JT15D ATA 72

Pratt & Whitney JT15D Series (CAT C)

ATA 72 – ENGINE

of 50 FOR TRAINING PURPOSES ONLY © JT15D - ISSUE 1, 2009


ATA 72 – ENGINE


ATA 72– ENGINE

0 TABLE OF CONTENTS

1 Low pressure compressor 5 1.1 Low pressure compressor (JT15D-1/1A/2B) 5 1.2 Low pressure compressor (JT15D-4/4B/4D) 7 1.3 Low pressure compressor (JT15D-5A) 9 1.4 Low pressure compressor (JT15D-5D) 11 1.5 Low pressure rotor trim balancing 13 2 Intermediate case 15 2.1 Purpose 15 2.2 Construction 15 2.3 Impellor inlet stator (JT15D-4 series only) 16 2.4 Maintenance 16 3 N1 and N2 speed sensors 17 3.1 Purpose 17 3.2 Construction 17 3.3 Operation 18 3.4 Maintenance 18 4 Tower shaft 19 4.1 Purpose 19 4.2 Construction 19 4.3 Operation 20 4.4 Maintenance 20 5 Accessory gearbox 21 5.1 Purpose 21 5.2 Construction 21 5.3 Breather impellor 22 5.4 Maintenance 22 6 High pressure compressor 23 6.1 High pressure compressor (JT15D-1 and 4 series) 23 6.2 High pressure compressor (JT15D-5 series) 25 6.3 Bleed valve (JT15D-5 series) 27 6.4 Bleed valve operation (JT15D-5 series) 28 6.5 Bleed valve logic (JT15D-5 series) 30 7 Gas generator case 31 7.1 Purpose 31 7.2 Construction 31 7.3 Maintenance 32


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8 Combustion chamber liner 33 8.1 Purpose 33 8.2 Construction 33 8.3 Maintenance 34 9 Small and large exit ducts 35 9.1 Purpose 35 9.2 Construction 35 9.3 Operation 35 9.4 Maintenance 36 10 High pressure turbine (and associated parts) 37 10.1 High turbine stator 37 10.2 Small exit duct 37 10.3 Shroud segments 37 10.4 High turbine air seal 38 10.5 High turbine baffle 38 10.6 Sealing rings (2) 38 10.7 Operation 38 10.8 Maintenance 39 11 High pressure turbine 40 11.1 Purpose 40 11.2 Construction 40 11.3 Operation 41 11.4 Reference 41 11.5 Maintenance 41 11.6 Tip clearance effect on engine parameters 42 12 High pressure rotor trim balancing 43 12.1 Purpose 43 12.2 Construction 43 12.3 Operation 45 13 Low pressure turbines and stators (and associated parts) 46 13.1 Low pressure turbine stators 46 13.2 Low pressure turbines 46 13.3 Inter-shaft transfer tube 47 13.4 Low pressure turbine stator support 47 13.5 Effect of 2

nd stage vane on T4 and N2 at a constant power 47

13.6 Maintenance 47


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14 Exhaust duct and No.4 bearing housing 48 14.1 Exhaust duct 48 14.2 No.4 bearing housing 48 14.3 No.4 bearing cover 48 14.4 No.4 bearing housing retention 48 14.5 No.4 bearing heat shield (all except post SB 7134) 49 14.6 Maintenance 49


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1 LOW PRESSURE COMPRESSOR

1.1 Low Pressure Compressor (JT15D-1/1A/1B)

1.1.1 Purpose

Provide the airflow to the core and bypass sections of the engine.

1.1.2 Inlet Cone

Double wall, continuously anti-iced with P3 air

Made of steel

Airflow to the inlet cone also supplies pressure to no. 1 bearing labyrinth seal

1.1.3 Low pressure compressor (fan)

19 titanium blades, titanium hub, dovetail retention

1.1.4 Inlet case

Stainless steel

Incorporate bypass stator, two staggered row of 66 vanes

Core stators single row, 33 vanes


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1.1.5 References

Rotation: clockwise Max speed (JT15D-1): 15540 rpm or 99% N1 Max speed (JT15D-1A/1B): 16540 rpm or 103.3% N1 Bypass ratio: 3.3:1 Maximum airflow: 73.6 Ibs/sec Bypass flow: 56.6 Ibs/sec Core flow: 17.0 Ibs/sec Fan blades tip clearances: 0.035 to 0.055 inches

1.1.6 Maintenance

Visually inspect fan blades for FOD

If FOD is within Fly back limits, engine can be operated for 10 hours before fan replacement

Visually inspect stator vanes for FOD

Inspect inlet case for rub

If fan tip clearance needs adjustment, use class shims (3 different classes) to obtain proper clearance.

