STG-3

Engine starting through STG-3

In starter mode, STG-3 receives power from the onboard battery system or ground source and turns the engine through the start drive. The high current used during this phase is normal for this type of unit, but the start cycle is limited by time and cooling requirements. After the engine reaches the required speed, the start circuit is disconnected and the starter-generator is no longer driven electrically. In maintenance, the start mode should be checked together with the start contactors, wiring, batteries, ground power connector and automatic start control devices.

STG-3 generator mode and onboard power supply

After start-up, STG-3 operates as a DC generator and supplies the helicopter onboard electrical network. In this mode it provides power for avionics, navigation equipment, lighting, instruments and auxiliary electrical systems. The output is controlled through the aircraft voltage regulation and generator control equipment. A voltage fault is therefore not always caused by the starter-generator itself. The regulator, generator contactor, protection relays, brushes, commutator and wiring should be checked as part of the same circuit.

STG-3 in helicopter electrical systems

The STG-3 starter-generator is used on transport and utility helicopters of Soviet and Russian origin. In typical installations it works with engine starting panels, automatic start relays, voltage regulators such as RN-120U, DC generator control circuits, batteries and ground power equipment. On aircraft with auxiliary power units or separate starting architecture, the exact role of the unit depends on the electrical system layout. Replacement should be confirmed by the aircraft parts catalog and the installed generator version, not only by the general STG-3 name.

Identification and ordering of STG-3

Before ordering STG-3, the nameplate marking, aircraft type, engine configuration and documentation should be checked. Starter-generators may differ by series, overhaul status, approved installation and supplied documents. For correct selection, provide the aircraft type, installed unit marking, required condition and document requirements. Available supply conditions may include new, overhauled or serviceable units, with inspection report, Form 1 or certificate on request. The product is also known under alternative designations STG-3, SGT-3 and СТГ-3.