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Re: Origin of flight



<<The wings of Archeopteryx were airfoils and produced lift of this 
type, but the tail was not; for at least 3 reasons: its long axis was 
parallel to the airstream;>>

     The functions of the modern avian tail are certainly many ( as 
shown by Gatesy ),  but Archaeopteryx is different,  it is dead,  so we 
cannot tell what its flying was like.  The best interpretation of the 
flight of Archaeopteryx would probably be a flight where the body is 
horizontal and the skull would be a leading edge and the thorax and the 
tail as a continuation of the airfoil.  This would make the whole body 
an airfoil and the tail would not produce much drag because it is 
"blocked" from the airflow by the thorax.  

<< it had no true "leading edge", and it was not cambered.>>

     See above.  

<<The type of lift generated by the tail would have been like a 
plank--or inclined plane--whether it formed a positive dihedral or not. 
A positive dihedral does not create lift, but it would--as you 
suggest--provides stability while gliding (but I can't see how you 
determined from a flat fossil that the tail formed a dihedral. A tail 
with a positive dihedral would form the letter "V" when viewed in 
tranverse section. When a  pidgeon glides, for example, its wings form a 
positive dihedral.)>>

     I understand your point and agree that it cannot be told for 
certain the shape of Archaeopteryx's tail.  I have always thought that 
the "lift" function of Archaeopteryx's tail was the best one because of 
the wide fan of feathers,  the distal declination of the tail feathers ( 
which would help make an airfoil ),  and the overall shape of the 
Archaeopteryx body as stated above.  Steering was probably a secondary 
function of the tail ( in Recent birds,  the tail contributes only 
slightly to the movement of the body in flight,  the wings and the 
skull/neck position contribute mostly to steering ).  I think that since 
Archaeopteryx seems to lack the mobile scapulacoracoid joint and a more 
dorsally facing glenoid that the wings would contribute little to the 
steering and the position of the skull would contribute more than in 
modern birds.

<< A flat plank will generate a lifting force if it is inclined at a 
small angle of attack, but that also creates a large amount of drag. 
Additionally, although it's true that most airplanes have vertical 
rudders to correct  yaw (side to side movement about a vertical axis), 
the horizontal tails of birds do assist the wings in controlling yaw by 
twisting, therefore performing like a rudder. But the primary function 
of a bird's tail is to  create drag to reduce airspeed and assist with 
such things as landing.>>

I cannot agree more with the above statement.  That only strenghtens my 
above point more.  

How the flight of Archaeopteryx can contribute to the origin of flight 
question is ambiguous.  I currently think that since Archaeopteryx 
lacked the complete triosseal fossa,  a more dorsally positioned 
acrocoracoid,  and a weak bicipital crest and tricipital fossa that the 
M. supracoracoideus was not as well developed in modern birds,  making 
it difficult to near-impossible to take off from level ground ( remember 
the supracoracoideus contributes mostly to the upstroke and backwards 
rotation of the humerus as shown by Glosow and Poole ;  and also taking 
off from the ground ).  I think that the more refined aerodynamics ( 
airfoil shape ) also show that it has come from an arboreal existence.  

Back to RCA.

Matt Troutman

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