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Microraptor gliding aerodynamics



From: Ben Creisler
bscreisler@yahoo.com
 
This paper was online back in September and is now officially published, but 
I'm not sure it's been mentioned on the DML:
 
Koehl, M. A. R., Evangelista, Dennis & Yang, Karen (2011)
Using Physical Models to Study the Gliding Performance of Extinct Animals.
Integrative and Comparative Biology 51(6): 1002-1018(17)
DOI: http://dx.doi.org/10.1093/icb/icr112
http://icb.oxfordjournals.org/content/51/6/1002.abstract
   
Aerodynamic studies using physical models of fossil organisms can provide 
quantitative information about how performance of defined activities, such as 
gliding, depends on specific morphological features. Such analyses allow us to 
rule out hypotheses about the function of extinct organisms that are not 
physically plausible and to determine if and how specific morphological 
features and postures affect performance. The purpose of this article is to 
provide a practical guide for the design of dynamically scaled physical models 
to study the gliding of extinct animals using examples from our research on the 
theropod dinosaur, Microraptor gui, which had flight feathers on its hind limbs 
as well as on its forelimbs. Analysis of the aerodynamics of M. gui can shed 
light on the design of gliders with large surfaces posterior to the center of 
mass and provide functional information to evolutionary biologists trying to 
unravel the origins of flight in the
 dinosaurian ancestors and sister groups to birds. Measurements of lift, drag, 
side force, and moments in pitch, roll, and yaw on models in a wind tunnel can 
be used to calculate indices of gliding and parachuting performance, 
aerodynamic static stability, and control effectiveness in maneuvering. These 
indices permit the aerodynamic performance of bodies of different shape, size, 
stiffness, texture, and posture to be compared and thus can provide insights 
about the design of gliders, both biological and man-made. Our measurements of 
maximum lift-to-drag ratios of 2.53.1 for physical models of M. gui suggest 
that its gliding performance was similar to that of flying squirrels and that 
the various leg postures that might have been used by M. gui make little 
difference to that aspect of aerodynamic performance. We found that body 
orientation relative to the movement of air past the animal determines whether 
it is difficult or easy to maneuver.