I have been thinking for a long time about what happens to the wing membrane of a pterosaur on the ground. I have tried to work it out in my head and through sketching, but to no avail. I also made small models with the membrane represented by polyethylene sheet, but it was not convincing.
As part of my work to build a flying model, I have been experimenting with thread reinforced latex membranes, and built the first one at one-third scale (of a 6m span individual). As discussed elsewhere (Pterowing) it flapped a lot when tested, but is certainly more lifelike than plastic sheet. I rigged the membrane on an articulated model I made ages ago when I first tried to visualise the articulation of the wing skeleton and it fitted very well. Pam is holding it so the ventral side is exposed in the first picture below. You can see the reinforcing threads and see how it is stretched by the attachment at the ankles.
We then articulated the arm and leg to represent a walking pose, which is the next row of pictures. Note how the membrane is actually just clear of the ground even where it is folded at the metacarpal/WP1 joint. But not by much, and in another pose, with the head lower, it does sort to touch. Elsewhere it is a long way from the ground. This may not be the end of the world – after all bats manage when they are on the ground. However, my membrane only changes shape to the extent that it is stretched in the flight pose – there are no active muscles represented.
So, following some comments from Mike Habib, I inserted some elastic threads across the membrane – somewhat arbitrary I know, but helps to get the feel of things and they are shown in the second image. I then extended then by about 40% and let the membrane retract. OK, it looks a bit crumpled and nature would no doubt do a cleaner job, but as the final image shows, that amount of muscle retraction lifts the membrane well clear of the ground.
