Preface
The object and scope of the present work have been stated at length in the preface to Vol. I., which appeared as recently as December, 1907; there is but little to add to this statement.
In conducting the investigations and otherwise in collecting and arranging the matter included in the two volumes now completed, the author has made an effort to do, in as thorough a manner as possible, that preparatory work which, in his opinion, should properly precede the serious and hitherto hazardous undertaking of full-scale experiment. It is in other words the author's intention to provide such foundation theory and data as to bring the problem of mechanical flight into the legitimate domain of the engineer, and to obviate in the future all need for empiricism.
The author is aware that considerable work remains to be done in the way of extension, both in the more complete elucidation of many questions relating to the flight of birds, and in the direction of the application of theory in the design of the flying-machine for aerial navigation. It has not been found practicable to deal specifically with these extensions in the present volumes, but much that is suggestive will be found embodied appropriately in the text. The passive mode of bird flight, as involved in gliding and soaring, has however been discussed at length, for it is in the study of this mode of flight that the greater part of that which is essential may be learned.[1]
- ↑ There is a false impression—one that is far too prevalent—that the essence of flight consists in the flapping of wings. Nothing is further from the truth.
So far is this error current that attempts have boon sometimes made tolimit the term flying-machine to appliances of the wing-flapping kind. As illustrative of this vein of thought the statement is sometimes made that an aerodrome is not a flying -machine at all, that it does not fly, and that it is only sustained (presumably like a satellite) by the speed at which it travels!
Critics who talk thus know little or nothing of the subject of flight as taught by nature. It is true that many of the smaller birds and most insects are capable of stationary flight, but the heavier birds, as for example the eagle, the vulture, the stork, the albatros, the larger gulls, and nearer home the swan, the goose, and even the wild duck, cannot fly without considerable horizontal velocity. When leaving the ground (or water) these birds require a run of many yards in order to attain the necessary velocity. According to Mouillard, who was an accurate observer, most birds of more than a pound or two in weight may be effectively "caged" if confined in a simple fenced enclosure (open to the sky) of appropriate size; they are unable to acquire the velocity necessary to their flight.
Beyond the above very many of the larger birds rarely use the active (wing-flapping) mode of flight at all, but nevertheless it is not said that they no longer fly on that account.