Reducing shims thickness by ± 0.005 inches increases the tip clearance by 0.001 inches.

Maximum shims thickness must not exceed 0.080 inches


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1.2 Low Pressure Compressor (JT15D-4/4B/4D)

1.2.1 Purpose


1.2.2 Inlet cone

Double wall, continuously anti-iced with P3 air

Made of steel




1.2.4 Inlet case

Stainless steel

Incorporate bypass stator, two staggered row of 66 vanes


1.2.5 Booster Stage


Increase the core inlet pressure

Rear stage stator behind booster, 37 vanes


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1.2.6 References

Rotation: clockwise Max speed (JT15D-4/4D): 16540 rpm or 104% N1 Max speed (JT15D-4B): 16860 rpm or 106% N1 Bypass ratio: 2.08:1 Maximum airflow: 77.8 Ibs/sec Bypass flow: 56.6 Ibs/sec Core flow: 21.2 Ibs/sec Fan blades tip clearances: 0.035 to 0.055

1.2.7 Maintenance

Visually inspect and blend repair fan blades for FOD


Visually inspect booster blades for FOD

Inspect inlet case for fan rub

Inspect and blend repair stator vanes for FOD

If fan tip clearance needs adjustment, grind fan positioning spacer to obtain proper clearance.

Reducing the spacer thickness by 0.005 inches decreases the tip clearance by 0.001 inches.

Grind the inlet cone positioning spacer to the same


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1.3 Low Pressure Compressor (JT15D-5A)

1.3.1 Purpose


1.3.2 Inlet Cone

Double wall, continuously anti-iced with impeller back face air pressure

Made of steel


1.3.3 Low pressure compressor (Fan)


1.3.4 Inlet case

Stainless steel

Incorporate bypass stator, single row of 60 vanes


1.3.5 Booster Stage





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1.3.6 References

Rotation: clockwise Max speed: 16540 rpm or 104% N1 Bypass ratio: 2.08:1 Maximum airflow: 80.1 Ibs/sec Bypass flow: 54.1 Ibs/sec Core flow: 26.0 Ibs/sec Fan blades tip clearances: 0.050 to 0.060 inches (if pre SB 7368) Fan blades tip clearances; 0.060 to 0.070 inches (if post SB 7368)

1.3.7 Maintenance








Grind the inlet cone positioning spacer to the same thickness as the fan positioning spacer.


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1.4 Low Pressure Compressor (JT15D-5D)

1.4.1 Purpose


1.4.2 Inlet cone

Single wall, continuously anti-iced with impeller back face air pressure

Made of aluminium alloy



Integral bladed rotor (IBR), made of titanium, 17 blades incorporated

1.4.4 Inlet case

Aluminium

Kevlar containment on the outside

Honey comb and abradable liner on the inside

Incorporate bypass stator, single row of 60 vanes


1.4.5 Booster Stage

Integral bladed rotor (IBR), made of titanium, 50 blades incorporated




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1.4.6 References:

Rotation: clockwise Max speed: 16860 rpm or 100% N1 Bypass ratio: 2.1:1 Maximum airflow: 82.8 Ibs/sec Bypass flow: 56.8 Ibs/sec Core flow: 27.0 Ibs/sec Fan blades tip clearances: 0.012 to 0.025 inches

1.4.7 Maintenance:








Grind the inlet cone positioning spacer to the same thickness as the fan positioning spacer.


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1.5 Low Pressure Rotor Trim Balancing

1.5.1 Purpose

The purpose of trim balancing is to correct for misalignment of rotor centrelines and to eliminate residual unbalance.

1.5.2 Operation

Prior to the engine assembly, the fan, the booster and the nose cone are individually balanced. Then at engine test, the low pressure rotor residual unbalance is corrected by the addition of trim weights to the front rim of the fan hub. The location of the trim weights is indicated on the engine trim data plate.

