How does icing affect aircraft aerodynamics and performance?

Icing degrades aircraft performance through: Increased drag (rough surface, disrupted flow, ice accumulation), Decreased lift (reduced CLmax up to 30-40%, changed pressure distribution), Increased weight (ice mass), Changed stability (altered aerodynamic moments, potential tail stall), and Control surface impairment (horn balance, gap seal issues). Performance effects include: Higher stall speeds, Reduced climb rate, Increased fuel consumption, and Lower service ceiling. Protection systems (de-ice/anti-ice) prevent accumulation, but residual ice or runback ice still affects performance. Ice shapes depend on conditions (rime vs. glaze) and affect aerodynamics differently. Certification testing (FAR 25 Appendix C, O) validates handling with ice.