[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: avian flight



>>so that the wings and tail are perpendicular to the direction of travel
(basically stall a moment before landing). I think some modern birds do
something similar, when landing on a narrow perch.<<

>For this, one needs to flap very fast (*big* flight muscles), excellent
control, and gimmicks like an alula.<

This reference to the function of an alula only works if you assume that the
alula functions aerodynamically like a protuberance or slot on the leading
edge of an airplane wing.  I suspect it does, but that has not been shown
empirically to be the case (at least I have not been able to find any wind
tunnel work that actually tests that assumption using bird wing models
tested at low wind speeds).  There is, however, a lot of published research
on the effect of protuberances and slots on airplane wings, some of which
even shows that protuberances of the same relative size and position as an
alula do actually continue to increase the wing's coefficient of lift at
AOA's in the range of 16-24 degrees when the same airfoil without the
protuberance stalls at 16 degrees (Jacobs NACA).  I also think that since
the manus claws of early flyers such as Archaeopteryx occupied the same
position on the wing and were approximately the same size as the alula of
later flyers, the manus claws probably functioned aerodynamically much the
same way as the alula.  It is very possible that the alula was not the
evolutionary flight innovation some think it was, but rather was an
exaptation of feathers that developed as the alular digit and the manus
claws became reduced.   It's interesting to note that bats and pterosaurs
also have/had leading edge protuberances in approximately the same leading
edge location.  My bet is that they also probably function(ed)
aerodynamically much the way manus claws did in early feathered flyers and
as the alula has since the early Cretaceous.

Pat