Measurements of propeller efficiency loss due to ice formation are supplemented by an analysis to establish the magnitude of efficiency losses to be anticipated during flight in icing conditions. The measure-ments were made during flight in natural icing conditions; whereas the analysis consisted of an investigation of changes in blade-section aero-dynamic characteristics caused by ice formation and the resulting pro¬peller efficiency changes. Agreement in the order of magnitude of effi-ciency losses to be expected is obtained between measured and analytical results. The results indicate that, in general, efficiency losses can be expected to be less than 10 percent; whereas maximum losses, which will be encountered only rarely, may be as high as 15 or 20 percent. Reported losses larger than 15 or 20 percent, based on reductions in airplane performance, probably are due to ice accretions on other parts of the airplane.
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