Operators may perform low rotor trim balancing as necessary to reduce vibration. This procedure requires the use of a vibration analyser, an optical tachometer, vibration sensor and reflecting tape.


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NOTE: The fan can be replaced without having to

rebalance the entire assembly as long as trim weights identical to those on the defective fan are installed onto the new fan in the positions indicated on the trim data plate. Refer to the engine maintenance manual for complete

procedure.


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2 INTERMEDIATE CASE

2.1 Purpose

Support engine mounts

Main support for engine and AGB

Airflow plenum

Integral oil tank

Support no. 1 and no. 2 bearings

2.2 Construction

Machined magnesium casting

Coated for corrosion protection

Rear cavity forms oil tank, sealed off by oil tank cover

Oil tank filler neck can be installed at 4 or 7 o'clock to suit engine/aircraft installation

Oil pressure and scavenge tubes pass through case to deliver oil to no. 1, 2 and 3 bearings

No. 1 bearing housing supports no. 1 bearing

Rear inner bore supports no. 2 bearing and air seal

Bypass air transfer tube (JT15D-1 series only) vent the cavity form by the oil tank

cover and the gas generator case


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2.3 Impeller inlet stator (JT15D-4 series only)

Direct airflow to impeller

Fit in rear inner section of intermediate case

2.4 Maintenance

Inspect studs and engine mount inserts for damage

Inspect coating condition


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3 N1 AND N2 SPEED SENSORS

3.1 Purpose

Provide N1 and N2 speed signals to the cockpit gauges and to the BVC.

3.2 Construction

N1 Speed sensor

One single coil sensor

Signal goes to the cockpit gauge

Treads are used to set the sensor gap N2 Speed sensors

Two single coil sensors

One sensor for the BVC and the other for the cockpit gauge

Shims are used to set the sensors gap


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3.3 Operation

Induction type speed sensors (pulse pickups) are installed adjacent to a toothed wheel or gear. Frequency output from sensor is proportional to rotational speed of gear.

3.4 Maintenance:

Remove and inspect sensors for evidence of rubbing, replace if rub is evident

Use Tech-Rep test set to measure internal resistance of coils

Adjust probe gap

- N1 = 0.0167" to 0.0194" (JT15D-5A) or 0.0417" to 0.0444" (JT15D-5D)

- N2 = 0.006" to 0.010"


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4 TOWER SHAFT

4.1 Purpose

Link the high pressure rotor to the accessory gearbox. Link the low pressure rotor to the N1 tachometer (JT15D-1 and 4 series).

4.2 Construction

High pressure rotor tower shaft

Steel shaft with two bevel gears

Duplex ball bearings support each bevel gear Low pressure rotor tower shaft (JT15D-1 and 4 series)

Steel shaft with one bevel gear and one gear shaft

Plain bushings support each gear and the shaft


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4.3 Operation

The high pressure rotor tower shaft provides the power to drive all accessories mounted on the accessory gearbox (JT15D all models). The low pressure

rotor tower shaft drive the N1 tachometer located on the top of the intermediate case (JT15D-1 and 4 series).

4.4 Maintenance

Replace rubber lip seal on the low pressure rotor tower shaft (JT15D-1 and 4 series)

None at field level (JT15D-5 series)


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5 ACCESSORY GEARBOX

5.1 Purpose

Provide mounting pads and drive for:

Fuel pump

Starter generator

Oil pumps

Hydraulic pump

N2 tacho generator (JT15D-1 and 4 series)

N2 speed sensors (JT15D-5 series)

5.2 Construction

Magnesium cast housing and rear cover

Coated for corrosion protection

Wet spline drive shafts

Hardened steel gears

Anti-foaming tray at bottom of AGB


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5.3 Breather impeller

Integral part of the starter gear shaft, separates air from oil, expelling oil radially and air overboard through the breather.

5.4 Maintenance

Carbon seal replacement

Rubber lip seals replacement

Oil pump assembly replacement

Studs replacement


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6 HIGH PRESSURE COMPRESSOR

6.1 High pressure compressor (JT15D-1 and 4 series)

6.1.1 Purpose

Provide the engine with the correct pressure and airflow to sustain combustion, cool hot section components and produce thrust.

