
Ch11-H6927.tex 20/6/2007 16: 37 Page 300
300 Flight Dynamics Principles
Since an accelerometer is rather more robust than an incidence sensor, normal
acceleration feedback to elevator is commonly used instead of, or to complement,
incidence feedback. Both feedback variables have a similar effect on the phugoid
and short period stability mode at practical values of feedback gain. However, both
modes are rather more sensitive to feedback gain since very small values result in
significant changes to the mode characteristics. As K
a
z
is increased the short period
mode frequency increases very rapidly whilst, initially, the damping decreases slowly.
However ...