Measurements of lift, drag, and moment coefficients were obtained for a rectangular planform wing with wettable and nonwettable surface coatings in light to moderate rain. Comparisons with surfacewater flow patterns show that the degradation of aerodynamic efficiency caused by rain depended on the location of rivulet formation and on the diameter of these rivulets. Drag forces increase with increasing diameter of rivulets. Lift forces decrease with a longer film-convection region. Wing surfaces with wettable coatings had thinner films, flatter thinner rivulets, and flatter droplets that resulted in the least loss in lift-to-drag ratio caused by rain, despite longer film-convection regions. Droplet and rivulet diameters are found to be more important to aerodynamic performance than the location of rivulet formation.