NR-3VMA-T

NR-3VMA-T fuel control pump on TV3-117VMA engines

The NR-3VMA-T is an aircraft fuel control pump used on TV3-117VMA turboshaft engines installed on Mi and Ka helicopters. The unit is mounted on the engine accessory gearbox and works as a main hydromechanical element of the engine control system. Its job is not limited to fuel pumping. The NR-3VMA-T meters fuel, follows engine control inputs, receives correction commands from related electronic units and helps keep the engine within safe operating limits. In service, this aggregate is treated as one of the most important units of the TV3-117VMA fuel and automatic control system.

Fuel metering function of the NR-3VMA-T

During start-up, acceleration, steady operation and throttle reduction, the NR-3VMA-T supplies the engine with the required fuel flow. It controls how much fuel reaches the combustion chamber through the fuel manifolds and working nozzles. The fuel schedule must be accurate: too little fuel may cause poor start or loss of acceleration, while excessive fuel can lead to temperature rise, unstable operation or incorrect power limitation. This is why condition, adjustment and bench-test results are especially important for this type of pump-regulator.

NR-3VMA-T in automatic engine regulation

The NR-3VMA-T works as part of the automatic regulation system of the TV3-117VMA engine. It supports regulation of turbocompressor speed and free turbine speed, participates in power synchronization on twin-engine helicopters, and provides fuel-flow limitation when required. In case of failure or absence of normal electronic correction, the hydromechanical part of the unit still provides reserve limiting functions within the design logic of the system. This makes the NR-3VMA-T important both in normal operation and in backup operating modes of the engine control system.

NR-3VMA-T with ERD-3VMA, IM-3A and IM-47

The pump-regulator operates together with electronic and electromechanical control units such as ERD-3VMA, ERD-3VM, IM-3A or IM-47, depending on the engine and aircraft configuration. The electronic regulator calculates correction commands, while the actuator physically changes the position of regulating elements inside the NR-3VMA-T. The RT-12-6 gas temperature regulator may also be involved in limiting fuel delivery when turbine gas temperature approaches the permitted limit. For troubleshooting, these units should be checked as one connected control chain rather than as isolated components.

Fuel system connections of the NR-3VMA-T

Fuel normally reaches the NR-3VMA-T after passing through the helicopter fuel supply system, booster pump and filtration elements. The DTsN-70A centrifugal booster pump supplies fuel to the inlet of the pump-regulator at the required preliminary pressure. After that, the NR-3VMA-T meters and distributes fuel to the first and second fuel circuits and then to the working nozzles. The unit is also connected with stop circuits, drainage elements and fuel return paths depending on the engine layout. Fuel cleanliness is critical because the aggregate contains precision hydraulic and metering components.

Compressor control through the NR-3VMA-T

The NR-3VMA-T also participates in compressor mechanization control. Fuel pressure is used as a hydraulic working medium for actuators that move inlet guide vanes and compressor guide vanes. The pump-regulator also works with compressor bleed valve control, which is needed during start-up and transient modes to prevent compressor instability. Because of this, a malfunction of the NR-3VMA-T can affect not only fuel supply but also acceleration quality, compressor stability, and the way the engine responds to pilot commands.

Installation of the NR-3VMA-T on Mi and Ka helicopters

The NR-3VMA-T is installed on TV3-117VMA engines used on Mi-8MT, Mi-17, Mi-8MTV, Mi-17-1V, Mi-172, Mi-24, Mi-35, Ka-32, Ka-50, Ka-52 and related helicopter types, depending on the engine version and aircraft configuration. The pump itself is located on the engine accessory gearbox in the powerplant compartment. It is mechanically driven from the engine and connected to fuel, hydraulic and electrical control lines. Exact applicability must be confirmed by the engine logbook, parts catalog and aircraft maintenance documentation.

NR-3VMA-T tropical execution and supply notes

The “T” index is generally associated with a tropical execution or a version intended for operation in more demanding climatic conditions, including high humidity and elevated ambient temperatures. For procurement, the designation NR-3VMA-T should be stated fully, because similar NR-3VM / NR-3VMA units may differ by execution, adjustment data, actuator connection or approved engine application. For aircraft use, the unit should be supplied with passport, test, repair or storage documentation. Bench-test confirmation is highly desirable, since external condition alone does not prove that the pump-regulator is correctly adjusted.

Product Type: Aircraft fuel control pump / pump-regulator
Designation: NR-3VMA-T
Base Model: NR-3VMA
Function: Fuel pumping, metering and automatic control in TV3-117VMA engine fuel systems
Application / Where Used: Fuel system and automatic regulation system of TV3-117VMA engines
System / Installation Area: Engine accessory gearbox; fuel control and engine regulation system
Compatible Engines: TV3-117VMA and related modifications
Compatible Aircraft / Equipment: Mi-8MT, Mi-8MTV, Mi-17, Mi-17-1V, Mi-171, Mi-172, Mi-24, Mi-35, Ka-32, Ka-50, Ka-52 depending on installed engine and configuration
Working Medium: Aviation kerosene
Approved Fuel Grades: T-1, TS-1, RT; foreign equivalents and approved fuels such as RT, VT, T5-1 depending on applicable documentation
Nominal Fuel Pressure: 6 MPa / 60 kgf/cm²
Maximum Fuel Flow: Up to 540 kg/h
Fuel Inlet Pressure During Start: 0.4–1.2 kgf/cm²
Fuel Inlet Pressure in Operating Modes: 0.4–2.8 kgf/cm²
Maximum PTK Drive Speed: 4100 rpm
Maximum PST Drive Speed: 4230 rpm
Ambient Temperature Range: −60 to +100 °C
Altitude Capability: Up to 5000 m within −38 to +55 °C operating conditions
Service Life Before First Overhaul: 1500 flight hours or 1500 cycles
Assigned Service Life: 4500 flight hours or 6000 cycles
Main Operating Functions: Fuel metering during start-up, acceleration, steady operation and deceleration
Regulating Functions: Control of turbocompressor speed and free turbine speed
Power Synchronization Function: Synchronization of compressor discharge pressure or engine torque between two engines, depending on system configuration
Compressor Mechanization Function: Control of inlet guide vanes and compressor guide vanes through fuel-hydraulic actuation
Reserve / Limiting Function: Maximum fuel-flow limitation at take-off mode in case of electronic regulator failure
Associated Electronic Regulators: ERD-3VMA / ERD-3VM
Associated Actuators: IM-3A / IM-47 depending on execution
Associated Temperature Regulator: RT-12-6
Associated Booster Pump: DTsN-70A centrifugal booster pump
Associated Starter: SV-78 air starter, depending on engine start system configuration
Associated Fuel System Elements: Fuel manifolds, working fuel nozzles, fine fuel filter, stop solenoid valves, drainage valve block
Pilot Control Interface: Engine control lever and collective-pitch / throttle linkage depending on helicopter configuration
Dry Weight: Approx. 27 kg
Technical Documentation: Product passport, test records, repair / overhaul documents and engine maintenance documentation as applicable

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