Tail Rotor Hub and Blade Assembly

The tail rotor hub and blade assembly is a delta hinge type that consists of the rotor hub and rotor blades.

Rotor blades

The rotor blade system provides the necessary aerodynamic lift force to push the tail rotor in the opposite direction of the torque applied by the main rotor. It also has provisions to control that force so the helicopter can be moved around the vertical axis. The rotor blade system includes the tail rotor blade assemblies.

Tail rotor blade assembly

Two tail rotor blade assemblies are used for the rotor blade system and both are interchangeable. Each tail rotor blade assembly includes a blade and a pitch horn.

The blade is a metal assembly with a stainless steel shell and honeycomb filler. The leading edge of the blade has an abrasive strip also made of stainless steel. The abrasive strip protects the leading edge against the abrasion caused by sand, water, and other particles. Two spherical bearings are mounted in the grip plates, on the pitch change axis, for attachment of the blade to the yoke of the tail rotor hub assembly. The movement of these bearings around the axis allows for the pitch of the blade to be changed. Ballast stations at the inboard trailing edge and at the tip of the blade are used to balance the mass of the blade chordwise and spanwise respectively. These weights are adjusted when the blade is made and are not field adjustable.

The pitch horn is installed on the root end of the blade. It is made of stainless steel and has provisions for attachment of the pitch link assembly to the tail rotor blade assembly. Adjustable counterweights are installed on each side of the pitch horn to decrease loads on the controls.

Rotor hub

The tail rotor hub assembly provides attachments for the rotor blades and a flapping axis for the rotor to prevent dissymmetry of lift. It is driven by the output shaft of the tail rotor gearbox to give the rotor blades the necessary angular speed to provide for lateral thrust. The rotor hub system includes the tail rotor hub assembly.

Tail rotor hub assembly

The yoke of the tail rotor hub assembly is made from an aluminum alloy casting. It has a 4° twist angle where each blade attaches to give additional thrust for high altitude performance. Inside the yoke, a splined trunnion made of steel provides for attachment of the tail rotor hub assembly to the output shaft of the tail rotor gearbox. A needle bearing is installed on each end of the trunnion so the yoke can move freely around the flapping axis of the assembly. These bearings fit in housing assemblies which close the open ends of the tail rotor hub assembly. Each housing assembly has a grease fitting to lubricate the needle bearings.

The tail rotor hub assembly includes the primary parts that follow:

• Yoke assembly

• Trunnion assembly

• Housing assemblies

• Needle bearings

Operation

During helicopter operation, the turning force from the output shaft of the tail rotor gearbox is transferred to the tail rotor hub assembly through the splined trunnion. The tail rotor hub assembly then transfers this force to the two rotor blade assemblies and allows for a limited flapping movement.

The fasteners that are used to attach the housing assemblies have weights and washers to balance the mass of the assembly chordwise. The washers that are used to attach the tail rotor blade assemblies to the yoke of the tail rotor hub assembly are also used to balance the mass of the assembly spanwise.