Harvey H. Hubbard

Sound-pressure measurements are reported for five shrouded propellers and are compared with those for an unshrouded propeller operating at approximately the same rotational speed and power. The maximum total sound pressure produced by a two-blade shrouded propeller is found to vary approximately from one-half to twice as much as that for an unshrouded two-blade propeller, depending on whether the flow at the shroud surface is unseparated or separated, respectively. Shroud chord is found not to be critical except insofar as the areodynamic considerations are affected. In general, if the shroud-propeller unit satisfies aerodynamic requirements, good sound characteristics will also be obtained.

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