Abstract: A helicopter has main rotor blades foldable over its tail cone and a tail rotor pylon which is foldable about a tail cone vertical hinge from its fore-and-aft flight position through an angle approaching 180.degree. to lie alongside the tail cone. Tail rotor pitch control mechanism includes a cable which extends across the foldable hinged members, direction change pulleys for the cable and an improved 4-bar linkage system which controls the movement of the pulleys within a small envelope circle and maintains a constant tension on the cable throughout the full fold cycle.

Abstract: A bifilar vibration absorber is provided for the main rotor of a helicopter in which the pendular mass is constrained so that the path of motion of its cg relative to the rotor hub is a cycloid.

Abstract: A helicopter main rotor has an improved fairing enclosing the rotor hub and blade root area for drag and vibration reduction purposes. The fairing has peripheral cutouts through which the blades project provided with rounded lips on the rim of the cutouts to streamline air flowing in and out of the fairing through the cutouts. Internal partitions divide the fairing into chambers, each of which subtends one cutout, thus preventing flow of air through the fairing and attendant drag caused thereby. The rotor pylon is provided with a well through which the rotor drive shaft projects having a rounded lip adjacent the fairing to produce streamline airflow out of the well.

Abstract: A helicopter cross beam rotor is shown including upper and low coaxial composite blade spars at right angles secured by tension bolts which pass through the composite spars and are held by threaded nuts to a rotor hub at the upper end of a rotor drive shaft. A metal cap plate above the upper spar and a spar-to-spar filler piece are also provided. Torque between the spars and the rotor hub is reacted by intermeshing ribs and grooves on the confronting faces of the hub, the filler piece and the cap plate. The bolt holes in the composite spars are oversize so that the bolts do not react torque between the rotor hub and the composite spars.

Abstract: A pushrod-to-bellcrank attachment includes a primary pivot connection and two secondary pin and slot connections so arranged relative to each other that there is a continuing operative connection of the pushrod to the bellcrank in the event the primary connection is lost by small arms fire. When the primary pivot is lost, the pins of the secondary connections act in conjunction with the slots, which are arcuate, as a large bearing struck about the primary pivot to maintain the rod and the bellcrank in their original relative positions about the primary pivot with no introduction of lost motion between bellcrank and rod.

Abstract: A shaft bearing retention means comprises a segmented ring having a conical inner surface which is placed about a large diameter shaft having a corresponding conical indentation about its periphery to receive the ring. The segments are retained in assembled position on the shaft by joining pins extended through interengaging lapped tongues on the ends of each segment and by attaching one or more flanged retaining rings thereto by screws or bolts. Additional clamping screws or bolts pass through the retaining ring and are threaded into the segments, projecting beyond the latter so as to bear against a thrust ring through which the shaft passes. The axially adjustable thrust ring engages a bearing assembly which is fixed against axial movement by a shoulder on the shaft. Axial force is produced against the bearing assembly by the clamping bolts due to wedging action of the mating conical surfaces on the shaft and the segmented ring.

Abstract: A helicopter rotor blade of composite material, characterized by the absence of a spanwise metal spar, has tip weight attachment means for supporting stacks of washer-like metal shim weights in the composite material of the blade adjacent its tip to obtain both dynamic chordwise and static spanwise balance of the blade. Three holes are bored in the composite material from the underside of the blade into which three tip weight assemblies are inserted and are adhesively or otherwise secured to the composite material. Each assembly includes a cylindrical liner, a central hollow stud and a nut which engages external threads on the stud for holding the weights in stacked configuration. A plate forming a closure for the hole completes the skin of the blade and a screw threaded into the end of the stud secures the plate in place.

Abstract: A multibladed helicopter rotor carries at least three bifilar absorbers which are tuned to eliminate in-plane vibrations of the rotor that otherwise would be transmitted to the helicopter fuselage. By drooping the radial support arms for the absorbers out of the plane normal to their axis of rotation, the resultant of the centrifugal forces acting on the pendulous elements of the absorbers and the weight of these elements acts normal to the axes of the tuning pins of the absorbers which minimizes internal frictional damping in the absorbers.

Abstract: A multibladed helicopter rotor carries at least three bifilar absorbers which are tuned to eliminate in-plane vibrations of the rotor which otherwise would be transmitted to the helicopter fuselage. Improved tuning pin assemblies and cooperating tracking inserts for the absorber reduce the undesirable frictional damping heretofore encountered in bifilar absorbers by centering the pendulous elements of the absorbers relative to their support members and reacting forces normal to centrifugal force by permitting flapping movement of the bifilar mass in the vertical plane.

Abstract: A hydraulic damper for controlling the lag-lead movements of a helicopter rotor blade has dual oil seals on its piston rods. A fluid conduit connects the area between the seals to the area beneath the piston of a cylinder-and-piston type indicator and also through a fluid restriction back into an open fluid system. A bypass conduit is extended from the fluid conduit on the downstream side of the restriction to the area above the indicator piston so that any back pressure in the fluid system which creates a pressure rise of the other side of the restriction also acts on the upper end of the indicator piston.

Abstract: An angle gear box for a helicopter main rotor drive has a more compact arrangement of the usual gear train elements of the input section as well as a freewheel unit. The input section gear train includes a power input shaft mounted on bearings and having a bevel pinion and a power output shaft mounted on bearings and having a bevel gear meshing with the pinion. The output shaft has an axial chamber in which the freewheel unit is housed and from which it can be readily removed without disturbing the mounting elements of the gear train and the critical relationship of the high speed bevel gears.