Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/357



§ 221. Introductory.—Experimental aerodynamics must at present be regarded as in its infancy. The methods employed up to date have not yielded results of an exactitude comparable to that readily obtainable in other branches of physical science.

There are in the main three methods of investigation open. Firstly, experiments upon planes or other bodies propelled through still air, the subject of experiment and the measuring appliances being mounted either on the arm of a whirling table or on the front of a locomotive vehicle. Secondly, the measurement of the reactions produced by a fluid in uniform motion on a fixed body. Thirdly, by measurement and deduction from experiments in free flight.

The first method is that most generally adopted, admirable work having been done in this direction by Dines. Langley and others. The second method has been used to some extent by Dines, and the third (the method of free flight) has been developed to a certain extent by the author.

The earlier experimenters. Robins (1761), Hutton (1787), and Vince (1794-5, 1797-8), employed a primitive form of whirling table, the invention of which is attributed by Hutton to Robins, and no earlier record appears to exist of the employment of this device for the purpose contemplated. The whirling table as known to Hutton is represented diagrammatically in Fig. 140, in which a horizontal arm A is mounted on a vertical axis B, which is caused to rotate by the silk cord C and weight D; the body on which experiments are to be made is mounted at the extremity