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Abstract
This paper describes the effects of a composite coupled blade spar on the performance of a slowed RPM helicopter rotor in high speed edgewise flight. A UH-60A-like rotor blade was chosen as a baseline for this study as it is the only production-level rotor optimized for hover that has been tested at high advance ratios up to 1.0. The analysis was performed using a full 3-D FEA based aeroelastic computational structural dynamics (CSD) solver, X3D. This type of analysis allows for the design of novel rotors and discrete/segmented spanwise variation of structural properties. For this paper the rotor spar was re-designed using a carbon fiber reinforced composite such that at 100% rotational speed the hover twist of the original UH-60 blade could be recovered while at slower rotational speeds the blade was automatically untwisted by up to 4-10 degrees (in vacuum) near the tip depending on the rotor speed. Thus the rotor carried different twists in hover and in high advance ratio flights. Preliminary investigations were conducted with simple aerodynamics (blade element with airfoil tables including shank drag) for different composite layup orientations, volume fractions, and radial segments. The current analysis show that significant performance (lift to drag ratio) enhancements of the rotor is possible for both full-span and half-span segmented layups of coupled composite spar at low blade loading. The detailed causes behind the observed performance benefits are part of ongoing investigation.

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