GA-8

GA-8 in the aircraft heading system

The GA-8 is an aircraft gyro unit used for determining, averaging and short-term memorizing of aircraft heading. It works as a heading reference sensor within onboard heading systems such as Greben-1 and BSFK-1. The unit is used in navigation complexes of Mi-8 and Mi-24 helicopters, where stable heading data is required for flight instruments, navigation indication and automatic flight control consumers. In the system, GA-8 helps convert unstable instantaneous magnetic heading information into a more usable and stable course reference.

Heading stabilization function of GA-8

During flight, magnetic heading signals can fluctuate because of aircraft maneuvers, vibration, banking, acceleration and magnetic disturbances. The GA-8 smooths and averages these heading indications, reducing unstable movement of the displayed or transmitted course value. This is especially useful for helicopters, where vibration and maneuvering can create less stable magnetic readings. By providing a more consistent heading signal, the unit helps the crew and connected systems maintain better orientation during flight, navigation and route tracking.

GA-8 in gyro-magnetic and gyro-compass modes

The GA-8 can operate in gyro directional mode as a gyro-semi-compass, supporting accurate holding of an orthodromic heading. It can also work with magnetic correction from an induction sensor, depending on the heading system configuration. In this arrangement, the gyro unit provides short-term stability, while magnetic correction prevents long-term drift. This combination allows the system to maintain a practical balance between gyro stability and magnetic reference correction during normal helicopter operation.

GA-8 within the Greben-1 system set

The GA-8 does not normally work as a fully standalone instrument. In a typical Greben-1 heading system, it operates together with the ID-6 induction sensor, KM-2 correction mechanism and PU-38 control panel. The ID-6 measures the Earth’s magnetic field, the KM-2 performs correction and mode-related functions, the PU-38 provides crew control and adjustment, and the GA-8 acts as the central gyroscopic unit. Together, these components form the heading reference chain for cockpit and external consumers.

Output of heading data from GA-8

The GA-8 supplies heading information to external consumers such as navigation indicators, autopilot circuits and other onboard systems that require heading reference. In practical use, the signal may be used for cockpit indication, route navigation, automatic stabilization or related heading-dependent functions. If the GA-8 is not operating correctly, the aircraft may experience unstable heading indication, increased drift, incorrect correction behavior or unreliable data transfer to connected equipment.

Power supply and heating of GA-8

The GA-8 requires connection to both aircraft AC and DC power supplies. The gyro motor operates from a three-phase 36 V, 400 Hz AC network, while 27 V DC is used for auxiliary circuits and built-in heating. The heating circuit may be activated automatically at low ambient temperatures and draws a significantly higher current than normal operation without heating. This makes correct power supply, wiring condition, connector quality and heater operation important for reliable startup and stable gyro performance in cold conditions.

Installation of GA-8 on Mi-8 / Mi-24 helicopters

The GA-8 is typically installed in the helicopter radio compartment on a shock-mounted frame. The unit has a cylindrical metal body mounted inside an external frame with rubber vibration dampers. Such installation helps reduce the effect of vibration on the gyroscopic mechanism and electronic circuits. Before replacement, technicians should check the mounting frame, shock absorbers, connectors, power supply lines and compatibility with the installed Greben-1 or BSFK-1 system configuration.

Supply and documentation for GA-8

For procurement, the full designation GA-8 should be stated together with the required condition, system application and documentation. The unit may be supplied as serviceable, from storage, repaired or in another agreed condition. For aircraft installation, the product passport and system documentation should confirm the designation, acceptance status, configuration, operating limits and compatibility with the target aircraft. Since heading system components work as a set, the GA-8 should be checked against the connected ID-6, KM-2, PU-38 and aircraft wiring.

Product Type: Aircraft gyro heading unit
Designation: GA-8
Alternative Designation: ГА-8
Function: Determination, averaging and short-term memorizing of aircraft heading
Application / Where Used: Aircraft heading and navigation systems
System / Installation Area: Greben-1 heading system; BSFK-1 basic heading formation system
Compatible Aircraft / Equipment: Mi-8, Mi-24 and other aircraft equipped with compatible heading systems
Main Operating Mode: Gyro-semi-compass mode
Correction Mode: Magnetic correction from induction sensor
Associated System Components: ID-6 induction sensor, KM-2 correction mechanism, PU-38 control panel
Output Consumers: Navigation indicators, autopilot circuits and other heading-data consumers
Gyro Motor Kinematic Moment: 4000 gf·cm·s
AC Power Supply: Three-phase 36 V ±10%, 400 Hz
AC Current Consumption: Not more than 0.65 A per phase in steady-state mode
DC Power Supply: 27 V ±10%
DC Current Consumption without Heating: Approximately 1.0 A
Built-In Heating Current: Not more than 5.1–6.0 A, activated at low temperatures
Gyro Drift in Gyro-Semi-Compass Mode: Not more than 1°–2° per 30 minutes, depending on latitude and compensation
Post-Turn Error: Not more than ±0.1° within one minute after turn, descent or climb completion
Automatic Synchronization Rate: 2°–3° per minute in normal mode
Fast Synchronization Rate: Not less than 10° per second
Recovery from Tumble / Forced Caging Time: Not more than 60 seconds
Installation: Shock-mounted frame in helicopter radio compartment
Approximate Dimensions in Frame: 210 × 190 × 190 mm
Housing Type: Cylindrical metal body inside external frame with rubber shock mounts
Weight: Not more than 3.5 kg
Technical Documentation: Product passport / heading system documentation

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