Potential influences of heavy rain on general aviation airplane performance

Recent NASA wind tunnel tests of airfoils in a simulated rain environment under extremely heavy rain conditions have shown reductions in maximum lift and increases in drag. Conventional airfoils were tested with and without high lift devices and tests of laminar-flow airfoils without high-lift devices were conducted. Both types of airfoils indicated performance decrements when exposed to a simulated heavy rain environment. For the laminar flow airfoil, the rain influence was observed to occur throughout the angle of attack range, whereas for the conventional airfoil in a high lift configuration, the rain influence occurred mostly at the higher angles of attack. The performance decrement for the laminar-flow airfoil appeared to be a result of laminar-to-turbulent boundary-layer transition whereas the performance penalty for the conventional airfoil appeared to be the result of premature separation. The results of these tests are presented and the implication of the results to general aviation airplanes are discussed.