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What is rotor polar?(a) Plot of power coefficient as a function of thrust coefficient(b) Plot of thrust coefficient as a function of power coefficient(c) Plot of power coefficient as a function of lift coefficient(d) Plot of power coefficient as a function of drag coefficientI got this question in homework.Question is taken from Blade Element Theory in chapter Helicopter Dynamics of Aerodynamics

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The correct answer is (a) Plot of power coefficient as a function of thrust coefficient

To EXPLAIN I WOULD say: Plot of power coefficient \(\frac {C_p}{σ}\) as a function of thrust coefficient \(\frac {C_T}{σ}\) is known as ROTOR polar. There is no loss of profile power for an ideal rotor and there is minimum induced loss. Due to profile power loss, the rotor polar for a real rotor is at an offset compared to the ideal polar, and power increases faster with thrust coefficient due to the larger induced power.



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