NR-3VMA

Fuel metering by the NR-3VMA during engine operation

The NR-3VMA meters fuel through the full operating range of the engine. During start-up, it supplies fuel according to the required schedule so that ignition and acceleration develop normally. When the pilot changes engine power, the pump-regulator changes fuel delivery without allowing excessive temperature rise, compressor instability or loss of power response. On steady modes, it keeps fuel flow matched to the required engine condition. A worn or incorrectly adjusted unit can cause difficult start, slow acceleration, unstable power, incorrect limitation or uneven engine behavior during transition between modes.

NR-3VMA in the TV3-117VMA automatic control system

The NR-3VMA is part of the automatic control system of the TV3-117VMA engine. It works with mechanical input from the engine control lever, hydraulic fuel pressure, and electrical correction signals from related control units. The pump-regulator participates in limiting turbocompressor speed, controlling free turbine speed and protecting the engine from exceeding permitted operating parameters. On twin-engine helicopters, the system also supports power matching between the left and right engines, which is important because both engines work through a common transmission and rotor system.

Interaction of NR-3VMA with ERD-3VMA and sensors

In the engine control architecture, the NR-3VMA works together with the ERD-3VMA electronic engine regulator and related sensors. The electronic regulator receives engine parameter signals and sends correction commands to the actuator elements of the pump-regulator. Speed sensors, temperature limiting devices and fuel pressure elements can also be involved in the control logic. Because of this, an engine control problem should not be diagnosed by the pump alone. The final cause may be in the fuel control pump, ERD unit, actuator, wiring, sensor feedback, fuel filtration or adjustment after overhaul.

Fuel path and engine components connected to NR-3VMA

Fuel is supplied to the inlet of the NR-3VMA by the booster side of the helicopter fuel system, normally through a centrifugal booster pump and fine fuel filtration. After metering, the fuel goes to the engine fuel manifold and working nozzles. The unit is also connected with the stop circuit through solenoid valves and drainage elements. After engine shutdown, residual fuel may be removed from certain lines through the drainage system. Since the NR-3VMA contains precision hydraulic and metering sections, fuel cleanliness and correct preservation are critical for reliable operation.

NR-3VMA control of compressor guide vanes

The NR-3VMA also uses fuel pressure as a hydraulic control medium for engine mechanization. Through related actuators, it participates in control of the inlet guide vanes and compressor guide vanes. This is needed to keep the compressor stable during start-up, acceleration, deceleration and changes in engine load. The pump-regulator therefore belongs to both the fuel system and the engine control system. Its work affects not only the amount of fuel entering the combustion chamber, but also the position of engine control mechanisms that shape airflow through the compressor.

Helicopter application of the NR-3VMA unit

The NR-3VMA and NR-3VMA-T are used with TV3-117VMA engines installed on Mi and Ka helicopter platforms. Typical applications include Mi-8, Mi-17, Mi-24 and related versions, as well as Ka-27, Ka-32 and Ka-50 family installations depending on engine version and aircraft configuration. The exact applicability must be checked by the engine logbook, aircraft parts catalog and maintenance documentation. Similar NR-series pump-regulators can differ by execution, adjustment settings, associated electronic regulator and installation details, so designation matching is not enough on its own.

Supply, inspection and documentation of NR-3VMA

For procurement or replacement, the full designation NR-3VMA or NR-3VMA-T should be specified. The unit may be supplied as new production, from storage, after repair or after overhaul, depending on availability and documentation. Before installation, the drive shaft, mounting flange, control levers, fuel fittings, electrical connectors, sealing plugs, preservation condition and documentation should be checked. For this type of aggregate, a clean exterior is not proof of serviceability. Passport data, overhaul records and bench-test results are especially important, because the unit must meet regulated fuel-flow and adjustment parameters.