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Aviation History
1950
1950 - 0804.PDF
322 FLIGHT A Special Series of Photographs by John Warham i ORNISCOPICS Photographic Interpretations of Bird-flight THESE photographs are of outstanding interest in thatthe various attitudes in which the birds have been"frozen" makes possible a leisured study of the con- figuration at a particular instant in the given flight manoeuvre. The Little Owl (i), for example, has launched itself into the air—giving a final kick-off with its left leg—whilst simul- taneously opening its wings for the first downbeat. The primary feathers are well separated and each acts as an individual aerofoil, whereas the secondaries are closed up and preserve the aerofoil section of the wing to its full chord. An entirely different form of take-off is shown in (2), the Swallow having been caught diving from its nest under the eaves of a roof. Here the wings are almost fully extended at the top of their stroke, with the primaries and secondaries virtually closed up. In thk condition, the wings are not pro- jducing lift, but, equally, they are not causing drag, which would unduly hamper get-away; at the same time they are in such a position that they are at immediate readiness to make the first lift-producing downbeat when required. Another shot taken at the top of the wing stroke is shown at (3), again of a Little Owl. Apart from showing the spreading of the first four primaries, this photograph also illustrates with remark- able clarity the multitude of small, downy feathers which make up the under-surface of the wing between the shoulder and butt—i.e., about semi-span—for the leading 50 per cent chord. The Bam Owl in (4) is actually flying upward and, as may be seen, has no freedom to fly forward, whilst the stroke of its starboard wing is restricted by the wall. It is, perhaps, for the latter reason that its tail feathers are fanned asymmetric- ally. The extension of the alula (the small surface at the butt of the •wing, suggestive of a Handley Page slat) is also note- worthy. By contrast, the Bam Owl shown making its final •__ jar;.,,... _..
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