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Fuel Control / Nf Governor control Air


Compressor Bleed Air Valve Control Air

Air Transfer Tubes: Transfers air from diffuser scroll to combustion section.


State the main purpose of the compressor bleed air system.

Bleeds air from the 5th stage of the compressor during starting, acceleration, and at low compressor pressure ratio operation to prevent / minimize compressor stalls and surging.

Identify the location of the compressor bleed air system.

Compressor bleed air valve is located at the 5th stage of axial compression approx. 2 ‘o clock.


Trace the path of air flow from the air intake through the engine by identifying the components in the proper sequence with respect to flow.

Ambient air enters the front support and is guided by the vanes to strike the first stage compressor rotor at the proper angle.  The rotor accelerates the air and directs it to the stator which slows the air, increasing static pressure.  The stator then directs the air to the second stage rotor.  This process continues through the six stages of axial compression.  At the 5th stage the compressor bleed air valve bleeds air as necessary to prevent a compressor stall.  After the 6 stages of axial compression, air enters the centrifugal compressor (1 stage).  After the single stage of centrifugal compression air is collected, in the diffuser scroll (6.5 times compression, 500oF) and a portion is bled off (Bleed Air Valve Control Air, Cabin Heating, Anti-Icing, Fuel Control / Nf Governor Control Air).  

The remaining air is directed from the diffuser scroll to the combustion section via the air transfer tubes.  In the combustion section 75% of the air is used for combustion cooling and the remaining 25% is mixed with fuel for combustion.  

The hot expanding gasses from the combustion section move forward to the 4 stage turbine section.  First the gasses reach the 2 stage Gas Producer turbine assembly (Ng).  The gasses are accelerated by the 1st stage nozzle and then directed to the 1st stage turbine wheel which converts heat energy to mechanical energy.  The 2nd stage of the gas producer turbine identical to the 1st (Nozzle followed by the turbine wheel).  The 2 stage Gas Producer turbine assembly extracts 2/3’s of the available energy from the hot expanding gases and drives the compressor on the Ng gear train.  The hot gases exit the Ng turbine and pass over 4 TOT thermocouples which sense the temperature and send an averaged signal to the 28v DC TOT gauge on the instrument panel.  After the 4 TOT Thermocouples the gases continue forward to the 2 stage Free Power Turbine (Nf) which consists of two sets of Nozzle then wheel pairs.  The Nf extracts the remaining 1/3 of energy from the gases to drive the Nf gear train.  

The remaining exhaust gases are collected in the exhaust collector and then out the twin exhaust.


Identify the type of combustor used in the 250C – 20J engine.

Single Can Type


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