Re: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur

[Michael Habib <mhabib5@jhmi.edu>]

Granted, the animal could adjust fore-aft sweep of the wings (assuming 
that the hindlimbs could reach close to horizontal, which I seriously 
doubt), but my original argument still holds: it is dangerous to assume 
the effective wing loading was simply halved by the hindwings.  As you 
have suggested, adjustments to the wings would be required for 
compensate for center of mass issues, and this could equalize effective 
loadings.  This is one possible solution to the unequal loading problem 
I raised, but my original point was that it needs to be taken into 
account in some way, and I feel that such a concern still holds.  There 
are also some complications with using the fore-aft sweep adjustments 
if the animal was using flapping flight.  If you are assuming a 
fixed-wing model (ie. gliding), then problems arise with the low wing 
loading suggested.

There is another problem with using the hindfoils as being roughly 
equal in effect to the forewings, which is that generated lift was very 
likely to be different between the two sets of foils.  The tip vortices 
from the hindwings would be very large, and result in significant 
induced drag.  In addition, the hindwings, if they actually were held 
behind the forewings, would likely interact with the trailing vortices 
of the forewings, significantly reducing their lift (this occurs in the 
tails of modern birds, Maybury et al., 2001).  Thus, the total lift 
from forewings and 'hindwings' might not be the same, and should not be 
assumed to be so.  Modeling under varying assumptions would be a safer 
approach, with vortex production explicitly considered.

These issues need to be taken into account before determining whether 
the the effective loading was actually halved by the hindwings, or 
reduced by some lesser amount (or not at all, if they were not held 
horizontal, but that becomes a different set of issues).

I am also curious what the function having a wing loading as low as you 
suggest would really be.  If the wing loading without the hind wings 
accounted for is in the middle of the range for flying birds of 
Microraptor's mass, then having a wing loading half of that value would 
seem strangely small.  Gliding for any distance would be very 
problematic (and slow), and even powered flight could suffer in some 
cases with such poor wind penetration.  Of course, there can be 
advantages, depending on flight mode, to having very low wing loadings. 
 While I am still very skeptical of the wing arrangement (and wing 
loadings) that you suggest, I am honestly curious to hear what function 
you would attribute to such an unusually low wing loading.


Cheers,

--Mike Habib

On Tuesday, December 13, 2005, at 07:39 PM, GSP1954@aol.com wrote:

> The arm wing area/total mass ratio of Microraptor is in the middle of 
> the
> range for flying birds of its mass, adding the hind wings doubles this 
> value.
>
> The argument that the loading of the similar sized fore and aft wings 
> is
> dependent upon the fore-aft distribution of the mass of the body is 
> not correct.
> Assuming that the leg wings could be splayed out sufficiently close to
> horizontal to generate close to the maximum possible lift, the 
> distribution of wing
> loading could be easily adjusted by adjusting the fore-aft sweep of 
> the two sets
> of wings as needed. If lesser loading on the forewings was desired 
> then sweep
> the leg wing or both wings backwards and the downwards pitch will be
> increased. Sweep the arm or both wings forward and the animal will 
> pitch up. For equal
> loading of the wings adjust to a neutral sweep...