ABSTRACT
Focussing primarily on the longitudinal phugoid mode, this chapter investigates the dynamic equations in slower motion variables V and γ. Purely from physical arguments based on energy exchange post perturbation in this mode, famous Lanchester's derivation of phugoid mode frequency is presented. Later, expressions for phugoid mode frequency and damping are derived from slower dynamics equations completely ignoring the fast mode variables. Furthermore, compressibility correction factors are introduced and aerodynamic modelling including Mach number variation is presented. Refined modal approximation for phugoid mode is derived incorporating residual effects from short-period mode. Additional damping term resulting from flow curvature effect is introduced in this chapter via a physical example.
