Discussion
Three of the following are longitudinal modes or longitudinal behaviour. The exception is
Dutch roll
The phugoid
The short-period oscillation
Aperiodic tuck divergence
Answer: D
Dutch roll is a lateral-directional mode: a coupled yaw and roll oscillation that comes out of the lateral characteristic equation, alongside the spiral mode and roll subsidence. It has nothing to do with the longitudinal quartic. The other three all do. The phugoid and the short period are the two oscillatory roots, and aperiodic tuck divergence is what appears when the last coefficient of the longitudinal quartic changes sign at high subsonic Mach number. Longitudinal and lateral motions decouple for small perturbations about symmetric flight, which is why they are solved as two separate problems.
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