Wing Design
Micro joints
Dragonfly wings have longitudinal veins that are intersected by cross veins. Exactly what these connections look like varies over of the wing. What they have in common however, is that they control the amount of flexibility of the joint under load. Some even allow for lots of flexibility - until they bend too far and they become stiff.
This allows the entire wing to bend during flight in such a way that helps the dragonfly to fly more efficiently.
Material exploration #1
We started by taking inspiration from a flapping wing drone designed by Japanese researchers (and the 3D printing files they provide!). One of the first challenges was to find a way to print onto a membrane. The material used by the Japanese researchers were not readily available so we developed a way to print onto laminating sheets to create our first wings.
[Link to paper]
Joint trials
The joints on dragonfly wings are so small you need a microscope to appreciate them. Creating little joints that function in a way similar to a dragonfly's joints is possible (and had been done by one of the post doctorate students in the MI Lab - [Link paper]) but they are bigger than we need for the size of wing we wanted to design.
This led to experiments with a much simplified joint (see the grid of joints to the left), essentially no more than a gap in the printed material so there is only a small piece of laminate sheet the forms a flexible joint. When the sheet is bent far enough the printed "veins" hit against each other and the whole becomes stiff. Depending on the size of the gap, we found some samples displayed elastic bouce back properties.
Material exploration #2
Dragonfly wings are corrugated! This gives them flexibility in one direction and stiffness in the other. This allows for camber of the wing which increases lift. This became a parallel project to find a method to achieve this.
The challenge lay in how to attach a membrane to a corrugated structure. The method of using PLA to print onto laminating sheets is very much a 2D system. Trials were done with some methods traditionally used for model aeroplanes (mylar film and tissue paper) however these were time consuming and the finish was not exactly elegant. On top of that the trial corrugation had parallel lines, whereas the dragonfly wing's corrugation tapers towards the wing attachment. Getting a good finish on that would be impossible.
The challenge was still on....
3D printing
The MI Lab is set up with 3D printers, an ever growing collection that has now been moved to a dedicated space, There are...XXXXXX printers. The advantage of using rapid prototyping is in the name: it is possible to quickly manufacture an idea and see what it does in the real world. It is also relatively cheap!
This allows for designs to grow and develop quickly in support of theory and research.
Material exploration #3
The MI Lab has visiting research students and this year Haruka Fukunishi is here from Japan to continue her work at LSBU. She has developed a flexible film which turns hard under the influence of UV light. This means it is possible to have a structure fully integrated with a membrane.
Not only that when a patterned film put under tension, the hard parts remain stretched while the soft parts bounce back, leaving a buckled surface. Work is underway to see what possibilities her method brings for new wing designs. It is a promising new avenue for the construction of a corrugated wing.
Written by Hiske Buddingh
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