
Ch09-H6927.tex 20/6/2007 16: 36 Page 234
234 Flight Dynamics Principles
For most aeroplanes the derivatives in equation (9.20) have negative values so that
the terms on either side of the inequality are usually both positive. M
w
is a measure of
the controls fixed longitudinal static stability margin, Z
u
is largely dependent on lift
coefficient, Z
w
is dominated by lift curve slope and M
u
onlyassumes significant values
at high Mach number. Thus provided the aeroplane possesses a sufficient margin of
controls fixed longitudinal static stability M
w
will be sufficiently large to ensure that
the inequality (9.20) is satisfied. At higher Mach numbers when M
u
becomes larger ...