8AT-7420

8AT-7420 slip ring assembly on the tail rotor

The 8AT-7420 is an aircraft slip ring assembly used on the tail rotor of Mi-8, Mi-17, Mi-171 and Mi-24 family helicopters. Its purpose is to transfer electrical power from the fixed onboard wiring of the helicopter to equipment installed on the continuously rotating tail rotor assembly. In practical terms, this unit is the electrical link between the stationary part of the helicopter and the rotating rotor hub area. Without this type of current collector, it would be impossible to feed electrical consumers located on rotating blades through a conventional fixed wiring connection.

Power transfer through the 8AT-7420 collector

The 8AT-7420 works through a collector-and-brush arrangement. Electrical current is supplied to the rotating collector rings, while carbon brushes maintain contact during rotation. This allows the anti-icing system to receive power while the tail rotor is spinning at operating speed. The unit must keep stable electrical contact under vibration, rotation, and changing helicopter operating conditions. For this reason, the condition of the collector rings and brushes is important during inspection, especially if there are signs of unstable heating, poor continuity, brush wear, or local overheating.

8AT-7420 in the tail rotor anti-icing system

The main aircraft system associated with the 8AT-7420 is the tail rotor blade anti-icing system. The current collector supplies electrical power to heating elements installed on the rotating tail rotor blades. These heaters prevent ice build-up on the blade surfaces during flight in icing conditions. The tail rotor is highly sensitive to imbalance and aerodynamic disturbance, so reliable anti-icing power supply is not just a comfort feature. It is part of the helicopter’s protection system, helping preserve controllability and stable tail rotor operation in difficult weather.

Installation area of the 8AT-7420 unit

The 8AT-7420 is installed in the tail rotor area, where the stationary electrical wiring must interface with rotating elements. The assembly works in a mechanically demanding zone: vibration, centrifugal effects, temperature changes, moisture, and contamination can all affect its service condition. The unit must be installed and inspected according to the helicopter maintenance documentation. Particular attention is normally given to brush seating, brush holder condition, collector surface condition, fastening security, wire connection points, and the absence of mechanical damage.

Maintenance role of 8AT-7420 brushes

The brush set is one of the most service-sensitive parts of the 8AT-7420. Brushes must maintain reliable contact with the collector rings without excessive wear, sticking, chipping, or overheating. If the brushes are worn or contaminated, the anti-icing circuit may become unstable even when the rest of the wiring is serviceable. During maintenance, technicians usually check brush length, contact quality, spring pressure, collector cleanliness, and signs of arcing. Replacement must be carried out using the specified brush type and size, not by visual similarity alone.

Aircraft compatibility and identification of 8AT-7420

The 8AT-7420 is used on helicopters of the Mi-8 and Mi-17 family, including Mi-171 variants, and is also associated with Mi-24 applications. Before ordering or replacing the unit, the designation should be checked against the parts catalog of the exact helicopter model and the anti-icing system documentation. Similar current collectors may differ in installation details, brush type, electrical rating, or connection arrangement. For supply, the item should be identified by its full designation, required condition, documentation status, and whether brushes or other consumable elements are included.

Product Type: Aircraft slip ring assembly / tail rotor current collector
Designation: 8AT-7420
Function: Electrical power transfer from stationary helicopter wiring to rotating tail rotor consumers
Application / Where Used: Tail rotor anti-icing and electrical power transfer systems
System / Installation Area: Tail rotor assembly; anti-icing power supply circuit
Primary System Function: Power supply to tail rotor blade heating elements
Compatible Aircraft / Equipment: Mi-8, Mi-17, Mi-171, Mi-24 family helicopters depending on configuration
Power Supply Voltage: 208 V ±20.8 V AC
Current Frequency: 400 ±20 Hz
Maximum Current Through One Ring: Up to 24 A
Collector Rotational Speed: 1130 rpm
Brush Type: MGS-7
Brush Size: 6.3 × 16 × 20 mm
Dimensions: 170 × 265 × 301 mm
Weight: Not more than 3.95 kg
Material Content / Precious Metals: Not provided
Material Content / Non-Ferrous Metals: Not provided
Completeness of Supply: Not provided unless specified separately
Technical Documentation: Product passport and aircraft maintenance documentation as applicable

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Warranty
All products are covered by a standard 6-month warranty.
Extended warranty is available upon request and is agreed individually; it may affect the final product price.