Aerodynamic penalties of heavy rain on landing airplanes

The aerodynamic penalties due to very heavy rain on a landing aircraft is addressed in this paper. Based on severity and frequency of occurrence, torrential rainfall rates of 100, 500, and 2000 mm/h were investigated. Significant momentum loss was found to occur at moderate and higher torrential rainfall rates. The weight of a water film on transport category aircraft was found to be only a small fraction of landing weight. Roughness of an airfoil in rain is caused by drop cratering and waviness to a thin film on the airfoil and fuselage. Both sources of roughness were found to separately produce drag increases of from 5 to 10% for a 100-mm/h rain increasing to 15 to 25% for a 2000-mm/h rain. In addition, lift decreases of 10% for a 100-mm/h rain to more than 30% for a 2000-mm/h rain were estimated. Exordium I N recent years, wind shears associated with strong thunderstorm downdrafts have been implicated as the cause of several airplane accidents. The Eastern Flight 066 accident at Kennedy Airport1 is a prime example. In the National Transportation Safety Board's reconstruction of the flight recorder data from the accident, extraordinarily large wind shears were estimated. The reconstruction considered no other external factors besides the wind. The performance degradation due to the torrential rain cell experienced by Eastern 066 was not taken into account. We feel it possible that the derived wind shears are too large because the effect of the very heavy downpour was ignored. An extensive literature source revealed only one other investigation2 which considered the effect of torrential rain on airplane performance. That investigation dealt with the case of an airplane encountering torrential rain at moderate