
Ch06-H6927.tex 20/6/2007 16: 34 Page 147
Longitudinal Dynamics 147
slow such that the angular accelerations, ˙q and ˙α( ˙w), are insignificantly small.
Consequently, the natural frequency of the mode is low and since drag is designed to
be low so the damping is also low. Typically, once excited many cycles of the phugoid
may be visible before it eventually damps out. Since the rate of loss of energy is
low, a consequence of low drag damping effects, the motion is often approximated
by undamped harmonic motion in which potential and kinetic energy are exchanged
as the aircraft flies the sinusoidal flight path. This in fact was the basis on which
Lanchester ...