Windxtasy said...The shape of those front wings is very similar to our sails, which have been developed through R & D to arrive at that shape. Perhaps the sails would perform even better if they were closer still to the butterfly shape. Look at that "mast bend curve".
I don't know a lot about aerodynamics but it seems to me at least that sail designers should reconsider orientation of battens to minimise turbulence over the foil so that the battens run more in the direction of the veins in the butterfly wing (red lines) which is the direction of air flow when the sail is raked back rather than the perpendicular to the mast pattern (yellow lines) that we have now.
But the shape of the front wings isn't similar to our sails when you see it the way the air does, when the butterfly is flying forwards. The wind first "sees" those front wings at the skinny part (top of the page) and then the air passes down to the section of widest chord further down the page.
That's like a windsurfer rig but upside-down.
The red lines you show are actually running at right angles to the general air flow over a butterfly's wing when the butterfly is flying forward, and the veins are close to 90 degrees to the airflow.
As has already been pointed out, there's physical problems in running battens along the flow of apparent wind. It's been tried long ago.
On top of that, a butterfly's wings are moving up and down across the airflow much faster than a windsurfer rig. If I recall correctly, the up-and-down stroke of the wings means that the butterfly is regularly working at angles of attack much higher than a board when planing.
That, in turn, means that the aerodynamics move towards those of a delta wing, with its leading edge vortex that "scrubs" the flow and re-energises it. That is very effective at creating high left AND high drag - so it works for a Concorde at landing speeds or for a butterfly. However, a high-lift/high drag shape doesn't work for a board at most high planing speeds. It's like shoving a Wally rig on a sinker - you get shedloads of power but so much drag that you end up going slower.
I just opened a 1928 book on sail aerodynamics, and the first chapter is headed "Nature as a guide to the construction of a sail". By construction, as the text and diagrams make completely clear, the author means construction and design.
So sail designers have been looking at nature as a model for aerodynamics for at least 80 years. Actually it's much longer, because pioneer flyers like Lilienthal and the Wrights were inspired by birds.
