
Ch06-H6927.tex 20/6/2007 16: 34 Page 167
Longitudinal Dynamics 167
In general it is essential that the short period mode, which has a natural frequency
close to human pilot natural frequency, is adequately damped. Otherwise, dynamic
coupling with the pilot may occur under certain conditions leading to severe, or even
catastrophic, handling problems. On the other hand, as the phugoid mode is much
lower in frequency its impact on the piloting task is much less demanding. The average
human pilot can easily control the aircraft even when the phugoid is mildly unstable.
The phugoid mode can, typically, manifest itself as a minor trimming problem when
poorly ...