The Swallowtail Challenge. Answered
Apparently, swallowtail butterflies have posed a bit of a puzzle to the sort of chap that studies that sort of thing.
Butterflies actually have two pairs of wings - fore and aft, if you like. Most butterflies have these pairs separated, to allow greater control over their flight, but swallowtail wings overlap, effectively becoming a single wing.
They are stuck with a simple up-and-down flap. The puzzle was; where does the control come from.
It is hard to measure the forces acting on and in a live butterfly, so the researchers built a model - a small version of the hobbyists rubber-powered ornithopter, the same size and weight of a real swallowtail.
They cast replica wings from fluorocarbons and polyurethane, and set it off in front of slow-motion video cameras.
The unique shape of the wing provides automatic control - the combination of flexibility of the wing and the rigidity of the veins provide a passive control and stability.
Why am I posting this here? As a challenge: the swallowtail ornithopter was (except for the wings), very basic - wire frame and a rubber band.
How small could such an aircraft go?
How tiny could you, dear reader, build a working ornithopter?
Institute of Physics article.
(Free registration required to read it in full, if you are quick)