SV-78BA

SV-78BA air starter for TV3-117 engines

The SV-78BA is an aircraft air starter used for starting TV3-117 family turboshaft engines. It is installed on the engine accessory gearbox and spins up the compressor rotor during engine start. The starter does not generate air by itself. It uses compressed air supplied from the auxiliary power unit, typically AI-9 or AI-9V on Mi-8 / Mi-17 family helicopters. In the starting system, SV-78BA is the unit that turns air pressure into mechanical rotation for the engine.

Starting sequence with SV-78BA

During engine start, compressed air is directed to the starter through the starting air system. Inside the SV-78BA, the air drives an active turbine, and the rotation is transmitted through a planetary reduction gear to the engine drive. The starter works only for a limited time during start, cold cranking, or false start procedures. After the engine reaches the required stage of acceleration, the starter is disconnected from the process by the control logic of the starting system.

SV-78BA in the Mi-8 / Mi-17 starting system

On Mi-8, Mi-17 and Mi-171 helicopters, the SV-78BA works together with the AI-9 / AI-9V auxiliary power unit, starting air lines, the air valve, ignition system, engine accessory gearbox, and starting automation. The system is normally controlled through the APD-78A starting automation panel. When the start command is given, the automation controls the sequence and supplies power to the starter valve circuits. The starter itself is only one part of that chain, so starting faults should not be linked to it before the air supply, valve operation, control wiring, and automation panel are checked.

Construction and operating role of starter SV-78BA

The SV-78BA assembly includes an active air turbine, planetary reduction gear, air valve, and command unit. This layout allows the starter to use low-pressure compressed air and deliver mechanical torque to the engine during the start cycle. Its operation is short, loaded, and tied to strict timing. Long operation beyond the allowed start cycle can overheat or overload the unit. For maintenance, the usual checks include external condition, air connection, valve operation, freedom of rotation, mounting area, and compatibility with the installed engine and starting system.

Identification and ordering checks for SV-78BA

Before ordering, the marking on the installed starter should be compared with the engine and aircraft documentation. The unit is normally associated with TV3-117 engines used on Mi-8 / Mi-17 / Mi-171 helicopters, but the exact starter configuration should still be checked by the aircraft parts catalog or engine documentation. A request should include the starter designation, helicopter type, engine model, and, if possible, a photo of the data plate. The product is also known under alternative designation СВ-78БА.

Product Type: Aircraft air starter
Function: Spin-up of TV3-117 engine compressor rotor during start
Application / Where Used: Engine starting system
System / Installation Area: TV3-117 engine accessory gearbox / starting air system
Compatible Aircraft / Equipment: Mi-8, Mi-17, Mi-171 helicopters with TV3-117 family engines
Working Medium: Compressed air from AI-9 / AI-9V auxiliary power unit
Main Components: Active air turbine, planetary reduction gear, air valve, command unit
Output Shaft Power: Approx. 30 hp
Air Pressure: 1.8–2 kgf/cm²
Maximum Continuous Operating Time: Not more than 55 s
Operating Temperature Range: −60 to +60 °C
Control: Through starting automation panel, including APD-78A-type systems
Technical Documentation: TV3-117 engine / Mi-8 maintenance documentation

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