PROPELLER and GEAR RATIO REQUIREMENTS for Aircraft Designed for Cruising Operation 440211

FOR aircraft designed for cruising operation it is important that there be high propulsive efficiency at the engine speed for minimum specific fuel consumption for almost all cruising conditions.
For a given airplane with a single-stage, two-speed engine supercharger there is ordinarily more than one combination of propeller diameter and gear ratio which give within 1% of maximum propulsive efficiency for all cruising conditions up to an altitude of 20,000 ft and up to maximum cruising speed. Of these combinations, that one is best which has the largest diameter and the lowest ratio of propeller speed to engine speed, because it gives the best take-off and climbing performance.


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