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

Re: uprightedness (was Re: SICB Report, part 1 (long)]



> John Bois wrote:
>
> > On Fri, 15 Jan 1999, James R. Cunningham wrote:
> > > Pheasants do
> > > pretty well with a long tail.  Archies' tail doesn't appear to me to have
> > > been a handicap in flight -- more of a benefit, I'd say.
> >
> > But a flesh and bone tail is heavier than a tail made of feathers.

> The only thing that really matters here is wing loading (or tail loading as 
> the
> case might be).  Qualitatively, Archie's doesn't appear to have been all that
> great.  In the numbers I quoted the other day, I assumed Archie's tail was 
> also
> supporting the weight of his legs, or qualitatively, about 15% of his body
> weight.  He would have done just fine while carrying that weight, and could 
> have
> carried more



> > >...since Archie probably didn't take off flat-footed from a standing
> > > start like a pigeon does...
> >
> > Being able to take off vertically is an advantage for avoiding predation.
> > It also means birds can spend more time foraging and less time planning a
> > take-off route.

> I agree whole heartedly with the statement above, but still doubt that Archie
> was capable of doing so (no supracoracoideus).

> > >...make me suspect that Archie was a fairly effective flyer, probably a
> > better
> > > fit for his specific flight niche than a pigeon would have been.  On the
> > > other hand, I also suspect pigeons fit the pigeon niche better than Archie
> > > would have.
> >
> > This is very difficult to argue.  One would have to have a competitive fly
> > off to know for sure.  Otherwise it seems to me a better position is:
> > the progressive reduction in tail size indicates a competitive advantage
> > for birds which possessed it.  Also, there are doubtless closer analogues
> > to archie than pigeons.

> I think you may be making an implicit assumption here which perhaps isn't
> supported by aerodynamics.  What causes the competitive advantage of reduced
> tail size for Archie?  In what way does the reduction help him?  As an 
> example,
> I seriously doubt that Archie would have been able to fly with his tail
> amputated, because I don't believe he could have launched in that condition.  
> So
> how could loss of his tail have helped him?  My point is that there are niches
> which need the tail, other niches that don't.  Other birds, filling other
> niches, do quite well without a tail, and can fly with their tail removed.  
> It's
> obvious that a bird that can fly with zero lift on the tail is generally going
> to have less induced drag in flight, and very likely less profile drag as 
> well.
> However, Archie may not have been able to take off (or land) without his tail.
> If that's indeed the case, then he needed it desperately.  I too agree that
> there must be a number of closer analogues to Archie than a pigeon is, but I
> don't know of any that have been so extensively tested in wind tunnels as
> pigeons.  The data I have available on magpies is flawed, so I didn't attempt 
> to
> use it. I had the wind tunnel comparisons handy for pigeons, but not for 
> other,
> more similar birds, partly because my focus is on pterosaur flight rather than
> that of early birds. Incidentally, Qsp and Qn flew quite well with a very 
> heavy
> aerodynamic structure (composed of legs and uropatagium) at their aft end, 
> with
> a 'tail' loading ('tail' in the aerodynamic, not biological sense) far greater
> than Archie's.

> Best wishes,

> Jim Cunningham