Biplane like flight of Microraptor gui

[Gautam Majumdar <gmajumdar@freeuk.com>]

This is an open access article in PNAS, probably not posted yet to DML

Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0609975104
http://www.pnas.org/cgi/content/abstract/0609975104v1

Biplane wing planform and flight performance of the feathered dinosaur 
Microraptor gui

Sankar Chatterjee and R. Jack Templin

ABSTRACT
Microraptor gui, a four-winged dromaeosaur from the Early Cretaceous of China, 
provides strong evidence for an arboreal-gliding origin of avian flight. It 
possessed asymmetric flight feathers not only on the manus but also on the 
pes. A previously published reconstruction shows that the hindwing of 
Microraptor supported by a laterally extended leg would have formed a second 
pair of wings in tetrapteryx fashion. However, this wing design conflicts 
with known theropod limb joints that entail a parasagittal posture of the 
hindlimb. Here, we offer an alternative planform of the hindwing of 
Microraptor that is concordant with its feather orientation for producing 
lift and normal theropod hindlimb posture. In this reconstruction, the wings 
of Microraptor could have resembled a staggered biplane configuration during 
flight, where the forewing formed the dorsal wing and the metatarsal wing 
formed the ventral one. The contour feathers on the tibia were positioned 
posteriorly, oriented in a vertical plane for streamlining that would reduce 
the drag considerably. Leg feathers are present in many fossil dromaeosaurs, 
early birds, and living raptors, and they play an important role in flight 
during catching and carrying prey. A computer simulation of the flight 
performance of Microraptor suggests that its biplane wings were adapted for 
undulatory "phugoid" gliding between trees, where the horizontal feathered 
tail offered additional lift and stability and controlled pitch. Like the 
Wright 1903 Flyer, Microraptor, a gliding relative of early birds, took to 
the air with two sets of wings.

-- 
gautam