
Ch03-H6927.tex 30/6/2007 12: 19 Page 44
44 Flight Dynamics Principles
3.3 LONGITUDINAL STATIC STABILITY
3.3.1 Controls fixed stability
The condition described as controls fixed is taken to mean the condition when the
elevator and elevator tab are held at constant settings corresponding to the prevailing
trim condition. In practice this means that the pilot is flying the aircraft with his hands
on the controls and is holding the controls at the fixed setting required to trim. This,
of course, assumes that the aircraft is stable and remains in trim.
Since the controls are fixed:
dη
dC
L
w
=
dβ
η
dC
L
w
= 0 (3.15)
and equation (3.14) may be written:
dC
m
dC
L
w
= (h −h
0
) −