Experiments in Aërodynamics ²

Abstract

THE subject of this memoir is of especial interest at the present time, when the skill of a distinguished inventor is understood to be engaged in attacking the many practical difficulties which lie in the way of artificial flight upon a large scale. For a long time the resistance of fluids formed an unsatisfactory chapter in our treatises on hydrodynamics. According to the early suggestions of Newton, the resistances are (1) proportional to the surfaces of the solid bodies acted upon, to the densities of the fluids, and to the squares of the velocities; while (2) “the direct impulse of a fluid on a plane surface is to its absolute oblique impulse on the same surface as the square of the radius to the square of the sine of the angle of incidence.” The author of the work³ from which these words are quoted, in comparing the above statements with the experimental results available in his time (1822), remarks:—“(i) It is very consonant to experiment that the resistances are proportional to the squares of the velocities. …(2) It appears from a comparison of all the experiments, that the impulses and resistances are very nearly in the proportion of the surfaces. … (3) The resistances do by no means vary in the duplicate ratio of the sines of the angle of incidence.” And he subsequently states that for small angles the resistances are more nearly proportional to the sines of incidence than to their squares.