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Re: Quetz wing questions



Hi all (particularly Jim),

"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 ? )."  

A brief overview of my mass work can be found at:

http://www.flickr.com/photos/markwitton/1386125619/

It's entirely irreverant and informal, but it should give you some gist
of where I'm coming from. The slightly less informal paper is in review
at the moment.

So long,

Mark

--

Mark Witton

Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk
>>> jrc <jrccea@bellsouth.net> 15/01/08 10:29 PM >>>
Comments inserted.
JimC

----- Original Message ----- 
From: "MICHAEL HABIB" <habib@jhmi.edu>
To: <dinosaur@usc.edu>
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 
Mike's model).

> 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,

Yes.

>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

>pretty trivial.

Yes.

> 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.
JimC