Which of these is an important parameter for selecting the rotor blade based on aerodynamic efficiency?(a) Solidity ratio(b) Structural ratio(c) Figure of merit(d) Hovering ratioI got this question during an interview for a job.My question is based upon Blades and Propellers in section Helicopter Dynamics of Aerodynamics

Which of these is an important parameter for selecting the rotor blade

1.	Which of these is an important parameter for selecting the rotor blade based on aerodynamic efficiency?(a) Solidity ratio(b) Structural ratio(c) Figure of merit(d) Hovering ratioI got this question during an interview for a job.My question is based upon Blades and Propellers in section Helicopter Dynamics of Aerodynamics
Answer» Correct option is (c) Figure of merit The explanation: Figure of merit is one of an essential MEASURE for choosing the rotor based on the aerodynamic efficiency. It is given by the formula: M=\(\frac {1}{Κ+\frac {3}{4}\frac {c_{d_0}/\overline {c}_l}{\lambda _h}}\) Where, Κ is an empirical factor which ACCOUNTS for LOSSES in the rotor cl is mean lift coefficient cd0 is profile DRAG High value of the figure of merit is achieved when the airfoil has LOW drag for high lift coefficient.

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