Unit One: Engines

STUDENT GUIDE T-39N/G NATOPS

UNIT ONE: ENGINES

REFERENCE: T-39 NATOPS MANUAL

ENABLING OBJECTIVE:

A.1

Locate and operate T-39N/G aircraft systems, given a mission in a T-39 in accordance with

NATOPS.

ENABLING STEP:

A.1.2 Recall the basic description, related systems, and operating limitations of the JT12A-8A gas

turbine engines in the T-39N/G.

NATOPS ONE: ENGINES

A. Pratt and Whitney JT 12A-8A.

1. A turbo jet engine mixes incoming air with fuel, ignites the mixture and creates thrust.

All incoming air passes through the combustion chambers.

2. Air is compressed by a single rotor, nine-stage, axial-flow compressor that is driven by a

two-stage reaction turbine.

a. The accessories gearbox is powered by the compressor. The gearbox drives the AC

& DC generators, oil pump, fuel control and engine driven fuel pump.

3. The air then passes into a can-annular combustion chamber.

a. The combustion chamber contains 8 burner cans in which the fuel is injected

through a single, dual orifice nozzle mounted at the inlet of each can.

b. Two igniters, one each in the No. 3 and No. 6 cans, ignite the fuel/air mixture.

Initially, this spreads to all burner cans through flame tubes, and is then self-

sustaining.

4. The hot expanding gas drives the two-stage turbine before being exhausted as thrust.

B. Thrust

1. Rated at 3300# takeoff thrust at sea level.

2. Engine Pressure Ratio (EPR) is the primary reference for setting thrust, provided RPM

and EGT are not exceeded.

3. FF, EPR, oil pressure, and fuel quantity gauges need electrical power; RPM and EGT are

self-generating through the accessory gearbox.

ENGINES

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