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Aviation Studies Powerplant 2A2J

Hogeschool van Amsterdam - AHT

Preface

This project demanded specific research into powerplant and the re-engining for NATOs AWACS E3Aairplanes. Noise limitations, environmental pollution and fuel prices have played a more important roleduring the years. This causes Airliners to make important and necessary decisions about theirengines.

This project would not have been accomplished without the guidance during this project. Thereforespecial thanks goes out to Rob Scholder for his guidance during this project. The group

hopes all readers of this report enjoy it.

Project group 2A2J,December, 2007

The engine you need in the time you want it

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Hogeschool van Amsterdam - AHT

Index

Introduction ......................................................................................................................................... 1Summary ............................................................................................................................................. 21 Gas Turbine Research ................................................................................................................... 3

1.1 NATO .................................................................................................................................... 31.1.1 Organisation and goal ....................................................................................................... 31.1.2 AWACS ............................................................................................................................. 3

1.2 Thermodynamics ................................................................................................................... 31.2.1 Laws of Thermodynamics ................................................................................................. 41.2.2 Brayton Process ................................................................................................................ 41.2.3 Gas Turbine Efficiency ...................................................................................................... 6

1.3 Theory engines ..................................................................................................................... 61.3.1 Engine components .................................................................................................................. 6

A Compressor .......................................................................................................................... 7B Combustion chamber ............................................................................................................ 9C Turbine .................................................................................................................................. 9D Exhaust ............................................................................................................................... 101.3.2 Types of aircraft gas turbines .......................................................................................... 101.3.3 Subsystems ........................................................................................................................ 121.3.3 Subsystems ..................................................................................................................... 131.3.4 Materials of the Engine ................................................................................................ 141.3.5 Forces on an Engine ....................................................................................................... 151.3.6 Vibrations ........................................................................................................................ 16

1.4 Demands and Regulations .................................................................................................. 181.4.1 Contractor Demands ....................................................................................................... 181.4.2 Regulations ..................................................................................................................... 18

2 Modification Possibilities .............................................................................................................. 212.1 Current Engine .................................................................................................................... 21

2.1.1 Specifications .................................................................................................................. 212.1.2 Points of improvement ..................................................................................................... 22

2.2 Demands new engine ......................................................................................................... 222.2.1 Performance .................................................................................................................... 222.2.2 Thrust Specific Fuel Consumption ................................................................................... 222.2.3 Durability, Emissions and Noise ...................................................................................... 22

2.3

Possible choices ................................................................................................................. 22

2.3.1 Pratt & Whitney 6124 ...................................................................................................... 232.3.2 CFM56-7B24 ................................................................................................................... 242.3.3 International Aero Engines V2528-D5 ............................................................................. 25

2.4 Pros and Cons .................................................................................................................... 272.5 Engine choice...................................................................................................................... 27

3 Modification Aspect .......................................................................................................................... 283.1 Old versus New ............................................................................................................... 283.2 Costs ............................................................................................................................... 283.2.1 Purchase ......................................................................................................................... 283.2.2 Modification......................................................................................................................... 283.2.3 Maintenance ....................................................................................................................... 293.2.4 Fuel ..................................................................................................................................... 293.2.5

Personnel ........................................................................................................................ 29

3.3 Conclusion .......................................................................................................................... 29

List of Literature ............................................................................................................................... 31Appendix list ..................................................................................................................................... 34

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Hogeschool van Amsterdam - AHT 1

Introduction

The project group 2A2J (year 2007-2008), from the engineering department of ALA is assigned by theNorth Atlantic Treaty Organization (NATO) to investigate a successor for the engine of an AWACS E-3A airplane. This report contains the research of and engine construction and its operation. Theproject group will also make a selection of three possible engines. The report itself has to comply withseveral requirements, for example the report must not exceed 40 pages, excluding appendices. Thereport will also be written conform Wenztel (2006).

This report is divided in three chapters in compliance with the general project requirements.

To get a clear view of an engine in general, the main aspects will be investigated and described inchapter one. This investigation contains research considering the types of engines and their operation.Usually an engine also has other functions besides providing propulsion. These subsystems areresearched and described. The general rules an engine and its subsystems must follow are alsohandled (1).

With this knowledge the search for a new engine can begin. Many engines are available on todaysmarket, the project group must choose the most suitable engine. Therefore the project group hasnarrowed the selection of engines to a number of three engines. Then all specifications of all threeengines are researched and compared. The project group can then evaluate the results and chose thebest engine (2).

To find out if the modification to the new engine can be realised, a cost-overview must be made.Furthermore, the project group will have made an own conclusion of their research. This will help theNATO to make the right choice for modification of their airplanes (3).

The most important source for this report is the paper Vliegtuiggasturbines of sir R. Scholder.

To explain all aspects as clear as possible, appendices are used. The list of appendices at page 34also contains several important documents such as the original project assignment, the pyramid modeland planning. The abbreviations used in this report will summarized on page 31.

This report also contains an excel sheet used for calculation of several values in an engine (appendixVII), page 12.

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Summary

The North Atlantic Treaty Organisation (NATO) is considering using the E-3A airplane with AirborneWarning And Control System (AWACS) for another fifteen years. The engines currently mounted onthe E-3A are not efficient and produce relatively much more noise than modern engines and thereforethe NATO wants to replace the old engine (TF-33). In order to be able to choose a suitable engine abetter understanding of gas turbines is needed. To get a better understanding of gas turbines a basicthermodynamic knowledge is needed. Thermodynamics is a part of physics, where heat is convertedin mechanical energy and vice versa. The First Law of Thermodynamics is also known as the law of

conservation of energy. According to this law the sum of all energy changes will always stay equal tozero. the Second Law of Thermodynamics states that mechanical energy can be converted into heat,but not all heat can be converted into mechanical energy. There will always be losses of heat to theenvironmental surroundings, because heat always tries to go from warm area to a cooler area.

An aircraft gas turbine can be divided into four main sections. These parts are from the front of theback of the engine to the compressor, combustion chamber, the turbine and the exhaust. In this axialcompressor the air pressure rises with every step and moves towards the combustor. At the end of thecompressor the air pressure has risen, the temperature is high and the volume is small. This air flowsto the combustors where the fuel is spread under high pressure through a nozzle into the combustionchamber which will be ignited by the igniters. This causes the mixture of air and the combustion gasexpand with high velocity towards the turbines. The turbines deliver power to the compressor and theturbine itself gets powered by the energy from the gas that comes from the combustion chamber. Afterthe turbine the mixture flows out of the exhaust. The exhaust provides a vortex free axial gas stream

and protect the aircraft from hot air.

