A robot that resembles a pigeon and can make tight turns like real birds may point to the future of aerospace engineering – a continuously morphing wing.
Understanding exactly how birds fly has always been tricky, because individual wings are made up of multiple feathers. These feathers are always interacting with each other, allowing the bird’s wings to morph continuously mid-flight.
To learn more, David Lentink at Stanford University in California and his colleagues first looked at the wing of a pigeon cadaver. Each wing had 40 feathers, 20 on the upper side, and 20 on the lower.
“We attached a marker onto each individual wing and we were able to carefully measure the relationship between feather motion and bone motion,” says Lentink. “We then just moved the wing, in and out.”
They found that the wrist angle determined the angles of all the flight feathers at any one time, meaning that the birds can change the shape of their wings without having to control each individual feather. This reduces the number of variables – or degrees of freedom – required to model the wings.
“We let go of the idea that you have to control every degree of freedom and I think future aircraft will benefit from this finding. Future airplanes may not flap their wings, but I think they will change shape,” says Lentink.
The team put this new finding to use in the construction of PigeonBot, a intended to recreate pigeon flight. It is powered by a propeller and has wrist and feather joints in each wing that can be controlled remotely. Its average speed is about 40 kilometres per hour, which is a bit slower than the average pigeon.
Lentink and his colleagues also found that this type of flight was possible only because of certain molecules embedded throughout the feathers. These molecules, which are just 10 micrometres across, allow feathers to move away from each other while ensuring they don’t get too far apart. This in turn reduces the level of individual feather control required for accurate flight.
PigeonBot also uses real pigeon feathers, because no synthetic material has this property. “Feathers also have these unique properties, they have a lightness, a firmness to carry the aerodynamic load, and they’re easy to repair,” says Lentink.
Journal reference: Science, DOI: 10.1126/scirobotics.aay1246