BECAUSE of the complexity of rotor theory which has been developed for tapered and twisted blades (for example, Sissingh's well known papers) there is a great tendency to use and draw conclusions from the simple theory developed for untwisted untapered blades. In the United States this practice appears to be almost universal, and much use is made of the highly questionable ‘equivalent chord’ when dealing with tapered blades. It cannot be too much emphasized that there is no such thing as an ‘equivalent chord’, and that its use not only masks the true effect of taper, but leads to solutions which in some cases are in considerable error.
Payne, P.R. (1954), "A General Theory of Helicopter Rotor Dynamics: An Analysis of the Dynamics of a Helicopter Rotor with Tapered and Twisted Blades", Aircraft Engineering and Aerospace Technology, Vol. 26 No. 8, pp. 247-251. https://doi.org/10.1108/eb032456
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