Most large aircraft use the turbofan engines. The air that is accelerated by a fan is split up; one part isdriven to bypass the core engine, the other part is driven through the core engine. The bypass ratio(BPR) is the ratio between the mass flow rate of air drawn in by the fan but bypassing the engine coreto the mass flow rate passing through the engine core.

During operation an aircraft engine is subject to different forces. The basic forces are gravity,propulsion and aerodynamic forces. Every rotating part in an engine has its own rotating moment. Dueto the rotations, a centrifugal force called Fcentrifugal is created. Vibration will occur in the engine. Themost important vibrations are the high cycle fatigue and low cycle fatigue. High cycle fatigue is avibration caused by blades that are in the hot gas stream.

One of the important design aspects of an engine is the noise. The engines need to comply with the

regulations set by the International Civil Aviation Organisation (ICAO). The noise levels are expressedin Perceived Noise Level (PNL) which is on a logarithmic scale in units Effective Perceived Noise inDecibel (EPNdB). There are also emission regulations which are set up to minimize environmentaldamage (Annex 16 volume II Aircraft Engine Emissions). Before an engine can be certified it must betested on its emission.

To make a modification possible it is necessary to know which engine is used this is the Pratt &Whitney TF-33 which is the military version of the JT3D, used by the civil aviation. The engine has amaximum power at sea level of 21,000 lb and the trust specific fuel consumption (TSFC) at maximumpower is 0.52 lb/lbt/h. With the characteristics of the old engine, a number of new variants can befound that comply with the demanded properties. The Pratt & Whitney 6124 is a turbofan engine whichcan deliver 23,800 pounds of thrust and the TSFC at cruise is 0.0672 Kg/N * h. The second possibleengine is the CFM56-7B24 which can deliver 24,200 pounds of thrust and also has a cruise TSFC of0.0615 Kg/N * h. The third possible engine is the V2528-D5 which can deliver 28,000 pounds of thrust

and the TSFC at cruise is 0.0625 Kg/N * h. The best suitable engine is the CFM56-7B24 cause theTSFC at cruise is lower, which means fewer emissions. Also the engine has a higher range andendurance.

The replacement of the old engine is very expensive. One CFM56-7B24 costs 3.93 million euro so toreplace all the engines and to have some spares a total of 72 engines is needed which will cost 283million euro. With the modification the improvement of the E-3A will be recognizable in a lower fuelconsumption, higher thrust, lower emissions and a lower noise level. As required, the new CFM56-7B24 engines will be able to operate under hot conditions, have a low TSFC, so that the endurancewill meet the demand of 10 hours non-stop flying at a speed of 380 kts. The final decision of thereplacement must be made by the NATO.

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1 Gas Turbine Research

The NATO has a couple of airplanes, provided with TF-33 engines. First, a brief explanation of thisorganisation will be given (1.1). To get a better idea of an engines operation, the theory ofthermodynamics will be explained (1.2). Main parts used to make operation of an engine possible, arediscussed (1.3). Besides the the North Atlantic Treaty Organisation (NATO) demands for the newengine, all engines have to apply to demands and regulations, set up by EASA (1.4).

1.1 NATOTo clarify the intention of re-enginging the E-3A airplane, it is necessary to know what kind oforganisation is assigning this project (1.1.1). The NATO uses airplanes equipped with an AirborneWarning And Control System (AWACS), and is used in several situations (1.1.2).

1.1.1 Organisation and goal

The NATO was founded after World War II. It is an alliance between 26 countries, generally fromEurope and North America. The organisation strives for international freedom. The main goal of theNATO is to support the North Atlantic Treaty, signed in Washington on the 4

thof April 1949. This

means that the organisation plays a fundamental role in providing freedom and security for allmembers of the NATO.

The NATO is a military alliance, supporting all forces on land, sea and in the air. The organisationsupports safety in a political and military way. A part of the fleet uses AWACS. The fleet that uses thissystem is called the NATO Airborne Early Warning and Control Force (NAEWF), owned and operatedby NATO. The NATO AWACS E-3 has seventeen trained crew, all with their own expertise.

1.1.2 AWACS

Currently the NATO uses 17 E-3A airplanes. These E-3A airplanes are the military variant of theBoeing 707-300, combined with the AWACS system. This system observes all movements in thesurrounding area. The system makes it possible to detect other airplanes and can be used as a look-down radar. It also communicates with other airplanes. While airplanes without AWACS have a smallrange of detecting aircraft, the AWACS system supports signals due to its wider range and strongersignal.

The AWACS is a large dome (figure 1.1) with a diameter of 9.1 meter. Its height is 1.8 meter and thelength from the body to the dome is 3.35 meter.

1

Figure 1.1: NATO E-3A

1.2 Thermodynamics

To get a better understanding of gas turbines a basic understanding of the thermodynamics is needed.Thermodynamics is a part of physics, where heat is converted in mechanical energy and vice versa.The thermodynamics consist of two laws, the First Law of Thermodynamics and Second Law ofThermodynamics (1.2.1). There is one process which occurs in every gas turbine, this process iscalled the Joule process or also called Brayton process (1.2.2). With the Brayton process theefficiency of gas turbine can be determined (1.2.3).

1. AWACS radar dome

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1.2.1 Laws of Thermodynamics

There are two thermodynamic laws, the First Law of Thermodynamics (A) and the Second Law ofThermodynamics (B).

A First Law of Thermodynamics

The First Law of Thermodynamics (formula 1) is also known as the law of conservation of energy.According to this law the sum of all energy changes will always stay equal to zero. This law is valid ifthere is an amount of heat, internal energy and outward work. This means that the supply of heat can

increase the internal energy of an object or by letting the object perform an outward work. But the totalamount of energy will always stay the same.

B Second Law of Thermodynamics

The first law of Thermodynamics stated that heat can be converted into mechanical energy and viceversa. But the Second Law of Thermodynamics states that a process will always go in one directionand is irreversible. This means that mechanical energy can be converted into heat, but not all heat canbe converted into mechanical energy. There will always be losses of heat to the environmentalsurroundings, because heat always tries to go from warm area to a cooler area. The nature strives for

disorder. The Second Law of Thermodynamics is also known as the law of entropy. Entropy is ameasure for disorder. In an irreversible process, the entropy will increase.

1.2.2 Brayton Process

The process in a gas turbine is an open cycle and was first used in the hot air engine of Joule. Thisprocess is called the Joule process or the Brayton process (A). This process is theoretically, in realitythe process is a bit different (B).

A Theoretic Brayton Process

An open cycle means that a medium is replaced by a new medium after the cycle. The Braytonprocess can be shown in a pressure-volume (P-V) diagram and a temperature-entropy (T-S) diagram(figure 1.2).

