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Re: pteros have lift-off


Bipedal launch would be facilitated either by bipedal running, or bipedal leaping. There are two scenarios for launch by bipedal running, and one for bipedal leaping. Reconstructions of pterosaurs in the bipedal posture usually have the angle of the spine oriented roughly about 20 to 30 degrees from the vertical. The consensus among pterosaur workers is that the trailing edge of the wing membrane is bound to the hindlimb. This presents constraints on the wing's launch angle of attack that do NOT apply to birds since the pterosaurs' inboard chord must now remain approximately parallel to the spine. Let's discuss those pterosaurian constraints. A few quick thoughts follow.

1)      Running bipedal launch

a) In typical bipedal posture with spine about 20 to 30 degrees from vertical - the angle of attack of the wing is closer to vertical than horizontal, approximately 42 to to 52 degrees greater than the stall angle of attack. Therefore the underside of the wing is facing forward and creating substantial flatplate drag. This is equivalent to trying to run with a drag chute strapped to your waist. Any effort to provide lift by flapping creates a "lift" vector that is oriented mostly to the rear, slowing the animal even further. Very little of the lift vector (about 34% ) is oriented in a direction that helps to lift the animal. Most (about 94%) is oriented aftward and acts to slow the animal's forward speed. This means that the animal will have to run very fast and then suddenly pitch forward in order to lift off.

b) An alternative is to rotate the torso, neck, and head forward from the hips into a near horizontal orientation that directs most of the lift vector upward. The downside is that the cg is now well forward of the feet. This is equivalent to a human holding a 5 meter piece of pvc pipe by one end and extending it out horizontally in front while also bending the torso horizontally forward from the hips. It is very difficult (or impossible) for a human to either stand or run in that position, and a pterosaur would incur similar difficulty for the same reasons.

2  Leaping bipedal launch

a) Bipedal leaping implies creating a force vector that is aligned fairly closely with the spine (approximately 20 to 30 degrees from the vertical for the bipedal posture). Therefore, the launch angle is also at about 20 to 30 degrees from the vertical. Consequently, most of the velocity created by the leap is vertical (about 87 to 94%) and a smaller fraction (about 34 to 50% is oriented parallel to the ground in a direction that will facilitate flight. In the horizontal direction, the same wing orientation, drag, and lift issues apply as are incurred in the running '1 a' scenario.

Any proponent of bipedal launch must have addressed these issues numerically. Does anyone wish to comment?