Historical Sketch of the Development of Aerodynamic Theory

Abstract

This paper is intended to give, in brief historical outline, a sketch of the development of aerodynamic theory from the time of Newton to the present day. Newton’s theory of fluid motion and the resulting formula for the force reaction resulting between an inclined plane and a fluid in relative motion are briefly stated and the insufficiency of the formulas noted. Reference is then made to the various mathematical aids which were developed during the next century, and which made possible the investigation of fluid motion based on the concept of continuous change and the “perfect fluid” of the mathematician. The limitations of this concept, especially with reference to the explanation of force reactions between the body and the fluid, are then noted, together with the introduction of the idea of “circulation” and generally of the physical picture as developed by Lanchester and then in mathematical form by Prandtl and his school. These are then briefly sketched and the results of the introduction of these new ideas indicated.

Reference is then made to the problem of the drag, only in part taken care of by the Lanchester-Prandtl vortex theory, and to von Karman’s work leading to his concept of the “Karman vortex street” and thence to the measurement of a further element of the drag; and finally to the third element (depending on skin friction) as at present dependent chiefly on direct physical measurement. In addition to the problem of lift and drag, the problems of stability and control in the air are briefly referred to, followed by mention of the dependence of theory on experimental research and to the vast amount of wind-tunnel investigation which has been made during the past two decades. Brief mention is then made of the two problems introduced by such work—the correction for “wall interference” and the “scale factor” due to the imperfect fulfilment of the conditions for kinematic similitude. This section closes with a mention of some of the problems which characterize the advancing fringe of progress in aerodynamic theory and which in large part still remain for future examination and study.

Then follows a brief section dealing with the screw propeller with reference to the chief stages of the development of propeller theory as suggested by the names Rankine, Froude, Drzewiecki, Prandtl, and closing with a suggestion of some of the problems which characterize the advancing fringe of this phase of general aerodynamic theory.