6.1.2 Construction

Impeller Housing

Impeller shroud housing contains air flow through the impeller

Impeller

Centrifugal compressor made of forged titanium

16 full blades, 16 splitter blades Shafts

Front, high pressure compressor shaft assembled to the front of impeller and supported by no. 2 bearing. Also incorporates inter-shaft carbon seal and bevel gear

Rear, high turbine shaft assembled to the rear of the impeller and supported by no. 3 bearing


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6.1.3 References

JT15D-1/1A/1B

Compression Ratio: 8.0:1 Core flow: 17.0 Ibs/sec Maximum N2: 95% - 31120 RPM JT15D-4/4B/4D

Compression Ratio: 10.2:1 Core flow: 21.2 Ibs/sec Maximum N2 (D-4): 96% - 31450 RPM Maximum N2 (D-4B/4D): 97% - 31800 RPM

6.1.4 Maintenance

Boroscope inspect the high pressure compressor for FOD

Perform compressor desalination washes

NOTE: Perform a boroscope inspection of high pressure compressor

before hot section inspection (HSI).


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6.2 High pressure compressor (JT15D-5 series)

6.2.1 Purpose

Provide the engine with the correct pressure and airflow to sustain combustion and cool hot section.

6.2.2 Construction

Impeller Housing

Impeller shroud housing contains air flow through the impeller

Incorporates bleed valve mechanism Impeller

Centrifugal compressor made of forged titanium

18 full blades, 18 splitter blades Shafts

Front, high pressure compressor shaft assembled to the front of impeller and supported by no. 2 bearing. Also incorporates inter-shaft carbon seal and bevel gear

Rear, high turbine shaft assembled to the rear of the impeller and supported by no. 3 bearing, also support no. 3

1/2 bearing


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6.2.3 References

JT15D-5A

Compression Ratio: 5.3:1 Core flow: 26.0 Ibs/sec Maximum N2: 96% - 31450 RPM JT15D-5D

Compression Ratio: 5.3:1 Core flow: 27.0 Ibs/sec Maximum N2: 97% - 31777 RPM

6.2.4 Maintenance

Boroscope inspect the high pressure compressor for FOD

Perform compressor desalination washes NOTE: Perform a boroscope inspection of high pressure compressor

before hot section inspection (HSI).


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6.3 Bleed Valve (JT15D-5 series)

6.3.1 Purpose

Prevent the booster stage from stalling during adverse operating conditions.

6.3.2 Construction

The system consists of an annular bleed valve, linkages, interconnecting rod, hydraulic actuator and a solenoid valve.

6.3.3 Operation

The forward section of the high pressure compressor impeller housing can be moved axially with the bleed valve linkages. As the impeller housing moves forward, P2.5 air pressure bleeds off and discharges into the bypass airflow via slots in the gas generator case. This air bleed helps to stabilise the airflow through the high pressure compressor therefore preventing the booster stage from stalling.


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6.4 Bleed Valve Operation (JT15D-5 series)

6.4.1 Bleed valve actuator

Consist of a piston, a solenoid valve and a pressure relief valve

Control the bleed valve opening as a function of the BVC command

6.4.2 Operation

The bleed valve actuator uses high pressure fuel to close or to open the bleed valve. With the solenoid valve in a normally closed position, the high pressure fuel flows only to the top portion of the piston. This causes the piston to stay down, therefore keeping the bleed valve in a closed position. A pressure relief valve (400 psid) limits the hydraulic force being applied to the piston by bleeding off excessive fuel pressure into the bypass fuel circuit. (See Fig 72-16a) When commanded by the BVC, the solenoid valve opens, allowing high pressure fuel to flow to both sides of the piston. Due to different working areas, the actuator piston moves up and causes the interconnecting rod and linkages to open the bleed valve.


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6.4.3 Maintenance

Perform rigging on bleed valve linkage as follows: Opened position

Remove bolt from rod end bearing

Push interconnecting rod up

Pull actuator yoke up

Align bolt holes using rod end bearing Closed position

Push actuator yoke down

Pull interconnecting rod

Align bolt holes using adjustment screw, then back off half a turn NOTE: Every time a fuel pump, FCU or bleed valve actuator is removed

or replaced, the bleed valve should be rigged again.


