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First published online November 19, 2007
Journal of Experimental Biology 210, 4136-4149 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.011197

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Automatic aeroelastic devices in the wings of a steppe eagle Aquila nipalensis

Anna C. Carruthers, Adrian L. R. Thomas and Graham K. Taylor^*

Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford, OX1 3PS, UK

View larger version (76K): [in this window] [in a new window]   Fig. 1. (A) Photograph of steppe eagle carrying a wireless video camera while soaring freely over a sea cliff. (B) Still frame from the onboard video looking out along the left wing.

View larger version (47K): [in this window] [in a new window]   Fig. 2. Notation used to describe wing feathers of the upper (A) and lower (B) wing surfaces: A, alula; S, secondaries; P, primaries; sl, lesser secondary coverts; pc, primary coverts; sm, median secondary coverts; sg, greater secondary coverts. (After Brown et al., 1987.)

View larger version (116K): [in this window] [in a new window]   Fig. 3. Deflection of lesser upper- and underwing coverts during flapping flight over a sea cliff, showing the downstroke (A–D) and upstroke (E–H). Interval between images: 20 ms. An animation of this sequence is provided in supplementary material Movie 3.

View larger version (124K): [in this window] [in a new window]   Fig. 4. Deflection of lesser upper- and underwing coverts during a mid-flight gust response over a sea cliff. (A–D) Covert feather deployment and (E–H) covert feather retraction. Interval between images: 20 ms between rows; 320 ms between columns. The coverts remain in approximately the same deflected position between frames D and E. An animation of the complete sequence is provided in supplementary material Movie 4.

View larger version (112K): [in this window] [in a new window]   Fig. 5. Gliding perching sequence (Run 9 of Table 1) taken using high-speed digital video camera. Time of frame t is shown at upper left of each panel, referenced to the point of maximum wing flexion t=0 ms (D). Phase 1 (A): gliding approach. Alula begins to peel upwards; tail flicked up and back. Phase 2 (B–D): pitch-up manoeuvre. Wrist sweeps forward. (E) Lesser underwing coverts begin to deflect from wrist (red arrow); alula starts to protract; wing begins to straighten; tail spreads and pushes downwards and forwards. (F) Lesser underwing coverts deflecting in travelling wave from wrist towards shoulder (red arrow). (G) Lesser underwing coverts fully deflected (red arrow). Phase 3 (H): deep stall. Wings outstretched to give parachute-like shape. An animation of the complete sequence at 500 frames s–1 is provided in supplementary material Movie 5.

View larger version (56K): [in this window] [in a new window]   Fig. 6. Flapping perching sequence (Run 14 of Table 1) taken using high-speed digital video camera. Time interval between frames: 40 ms. (A–D) final wingbeat of flapping approach. (E–L) Main deceleration wingbeat, involving pitch-up motion of wings (E–H) followed by deep stall (H–J). The lesser underwing coverts deploy towards the end of each downstroke and close shortly after the beginning of each upstroke (red arrows). An animation of the complete sequence at 500 frames s–1 is provided in supplementary material Movie 6.

View larger version (62K): [in this window] [in a new window]   Fig. 7. Alula mechanics during gliding perching manoeuvre. Time interval between frames: 80 ms. (A) Alula is flush with the wing during the early stages of the gliding approach. (B) Alula peels from the tip towards the end of the gliding approach. (C) Hand-wing begins to sweep back, causing peeling alula to protrude further from wing surface. (D) Alula actively protracts. An animation of the complete sequence at 500 frames s–1 showing the entire bird is provided in supplementary material Movie 7.

View larger version (53K): [in this window] [in a new window]   Fig. 8. Pitch-up phase of gliding perching sequence (A), leading into deep stall (B–D). Time interval between frames: 40 ms. Red brackets show extent of deflection of the secondary upperwing coverts. An animation of the complete sequence at 500 frames s–1 is provided in supplementary material Movie 8.

View larger version (6K): [in this window] [in a new window]   Fig. 9. Cartoon of cross-parachute aerodynamics. Broken streamlines denote jets passing between arms of parachute; solid streamlines denote flow that attaches and then separates from the upper surface. (Redrawn from Shen and Cockrell, 1988.)

View larger version (4K): [in this window] [in a new window]   Fig. 10. M-wing planform with adjustable leading edge flaps, used in wind tunnel testing of subsonic and transonic wing designs in the 1960s. (Redrawn from Wyatt and Ilott, 1967.)