The Measurement of Speeds: Errors Inherent in the Standard Installation and Methods for Determining True Air Speed Accurately

“WHAT is its top speed?” This is the question which is perhaps most frequently asked about any new aeroplane, and it is certainly a question which is usually incorrectly answered. By this is not meant the natural tendency of manufacturers to be optimistic as to the paces of their latest progeny, but merely that the top speed of an aeroplane cannot be stated with accuracy until a number of careful and methodical measurements have been made. In this article a short account will be given of the errors inherent in the ordinary methods for indicating speeds, and descriptions of some of the methods evolved to measure speed—not only top speed but speed generally—to a high degree of accuracy.