To get a better understanding of the Brayton process, the process is illustrated below in a gas turbine(figure 1.3).

Q = U + WQ = HeatU = Internal EnergyW = Outward work

Q in J (1)U in JW in J

Figure 1.2: P-V diagram and T-S diagram

V

P

S

T 1-2 Inlet2-3 Compression3-4 Combustion4-5 Expansion5-6 Exhaust

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The Brayton process consists of different routes:

Route 1-2 (Inlet)

Route 2-3 (Compression)

Route 3-4 (Combusting)

Route 4-5 (Expansion)

Route 5-6 (Exhaust)

Ad 1 Inlet

The air flow enters the inlet (1), this inlet is divergent. With the law of continuity (formula 2) can beexplained that the pressure and temperature increases. The velocity of the influent air will decrease.This is called the ram recovery effect.

Ad 2 Compressor

After the inlet, the air flow will be compressed (2), which causes the temperature and pressure toincrease. During the compression the velocity of the air will remain constant. Also the volume of thegas will decrease.

Ad 3 Combustion

After the gas is compressed it enters the combustion chamber(3). In the combustion chamber there isconstant burning process. By burning fuel, this is the heat which added to the process and is calledQin. Now the temperature, volume and gas velocity will increase. Theoretically the pressure will be

constant, but in reality the pressure will decrease. These are the losses in the combustion chamber.

Ad 4 Expansion

Now the gas will expand (4), which will cause the pressure and temperature to decrease intense. Thevolume of the gas and velocity increases. The energy of the gas will be converted into a mechanicalenergy, which will drive the compressors.

Ad 5 Exhaust

At last the gas will go through the exhaust (5) of the gas turbine, also called propelling nozzle. Thenozzle is convergent, so the pressure and temperature will decrease, and the volume and velocity willincrease. De velocity of the gas reaches its maximum in the nozzle.

* A * V = constant = Density

A = SurfaceV = Volume

kg/m3 (2)A m

2

V m3

1 2 3 4 5

1. Inlet2. Compression3. Combustion4. Expansion5. Exhaust

Figure 1.3: Gas turbine Brayton process

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B Real Brayton Process

As explained before, in reality the Brayton process encounters several losses (figure 1.4).

Figure 1.4: P-V diagram Figure 1.5: T-S diagram

The dotted lines represent the real process (1), and the solid line the theoretic process (2). This isbecause in the combustion the pressure decreases, and this causes losses in the compressor andturbine. The losses in the compressor are a consequence of vortices and friction in different stages ofthe compressor. There will also be losses in the combustion chamber. As a result of the losses, morefuel has to be added to the mixture. This will cause a higher fuel usage. At the same time at the

combustion process a decrease in pressure will occur, this is necessary, because otherwise the gaswill not flow towards the turbine. The loss in pressure is about four percent of the end pressure. Forthe turbine does the same story as the compressor count, in this stage losses also occur whileexpansion of the gas. Expansion vortices and friction causes the gas temperature to increase (figure1.5). This results in the fact that the temperature after the turbine will be higher (1) after isentropicexpansion (2).

1.2.3 Gas Turbine Efficiency

With the thermodynamics it is possible to calculate the efficiency of a gas turbine. Before the efficiencycan be calculated, first some important ratio has to be determined. Temperature ratio over thecompressor is (appendix III, 1). Another important ratio is temperature ratio of the lowest and highesttemperature which occur(2). This is the ratio of the inlet temperature before the turbine, this is calledTurbine Inlet Temperature (TIT), and the temperature before the compressor. Besides temperature

ratio, there is pressure ratio. The pressure ratio is the ratio over the compressor(3).With these ratios it is possible to determine different efficiency; Due to the losses in the compressorthe compressor efficiency (c) is made (4). The compressor efficiency of old gas turbine is about 85%and 87%, but the gas turbine which are used these days have an compressor efficiency of over the90%. The turbine also has a efficiency and is called the turbine efficiency (t). The turbine efficiency isabout 88% and 90% (5). With these two it is possible to determine the thermodynamic efficiency(thermodynamic) (6).

1.3 Theory engines

Before a new gas turbine for the E3-A can be found a thorough component research needs to bemade. The engine components are the compressor, combustion chamber, turbines and the exhaust(1.3.1). There are also three different kind of engines these are the turbojet, turbofan and theturboprop (1.3.2). On an gas turbine there are several subsystems like the thrust reversers and thepneumatic system (1.3.3). For the different engine component there are different materials used thatmust be able to withstand the temperatures and the pressures in the engine (1.3.4). During operationthere are basic forces on the engine like the gravity and propulsion, but there are also centrifugal andpressure differences forces (1.3.5). Vibrations are a bad side-effect which occurs in every engine(1.3.6).

1.3.1 Engine components

An aircraft gas turbine can be divided into four main sections. These parts are from the front of theback of the engine to the compressor, combustion chamber, the turbine and the exhaust. (figure 1.6).The compressor is used to compress the air (A) and the combustion chamber is used to expand the

1

2

1. Real process2. Theoretic process

1

2

1. Real temperature2. Theoretic temperature

S

T

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gas with the use of fuel (B). Turbines are used for powering the compressor(C) and after the turbinesthe air flow goes through the exhaust which increases the velocity of the gas (D).

Figure 1.6: Engine sections

A Compressor

The compressor compresses the air before it sends the air to the combustion chamber. There are twokinds of compressors:

1. Centrifugal compressor2. Axial compressor

Ad 1 Centrifugal compressor

In the centrifugal compressor the air flows parallel to the rotation axel and in radial direction out (figure1.7). The impeller is a disc with blades on top of it (1). This part is powered by the turbine and sucksthe air in. The diffuser(2) and the compressor manifold (3) are non-moving parts.

1

2

3

Figure 1.7: Centrifugal compressor

The air flows in at the front of the impeller and gets pushed up to the diffuser. During this process thevelocity (1) will increase and because of the divergent shape the pressure (2) will also increase (figure1.8).

1

2

Figure 1.8: Pressure and velocity in compressor

1. Impeller2. Diffuser3. Compressor manifold

1. Velocity2. Pressure

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The diffuser is also divergent and consists of vanes. In some engines there are two diffusers aftereach other. One radial (2) and one axial (3) diffuser which moves the air in 90 degrees straight back(figure 1.9). This will cause an extra rise in pressure while the velocity drops to approximately thesame as when it entered the impeller.

1

23

Figure 1.9: Diffuser

Ad 2 Axial compressorIn the axial compressor the air flows parallel to the rotation axel through the rotor (figure 1.10). Thistype of compressor consists of two parts: the rotor(1) and the stator(2).

