Units and Dimensions

The postwar dominance of British and American aeronautics has kept the use of the foot-pound-second (FPS) system current, despite the use of nondecimal frac­tions and the ambiguity of the word pound in referring to both mass and weight. The benefits of the system international (SI) are undeniable: a decimal system and a distinction between mass and weight. However, there being “nowt so queer as folk,” I am presented with an interesting situation in which both FPS and SI systems are used. Operational users prefer FPS (i. e., altitudes are “measured” in feet); how­ever, scientists and engineers find SI more convenient. This is not a problem if one can become accustomed to the conversion factors. Appendix A provides an exhaus­tive conversion table that adequately covers the information in this book. However, readers will be relieved to know that in most cases, the text follows current interna­tional standards in notation units and the atmospheric table.

Aircraft performance is conducted at the International Standard Atmosphere (ISA) (see Section 3.3). References are given when design considerations must cater to performance degradation in a nonstandard day.