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Articulated Rotor Blade Flapping Motion at Low Advance Ratio

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At low advance ratio, articulated rotors exhibit an excessive amount of lateral flapping due primarily to major nonuniformities in induced velocity along the longitudinal axis of the rotor. Experimental study of this blade motion characteristic was conducted with a 5.5 foot diameter, CH‐47Cmodel rotor in the 20 × 20 ft Boeing V/STOL Wind Tunnel. Data taken over an advance ratio sweep from 0 to 0.24 at coustant lift showed maximum lateral flapping of 3.4° at 0.08 advance ratio. Classical rotor aerodynamic theory assuming uniform downash accounts for ouly 0.4° of this lateral flapping. Experimental data for longitudinal flapping illustrates that lateral nonuniformity in induced velocity is considerably less signifiecant. Variations in both shaft tilt and callective pitch at an advance ratio of 0.08 produced experimental blade motion trends that were nearly linear with both variables. Nonuniformity in downwash appears dependent primarily on advance ratio and, to the first order, proportional to rotor thrust.

Document Type: Research Article

Affiliations: V/STOL Wind Tunnel, The Boeing Company, Vertol Division, Philadelphia, Pennsylvania

Publication date: January 1, 1972

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