Presented is an introduction to the basic principles of the Advancing Blade Concept (ABC) rotor and a review of the related experimental and analytical research conducted in support of the Sikorsky ABC helicopter program. The ABC helicopter is comprised of two coaxial, counter‐rotating rotors having blades rigidly attached to the hub except for feathering freedom. The blades are significantly stiffer than conventional rotor Blades and are capable of supporting large moments without excessive tip deflections. Improved forward flight efficiency and the elimination of retreating blade stall results from the ability of the ABC rotor to utilize to a large extent the lifting potential of the advancing blades—a capability not present in conventional single rotors. Results of various small‐scale wind tunnel experiments are presented along with summaries of several analytical investigations which were conducted to provide information concerning rotor performance, blade dynamics, vibration, and stability and control
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M. C. Cheney (1969) studied this question.