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Safety Devices in Wings of Birds*

Published online by Cambridge University Press:  28 July 2016

R. R. Graham
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Extract

A noticeable peculiarity in the flight of a certain number of birds is the way their wing-tip feathers separate, both in flapping and in gliding flight. So wide do the gaps between the feathers become, at times, that the outer parts of the wings take on the appearance of hands with their fingers spread out. One's first thought about the matter is that there is probably nothing in it; that the feathers separate simply because they are feathers, and, as such, cannot help themselves; but, on investigation, this turns out to be one of the most interesting of the many aspects of the flight of birds; interesting, not only because it brings to light the infinite care and cunning that have been bestowed on the construction of their wings, but also because it demonstrates the possibility of applying some of the lessons that birds can teach us, to the design of flying machines—gliders in particular. When considering such questions we should always humbly remember that birds are the outcome of the law of the survival of the fittest through countless ages of flying, while we have been at it only for about thirty years.

Type
Research Article
Information
The Aeronautical Journal , Volume 36 , Issue 253 , January 1932 , pp. 24 - 58
Copyright
Copyright © Royal Aeronautical Society 1932

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Footnotes

*

Reprinted by permission from British Birds.

References

Note on Page 27 * In some birds the emargination of the rear webs is very indistinct, particularly in the feathers that form the hindmost slots. The Pheasant's wing is a good example.

Note on Page 32 * Probably the spreading of the webbed feet, ready to continue the “ braking ” in the water, assists the wings slightly in this.

Note on Page 36 * Only a few wings have been examined for this peculiarity, but it is suspected that all slotforming feathers possess it to a greater or less degree.

Note on Page 37 * Sir G. T. Walker, in his paper on this subject, which appeared in the Journal of the Asiatic Society of Bengal, in 1924, makes out this incidence to be in the region of 28 degrees for a soaring Vulture.

Note on Page 38 * The Pterodactyl described has been superseded by a new type (1931) whose control surfaces are not designed to operate in the manner described.

Note on Page 39 * Some years ago Mr. Handley Page, without knowing that this type of slot was to be found in birds' wings, assigned and tested a model, having seven slots, arranged in much the same way. He found that it increased the maximum lift by 250 per cent. at an angle of 42 degrees, as compared with the unslotted wing.

Note on Page 42 * The reason in technical language is that a gas which is compressed will tend to expand equally in all directions. By the same token it will tend to flow into a space where there is a reduced pressure; that applies to the, top of .the wing.

Note on Page 50 * Data on these matters will be found in the table.

Note on Page 56 * For the sake of simplicity in explaining, it is more convenient to think of the air as being in motion relative to a wing in flight, than of the wing as moving through the air.

Note on Page 58 * Mr. Higham's last paragraph raises a point about which there may be some doubt. No breeze can ever possibly blow a bird's feathers up from behind, because the bird is “ carried ” by the air and superimposes its own speed upon that at which the air is travelling. A bird in flight detects wind merely by the fact that it carries him in the direction in which it is flowing at the speed of the wind; he does not feel it in the same manner as we do. All he actually feels is the “ bumping ” effect due to eddies in the wind, an effect which is familiar to all who fly in aeroplanes.—R.R.G.