Here we are then, apologies for the unsharpened pencil, lack of drawing paper and inadvertent plug for copy centre (I don't know where I got the paper from) my scanner betrays me often and cuts bits off, and the leading edge of the top hinged part looks all wrong, but I believe it will do for Illustration.
The cloth is supposed to be a tube of sorts stretched over the assembly.
The thin bar at the rear is intended to be fixed but could be moved up and down if anyone thought a greater angle of attack was useful.
As I said before I'm not aero minded but I understand the principal that a lesser distance top or bottom gives lift on that side. Both top and bottom would move up/down totether to keep the length of cloth/fabric equal in all positions Would this be of any use? assuming the surface area available for movable aero was enough to offset the disavantages of weight???
Obviously there will be a mechanism to move it, but they already have something for what they've got, it could be as simple as cables for this depending on how the guides were designed??? The plastic could be substituted for any suitable material but at the moment I'm advised that Acetal would be O.K. Light, strong, flexible and with a memory.
Oh and use your imagination with the proportions, it's certainly not to scale!