8-3904-000

Yaw control function of the 8-3904-000 tail rotor

The 8-3904-000 tail rotor assembly changes the amount and direction of lateral thrust through blade pitch control. When the pilot commands yaw movement through the pedals, the control system changes the pitch angle of the tail rotor blades. This allows the helicopter to counter main rotor torque, hold heading and perform controlled turns around the vertical axis. The tail rotor must respond predictably during hover, takeoff, climb, cruise, descent and landing. If the hub, blades, pitch-control mechanism or mounting interfaces have defects, the system may develop vibration, reduced control response or abnormal thrust behavior.

8-3904-000 as a three-blade variable-pitch reversible rotor

The 8-3904-000 assembly is built as a three-blade, variable-pitch, reversible tail rotor. The three-blade layout provides the aerodynamic working surface required for lateral thrust generation, while variable pitch allows the thrust level to change during operation. The reversible design allows the rotor to work through the required pitch range for the helicopter’s directional control system. The assembly must maintain correct geometry, balance and control movement under aerodynamic and centrifugal loads. For this reason, inspection of the blade set, hub, pitch-change mechanism and logbook records is important before installation or acceptance.

Assembly composition of 8-3904-000

The 8-3904-000 tail rotor assembly consists of the tail rotor hub 8-3901-000 and tail rotor blades 8-3922-000. The hub is the primary load-bearing and control-transmission unit of the assembly. It provides blade attachment and transfers control forces required for pitch variation. The blades generate aerodynamic lateral thrust during rotation. These elements should be treated as parts of one operating rotor system, not as unrelated spare parts. Compatibility between the hub, blade set, aircraft configuration and documentation must be confirmed, especially when the assembly is supplied for overhaul, maintenance or replacement.

Application of 8-3904-000 on Mi-8, Mi-14, Mi-17 and Mi-24

The 8-3904-000 tail rotor assembly is used on Mi-8, Mi-14, Mi-17, Mi-24 and related helicopter models, depending on the installed tail rotor system and aircraft documentation. These aircraft may differ by modification, production series, repair history and service bulletin status, so applicability should not be confirmed only by a general platform name. Before supply or installation, the assembly designation, hub part number, blade part number and aircraft parts catalog should be checked. This is especially important when supplying individual components instead of a complete tail rotor assembly.

Manufacturer and supply format for 8-3904-000

The 8-3904-000 tail rotor assembly is manufactured by Moscow Machine-Building Plant “Vpered” / MMZ “Vpered”. Depending on the supply requirement, the product may be delivered as a complete tail rotor assembly or as individual components for overhaul and maintenance work. For correct ordering, it is useful to specify the helicopter type, required configuration, condition, component logbook availability and operational documentation. If supplied as separate parts, the hub and blade set should be matched by documentation and accepted configuration. Service records are important because the tail rotor is a controlled rotating assembly with direct effect on flight control.