Ornithopters are fun

Ornithopters are flying machines that use flapping wings to generate lift. They are fun bits of biomimicry, and since the models mostly use incredibly thin flat sheets of flexible but non-stretching material, the wing surface is normally a developable one. This means, among other things, the wing surface at all points in the wing stroke cycle, should be amenable to modelling. They in turn provide inspiration for lightweight roof and pavilion structures.

This particularly amazing ornithopter uses a joint in the mid wing. The wing forms a developable surface that is quite rigid on the downstroke, and neatly folds up on itself to minimise wind resistance on the upstroke. The system is described (with extra videos) in this paper: https://ieeexplore.ieee.org/document/9849140/media#media

If you want to make one, a similar design CAD outline can be bought here:
https://jisaku-koubou.com/downloads/ornithopter001

There’s a much simpler rubber band powered ‘Pterosaur’ design that has a few demonstrations on youtube. They all appear to be the same design, but different videos may be clearer or solve different wee problems for you:
1) https://www.youtube.com/watch?v=NvFmh8MMyfI

2) https://www.youtube.com/watch?v=pn_H4ckwgEY

3) https://www.youtube.com/watch?v=j6IXumMkYOk (my favourite)

As a bonus, here’s two other flapping models to make: a butterfly that’s actually propeller driven (but is a quick and fun make), and a dragonfly model that uses two offset rigid opposed wings.

Finally, This is the Flying Karakuri Channel. It’s in Japanese, and needs care to explore, but looks to be a goldmine for the dedicated or fluent.

https://www.youtube.com/channel/UCFrWH5mtCezh1HpHV__dFjw/featured