Abstract: A system for opposing helicopter blade flapping applies restraining forces at a low spring rate at low flap angles and at a high spring rate at flap angles greater than a predetermined angle. More particularly, bearings rotatably support the blade yoke on rotor hub trunnions which form a flapping axis. A resilient mechanical coupling between the blade yokes and the hub trunnion applies a restraining force having a characteristic linear with flapping angle. A second restraint mounted to rotate about the flapping axis with the rotor, applies a nonlinear restraining force which preferably rapidly increases beginning at a predetermined flap angle, and over the range short of hard flapping contact between the rotor and the rotor mast.

Abstract: A method and system which isolates two-per-rev hub spring moment vibrations while providing control power during zero-g flight in a two-bladed teetering rotor helicopter. Hub spring structure is connected between the rotor and the pylon to resist rotor flapping about the teeter axis and thus provide control during zero-g flight. To isolate from the fusilage the hub spring moment two-per-rev vibrations, the rotor is coupled to the pylon below the rotor center of gravity at a distance related to both the hub spring rates and the in-plane frequency of the helicopter blades.

Abstract: A helicopter main rotor has blades with an inboard airfoil having a high lift-drag ratio for efficient hovering and a "shock-free" outboard airfoil for high speed cruise. Each rotor blade has a structural section composed of metal spars and metal skins forming torque boxes accompanied by a nonstructural fairing and after body. Secured within the torque boxes and the after body are honeycomb cellular structures of a metallic and nonmetallic material, depending on the area wherein the cellular structure is secured. At a point along the blade radius, between 60% and 75%, the upper metal skin of the aft torque box changes from an outer contour surface of the blade to a flat surface parallel to and above the cord line. A fairing of fiberglass skin is secured over a nonmetallic cellular structure over the flat surface of the upper metal skin to complete the upper outer airfoil contour outboard of the 75% radius dimension.