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6.5 Bleed Valve Logic (JT15D-5 series)

6.5.1 Operation

The bleed valve is closed at a pressure altitude less than 25,500 feet. Above this pressure altitude, the bleed valve: Closes when:

N2 speed is higher than 86%

N2 speed is between 76% and 86% and the rate of acceleration or deceleration is less than established limits (schedule "B", slow accel/decel)

Opens when:

N2 is lower than 76%

N2 speed is between 76% and 86% and the rate of acceleration or deceleration is greater than established limits (schedule "A", fast accel/decel)

NOTE: If pressure altitude drops below 25,500 feet and the

bleed is in an open mode, it stays open for 5 more seconds before closing.


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7 GAS GENERATOR CASE

7.1 Purpose

Houses and supports various engine components

The diffuser pipes change the air velocity into static pressure and cause the compressor air to turn 90°

7.2 Construction

Welded assembly of steel alloy machined parts and sheet metal with a corrosion resistant coating

20 diffuser pipes (JT15D-1 and 4 series)

24 welded diffuser pipes (JT15D-5 series)

The case provides: - Support for the impeller housing - Support for the no. 3 bearing - 2 bosses for igniter plugs - 2 bosses for drain valves - 2 bosses for P3 air (airframe bleed) - 2 bosses for P3 air (anti-ice stators, T1

probe and FCU) - Support for the large exit duct and

high pressure stator assembly. - Locate deflector segments, strips and

support ring (JT15D-1 and 4 series)


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7.3 Maintenance

Visually inspect case, diffuser pipes, deflector segments, strips and support ring for wear, cracks and general condition whenever engine disassembly is sufficient to permit inspection.

At hot section inspection, visually inspect case and diffuser pipes for wear and cracks.


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8 COMBUSTION CHAMBER LINER

8.1 Purpose

Provide an area for combustion of the fuel/air mixture.

8.2 Construction

Annular, reverse flow type combustion chamber

Made of nickel alloy sheet metal

12 fuel nozzle adapter bosses

2 spark igniter bosses at 5 and 7 o'clock position

Cooling rings maintain a layer of cooling air to protect the combustion chamber walls from the flame

Liner is supported by 6 support pin through low turbine support case


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8.3 Maintenance

At HSI, visually inspect for evidence of burning, cracking, buckling, etc.

Some damage is acceptable (refer to the maintenance manual)

Re-gap cooling rings if they are distorted


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9 SMALL AND LARGE EXIT DUCTS

9.1 Purpose

Direct the gasses from the combustion chamber to the high turbine stator by changing the direction of airflow 180° (reverse flow).

9.2 Construction

The small and large exit ducts consist of two layers of heat resistant steel in the JT15D-1 and 4 series. The

small and large exit ducts consist of two layers of nickel alloy sheet metal in the JT15D-5 series. P3 air

flows through and cools the two ducts. P3 air flows to the high turbine stator via the small exit duct for internal cooling of each vane.

9.3 Operation

P3 air enters the combustion chamber through holes in the inner and outer liner walls. The shape, size and location of these holes provide the correct fuel/air ratio for all operating conditions. The combustion chamber combined with the large and small exit ducts form an envelope that turns the gas 180° (reverse flow). This configuration permits location of the turbines closer to the compressor and within the combustion chamber area, thus making the engine shorter and lighter. Cooling rings direct P3 air into the combustion chamber, close to the walls, to form a flame barrier.


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9.4 Maintenance

During a Hot Section Inspection, inspect the small and large exit ducts for evidence of burning, cracking or coating loss.


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10 HIGH PRESSURE TURBINE STATOR (AND ASSOCIATED

PARTS)

10.1 High turbine stator

Direct the gases toward the high turbine at optimum angle and speed

Convergent vanes change the static pressure into velocity

Nickel or cobalt alloy casting coated using a diffused aluminide process (JT15D-1 and 4 series)

Nickel alloy casting coated using a diffused aluminide process (JT15D-5 series)

Air cooled core passages allow P3 air to flow through each vane (15 on JT15D-1 series, 14 on JT15D-4 series)

Air cooled vanes (JT15D-5 series)

Locate small exit duct

10.2 Small exit duct

Locate sealing ring

Support shroud segments

Slots in the duct match with corresponding lugs on the high turbine stator to prevent side play

10.3 Shroud segments

15 on JT15D-1 series



Manufactured from nickel alloy steel, provide adequate turbine blade tip clearance and minimise gas leakage

