Technology often mimics nature in its quest to achieve efficient, stable and manoeuvrable flight. Over the past two decades inspiration for flying machines has often been drawn from the insect world. The flapping motion of insects’ wings has given insight to flight enthusiasts but stabilising machines with insect-like flapping wings poses some problems. In the so-called ‘normal mode’- the wing motions used by bees, flies and hummingbirds- flight is prone to instability. The other mode of flight- the up-and-down flapping of a dragonfly- is understood less well but robots designed to mimic these up-and-down motions often require extra controls to stay upright. The new design in this study avoids inherent instability, which can require sails, tails or feedback to correct, and instead ‘exhibits intrinsic stability using flapping wings alone’ say the team from New York University.
The team behind this new research searched for inspiration for their new flying machine not in the skies but in the seas. The team have developed an aircraft with four flapping wings which are pushed in-and-out in pairs. Wings on opposite sides of the machine flap simultaneously with the second pair of wings following close behind. This allows the conical body of the flying machine to effectively open and close to generate lift. ‘While there is no known flying animal that employs such a scheme, this design is reminiscent of the swimming motions of jellyfish,’ say Leif Ristroph and Stephen Childress- the scientists behind the study. The team suggest that the motion of the wings generates a jet flowing downwards which provides the machine with lift; much like the domed bell used by jellyfish to propel themselves through water.
The team came up with the concept for the flying machine using experiments by the Applied Math Lab at New York University. The scientists determined that a flying machine shaped like a cone or pyramid might be able to achieve stable hovering by flapping aerodynamic wings with no need for extra sails or tails. Using their theory the researchers designed and built their miniature flying machine. The machine, which is made of carbon fibre loops and thin mylar film for the wings, is powered by a tiny motor which weighs just 1.1g. The lightweight machine’s wings are just 8cm long but provide enough lift and stability to keep the small machine in the air.
Currently the jellyfish-like aircraft carries a motor powered by an external power supply but the team predicts that fine tuning the wing size would increase lift and make carrying an onboard battery possible in later models. The team say their study is ‘a step towards a feasible device’ and suggest that such small-scale flapping-wing aircrafts could be used for surveillance and reconnaissance as well as traffic and air quality monitoring in the future.