KM-8

Course correction through the KM-8 mechanism

The KM-8 corrects heading information before it reaches the gyro unit and cockpit indicators. It is used to compensate quarter deviation and other system errors that appear in magnetic heading channels. The correction is made through a built-in cam mechanism, adjusted during deviation compensation on the aircraft. After adjustment, the mechanism introduces a small mechanical correction angle into the signal path. In normal operation this helps the heading system provide a more accurate course value than the raw signal coming from the induction detector alone.

KM-8 cam device and deviation adjustment

One of the most recognizable parts of the KM-8 is its cam correction device. Inside the mechanism, a tracking roller moves along a flexible steel tape. The shape of this tape is adjusted by screws placed around the mechanism at regular angular intervals. During deviation compensation, the tape is set so that the lever system turns the synchro stator by the required correction angle. This is a practical mechanical way of storing the deviation correction curve inside the instrument itself, without relying on a separate electronic memory or external computing unit.

Magnetic variation input on the KM-8

The KM-8 also allows magnetic variation to be introduced into the heading system. This is needed when the crew or maintenance personnel need the system to work with true course rather than only magnetic course, depending on the selected operating mode and aircraft procedure. The variation input is made through the control mechanism on the instrument. In service, this function must be checked carefully, because incorrect variation setting can shift the heading information passed to indicators, autopilot channels or navigation users connected to the GMK-1 system.

KM-8 indication and system control functions

The KM-8 has its own course scale, allowing the current magnetic course to be read directly on the instrument. The scale is useful during setup, inspection and system checks, especially when comparing KM-8 indication with main cockpit indicators such as UGR-4UK. The unit also participates in switching circuits used for checking the heading system. During control tests from the navigator’s panel, the KM-8 must respond to defined test angles. This makes it useful not only as a correction device, but also as a reference point during troubleshooting.

Internal elements of the KM-8 unit

The KM-8 contains two synchro receivers, a small electric drive with a reduction gear and an internal semiconductor amplifier. One synchro receiver works in the tracking channel and aligns its rotor with signals coming from the ID-3 induction detector. The second synchro transfers the corrected magnetic heading signal to the GA-6 gyro unit. Because the instrument combines mechanics, synchro circuits and an electric drive, faults may appear as mechanical sticking, incorrect indication, poor tracking, loss of signal, or mismatch between the KM-8 and the main course indicators.

Aircraft use and replacement of KM-8

The KM-8 is used on aircraft and helicopters fitted with GMK-1 heading systems, including Mi-8 / Mi-171 helicopters and aircraft such as Yak-18T, depending on installed equipment. On some aircraft it is mounted on the instrument panel; on Mi-8-type helicopters it may be installed on an equipment rack behind the pilots. Before ordering or replacing the unit, the exact GMK-1 version, connector type, condition, documentation and compatibility with the aircraft wiring should be checked. Similar correction mechanisms should not be treated as interchangeable without confirmation by system documentation.