Wing performance in moderate rain

Emphasis is placed on the correlation of surface-film behavior including rivulet formulation with measured values of lift, drag, and moment at angles of attack up to stall. Four regions of surface flow are identified: 1) the droplet-impact, 2) film-convection, 3) rivulet-formation, and 4) droplet-convection regions. The extent that each of these regions covers the airfoil surface changes with incidence and correlates with changes in aerodynamicforce coefficients. Additionally, results quantify effects of the use of boundary-laye r trips for linking flight and wind-tunnel models in rain, and show that surface water phenomena affect laminar-to-turbulent transition in a manner that is inconsistent with the use of transition fixing to increase the effective test Reynolds number. Nomenclature ^wing = wing planform area Cd = drag coefficient, DRAG/^wing C, = lift coefficient, LIFT/^wing Cm — moment coefficient, PITCHING MOMENT/^wing c = chord length Re = Reynolds number based on chord length and freestream velocity a = angle of attack AQ = drag coefficient increment, (Crf)wet - (Cd)dry AC/% = percent change in lift coefficient, 100 x [(Q wet ~ (Q^MQ^ ACm .= moment coefficient increment, (Cw)wet - (Cm)dry