Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/15

Rh devised and carried out by the author as a direct test, and the application of the theory to the investigation of the stability of birds in flight, and to pre-existing flight models, including the gliding machine of the late Herr Lilienthal. The results are conclusive.

Chapter VII. consists of a series of investigations on lateral and directional stability, and may be looked upon as an independent section of the work. The method of treatment adopted is the initial discussion of these two kinds of stability separately, and their subsequent treatment in combination under the title rotative stability; this investigation also culminates in an equation which defines the limiting conditions of the stability of the kind under consideration.

Chapter VIII. constitutes in part a resume and in part an extension of that which has gone before. It comprises a review of the groundwork of the theoretical investigations, with some notes and discussion of the limitations and existing deficiencies of the work; also an extension of the investigation of Chapter V, to cover the conditions that arise in the case of an aerodrome propelled by prime mover and screw propeller, with a further investigation on the rate of damping of the phugoid oscillation. The chapter concludes with a discussion of the theory of corresponding speed and its application to scale model experiment, and with some remarks on forms of aerodone that may be considered as departures from elementary type.

Chapter IX. is a distinct branch of the work and deals with the phenomenon of soaring, both from the point of view of observation and in the light of theory, much of the preceding work being brought to bear on this complex subject with considerable effect. The first portion of the work includes quotations from observations by Darwin, J. A. Froude, Mouillard, Langley, and others, and the theoretical investigations have for their starting point the well-known dictum of Rayleigh, that when soaring is possible the motion of the wind is either not horizontal or not uniform.