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Re: Quetz wing questions



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