1. Recent observations and theoretical developments concerning the flight o f aircraft i n a heavy rain environment have uncovered a surprisingly neglected problem i n aerodynamics. Though aircraft have been flying in rain, and i n some cases, extremely heavy rain, as long as anyone cares t o remember, only the sail plane enthusiasts, with laminar flow airfoils, have seriously heeded the lack of performance i n such an environment. Only i n the last few years have theoretical studies [Ref. 1-51 been conducted that consider the possible performance degradation of transport category and general aviation aircraft i n heavy rain. penalties t o roughness associated with both raindrop impaction and a wavy water f i l m present on the wings as a result of the aircraft penetrating a heavy rain shower. The studies conclude that transport category aircraft with fully turbulent winqs, can experience a significant loss i n lift, especially near C L M ,and a corresponding drag increase, when exposed t o a sufficiently heavy rain fall rate of at least 100 - 150 mm/hr. For general aviation aircraft with smaller wings and lower operating Reynolds numbers, the theoretical analysis indicates that adrod.ynamic penalties would he expected t o initiate a t lower rain rates; Derhaps as low as 50 mm/hr. These analysis further conclude that such extreme rain rates embedded, with wind shear, i n a thunderstorm environment have heen a significant contributor t o several aircraft accidents previously attributed totally t o wind shear.
2. The DOE-NASA 100 kilowatt experimental wind turbine a t the NASA Plum Brook-Station i n Sandusky, Ohio i s an experimental wind turbine that has heen i n operation for several years [Ref. stands 38 meters above the ground. Blades can be interchanged on the turbine for experimental testing. Generally blades having a radius i n the range of 15-19.5 meters have been used. The wind turbine when equipped with a 19.5 meter blade i s designed t o rotate at 20 revolutions per minute, producing chord Reynolds numbers between 2 and 2.5 million throughout most of the outer half of the blade. For a fixed pitch blade the angle of attack varies thoughout the span. Typically for a 19.5 meter blade and an 8 meter per second wind speed, the angle of attack varies from approximately 13 degrees at the t i p t o 22 degrees a t 50% span. Figures 1 and 2 extracted from Ref. 8 shows Reynolds numbers and angle of attack variations for a typical blade and environmental condition. More details about the FIASA wind turbine are contained i n Ref. 9 and 10. 81. The wind turbines axis of rotation
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