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Re: Quetz wing questions
----- Original Message -----
From: "MICHAEL HABIB" <firstname.lastname@example.org>
Sent: Tuesday, January 15, 2008 3:28 PM
Subject: Re: Quetz wing questions
However, because I support quite a sharp turn to the hind limb (for
several reasons that I think are well-supported), the actual membrane
extent is only very slightly greater than the one that Jim uses.
I would agree that if there is a hindlimb connection, I would expect the
merge to be rather acute as well. This implies a distinct change in
membrane properties right at the merge. The model that I generally use does
not have that. It proposes a change in properties near the wrist (as does
I think we may use a slightly different tip shape
Perhaps. Ph IV-4 is only projected to be 10 cm long in Qn (about 4 cm in
Qsp). In Qsp, it has a circular cross-section with a very plate-shaped
proximal end, and I suspect it curved aftward to alleviate the concentration
of spanwise tip stresses in the wing membrane by somewhat blunting the tip.
Since the lazy-Y shape of PhIV-3 will rotate in torsion if deflected aftward
to any significant extent, and since the bracing in bending is oriented to
resist aftward bending, I generally reconstruct IV-3 as being fairly
straight fore & aft with variations in tip loading due to gusts and flapping
causing most of the skeletal torsional deflection. I don't see much
liklihood of significant roach in the outer wing (I think Mike does accept
some roach) so, my tip is rounded, but my outer wing chord tends to be less
than his. Roach is an aftward extension of the chord, such that the
trailing edge would be aft of a straight line drawn from the tip to the
wingroot. In the pterosaurian wing, substantial roach would result in wing
flutter. Our differences in planform are minor and don't amount to much
difference in area.
and trailing edge approach, as well,
which further broadens my wing relative to his, but my uropatagium
reconstruction is slightly more narrow. My actual hind limb attachment
point varies; I have tried both knee/thigh and ankle attachments. With the
sharp approach angle, the difference in wing shape and area is actually
I like to play with varies attachments just to see what comes out.
I have done so as well. I've not seen any structural advantage to the
hindlimb connection, and there are several aerodynamic disadvantages. No
evidence of attachment either way is preserved in the fossil record, so both
venues need to be investigated. If there is a hindlimb connection of the
wing (and there could be), I suspect the reason is not aerodynamic.
With a broader wing, I generally assume greater mass, as well. Overall, I
prefer a bit more body mass than Jim
Note that, as MacCready has previously pointed out, optimal cruise CL is
related to aspect ratio. Since I use a slightly higher aspect ratio than
Mike, my cruise CL tends to be slightly lower which for a given weight
implies a speed increase, so even though he uses a higher weight, I suspect
our cruise speeds are similar (and quite fast for a vertebrate flyer --
these animals would have been good travelers). Note that neither of us has
actually calculated a mass for Qn. My projection of 150 Kg is based on
optimal CL for the aspect ratio that I generate, and his is based on Mark's
estimate (which I haven't seen -- can anyone send me a copy of Mark's
calculations or summary ? ). Note that Greg Paul uses an estimate of 200
Kg. Qn could fly at that weight, but the CL would be a good bit higher than
MacCready's optimal CL. As an aside, even at my presumed weight -- in
no-lift conditions, Qn would have to flap slightly more than half the time
in order to maintain level flight. If more heavily loaded, I would expect
Mike's model to have to flap a bit more than mine. Another aside. The need
to constrain the flapping lift coefficient variation to roughly about 40% of
the optimal CL, combined with the lower limit on CL due to aeroelastic
number and the flutter limit would likely push the time-averaged CL during
flapping to a number somewhat greater than the optimal CL for cruise flight.
In other words, the animal would likely fly at a slightly slower speed while
flapping than while gliding (there are other reasons for this to occur as
well). Combined with the long neck and limited lung capacity, this means
that Qn (and Qsp) would be unlikely to travel long distances in no-lift
conditions. That's not much of a limitation, since unsuitable days would be
very rare. On the other hand, all pterosaurs are very susceptible to long
durations of days unsuitable for soaring flight, which is what I think
killed them off. After being around for 160 Myrs or thereabouts, they
finally got a succession of unsuitable days worldwide that was long enough
to do them in.
; I have also run some very quick calculations with a mass estimate
from Mark Witton's work, presented at the Flugsaurier meeting in Munich,
which is on the higher end. The upshot is that my wing loadings are the
same to greater, despite preferring a bit more wing area, give or take.
What this means is that our two models would fly satisfactorily and
similarly in the same atmospheric conditions. If my model can launch, fly,
and travel, so can his and vice versa.
Otherwise, my thoughts are the same as Jim's (metacarpal ratios, etc) so
I'll leave that to him.
Those are Wann's, and I'll leave publication of them to him. Myself, I'll
sort of talk around that.