A generalization of the classical theory of flight dynamics is presented that includes quasi-steady aeroelastic effects using residualization approach. This is then used to investigate static stability of the aircraft, which may result in torsional divergence, as well as its controllability, which results in a metric for control effectiveness and potentially control reversal. Several illustrative problems are finally considered: a simplified model for the dynamics of a aircraft with a rigid fuselage, the aeroelastic trim of an aircraft with high-aspect ratio wings, and roll control with aeroelastic effects.