NR-9V

Fuel metering function of the NR-9V

The NR-9V automatically meters fuel from the start phase to the operating mode of the auxiliary engine. During operation, the unit adjusts fuel flow according to rotor speed and load conditions. This allows the engine to accelerate correctly, reach its working speed range and remain stable during load changes. The pump-regulator also limits fuel supply when required, preventing excessive rotor speed and protecting the engine from overspeed conditions. In practical maintenance, incorrect metering may show as unstable start, poor acceleration, overspeed trips or failure to reach rated speed.

Installation of NR-9V on the AI-9 / AI-9V engine

The NR-9V is installed directly on the accessory gearbox of the AI-9 or AI-9V auxiliary gas turbine engine. The unit is mounted on the gearbox flange and driven through a splined shaft. The drive ratio from the engine rotor to the NR-9V shaft is 1:1. Rotation is counterclockwise when viewed from the drive side. Since the pump-regulator is mechanically driven by the engine, serviceability depends not only on the fuel hydraulic part, but also on the drive interface, mounting flange, shaft condition and sealing at the installation point.

Hydromechanical design of the NR-9V

The NR-9V is a monoblock hydromechanical unit. Its design includes a high-pressure centrifugal fuel pump, a speed governor, a metering element, a shut-off solenoid valve, speed signal devices and fuel filters. The pump section supplies fuel under pressure, while the governor controls metering according to rotor speed. The shut-off solenoid valve quickly cuts fuel supply during shutdown or protection operation. Filters protect precision internal parts from contamination, which is important because even small particles in the fuel can affect regulator accuracy.

Overspeed protection and shut-off function of NR-9V

The NR-9V includes protection logic connected with rotor speed. If the rotor reaches the fuel cut-off setting, the unit stops fuel delivery to prevent engine overspeed. The shut-off valve is electrically controlled and operates from the aircraft DC power system. This function is critical for APU safety, because the AI-9 / AI-9V engine operates at very high rotor speeds. Proper operation of the shut-off valve, speed signal devices and governor setting must be checked during testing or overhaul of the unit.

NR-9V output signals to the automatic control system

The NR-9V can provide electrical signals to the automatic control system of the auxiliary engine. These signals indicate that the engine has reached operating or limiting rotor speed values, depending on the aircraft and APU control logic. The automatic control system uses this information during start, stabilization and shutdown sequences. A fault in the signal section can cause incorrect start logic, false indication or failure of automatic transition between operating phases. For this reason, both hydraulic and electrical functions should be checked before installation.

Fuel used by the NR-9V pump-regulator

The NR-9V operates with aviation kerosene grades T-1, TS-1 and RT. Fuel cleanliness is important for the unit because the internal regulator, filters, metering parts and valve elements operate with small clearances. Contaminated fuel may lead to unstable fuel metering, clogged filters, delayed response of the regulator or wear of precision components. During maintenance, technicians normally check fuel inlet pressure, outlet pressure, fuel flow, filter condition, valve operation and the response of the governor at the specified rotor speed.

Aircraft application and NR-9V modifications

The NR-9V is used with AI-9 and AI-9V auxiliary gas turbine engines installed on Mi-8 / Mi-17 family helicopters, Mi-24, Mi-28, Mi-35, Mi-14, Ka-27, Ka-29, Ka-32, selected Ka-52 configurations and Yak-40 aircraft, depending on engine and aircraft configuration. The NR-9V-1 modification is associated with the AI-9-3B engine used on An-140 aircraft. When ordering, the exact designation must be confirmed, because NR-9V and NR-9V-1 are not simply generic fuel units; they are matched to specific APU versions and aircraft documentation.