Page 35 - Aeronautical Engineer Data Book
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22 Aeronautical Engineer’s Data Book
Step 4: Expand and cancel*:
0.16 lb � kg �� in 3 3 �
# = 3 3 33
3
in 3 2.205 lb (25.4) mm
� (1000) mm 3 �
3
33
3
m
0.16 kg (1000) 3
# = 33
3
2.205 (25.4) m 3
# = 4428.02 kg/m 3 Answer
*Take care to use the correct algebraic rules for
the expansion, e.g.
N
N
N
(a.b) = a .b not a.b N
� 1000 mm 3 (1000) (mm) 3
�
3
e.g. 33 expands to 33
3
m
(m)
Unity brackets can be used for all unit conver
sions provided you follow the rules for algebra
correctly.
2.6 Imperial–metric conversions
See Table 2.11.
2.7 Dimensional analysis
2.7.1 Dimensional analysis (DA) – what is it?
DA is a technique based on the idea that one
physical quantity is related to others in a
precise mathematical way.
It is used in aeronautics for:
• Checking the validity of equations.
• Finding the arrangement of variables in a
formula.
• Helping to tackle problems that do not
possess a compete theoretical solution –
particularly those involving fluid mechanics.
2.7.2 Primary and secondary quantities
Primary quantities are quantities which are
absolutely independent of each other. They
are:
