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If we are talking about a slow flying aircraft with subsonic propeller tips, will adding a shroud increase efficiency, all else being the same?(ignoring the friction drag)

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  • $\begingroup$ By ignoring the friction drag you remove the basis for a fair comparison. A friction-less shroud will help to increase thrust, but not efficiency. $\endgroup$ – Peter Kämpf Sep 28 '17 at 22:29
  • $\begingroup$ Can you expand on that a bit? Why doesn't the efficiency increase, is it because of the added weight? $\endgroup$ – j.doe Sep 28 '17 at 22:59
  • $\begingroup$ No, because of higher induced losses. The minimum is reached with fairly lightly loaded tips. Adding a duct will allow to load the tips more, so more thrust is generated, but disproportionally higher torque is required to keep the prop spinning. $\endgroup$ – Peter Kämpf Sep 28 '17 at 23:09