Re: large fossil birds

[don ohmes <d_ohmes@yahoo.com>]

jrc wrote:
>>>My impression for pterosaurs is that takeoff didn't
involve a bunch of 
mad 
flapping or running.  My perception is that they
sidestepped the power 
required versus power available issue that limits
birds, and did so by 
using 
a launch technique that reduced the power requirements
on the pectoral 
muscles.<<<<

You've really got my curiousity aroused; are you
willing to be more specific about launch technique?
Are you referring to the "boxkite" scenario?

Don


--- jrc <jrccea@bellsouth.net> wrote:

> 
> ----- Original Message ----- 
> From: "Michael Habib" <mhabib5@jhmi.edu>
> To: <dinosaur@usc.edu>; "jrc" <jrccea@bellsouth.net>
> Sent: Tuesday, November 29, 2005 1:11 PM
> Subject: Re: large fossil birds
> 
> 
> > My main point is that maximum span versus mass
> relationships may not have 
> > been the defining difference in max size between
> birds and pterosaurs.
> 
> My perception is that the relationship between span,
> mass, and required 
> power probably isn't as closely coupled in
> pterosaurs as it is in birds, due 
> to a difference in launch and landing technique
> (mostly launch).
> 
> > The very largest flying birds by mass are swans
> and kori bustards.  The 
> > former have relatively high aspect ratio wings,
> while bustards have very 
> > low aspect ratios (because they only fly for short
> distances at low 
> > speeds).
> 
> The largest individual bird that I know of that
> flies by means of continuous 
> flapping flight is a male Whooper Swan that has been
> designated 'JAP' by the 
> folks who study him (I don't know if he is still
> alive).  I'm probably too 
> close to pterosaurs, because I think of him as being
> 'relatively' low aspect 
> ratio.  Though he is quite high aspect ratio for a
> swan, it's only about 
> half the aspect ratio of a pterosaur using either
> the Bennett or Padian 
> planform.  It might be similar to the aspect ratio
> of the Unwin planform 
> (don't remember off the top of my head).  As an
> aside, some years ago, 
> during a gale off the coast of Iceland, JAP made one
> of the most remarkable 
> emergency flights I've ever heard of.  He is or was
> a pilot's pilot.
> 
> > If anything, the situation is 'messy' enough that
> I probably shouldn't 
> > have tried to make the comparison between chords
> in large avians and large 
> > pterosaurs in the first place.  I guess I had
> seabirds on the brain at the 
> > time.  Oh well, my mistake.
> 
> Not necessarily.  If you buy into the Unwin
> planform, what you said earlier 
> might well be true.
> >>> resulting in a more favorable wing loading:mass
> scaling relationship.
> 
> > I suppose I was mostly concerned with the
> thresholds of being able to take 
> > off when I made that comment.
> 
> My impression for pterosaurs is that takeoff didn't
> involve a bunch of mad 
> flapping or running.  My perception is that they
> sidestepped the power 
> required versus power available issue that limits
> birds, and did so by using 
> a launch technique that reduced the power
> requirements on the pectoral 
> muscles.
> 
> With regard to landing, being quadrupedal on the
> ground was a huge asset in 
> avoiding the pitfalls of the fanny over teakettle
> technique used by 
> albatrosses.
> 
> >  With regards to the trend, I probably
> underestimated the loadings in 
> > pterosaurs.  I really am much more familiar with
> the wing shape trends in 
> > birds, after all.
> 
> I've recently done a volumetric mass estimate on A
> piscator.  For a given 
> span, pterosaur mass doesn't appear to be much
> different than that for 
> equivilently spanned birds.  Pterosaurs tend to have
> smaller bodies, but 
> offset that with larger heads and necks.  And though
> pterosaur bones have 
> thinner bone walls for a given diameter than birds
> do -- for a given span 
> the gross size of the pterosaur bones tends to be
> much larger, with more 
> area available for muscle attachment.  The preceding
> is a visual analogy 
> that can be pushed too far, but since pterosaurs
> were soarers, and since 
> high wingloading is an advantage for soarers that
> want the ability to cover 
> distance as well as loiter, I don't think they were
> under much selective 
> pressure to reduce mass.  Only to support it
> effectively, both on the ground 
> and in the air.
> 
> > I have not done any calculations on that problem
> myself [insert -- # of 
> > continuous beats], but it certainly sounds
> reasonable.  Incidentally, any 
> > thoughts on the apparent adaptations for dynamic
> soaring in Qspp given 
> > they show up in terrestrial deposits?
> 
> Sure.  Both Qsp and Qn appear to have been inland
> animals.  I used to do a 
> lot of very low level flying along the margins of
> long, narrow lakes while 
> doing search and rescue work.  When there was a
> wind, I noticed quite a bit 
> of turbulence near the margins of those lakes that
> would have been quite 
> usable for a pterosaur.  You get an updraft on the
> leeward side of the lake, 
> and a vortex on the windward side.  Energy can be
> extracted from both.  I 
> see flying on the windward side of a lake as being
> similar to the lee shear 
> soaring that albatrosses use so effectively (making
> use of shoreline 
> effects).  Flying on the leeward side of the lake
> (the windward side of the 
> adjacent shoreline) is similar to slope soaring.
> 
> > There are vultures somewhat adapted for burst
> flapping, but they still use 
> > convective soaring most of the time.
> 
> I know you're aware of this, but soaring animals of
> any aspect ratio can use 
> convective soaring when it is available.
> 
> > I'm just forseeing problems with vertical wind
> shear gradients being too 
> > low
> 
> Given a wind, they aren't too low along the margins
> of lakes.  And again, 
> high aspect ratio animals can effectively use
> convective lift too.  In fact, 
> they find it easier to travel inland than do lower
> aspect animals, with 
> their lower lift/drag ratios.  As an
> oversimplification, about 20% of the 
> sky is covered by updrafts, 80% with downdrafts. 
> You want to be able to 
> move through the downdrafts between updraft areas as
> efficiently as 
> possible, and high aspect ratio and high wing
> loading both facilitate that 
> (particularly with the facility for occasional burst
> flapping).
> 
> > (unless they were actually coastal and just
> happened to die overland).
> 
> I'm personally convinced that they (Quetz) weren't
> coastal; that they made 
> their living inland and did a lot of traveling in a
> generally north-south 
> direction.
> 
> > I've only just begun learning the mechanical
> implications of 
> > spanloading).
> 
> Paul MacCready has used spanloading to enormous
> benefit in several of his 
> aircraft.  you can get a quick insight into
> spanloading by looking at some 
> of them.
> 
> Jim 
> 
>