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Contra-Rotating Propeller's efficiency improvement This picture is taken from here.

In that video is mentioned that contra-rotating propeller increases efficiency up to 6-16%. Regardless of the number that could be vary from one airplane to another, what I am asking here are: how the efficiency increase is calculated, how it is compared, to what parameter the efficiency increased is compared? Is it representing overall efficiency after calculated including the weight it added? The noise it created we may neglect, not part of my question.

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  • $\begingroup$ So you are asking if there is a standardized, generally accepted definition of the "efficiency" of a propulsion system, and does this definition take the weight of the system into account? Or you are asking what the intended meaning of efficiency would most likely be in the particular context of the quote in this video, i.e. what this particular author intended? Not exactly the same question, could be some room for clarification here. $\endgroup$ Jan 14 at 10:40
  • $\begingroup$ @quietflyer, Yes, more or less like "does this definition take the weight of the system into account?". Because, when it measured the trust alone it can be increased. But when it is put to the air plane, the additional device to make contra-rotating will give more weight, which in turn need more thrust/power to push the airplane to make it fly. I just don't have a clear understanding whether the efficiency is measured as standalone or as overall when it mounted and used in the airplane. $\endgroup$ Jan 15 at 3:15
  • $\begingroup$ @quietflyer, say that we have two identical airplane, one is using single rotating propeller and another one is contrarotating propeller. Both the airplane fly form one place to the another place at the same time. Will the contra-rotating propeller be more efficient to compared the one with not contra-rotating? I hope you understand my question. Sorry for my English limitation to make a good phrase. $\endgroup$ Jan 15 at 3:24

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