1, phase ‘I’ shows the beginning of the stoop and ‘II’ is when the bird is diving at maximum speed in a T-shape configuration expanded in the corresponding live image.

The two live images show the real morphology corresponding to the two main silhouettes in the schematic representation. 1 together with the silhouette of the wing configurations adopted during various stages of the stoop. Complementary Computational Fluid Dynamics (CFD) simulations helped in confirming the experimental findings and provided more details of the flow field in locations where measurements were not possible.įrom the live recordings during the field experiment conducted at the Oleftal dam in Hellenthal, Germany, the dive path of a trained falcon was reconstructed and this is shown schematically in Fig. Further postprocessing of the velocity field helps in resolving the vortices and investigate their dynamics. Their trajectories are recorded by a high-speed digital camera, and using image-processing algorithm the velocity vector is determined by resolving the displacement of the tracer particle for a known time interval. In this technique, the motion of micrometre-sized particles seeded in the flow are traced while illuminated by a laser sheet. Digital particle image velocimetry 11 (DPIV) was employed to gather more detail about the development of the vortical structures in the wake of the bird, which interact to reduce the downwash effect. First, oil flow visualisation technique was used to capture the flow topology and analysis of the near-surface streamlines revealed the presence of strong transverse velocity component and a vortex-dominated flow over the bird. Our wind tunnel experiment sheds light on the flow mechanisms that assist the bird in executing this manoeuvre. From a flight mechanics point of view, in order to perform such manoeuvres the bird needs to generate drastic forces during these ‘strenuous’ conditions. In the M-shape, lift increases dramatically and can even reach ~ 18 times its weight 10, but this theoretically derived figure should be regarded with some scepticism. This sudden alteration of morphology to achieve such a complex manoeuvre is enabled by the robust musculo-skeletal structure and the superior mechanical strength of the feathers 9. Despite the rapid deceleration in this configuration, the bird is still flying at moderately high speed, which prevents it from stalling and also allows it to spiral back for another attack if needed. 5 and is in agreement with previously broadcasted live recording 6, 7, 8. This observation was confirmed from the live recordings also reported in ref. During the M-shape the arm opens up further into the horizontal plane and the primary feathers are aligned with the axis of the bird to form an M-shaped planform when viewed from the top. In C-shape the arms are slighly untucked, creating a cavity between the body and the primary feathers, which are oriented vertically. 4) and the M-shape (the focus of this manuscript). The success of the attack largely depends on the manoeuvrability during the second phase of the stoop, when the bird 1 starts to pull out from the dive, while undergoing two important morphological transformations, namely the cupped-wing shape (C-shape, detail presented in ref. Within the initial phase of the stoop it adopts a ‘teardrop’ shape (T-shape) where the wings are folded and feathers tucked in a streamlined shape, which is intuitively the lowest drag configuration. While soaring, the falcon first climbs with the wings completely stretched out to increase lift, collected from vertical columns of rising air known as ‘thermals’ 3. Diving from high altitude is necessary to build-up such speeds. These findings could help in improving aircraft performance and wing suits for human flights.ĭuring stoop, peregine falcon ( Falco peregrinus), can dive at 39 ms −1 1 to 51 ms −1 2, making it the world’s fastest animal.

A vortex pair with a sense of rotation opposite to that from conventional planar wings interacts with the main wings vortex to reduce induced drag, which would otherwise decelerate the bird significantly during pull-out. The stronger wing and tail vortices provide extra aerodynamic forces through vortex-induced lift for pitch and roll control.

These vortices enhance mixing for flow reattachment towards the tail. Both experiments and simulations on life-size models, derived from field observations, revealed the presence of vortices emanating from the frontal and dorsal region due to a strong spanwise flow promoted by the forward sweep of the radiale. Here we demonstrate that the superior manoeuvrability of peregrine falcons during stoop is attributed to vortex-dominated flow promoted by their morphology, in the M-shape configuration adopted towards the end of dive.

The peregrine falcon ( Falco peregrinus) is known for its extremely high speeds during hunting dives or stoop.

Chris myer peregrin falcon