pterosaur wing sections from thin curved sheets of epoxy resin/ carbon fibre composite, those sections then being tested in a wind tunnel. From those test the two dimensional characteristics of pterosaur wings were characterised fort he first time. This showed that the creatures were considerably less aerodynamically efficient and were capable of flying at lower speeds than previously thought.
Colin Palmer, trained as an engineer, originally in ship science and has over forty years of industrial experience. His interest in the propulsion of sailing vessels led to a study of the performance of thin aerofoil’s and low speed aerodynamics. He is now applying that knowledge and experience to the analysis of vertebrate flight, focusing on large pterosaurs for his PhD. His approach uses a combination of wind tunnel and vortex-lattice theoretical modeling to understand how pterosaur wings performed. More sophisticated aerodynamic analysis, using computational fluid dynamics, is to follow with the intention of providing enough information to create a free-flying model of a pterosaur.
The story reminds me of that of a particular type of dinosaur that was thought to live in marshes so that its body partially floated, due to its body structure, particularly its legs, being unable to bear its full weight. Sometime in the 1960s, or 1970s, an engineer carried out structural calculations to show that the creature’s skeletal structure was indeed capable of bearing its weight. Oddly, as I recall, the person concerned was an electrical engineer at the University of Reading. In a sense, not so odd as engineers have a good understanding of each other’s disciplines; my first year at Brunel University was a common one for all engineers; mechanical, electrical and production engineering. Either way both stories are a good example of why such matters should be investigated by other than just scientists.
Colin Palmer’s paper “Flight in slow motion: aerodynamics of the pterosaur wing” is in the Proceedings of the Royal Society B at rspb.royalsocietypublishing.org/content/early/2009/12/01/rspb.2009.1899.abstract.