12

Figure 1.10: Axial compressor

The rotor is a cylinder with a large amount of vanes (appendix IV). Between a line of rotor vanes thereis a line of stator vanes. A line of rotor vanes and a line of stator vanes is called a stage (figure 1.11).

Figure 1.11: Compressor stage

In this axial compressor the air pressure rises with every step and moves towards the combustor. Atthe end of the compressor the air pressure has risen, the temperature is high and the volume is small.This air flows to the combustors.

1. Impeller2. Radial diffuser3. Axial diffuser

1. Rotor vanes2. Stator vanes

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B Combustion chamber

The combustion chamber consists of two cylinder shaped tubes. The flame tube or combustion linerand the air casing (figure 1.12). Twenty-five to thirty percent of the air from the compressor goesstraight into the combustion chamber, while the rest will be added at a later stage. On the left side thecompressed air from the compressor flows into the combustor. The fuel is spread under high pressurethrough the nozzle into the combustion chamber which will be ignited by the igniters. Before the airfrom the compressor enters the combustion chamber, the axial speed must be reduced for an optimalcombustion. This speed should be around sixty meters per second while the velocity of the air from thecompressor is about 100 to 200 meter per second. Therefore, swirl vanes are installed (1). Thesecondary air is added to the combustor through a large amount of dilution holes (2). This makes thetemperature drop to acceptable values for the combustion chamber.

Figure 1.12: Combustion chamber

The mixture of the large amount of air and the combustion gas expands with high velocity towards theturbines.

C Turbine

The turbine delivers power to the compressor and several other engine accessories. The turbine itselfextracts its energy from the gas that is produced in the combustion chamber. Most gas turbines usetwo turbines (figure 1.13) and thus two shafts (N1 and N2) (1 & 2).

12

34

56

Figure 1.13: Turbines

1. Swirl vanes2. Dilution holes

1. N1 shaft2. N2 shaft3. High pressure turbine4. High pressure compressor5. Low pressure turbine6. Low pressure compressor

2

1

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The high pressure turbine (3) powers the high pressure compressor(4) and the low pressure turbine(5) powers the low pressure compressor (6). The hot gas from the combustors will flow through theturbine vanes (figure 1.14). These gas will exert a force on the vanes. In reaction the vanes will exerta force on the shaft which will cause the shaft to turn.

Figure 1.14: Turbine vanes

The remaining energy of the gas will be used for the other steps of the turbine and also for propulsion

of the aircraft.

D Exhaust

The exhaust provides a vortex free axial gas stream and protect the aircraft from hot air. The exhaustalso makes the gas velocity as high as possible. This is done by using a convergent nozzle pipe(figure 1.15). This pipe is directly behind the turbine and is called the exhaust duct. This duct is placedto overcome the ring shaped form of the turbine to the round shape of the nozzle.

Figure 1.15: Nozzle

Because the airflow at the end of the engine has a much higher velocity compared to the gas at theinlet of the engine there is propulsion.

1.3.2 Types of aircraft gas turbines

In aviation, three basic types of gas turbine engines are used as a mean of propulsion on aircraft. Themost basic design is the turbojet (A). The modern, more efficient version, which is used on manytransport category aircraft today, is the turbofan (B). The propeller of the turboprop (C) is driven by agas turbine engine.

1. (Convergent) propelling nozzle

1

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A Turbojet

The turbojet (or straight jet) is the oldest and most simple type of jet engine. The design (figure 1.16)comprises all the basic part described in paragraph 1.3.1, and was the only type of gas turbine used inaviation for a long time. The first jet aircraft flew with turbojets with a single compressor and turbine.

Turbojets proved to be powerful engines, but as gas turbine knowledge improved downsides of theengine were found. The high fuel consumption is the main disadvantage. Namely, the kinetic energythat comes from the fuel energy, varies with vjet

2, while the thrust varies with vjet. Therefore, the fuel

consumption rises drastically when higher thrust is needed. The propulsion efficiency of a turbojet is

therefore relatively low at the speed that is desired for commercial aviation.

Secondly, the turbojets noise level is high compared to other engines. This is caused by the gas thatexits the nozzle at high velocity. The turbojet accelerates a relatively small mass of gas to a highvelocity. This hot gas exits the nozzle and contacts the ambient colder, slower air, which makes theturbojet very noisy.

Figure 1.16: Single-spool axial flow turbojet

Today, turbojets are only used in military aircraft. Their higher operating speeds make the turbojetmore efficient. Also, high fuel consumption and high noise levels are of less importance, as militaryaircraft are not bound to civil regulations. On some military turbofans, an afterburner is installed. Toachieve a great thrust boost, the afterburner can spray fuel directly into the hot exhaust gas. The fuelconsumption drastically increases when the afterburner is used.

B Turbofan

Turbofan jet engines feature the parts of a turbojet engine (figure 1.17), but a low-pressurecompressor and turbine are added respectively in front of the compressor and at the end of theturbine. The low-pressure compressor or fan acts as an extra stage of compression while the low-pressure turbine extracts energy from the exhaust gases. As a result, the pressure after the fan isincreased, and the temperature and pressure of the exhaust gases are lowered.

The air that is accelerated by the fan is split up; one part is driven to bypass the (core) engine, anotherpart is driven through the core engine. The bypass ratio (BPR) is the ratio between the mass flow rateof air drawn in by the fan but bypassing the engine core to the mass flow rate passing through theengine core. Depending on the engine type, the BPR can vary from less than three (low bypass ratio)to more than five (high bypass ratio). The Rolls Royce Company produces high bypass jet engines upto a bypass ratio of 11:1.

Compared to turbojets, turbofans accelerate a large mass of air to a relatively slower speed. Thismeans that, at jet airliner speeds, for the same fuel consumption, the given thrust of a turbofan engineis much greater. The propulsion efficiency is therefore more suitable for commercial jet aircraft.Furthermore, the total velocity of the air exiting the nozzles and bypass duct is lower, which leads to areduction of sound level.

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Figure 1.17: Triple-spool high bypass ratio turbofan

The turbine of a turbofan drives both the low pressure and high pressure compressors. Because oftheir different diameters, the low and high pressure compressors rotate at different speeds. Thus, the

engine requires multiple shafts to propel the compressors. Two shafts are most common, sometimesthree shafts are used.

C Turboprop

On turboprop engines, almost all of the useful power output is used to drive a shaft, which at its turndrives an unducted propeller via a gearbox mechanism. The gearbox is necessary because theefficiency of the propeller tips drops when they approach the speed of sound. The turbine rotates at amuch greater speed. The air that leaves the nozzle after the large turbine only provides a small part ofthe total thrust. The turbine is larger than on the other types of engines.

