Swifts (Apus apus) are renowned for their extremely aerial life style. From the moment the young swift leaves the nest it sets out on a very long journey. It will spend almost its entire lifetime in the air, day and night. The only time swifts land for a considerable time period is during breeding. They forage on the wing, collect nest materials on the wing, sleep on the wing and perform yearly migrations between Europe and Africa.
This extremely aerial lifestyle is naturally associated with a special aerodynamic design. The swifts have long slender aft-swept wings and a stream-lined body. Furthermore, the wings have a very short arm section and a very long hand section compared with most other birds (see figure to the right). This special design together with the extreme lifestyle makes this bird interesting to study since it is potentially yet another important piece of the puzzle of understanding animal flight.
We have studied the kinematics and the wake patterns of the flying swift in the Lund wind tunnel. The kinematics is recorded using high-speed cameras and the wake is captured using PIV.
The results have shown that the flight manner, both regarding kinematics and wake structure, differs between swifts and other bird species studied before. The swift flies with relatively rigid wings, flexing them very little during the upstroke. This results in a different wake, with more or less constant shedding of vortices into the wake throughout the complete wingbeat, both down and up, which suggests that the change in forces generated is smooth.
The simplified 'cartoon' wake of the swift in flapping flight.
Last modified 16 Oct 2012