The aerodynamic effect of heavy rain on airplane performance

The National Aeronautics and Space Administration has been conducting a series of tests to determine the effect of heavy rain on airfoil aerodynamics. The results of these tests have shown that heavy rain can significantly increase drag as well as decrease lift and stall angle of attack. This paper describes a recent effort to use the heavy rain airfoil data to determine the aerodynamic effect on a conventional twin-jet transport. The paper reports on the method used to model the heavy rain aerodynamic effect and the resulting performance degradation. The heavy rain performance effect is presented in terms of the diminished climb performance associated with increasing rain rates. The effect of heavy rain on the airplane's ability to escape a performance-limiting wind shear is illustrated through a numerical simulation of a wet microburst encounter. The results of this paper accentuate the need for further testing to determine scaling relationships and flow mechanics, and the full configuration three-dimensional effects of heavy rain.