NK-8

The turbofan engine NK-8 is a twin-shaft turbofan engine with mixing flows of the external and internal circuits and with a reversing device. The compressor is an axial, two-stage, consists of a two-stage fan (low pressure compressor) with two retaining stages and a six-stage high pressure compressor. The combustion chamber is annular, multi-nozzle. The turbine is an axial, three-stage, jet, includes a single-stage high-pressure turbine and a two-stage low-pressure turbine. Flow mixing chamber - petal type. The reversing device is located after the mixing chamber before the exit section of the jet nozzle. It is made with two oppositely located shutters (dampers), which in the reverse thrust mode overlap the gas path of the engine and direct the gas flow into the deflecting grilles. Serial production: 1964 ÷ 1969 ^[1] [Shoshin_2002 (44)]

On the main jet aircraft Tu-154, Tu-154A, Tu-154B, Tu-154B-1 and Tu-154B-2 engines NK-8-2 and NK-8-2U are installed, on the Il-62 - NK-8- four. The NK-8 turbojet engine is a dual-circuit, twin-shaft, gas turbine engine with a mixture of circuit flows (external and internal). The engine can be installed as a simple jet nozzle, or a reversing device mounted on the extreme engines - No. 1 and No. 3 in the Tu-154, No. 1 and No. 4 in the IL-62. The reverse allows you to direct the gas stream in the direction of flight, thereby creating a significant braking force. ^[2] Due to the fact that the reversed jets are directed at an angle of 45 ° to the longitudinal axis of the aircraft, the reverse thrust force of the engine on the reverse is much less than the direct thrust force in the same mode.

The main difference between the Tu-154A and its predecessor is the replacement of the NK-8-2 engine with take-off thrust of 9,500 kgs with the NK-8-2U engine with a higher take-off thrust. This engine is a modification of the NK-8-2 engine, it has increased thrust, reduced specific fuel consumption and increased reverse thrust. On take-off and cruising modes, the NK-8-2U engine has higher gas-dynamic stability reserves. The NK-8 engine is built on the basis of the NK-6 engine (turbofan engine with afterburner in the external circuit).

The engine consists of:

• - input guide vane (VNA);
• - a four-stage low pressure compressor (LPC) driven by a two-stage low pressure turbine;
• - a six-stage high-pressure compressor (HPC) driven by a single-stage high-pressure turbine;
• - the middle support, transmitting the main load from both shafts to the engine nacelle, as well as serving to take power from the high-pressure rotor to the gearbox of the motor unit;
• - An annular combustion chamber with 139 working nozzles. According to some reports, this camera was copied from the Pratt & Whitney J57 engine , which was installed on a Lockheed U-2 reconnaissance aircraft shot down over Sverdlovsk on May 1, 1960;
• - and other elements.

The first two stages of the low pressure switch operate on both engine circuits (cold external and hot internal), all other compressor stages work on the hot circuit. KVD stages 3 and 3A are actually two separate stages (two rows of blades), but are considered as one stage, therefore the KVD can be called 5-stage, and the entire compressor - 9-stage. Behind the last stage of the compressor, air is drawn to the VNA anti-icing system, coca, air intake, pneumatic drive of the reversing device and to the aircraft compressed air system to start other engines, condition the pressure chamber, operate the aircraft de-icing system and pressurize the tanks.

Compressor anti-surge mechanization - an adjustable guiding apparatus (RNA) between the low pressure switch and the high pressure switch, having two positions (open and starting), switched by the AU-8-4U unit depending on the low pressure switch, and air bypass valves installed in the external circuit for the 7th compressor stage, closed by the unit AUP-8-2 at high revs. With the starting position of the PHA in the cockpit, the yellow placard “PHA is closed” is lit, with the bypass valves open, the yellow placard “Bypass valves” is lit. To protect the turbine from a dangerous temperature increase, the RT-12 electronic temperature controller works with the engine and is connected to the same thermocouples as the temperature gauge.

RT-12 comes into operation by a signal from a pressure switch at altitudes above 5000 m with closed bypass valves, at a dangerous gas temperature it starts to cut off fuel, which is indicated by the burning of a red panel “Dangerous t ° of gases” in the cabin, with a further increase in temperature, it turns off the engine by energizing shutdown electromagnet, while the yellow board “Stop t ° of gases” lights up. The lock is removed by setting the engine stop lever to the “Stop” position. At altitudes below 5000 m, the RT-12 works only for signaling.

The maximum speed at which the limiters are triggered and the fuel supply is cut off: 7230 / 98.5 * for high pressure fuel pump, 5700/101 * for low pressure fuel pump.

Turns of opening / closing of bypass valves: 5500 / 74.5 * KVD, when closing, the temperature of the exhaust gases drops by 10-20 ° С. With pick-up, closing at 80% is allowed, with a reset - opening at 60%.

Turnover adjustment of the PHA: 2425/43 * KND. When tuning to the open position, the rotational speed increases by about 6%, while tuning to the starting position, they fall by at least 6%.

  * - in the numerator, the revolutions are indicated in min –1 , in the denominator - in percent for the device.
 ** - parameters are indicated with closed bypass valves.

1. ↑ "Kharkov Aviation Institute" Yu. S. Shoshin. Main technical data of marching aircraft engines of the USSR, Ukraine, Russia. Tutorial. Kharkiv “KhAI” 2002, p. 44
2. ↑ Design and flight operation of the NK-8-2U engine. Timofeev N.I., M., Mechanical Engineering, 1978, 144 pp.

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