STG-3 s2

STG-3 Series 2 starter-generator for aircraft APU systems

STG-3 Series 2 is an aircraft DC starter-generator used mainly with AI-9 and AI-9V auxiliary power units. These APUs are installed on Mi-8 family helicopters, including Mi-8MT and Mi-17, as well as Mi-24 helicopters. The unit combines two functions in one electromechanical machine: it starts the APU in motor mode and then works as a DC generator after the APU reaches self-sustaining operation.

Starting mode of STG-3 Series 2

During start, STG-3 Series 2 receives power from onboard batteries or an external ground power source. In this mode it works as a DC electric motor and accelerates the APU rotor through the drive. The starting phase is short and uses high current, so the condition of contactors, cables, batteries, ground power connection and start control relays is important. If the APU does not accelerate correctly, the fault is not always inside the starter-generator itself.

Generator operation of STG-3 Series 2

After successful start, the automatic start system removes starter power. The running APU then drives STG-3 Series 2 mechanically, and the unit changes to generator mode. In this mode it supplies 28.5 V DC to the onboard electrical network and can support aircraft systems or charge batteries, depending on the aircraft circuit. Voltage regulation works through external regulator and generator control equipment, so brush condition, commutator surface and field circuit should be checked together.

STG-3 Series 2 installation and maintenance points

STG-3 Series 2 has forced air cooling, with airflow supplied by the onboard system. The brush-commutator assembly is one of the main service points. The unit uses aviation copper-graphite brushes of MGS-7 type. Brush wear, spring pressure, commutator condition and signs of overheating should be checked during maintenance. Series 2 is generally treated as an improved version of the earlier STG-3 series, while remaining interchangeable by mounting points where approved by documentation.

Identification and ordering of STG-3 Series 2

Before ordering STG-3 Series 2, the nameplate, aircraft type, APU type and maintenance documentation should be checked. It is better to confirm whether the request is for a new, overhauled or serviceable unit, and what documents are required with delivery. For correct selection, provide the aircraft type, installed APU, current unit marking and photos of the data plate if available. The product is also known under alternative designations STG-3 Series 2, STG-3 2nd series and СТГ-3 2-й серии.

Product Type: Aircraft DC starter-generator
Function: APU start and DC onboard power generation
Application / Where Used: Auxiliary power unit starting and DC power supply systems
System / Installation Area: APU starting system / DC electrical power generation system
Compatible Aircraft / Equipment: AI-9, AI-9V APUs; Mi-8 family helicopters, Mi-8MT, Mi-17, Mi-24
Operating Voltage: 28.5 V in generator mode; 24 V in starter mode
Rated Output Power: 3.0 kW in generator mode
Rated Load Current: 100 A in generator mode
Rotational Speed Range: 6250–11250 rpm in generator mode
Rotation Direction: Left-hand rotation, viewed from drive side
Cooling: Forced air cooling
Brush Type: MGS-7 aviation copper-graphite brushes
Brush Size: 10 × 16 × 32 mm
Dimensions: Ø159 × 340 mm
Weight: Approx. 16 kg
Interchangeability: Series 2 remains interchangeable by mounting points with earlier STG-3 versions where approved by documentation
Condition: New / Overhauled / Serviceable
Technical Documentation: Test report, product passport, Form 1 or certificate on request

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Returns & Changes (Restocking Fee)
For selected items, a RESTOCKING FEE of 10% may apply in case of return, order cancellation, or changes to the order specifications. This condition applies only to certain products and is confirmed at the order approval stage.

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.