Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/220



'''§ 144. Introductory. Present State of Knowledge.'''—The problem presented by the inclined aeroplane is of very great complexity, and no general solution has at present been found. Our knowledge of the behaviour of the plane inclined to its direction of motion is in the main confined to the immediate results of experiment, extended it may be by the drawing of smooth curves through the observed points plotted on a co-ordinate chart. In certain extreme cases theoretical solutions have been found, and in other instances empirical formulae have been proposed, in fairly close agreement with the results on which they are based.

In addition to the considerations that weigh in the case of the normal plane, we have now not only to deal with some unknown law correlating pressure and angle, but we have also to take account of the remarkable effects due to the influence of aspect.

The early writers on fluid dynamics did not draw a proper distinction between an aeroplane and the surface of a solid of similar form, such for example as the wall or roof of a building; this has resulted from a too literal application of the impact theory of Newton. The pressure on a circumscribed area of the surface of a solid cannot be given by any formula, or, in fact, at all, unless the form of the remainder of the solid be known; any equation or theory that attempts to give a solution for the individual elements of the surface of a body independently of its