Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/199



§ 128. Introductory.—Any material plane, that is to say any thin rigid plate bounded by parallel plane surfaces, when propelled through the air or held stationary in air in motion, experiences a reaction of greater or less magnitude. Any such "plane " is, from the manner of its employment, termed an aeroplane.

Theoretically an aeroplane is regarded as being material and rigid without possessing thickness. In practice, a certain amount of thickness being necessary, the edges may either be cut square, as in the planes employed by the late Professor Langley, in which case an allowance requires to be made for the edge effect, or, the edges may be carefully bevelled and rounded off, so that the aeroplane becomes an equivalent body of streamline form, in which case it is believed that no allowance is required.

The study of the aeroplane may be said to form the elementary basis of experimental aerodynamics as relating to the problem of flight. Whilst laying due stress on this fact, it may be pointed out that the importance of aeroplane study consists in its educational value and its bearing on certain subsidiary problems, rather than in the direct application of the aeroplane to the main function of flight, i.e., the support of the weight. This statement might appear somewhat unexpected, but it may be explained at the outset that the author does not employ the term aeroplane outside its correct signification, that is to say, to denote other than a true or plane aeroplane; the misuse of the word being avoided by the introduction of the term aerofoil, to denote a