What do a bat, a jellyfish and a humpback whale have in common? For one thing, these animals use their natural propulsors, such as wings, bells and flukes, to move through their environment, be it air or water. Last week a group of researchers published a study in Nature Communications that indicates that these and many other animals from distantly related groups seem to have attended the same school of propulsion. And one of the subjects they studied there was all about being flexible.
By analysing videos of 59 animals in steady motion, the researchers have discovered that most animal propulsive structures are surprisingly finely tuned as they bend at the tip in a way that shows very little variation across taxonomic groups, fluid medium and size – with the bending angle ranging from about 15° to 40°. No matter whether it is an insect, a bird, a fish, a mollusk or a cetacean, these newly discovered bending rules of propulsion apply to practically all of them.
The study suggests that this unique kinematic property of natural propulsors was independently reinvented again and again through evolutionary processes in entirely different groups of animals – a phenomenon that the authors of the study attribute to the advantages that bending propulsors imply for energy efficient thrust production.
The results of the study may open new possibilities in the design of biologically inspired propulsion systems, such as Robojelly, a Navy-funded robot jellyfish we featured in one of our previous posts, or its big brother Cyro, both of which have already confirmed the importance of flexible propulsors in underwater vehicles.