In the 400-700 km/h domain, the turboprop provides more thrust and is much lighter, when comparedto piston engines. Compared to a turbofan, the turboprop is lighter (because it lacks a nacelle) andrequires less fuel for a given fuel consumption. The thrust that a turboprop produces collapses at

higher speeds however, this prevents their use in high-velocity applications.

1.3.3 Subsystems

Using the right materials are essential to the correct functioning of the engine. There are sereral typesof materials used that are chosen by its needed specifications like withstanding extreme highpressures in the compressor(A) or extreme heat in the combustion chamber(B).Also the turbine hasto be able to withstand extreme heat and pressure (C). The exhaust nozzle has to be able to campwith the heat and speed of the gasses (D).

A Compressor

The materials that are used for the compressor blades has to be a light and very strong metal. One ofthe most used metals in the compressor of most civil aircraft is very strong but light titanium alloys. In

early years the compressor was made out of an alloy of aluminum. The high pressure compressor wasthen made out of a steel alloy.

B Combustion chamber

Because of the high temperature and relative high pressure the combustion chamber is one of themost delicate parts of the whole engine. This will result in the use of very tough materials that will haveto restraint the heat that is produced. This was done by using the best heat resisting materials andlayers of heat resistant coating and cooling of the inner was wall. The metal that is used is a steel alloythat is treated so that it can withstand the enormous heat.

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C Turbine

The turbine in his way will produce the force to drive the sub systems and return the power to thecompressor. The turbine suffers extreme high temperatures and pressures. The material that is usedis therefore a metal that is capable of resisting the heat and pressure. The metal that is used in theturbine is therefore an alloy of titanium.

D Exhaust nozzle

The nozzle is where the thrust is produced, the nozzle must be capable of withstanding the heat of the

gas. Therefore nickel of titanium will have to be used. Also the heat that is produced and partialsabsorbed may not be transferred to the rest of the aircraft structure. This is done by or ventilationaround the heat pipe or by placing several layers of insulating blanket.

1.3.3 Subsystems

There are six subsystems attached to the engine, the system that will drive the hydraulic engines (A).Further on there is a system that will produce the electricity that is needed (B) and the third system isthe pneumatic system (C). The engine needs to be started by a separate engine (D), this is also a sub-system. To keep the engines running a fuel pump is required (E) and for the smooth operation of theengine, pumps that will pump lubrication oil into the engine are also installed (F). When the aircraftafter flight touches down on the runway the engines will reverse their thrust and this is the last sub-system (G).

A Hydraulic System

The hydraulic system is pressurized by a pump that is connected to the gearbox that is linked to theengine shafts. The shaft that is linked to the pump that is pressurizing the system is in the earlyengines directly mounted to the high pressure compressor shaft.

B Electric System

The electric system is powered by a generator. This generator is driven by the high pressure turbineshaft. The Power is produced by linking a generator to the accessory gearbox that is mounted on N2axle. The N2 axle is the shaft that runs from the air turbine to the front of the engine to the Highpressure compressor.

C Pneumatic System

The system is used to cool/heat the cabin and to cool the computers and radar screens that are usedduring flight. The air that is used for the air-conditioning of the cabin is air bled from the compressor.This air is sent to the A/C pack (air conditioning) and due to expanding the temperature drops and theair is pumped into the cabin. An anti ice system is added (hot air system) to provide several parts inthe engine with heating. This heating is necessary to prevent parts from damaging due to coldsituations. Ice can enter the inlet and damage the blades. Anti icing is used on parts sensitive fordamage. For example the nose cone, leading edge of the nose cowl and the front stage of thecompressor stator blades.

D Starting Motor

To start the engine a separate motor is installed. This motor will initiate the turning of the high pressurecompressor. Because of the aerodynamic linkage the low pressure will start turning also. And after the

starting fuel is injected and the engine is at the right RPM the fuel nozzle will automatically start theflow from the main fuel. Then the starting fuel is shut off.

E Fuel Pumps

Main fuel pressure pumps for gas turbine engines generally have one or two gear type, positivedisplacement or high pressure elements. These gears are driven by the N2 shaft earlier explained.Each of these elements discharges fuel through a check valve to a common discharge port. If one ofthese elements fails, the remaining element continues to supply sufficient fuel for engine operation.

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F Lubrication Pumps

Oil pumps for turbine engines are usually of the positive displacement gear type, with a relief valve toprevent excessive pressure.The gear type pump consists of a driving and driven gear. The pump isdriven from the engine accessory section and causes the oil to pass around the outside of the gears inpockets formed by the gear teeth and the pump casing. The pressure developed is proportional toengine rpm up to the point where the pressure relief valve opens and limits the pressure output of thepump.

G Reverse Thrust

The reverse thrust system is not built in the engine but it is systems that will propel the bypass air backout to the front. This will mean that the propulsion that is created backwards is used to slow the aircraftdown when it is landed. The air is pushed back out on an angle of approximately 45 degrees.

1.3.4 Materials of the Engine

Using the right materials are essential to the correct functioning of the engine. There are several typesof materials used that are chosen by its needed specifications like withstanding extreme highpressures in the compressor(A) or extreme heat in the combustion chamber(B). The turbine also hasto be able to withstand extreme heat and pressure (C). The exhaust nozzle has to be able to campwith the heat and speed of the gasses (D).

A Compressor

The materials that are used for the compressor blades have to be made of a light and very strong

metal. One of the most used metals in the compressor of most civil aircraft is very strong but lighttitanium alloys. In early years the compressor was made out of an alloy of aluminum. The highpressure compressor was then made out of a steel alloy.

B Combustion Chamber

Because of the high temperature and relative high pressure the combustion chamber is one of themost delicate parts of the whole engine. This will result in the use of very tough materials that will haveto restraint the heat that is produced. This was done by using the best heat resisting materials andlayers of heat resistant coating and cooling of the inner was wall. The metal that is used is a steel alloythat is treated so that it can withstand the enormous heat.

C Turbine

The turbine in his way will produce the force to drive the sub systems and return the power to thecompressor. The turbine suffers extreme high temperatures and pressures. The material that is usedis therefore a metal that is capable of resisting the heat and pressure. The metal that is used in theturbine is therefore an alloy of nickel.

D Exhaust Nozzle

The nozzle is where the thrust is produced. The nozzle must be capable of withstanding the heat ofthe gas. Therefore nickel of titanium will have to be used. Also the heat that is produced and partialsabsorbed may not be transferred to the rest of the aircraft structure. This is done by or ventilationaround the heat pipe or by placing several layers of insulating blanket.

1.Normal no thrust reverser active

2.Reverse thrust active

Figure 1.18 reverse thrust system.

