Page 269 - Aeronautical Engineer Data Book

Section 12

Basic mechanical design

The techniques of basic mechanical design are
found in all aspects of aeronautical engineering.

12.1 Engineering abbreviations
The following abbreviations, based on the
published standard ANSI/ASME Y14.5 81:
1994: Dimensioning and Tolerancing, are in
common use in engineering drawings and speci­
fications in the USA (Table 12.1).
In Europe, a slightly different set of abbrevi­
ations is used (see Table 12.2).

12.2 Preferred numbers and preferred sizes
Preferred numbers are derived from geometric
series, in which each term is a uniform percent­
age larger than its predecessor. The first five
principal series (named the ‘R’ series) are
shown in Figure 12.1. Preferred numbers are
taken as the basis for ranges of linear sizes of
components, often being rounded up or down
for convenience. Figure 12.2 shows the devel­
opment of the R5 and R10 series.

Series Basis Ratio of terms
(% increase)
R5 5√10 1.58 (58%)
R10 10√10 1.26 (26%)
R20 20√10 1.12 (12%)
R40 40√10 1.06 (6%)
R80 80√10 1.03 (3%)

Fig. 12.1 The first five principal ‘R’ series