What is wing aspect ratio and how does it affect aircraft performance?

Aspect ratio (AR) is wingspan squared divided by wing area (b2/S), or equivalently span/mean chord. Typical values: Gliders 20-40, Commercial transports 8-10, Fighters 3-5. Effects: High AR - Lower induced drag (more efficient lift), better range and fuel efficiency, but increased structural weight (bending loads), flutter concerns; Low AR - Lower weight, better roll rate, higher structural efficiency, but more induced drag, lower L/D. Trade-offs: Range efficiency favors high AR, Maneuverability favors lower AR, Wing span limited by airport gates, and Weight increases non-linearly with AR. Modern transports use 9-12 AR with winglets for practical span limits. Optimum AR balances: Aerodynamic efficiency gain vs. weight penalty, Manufacturing cost, and Operational constraints. Wing taper reduces structural weight for given AR.