21

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1.3.5 Forces on an Engine

An airplane engine is subject to different forces. The basic forces are gravity, propulsion andaerodynamic forces (A). When the engine is in use, several parts are rotating. This causes centrifugalforces (B). A direct consequence of the rotating parts is the rigidity that occurs on the engine (C).Inside the engine pressure differences are present. Those differences result in forces working insidethe engine (D).

A Basic Forces

Due to earths gravity, the engine will always be subdue to gravity forces (1, figure 1.18). Gravity orFgravity is calculated with the following formula:

Fgravity = m x g Fgravitymg

= gravity= mass of the engine= gravitational force

Fgravity mg

N (3)kgm/s

The goal of an engine is to accelerate the surrounding air. According to the 3rd

law of Newton, anaction gives an equal opposite reaction. So when the air accelerates in the right direction, an exactforce is created in the opposite direction. This force is called propulsion or Fthrust (2, figure 1.18). Fthrustdepends on the mass and speed of the surrounding air and is calculated as followed:

Fthrust = M x (cJ ci) FthrustmcJci

= propulsion= airflow mass per second= incoming airflow speed= exhaust airflow speed

Fthrust mcJci

N (4)kgm/sm/s

The aerodynamic forces an engine is subject to, is created by the colliding air molecules. This causesa force backwards of the airplane, also called drag (3, figure 1.19).

1. Propulsion2. Gravity

3. Drag

Figure 1.19: Propulsion, gravity and drag on an aircraft engine

B Centrifugal Forces

Every rotating part in an engine has its own rotating moment. Due to the rotations, a centrifugal forcecalled Fcentrifugal is created. To calculate the centrifugal force, the following formula is used:

Fcentrifugal = m x 2 x r Fcentrifugalmr

= centrifugal force= mass= rotation speed= radius

Fcentrifugalmr

N (5)Kgm/sm

The Fcentrifugal depends on the rotation speed of the parts, since the rotation speed is the only variable.Fcentrifugal is a very important force as it can develop tension within the engine.

1

2

3

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C Gyroscopic effect

Rigidity is caused by the non-stop rotation of the earth and engine axes. This has several effects onthe engine. Rigidity occurs when an object has a high rotating speed. The engine will also possesthese gyroscopic characteristics. Rigidity depends on three factors, namely the mass, the rotationspeed and the distance the object is form the centre. The engine will then try to maintain its angularposition according to the earth. For example, while an aircraft is yawing, the engine wants to stay inposition. This causes great forces on the suspension of an engine. The suspension of an engine iscalled a pylon. During rotation, the pylon is heavily stressed due to the gyroscopic effect.

D Pressure Differences

Inside the engine different pressure values are present. Thus, the pressure inside the combustionchamber is higher than the pressure at the fan. These pressures practise great forces on the materialof the engine. This can lead to cracks in the material. Cracks can lead to domestic damage. DomesticObject Damage (DOD) is the damage created by objects like screws and bolts. This damage is theresult of parts of the engine getting loose and damaging the engine.

1.3.6 Vibrations

Vibrations will always occur in an aircraft engine. The vibration on the engine is a disadvantage for theperformance of the engine. There are different causes of vibration (A) that could occur. It is necessaryto measure the vibrations (B) in the engine to know what the situation is.

A Causes of vibration

Many causes for aircraft engine vibrations are known, such as:

1. Torsion vibration2. Offset3. Eccentricity4. Whirl5. Whip6. Resonance7. Aerodynamic forces8. Misalignment9. Rubbing10. Wrong bearings

11. High cycle fatigue

Ad 1 Torsion VibrationVibrations that occur around the rotation centre line. Because of the mass inertia the axis of the gasturbine a rotor wheel can lag behind in relation to the axis of the gas turbine. The forces on the axiscan cause vibration and if the forces are getting too large the axis can break.

Ad 2 OffsetAn unequal partitioning of the mass surrounding the rotation centre line. This is one of the mostimportant causes of vibration but it is easy to solve. Usually offset is caused by manufacturing errors.

Ad 3 EccentricityIf the centre line of the rotating axis does not coincide with the centre line of the rotation. This cancause small vibrations.

Ad 4 WhirlA phenomenon that occurs under influence of lubrication. The bearings are lubricated between theaxis and the balls. When the pressure is not equal on all sides, the axis will change from positioning inthe bearing this causes vibrations. The oil circulates with the axis but if the oil somehow is debilitatedby an obstacle, the axis will slow down, this also causes vibration. The whirl usually occurs by the halfof the rotation frequency at the critical speed. The whirl is also called half frequency whirl. It can bedetected by measuring the displacement of the axis in the bearing.

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Ad 5 WhipIs caused in the same way as the whirl. The only difference is that the whip occurs by two times thecritical speed. At this speed a mechanical resonance can be created. An other phenomenon is the drywhip. This occurs when there is not enough oil in the bearing.

Ad 6 ResonanceDifferent kind of parts that vibrate at the same frequency. If somewhere in the engine a part starts tovibrate with an own frequency and a different part has the same own frequency this part will alsovibrate.

Ad 7 Aerodynamic ForcesForces on the blades of the gas turbine can cause vibrations. The forces on the blades are not harmfulfor the engine. The forces working on the blades can cause resonance and that is harmful for theengine.

Ad 8 MisalignmentIf the two centre line of the axis crosses each other in stead of overflowing each other. The forces thatare working on the axis can be divided in a horizontal and vertical force on the axis. This causes avibration in the axis. A miss alignment can be established by an offset and a combination of missalignment and offset

Ad 9 RubbingWhen the rotor rubs against the casing vibrations will occur. When this happens a lot of noise will begenerated. Rubbing that occurs regularly does not give any seriously problems.

Ad 10 Wrong BearingsWhen the slide or roller bearing is not installed correctly, vibrations can occur because of the forcesworking on the bearings.

Ad 11 High Cycle FatigueBlades that are in the hot gas stream will cause vibrations. Especially the blades that are locked onone side can break. To make sure that the blades will not break, the blades have to be cooled.

B Measurement

To measure the vibration on the engine sensors are needed. There are three different kinds ofvibration sensors:

1. Proximity transducer2. Velocity transducer3. Accelerometer

Ad 1 Proximity TransducerIs a non contact vibration sensor that is at a certain distance of the engine. The most commontransducer is the Eddy current transducer. This transducer exists out of a spool that is provided by afrequency of one megahertz. When the distance changes between the spools it will give a current thatis associated with a kind of vibration. The proximity transducer is usually used for the measurement ofthe distance between the bearings and the axis.

Ad 2 Velocity TransducerIs an electro dynamic transducer and it measures the vibrations. The transducers consist of a spoolthat is positioned in a magnetic field. If the spool gets in motion an electrical current will flow and the

size of the current can be associated with the vibration. The velocity transducer is very suitable formeasuring low frequencies and vibrations of light engine parts.

