The mechanical design of a new variable pitch fan system for high bypass turbofan engines is presented, offering 10–14% fuel savings for next generation turbofan engines. Comparable in weight to current fans, the new design incorporates a compact pitch change mechanism that fits within a current fan’s center body. The key to compactness is the use of multiple high strength tension/torsion straps, which support blade centrifugal loads with unique structural efficiency and redundancy, while allowing ten to fifteen degrees of blade pitch rotation. The new retention system also offers significant reduction of pitch control forces by balancing blade centrifugal twisting loads with strap restoring moments, achieving a desired pitch setting. The use of a pin root fan blade facilitates on-wing blade replacement. Fan blade incidence angles are decreased at low aircraft speeds to avoid fan stall flutter problems. Therefore, advanced engines no longer need the addition of a variable area nozzle to the exit of the fan duct to prevent flutter, saving additional weight, complexity, and cost. This new fan system offers the best solution for achieving a major improvement in turbofan engine efficiency, at the lowest weight.

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