Pratt & Whitney PW-4000 series engines (used on the MD-11):

Each engine has a "gear box" which is driven by a shaft splined directly into the N1 shaft. The gear box on EACH engine mechanically drives the following components: 1 fuel pump, 1 generator, 1 oil pump, & 2 hydraulic pumps.

The Pratt & Whitney 4000 series engines used on the MD-11's have an N1 and N2 shaft. The N1 shaft runs the length of the engine. The N1 shaft has the Low Pressure Compressor (LPC) section on the front which is comprised of 5 stages. On the rear end of this shaft is the Low Pressure Turbine (LPT) section which has 4 stages. The N2 shaft fits around the N1 shaft like a sleeve. The N2 shaft is about 2/3 the length of the N1 shaft and is positioned in the middle (front to back) of the N1 shaft. On the front of the N2 is the High Pressure Compressor (HPC) section which has 11 stages. On the rear is the High Pressure Turbine (HPT) section which has 2 stages.

As air passes into the bellmouth inlet of the engine, it goes into the first stage of the LPC (front of N1). About 70% of this air becomes "secondary" (fan) air and is blown around the core of the engine to be mixed with the exhaust at the rear of the engine. The rest (about 30%) becomes "primary" (core) air and is directed into the inside of the engine. After the primary air passes through all 5 stages of the LPC, it goes into the HPC (front of N2). As it exits the HPC it has been compressed to high pressure (which also heats it up) and enters the burner can section called the Diffuser and Combustor (C&D) section. As it exits the C&D, it is at extremely high pressure AND temperature. It then hits the 2 stages of the HPT (rear of N2), and passes through the LPT (rear of N1) before it finally exits the rear of the engine as exhaust (thrust).

The relationships between the sections (LPC, HPC, HPT & LPT) are the key to how the engine sustains power. Basically, at idle, there is basically just enough fuel being burned in the C&D to generate just enough pressure to sustain a flow of air through the engine. As the throttles are increased, more fuel is burned in the C&D section, increasing the pressure (speed) of the air hitting the HPT (rear of N2) and LPT (rear of N1) sections. The increased pressure (speed) of the air out of the C&D section drives the HPT and LPT sections faster, which is translated forward via the N1 and N2 shafts. Since the HPC is on the front of the N2 shaft, and the LPC is on the front of the N1 shaft, as both these shafts go faster, the LPC and HPC suck more air into the engine and compress it more (which also heats it more) before it enters the C&D section.

The FADEC is the brain which controls all fuel flow operation. It monitors all engine performance/status sensors and signals the fuel metering unit on how much fuel to supply to the burner cans to meet the thrust settings of the throttles. As throttles are moved forward from idle, requesting increased thrust, the FADEC instructs the fuel metering unit to increase fuel flow, then monitors engine performance sensors to constantly adjust fuel flow and maintain thrust to match the throttle setting.

Weight:	12,000 lbs.
Inlet diameter:	97 inches
Length:	154 inches
Thrust (per engine):
- Fan:	46,800 lbs (78% of total thrust)
- Primary:	13,200 lbs
- Total:	60,000 lbs
Bypass Ratio:	Fan Airflow/Primary Airflow = 4.85 to 1

Minimum Idle Settings:
Parameter	Setting / Result
N1	24% (of rated max) = 850 rpm
N2	63.5% = 6,300 rpm
EGT	340° Celsius
EPR	1.01
Thrust	1,880 lbs.

Cruise settings @ FL350 & 0.8 Mach:
Parameter	Setting / Result
N1	86% 3.100 rpm
N2	88% 8.700 rpm
EGT	340° Celsius
EPR	1.3
Thrust	9,000 lbs

 

Takeoff settings:
Parameter	Setting / Result
N1	103.3% 3,717 rpm
N2	99.8% 9,889 rpm
EGT	500° Celsius
EPR	1.62
Thrust	60,000 lbs.

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