Page 28 - Aeronautical Engineer Data Book

16 Aeronautical Engineer’s Data Book
2.3.9 Torque
The basic unit of torque is the foot pound (ft.lbf)
(in SI it is the newton metre (N m)). You may
also see this referred to as ‘moment of force’ (see
Figure 2.5)
1 ft.lbf= 1.357 N m
1 kgf.m = 9.81 N m

2.3.10 Stress
2
Stress is measured in lb/in – the same unit used
for pressure although it is a different physical
quantity. In SI the basic unit is the pascal (Pa).
1 Pa is an impractically by small unit so MPa is
normally used (see Figure 2.6).
2
1 lb/in = 6895 Pa
2
1 MPa = 1 MN/m = 1 N/mm 2
2
1 kgf/mm = 9.80665 MPa
2.3.11 Linear velocity (speed)
The basic unit of linear velocity (speed) is feet
per second (in SI it is m/s). In aeronautics, the
most common non-SI unit is the knot, which is
equivalent to 1 nautical mile (1853.2 m) per
hour. See Table 2.8.

2.3.12 Acceleration
The basic unit of acceleration is feet per second
2
2
squared (ft/s ). In SI it is m/s .
2
1 ft/s = 0.3048 m/s 2
2
1 m/s = 3.28084 ft/s 2
Standard gravity (g) is normally taken as
2
2
32.1740 ft/s (9.80665 m/s ).
2.3.13 Angular velocity
The basic unit is radians per second (rad/s).
1 rad/s = 0.159155 rev/s = 57.2958 degree/s
The radian is also the SI unit used for plane
angles.
A complete circle is 2π radians (see Figure 2.7)
A quarter-circle (90°) is π/2 or 1.57 radians
1 degree = π/180 radians