Classed for different high turbine wheel diameters


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10.4 High turbine air seal

Directs airflow over high turbine disk for cooling and to no. 3 bearing labyrinth seal

Locates and supports high turbine stator

10.5 High turbine baffle

Control cooling of high turbine disk

JT15D-1 and 4 series; two configuration, pre

SB7399 (sheet metal type) or post SB7399 (machined)

JT15D-5 series; two configuration (D-5A only),

pre SB7399 (sheet metal type) or post SB7399 (machined)

10.6 Sealing rings (2)

One prevents P3 air leakage between high turbine stator and the small exit duct. The second one prevents P3 air leakage between small exit duct and the low turbine support case

10.7 Operation

The high turbine stator receives hot gases from the combustion chamber. The stator directs the gases at optimum angle to drive the turbine while the convergent shape of the vane airfoils changes the gas pressure into velocity. The high turbine stator is subject to the highest temperatures within the engine and cooling of the stator determines its life expectancy. P3 air flows inside each vane airfoils to keep them at a temperature lower than the gases flowing on the outside. After cooling, air is ejected in the gas path (JT15D-1 and 4 series). After cooling, air is ejected from each vane trailing edge into the gas path (JT15D-5 series).

Segments come in different classes to fit different high turbine diameters and maintain the necessary clearance between the high turbine blades and the segments.


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10.8 Maintenance

During a Hot Section Inspection, inspect components for evidence of burning, cracking and coating loss

Insure proper sliding fit (lugs to slots) with mating parts

Check small exit duct sealing face

Check sealing ring diameter in small exit duct


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11 HIGH PRESSURE TURBINE

11.1 Purpose

Extract energy from the hot gases to drive the high pressure compressor.

11.2 Construction

The high turbine is a two-plane balanced disk assembly, the disk is made of nickel alloy steel with fir tree serrations that provide a firm attachment as well as allowing for thermal expansion between the blades and the disk. Rivets are used to axially retain the 71 blades on the disk. A master spline ensures reinstallation of the high turbine in its initial position on the high turbine shaft during maintenance. High turbine blades PRE SB7293 are made from a nickel based alloy. Features include triple taper design, fir tree retention, growth check pad and diffused corrosion resistant protective coating. (JT15D-1 and 4 series).

High turbine blades POST SB7293 are made from a nickel based alloy using a directionally solidified casting process known as "D.S. blades". Features include triple taper design, fir tree retention, growth check pad and a diffused corrosion resistant protective coating. (JT15D-1 and 4 series).

High turbine blades are made from a nickel based alloy using a directionally solidified casting process known as "D.S. blades". Features include triple taper design, fir tree retention, growth check pad and a diffused corrosion resistant protective coating. (JT15D-5 series).


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11.3 Operation

Expanding gases accelerate through the stator and hit the turbine blades. The energy available in the gases converts into rotational movement to drive the high pressure compressor and the engine accessories. Two thirds of the energy available is used to drive the high pressure compressor and the remaining energy drives the low turbines and generates thrust.

11.4 Reference N2 at 95% 31,129 RPM (JT15D-1 series) N2 at 96% 31,450 RPM (JT15D-4) N2 at 97% 31,800 RPM (JT15D-4B/4D) N2 at 96% 31,450 RPM (JT15D-5A) N2 at 97% 31,777 RPM (JT15D-5D)

The turbine is individually balanced on two planes with detail weights. This feature allows for turbine replacement in the field.

11.5 Maintenance

During a Hot Section Inspection, inspect turbine blades for: tip rub, cracks, sulphidation, erosion, burning and coating loss

Tip clearance (JT15D-1 and 4 series):

- new segment 0.023" - 0.029" - old segment 0.015" - 0.029"

Tip clearance (JT15D-5 series):

- new segment 0.028" - 0.033" - old segment 0.020" - 0.033"


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11.6 Tip clearance effect on engine parameters

When the turbine tip clearance is too large, more gases leak at the tip of the blades, preventing the turbine from extracting all the power it takes to drive the compressor. However to maintain a constant power, fuel flow and T5 must increase, but N2 remains below normal because of the inefficient turbine. NOTE: High turbine blades POST SB7293 are no longer time limited.

