Drawing: Cobra Drawing: Cobra

Air Inlet

The air inlet section provides a streamlined air passage to the compressor section. It is a single cast construction and consists of an inner and outer housing separated by six hollowed struts. the struts are hollowed to allow for anti-icing. Five of the struts are heated by hot compressed (bleed) air and the sixth - on the bottom - is heated by hot returning lubricating oil. The inner housing contains the n2 turbine rpm reduction gears and the torquemeter assembly. The outer housing supports the n1 and n2 gearboxes. Located between the inner and outer housing, on the exit side, are variable inlet guide vanes.

Drawing: Air Inlet Section

Reduction Gears: The output reduction gears and carrier assembly provide a 3.22 to 1 rpm reduction between the n2 turbine speed and the output shaft speed. The normal operating speed for the output shaft is 6600 rpm. This means the speed of the n2 turbine is approximately 20,000 rpm. The rpm of the output shaft is indicated on the outer scale of the dual tachometer in the cockpit.

Torquemeter Assembly: The torquemeter is a hydromechanical torque measuring device used to measure the torque applied to the power output shaft in oil pressure (PSI) The torquemeter consists of two plates separated by steel balls in conical (inclined) sockets and a spring loaded oil control poppet valve which controls oil pressure in the cavity. The resistance to rotation of the reduction gears due to load on the power shaft causes the moveable plate to rotate slightly. This movement displaces the balls in their sockets which forces the moveable plate aft, opening the poppet valve. High pressure oil from the torquemeter oil pump enters the cylinder cavity which equalizes torque forces and stop the plate from moving. The amount of oil pressure required to stop the plate is directly proportional to the torque on the power shaft and is indicated in psi on the torquemeter gauge in the cockpit.

n1 Accessory Gearbox: The n1 accessory gearbox is mounted to the outer housing of the air inlet section at the six o'clock position. The gearbox is driven by a shaft and gear train from the forward end of the compressor sleeve. The accessories mounted to the gearbox are the engine's main oil pump, fuel control unit, starter generator, and gas producer (n1) tachometer generator. The oil pump is a dual element (pressure and scavenge) rotary type, mounted on the front of the n1 gearbox. It is equipped with a pressure relief valve and thermobulb as well as an oil filter. The fuel control is a hydromechanical unit which is comprised of a regulator assembly that senses n1 speed (RPM) and automatically programs the correct amount of fuel to the combustor, to maintain a correct fuel/air ratio. The starter generator is a dual purpose component. By selection of the starter gen switch it may act as a starter motor or generator. The tachometer generator develops enough electrical power to drive the gas producer (n1) tachometer.

n2 Accessory Gearbox: The n2 accessory drive gearbox is mounted at the 10 o'clock position on the air inlet outer housing and is driven by a shaft from the n2 power output shaft. The gearbox drives the torquemeter oil boost pump, the engine overspeed governor and the n2 tachometer generator. The torquemeter pump is operated by the n2 because n2 operates at a constant rpm, thus a constant oil pressure to the torquemeter system which provides a more accurate indication on the torque indicator. The overspeed governor senses n2 turbine rpm, and if turbine speed changes more than 50 rpm, the governor mechanically reacts on the fuel control so it may deliver more or less fuel to maintain n2 rpm. The tachometer generator develops enough electrical power to drive the engine rpm indicator of the dual tachometer.

Variable Inlet Guide Vanes: The air inlet guide vanes are mounted between the inner and outer housings in the rear of the air inlet section. They function to straighten the air flow and direct it onto the first stage of the compressor rotor at the correct angle. The angle of the incoming air must varied to provide a surge margin in the engine. Therefore the guide vanes have been designed to automatically change their angle to provide this characteristic. They, like the six struts are also hollow so that hot bleed air may flow through them when the engine anti-icing switch is ON.

T-53-L-13 Compressor Diffuser Combustor Exhaust diffuser


Generic information on the air inlet

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Updated: 12 January 2008
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Born on 18 February 1999