Quest for Performance: The Evolution of Modern Aircraft
Chapter 7: Design Trends
[151] This chapter briefly summarizes the progress in design of propeller-driven aircraft since the end of World War I by showing how a number of important design and performance parameters varied over the years 1920 to 1980. The following parameters are discussed:
(1) Maximum speed, Vmax
(2) Stalling speed, Vs
(3) Wing loading, W/S
(4) Maximum lift coefficient, CL,max
(5) Power loading, W/P
(6) Zero-lift drag coefficient, CD,O
(7) Skin friction parameter, CFskin friction parameter
(8) Maximum lift-drag ratio, (L/D) max
The values of each of these parameters, obtained from tables I, II, and III (appendix A) and reference 90, are plotted against the appropriate year in figures 7.2 to 7.9. All of the parameters could not be obtained for some of the aircraft; in particular, the zero-lift drag coefficient and the maximum lift-drag ratio could not be determined for a number of the aircraft because of insufficient performance data from which to make the desired calculations. The symbols identifying each aircraft are given in figure 7.1 and have been used throughout the subsequent figures. At the left side of each figure (figs. 7.2 to 7.9), bars have been drawn to indicate the spread of each parameter during World War I as obtained from the data in table I. The year for which the characteristics of a given aircraft are plotted is in some degree arbitrary. For example, most of the World War II aircraft characteristics are plotted for the year 1942. In other cases, aircraft that were used for a number of years are shown at a year corresponding to the first year of production, or....

chart of reference symbols
[152] Figure 7. 1 - Symbols used in figures 7.2 to 7.9.
.... after the aircraft had achieved a fully developed status. The points for the different aircraft show a large spread in the different figures; hence, lines representing an upper and lower bound are shown on each figure. (The shape of these bound lines may be varied according to the manner in which the data are interpreted. The lines shown are only suggested fairings of the data points presented.) One of these bounds corresponds to aircraft developed with the highest technology available at a particular time, and the other is for aircraft of a relatively low and slow-changing level of technology. Neither of these bounds represents boundaries of maximum and minimum values but, rather, corresponds to higher and lower levels of technology for operational aircraft of a particular time period. No data for racing or special performance aircraft are given in the figures.