(JT15D-1 and 4 series)


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12 HIGH PRESSURE ROTOR TRIM BALANCING

12.1 Purpose

The purpose of trim balancing is to correct for misalignment of rotors centrelines and to eliminate residual unbalance.

12.2 Construction

The high pressure rotor consists of the high pressure compressor, the high pressure compressor shaft, the high turbine, the high turbine shaft, the no. 2, 3 and 3

1/2 bearings

and their associated air seals.


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12.3 Operation

The high pressure compressor and high turbine are individually balanced. The high pressure rotor is then assembled and balanced again (trim balance). Trim weights are added to the front and rear faces of the high turbine and to the high pressure compressor rear face. To make the turbine field replaceable without having to rebalance the whole rotor, turbine trim weights (sizes and positions) are indicated on the data plate. Whenever a new high turbine is installed, trim weights must be added to the front and rear faces of the high turbine according to the data plate.


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13 LOW PRESSURE TURBINES AND STATORS (AND

ASSOCIATED PARTS)

13.1 Low turbine stators

Direct the gases toward the low turbine at optimum angle and speed to drive the low turbine

Convergent vanes change the static pressure into velocity

Cobalt alloy casting (2nd stage) and nickel alloy casting (3rd stage)

Baffle with air seal to control cooling

Only 2nd stage stator exit area is classed

13.2 Low turbines

Extract energy from the gases to drive the fan and booster

The low turbines are a two-plane balanced disks assembly

The disks are made of nickel alloy steel

Fir tree serrations provide a firm attachment and allow for thermal expansion between the blades and the disks

Rivets axially retain the 61 blades (2nd stage) and 55 blades (3rd stage)

The blades are shrouded at the tip to prevent hot gases leakage

Both turbines are mounted on the low turbine shaft which is supported by no. 4 bearing


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13.3 Inter-shaft transfer tube

Supply oil to the No. 31/2 bearing

Hollow tube made of steel

Carbon seal at rear end minimizes leakage

One support diameter prevent tube deflection at operating speed (JT15D-1 and 4 series)

Two support diameters prevent tube deflection at operating speed (JT15D-5 series)

13.4 Low pressure turbine stator support

Locate and support the 2nd and 3rd stage stators, fuel nozzles, fuel shut-off valve and combustion chamber liner

Annular construction made of nickel alloy steel

6 pins support the combustion liner

Slots in case match with corresponding lugs on 2nd and 3rd stage stators

Sealing ring diameter for the interstage sealing ring

13.5 Effect of 2nd stage vane area on T5 and N2 at a constant power

Increase area N2 up T5 down Decrease area N2 down T5 up

13.6 Maintenance

During a Hot Section Inspection, inspect the low turbines for: cracks, burning, coating loss, corrosion, impact damage and blade shift

Return the low turbines assembly with the inter-shaft transfer tube to an authorized overhaul facility if the low turbine assembly needs to be repaired.


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14 EXHAUST DUCT AND NO. 4 BEARING

HOUSING

14.1 Exhaust duct

Direct exhaust gases to the atmosphere

Made of nickel alloy steel

Support the no. 4 bearing housing, automatic fuel shut-off mechanism, T6 probes, oil supply and scavenge transfer tube

A boroscope inspection port is located in the tail cone

14.2 No. 4 bearing housing


Provide support to no. 4 bearing

The no. 4 bearing labyrinth seal stator is part of the housing

14.3 No. 4 bearing cover


Support the inter-shaft transfer tube carbon seal, actuator rod, and emergency shut-off mechanism

Provide oil supply for the no. 31/2 and 4

bearings

14.4 No. 4 bearing housing retention

Studs and slab nuts or t-head bolts and spacer sleeves (post SB7193) retain the no. 4 bearing housing in position in the exhaust duct (JT15D-1 and 4 series)

T-head bolts and spacer sleeves retain the No. 4 bearing housing in position in the exhaust duct (JT15D-5 series)


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14.5 No. 4 bearing heat shield (all except post SB7134)

Sheet metal construction, bolted over the no. 4 bearing housing to protect it from the hot gases

14.6 Maintenance

At hot section inspection inspect:

Exhaust duct for cracks

No. 4 bearing housing for security of shut off mechanism

Oil leaks and rub mark on labyrinth seal runner

Carbon seal condition


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JT15D ATA 72

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