Ad 3 AccelerometerIt works according the piezo-electric principal. It exists out of two piezo-electrical elements that areconnected with each other. If there is pressure on the piezo a potential difference will occur. Theaccelerometer transforms vibration into a potential difference. The accelerometer is mostly used forhigh frequency vibrations. It is very important that the accelerometer is very good connected to theconcerned part.

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1.4 Demands and Regulations

A new engine design cannot be chosen randomly. The new engine requires several specifications.These demands are set up by the NATO. (1.4.1) However, the aircraft also has to maintain itsairworthiness with the new engines. The airworthiness certificate can be obtained by following therules set up by the European Aviation Safety Agency (EASA) in CS-25. (1.4.2)

1.4.1 Contractor Demands

The goal off this report is to find a new engine for the AWACS E-3, which fulfils the demands of theNATO. The main reason for choosing a new engine is the low effectiveness, due to high fuelconsumption, and the high noise pollution of the current engine (Pratt & Whitney TF-33 (JT3D)).Therefore, the new engine must have low fuel consumption and must be more silent than ispredecessor. As a result of the high effectiveness, the aircraft must be able to maintain a speed of 380kts for 10 hours without refuelling. Further demands are the requirement of an Extended-Range Twin-Engine Operation (ETOPS) and thrust reverse. With the new engine, enough thrust must be providedso the aircraft will be able to depart from every major airport, with a maximum elevation of 6000 ft,under all weather conditions.

1.4.2 Regulations

EASA regulations comprise certification specifications for large aeroplanes (CS-25), certificationspecifications for aircraft jet engines (CS-E 30) (A). Noise (B) and emissions (C) are regulated in

International Civil Aviation Organisation (ICAO) Annex 16.

A Engine Regulations

All engines must have an airworthiness code that is applicable for the engine according to the CS-E30. All other aircraft parts and equipment that are mounted on, or driven by, the engine and notcovered by the engine certificate type must be identified. The engine must have a manual thatcontains instructions for installing and operating the engine. These instructions must include adefinition of the physical and functional points of contact with and equipment of the airplane. Theymust also contain a description of the primary, all alternate modes and any back up systems. Servicinginformation that defines details regarding servicing points, capacity of tanks, reservoirs types of fluidsto be used. The limitations of the engine control system and its points of contact with the aircraftsystems must also be clarified. Engine capacity data, consistent with the acceptance and operatinglimitations, must be provided for the aircraft performance, handling and stressing purposes.

The maximum stresses developed in the engine must not transgress values of the material that isused in the engine. Where new type material is involved, evidence must be available to prove theassumed material characteristic and the effects of any residual stresses. The materials must havesufficient strength to withstand the flight and ground loads for the aircraft as a whole in combinationwith the local loads arising from the operation of the engine. Each engine must be developed andconstructed to function throughout its stated flight envelope and operating range of rotational speedsand power/thrust without inducing stress or vibrations forces to the aircraft structure and engine.

B Noise

The noise an engine produces is one of the main factors for engine manufacturers to base an enginedesign on. The aircraft noise regulations for Europe are set up by the European Aviation Safety

Agency to regulate the amount of noise an aircraft may produce. These regulations are based on

those of the ICAO. If aircraft comply to these regulations the Federal Aviation Organisation (FAA)classify them into four groups (appendix V). These regulations can be found in Annex 16 volume I:Aircraft noise. Before an aircraft is certified the noise levels are measured. These levels are expressedin Perceived Noise Level (PNL) which is on a logarithmic scale in units Effective Perceived Noise inDecibel (EPNdB). The noise levels of each aircraft is measured at three points (table 1).

The lateral full power measurement point is for jet powered aircraft on a line parallel to and450 meters from the runway centre line. This is the point where the noise level is at amaximum at take-off.

The second line is the fly-over measurement point. This is the point on the extended centreline of the runway and at a distance of 6.5 km from the start of roll.

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The third measurement point is the approach point. This measurement point is on the ground,on the extended centre line of the runway, 2 km from the threshold. On level ground thiscorresponds to a position 120 m (394 ft) vertically below the 3 descent path originating from apoint 300 m beyond the threshold.

Measurement point Low MTOW (EPNdB) High MTOW (EPNdB)

Lateral full power 94 (MTOW 35000 kg) 103 (MTOW 400000 kg)Fly-over

Two engines or less

89101 (MTOW 385000 kg)

Three engines 104 (MTOW 385000 kg)Four engines or more

106 (MTOW 385000 kg)Approach 98 (MTOW 35000 kg) 105 (MTOW 280000 kg)Table 1: Maximum noise levels

C Emissions

These regulations are set up to minimize environmental damage (Annex 16 volume II Aircraft EngineEmissions). Before an engine can be certified is must be tested on its emission. There are severalconditions which an engine must comply with.

The following emission shall be controlled for certification of an engine.SmokeGaseous emission

Unburned hydrocarbons (HC)Carbon monoxide (CO)

Oxides of nitrogen (NOx) The smoke emission is measured in terms of smoke number (SN)

The mass (Dp) of the gaseous pollutant HC, CO and NOx emitted during the referenceemissions landing and takeoff (LTO) cycle shall be reported and measured in grams (table 2).

Phase Time in operation mode, minutes

Takeoff 0.7

Climb 2.2

Approach 4.0

Taxi/ ground idle 26.0Table 2: Reference emissions landing and takeoff (LTO) cycle

The engine shall be tested at sufficient power setting to define the gaseous and smokeemission of the engine so that the mass emission rates and Smoke Number corrected to the

reference ambient conditions.

Phase Thrust settings

Takeoff 117 per cent F00

Climb 85 per cent F00Approach 30 per cent F00

Taxi/ground idle 7 per cent F00Table 3: Thrust settings

The Smoke Number at any thrust setting when measured and computed in accordance withthe procedures of Appendix 2 and converted to a characteristic level by the procedures of

Appendix 6 shall not exceed the level determined (formula 6).

The engine shall be representative of the certificated configuration; off-take bleeds andaccessory loads other than those necessary for the engines basic operation shall not besimulated.

Regulatory smoke number= 83,6 (F00)

-0.274

(6)

F00 = Max thrust available for take-off under normaloperation conditions, at ISA sea level static conditions

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Gaseous emission levels when measured and computed in accordance with the procedures ofAppendix 3 and converted to characteristic levels by the procedures of Appendix 6 shall notexceed the regulatory levels determined from the following formulas

Hydrocarbons: Dp/F00= 19.6Carbon monoxide: Dp/F00=118

The following derived information shall be provided for each engine tested for certificationpurposes: emission rate, total gross emission of each gaseous pollutant measured over theLTO cycle, values of Dp/F00 for each pollutant gaseous pollutant and the maximum smokenumber.

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2 Modification Possibilities

To make a modification possible it is necessary to know which engine is used (2.1). From thatperspective, a summary of possible improvement points for the new engine can be made (2.2).Subsequently, new engines that are compliant to these points are found, and examined (2.3). A tableof advantages and disadvantages can be set up, and the engines are compared (2.4). From the table,the best alternative engine is chosen (2.5).

2.1 Current EngineWhen looking for a possible new engine, a comparison has to be made with the currently used engine.To make this comparison possible, research to the specifications of the current engine has to be done(2.1.1). The most important specifications concerning the modification are reviewed. After this,research can be done for improvements of the new engine, which will be brought along the possiblealternatives for the new engine (2.1.2).

2.1.1 Specifications

Following table 4 shows the specifications of the Pratt & Whitney TF-33 engine.

SpecificationsBypass ratio: 1.4:1

Take-off thrust (lb): 21,000Specific fuel consumption at max. power (lb/lbs/h)i: 0.56Fan tip diameter (inch): 54Length, flange to flange (inch): 142Compressor stages: 16Turbine stages: 4Dry weight (lb): 4,790HC emission (g/kN): 0.0CO emission (g/kN): 56.7NOx emission (g/kN): 45.7Smoke number (g/kN): 6.7Table 4: Specifications P&W TF-33

The current engine used by the E3-A airplanes

is the Pratt & Whitney TF-33 (figure 2.1). Thisengine is manufactured by Pratt & Whitney andis the military version of the JT3D, used by thecivil aviation. The TF-33 is the turbofan versionof the J57 turbojet.

The JT3D is an axial-flow turbofan with a 15-stage split compressor. A nickel alloy is used inthe combustion chamber because of its highmelting temperature. The turbine sectionconsists of a four-stage gas turbine. A divergentform is used for the nozzle and consists of anickel and steel alloy. The engine has amaximum power at sea level of 21,000 lb and a compression ratio of 13:1. Its trust specific fuelconsumption (TSFC) at maximum power is 0.52 lb/lbt/h. The estimated service life of this engine is6000 hours. Which means the engine can deliver 6000 hours of operation without any new parts. Intable 5 noise emission during several stages of flight can be seen for the TF-33 engine.

TF-33 Noise emission (EPNdB) Stage

Take-off 1032SL 97.6

Approach 105.3

Table 5: Noise emissions of the TF-33

Figure 2.1: Pratt & Whitneys TF-33

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2.1.2 Points of improvement

The TF-33 has some disadvantages, for example a low by-pass ratio. Due to this low by-pass, ahigher thrust specific fuel consumption is obtained. Consequence of this high TSFC is the relative highfuel consumption, compared to higher by-pass engines. This is logically quite uneconomical. Due tothis high fuel consumption, it will produce a higher emission of gasses. Besides the high TSFC, thisengine is susceptible to high noise production. Its high noise production does not meet the currentFAA noise requirements (year 2000).

2.2 Demands new engineThere are various alternative engines to replace the TF-33 turbofan on the AWACS E-3A. Before themodification plan is worked out, three regular used engines are primarily rated for their performance(2.2.1) and their fuel consumption during operation (2.2.2). They are also rated according to enginesnoise, other emissions and finally for compatibility and durability during use on the AWACS E-3Aairplanes (2.2.3).

2.2.1 Performance

In the domain of engine performance, the primary concern is thrust. The TF-33 engine on a E-3Aprovide a maximum of 21,000 pounds of thrust. The newly chosen engine must have a similar thrust,preferably higher. Engine can be compared by their specific thrusts, which can be calculated bydividing the output thrust by the engine inlet mass flow. This cancels out the various diameters of the

engines.

2.2.2 Thrust Specific Fuel Consumption

An engine uses fuel to produce thrust. The amount of fuel used to generate enough thrust is animportant factor. The fuel efficiency is called Trust Specific Fuel Consumption (TSFC). TSFC is themass of fuel burned by an engine in one hour divided by the thrust that was produced. To calculatethe TSFC of an aircraft, a formula is used (formula 7).

TSFC = f / Fpropulsion TSFCfFpropulsion

= Trust Specific Fuel Consumption= Fuel burned in one hour= Thrust created in one hour

TSFCfFpropulsion

(7)(Kg/N) per hourKgN

The TSFC is used to compare engines with each other. The lower the TSFC the higher the efficiencyis. The TSFC can also be used to figure out how much fuel is required to perform a procedure. Thenew engine must remain a constant speed of 380 kts ( 380 kN) during a time of 10 hours, withoutrefuelling. The Boeing 707 has an capacity of 17,866 litre. The TSFC of the TF-33 is 0.56 lb/lb.h.

2.2.3 Durability, Emissions and Noise

The NATO has several demands for the new engine design. The engine must be suitable for the E3-AAWACS planes. Noise regulations set up by the EASA may not be exceeded. Noise levels higher than101 EPNdB are forbidden. This is an important factor of the engine design. The engine may notexceed the emission levels stated by EASA Annex 16. E3As new engine must not exceed 26 gramsper minute during ground idle and by the approach not more than four grams per minute. The smoke

number and engine rates must be kept in the reference ambient conditions. Durability of the engine isimportant because it can reduce costs compared to the old engines. The engine must be able toperform 22,000 lbs of thrust on MSL at standard day conditions. The endurance of the engine must beat least more than ten hours without refuelling at a speed of 380 knots.

2.3 Possible choices

With the characteristics of the old engine, a number of new variants can be found that comply with thedemanded properties. These three engines will be discussed on their its most important features. Thethree engines are produced by different manufacturers and can be compared to the old engine. Thechosen engines are the PW6124 (2.3.1), the CFM56-7B (2.3.2) and the V2528 (2.3.3).

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2.3.1 Pratt & Whitney 6124

In table 6, specifications of the Pratt & Whitney 6124 can be seen.

SpecificationsBypass ratio: 4.9:1Take-off thrust (lb): 23.800Specific fuel consumption at max. power (lb/lbs/h): 0.37Fan tip diameter (inch): 56.5Length, flange to flange (inch): 108Compressor stages: 4, 6Turbine stages: 1, 3Dry weight (lb): 5,050HC emission (g/kN): 0.0CO emission (g/kN): 56.7NOx emission (g/kN): 45.7Smoke number (g/kN): 6.7Table 6 Specifications P&W 6124

Figure 2.2: PW6124

The Pratt & Whitney 6124 (figure 2.2) is a turbofan engine which can deliver 24,000 pounds of thrust.This is enough for the AWACS E-3A. The engine is relatively new (entered service in 2005) and iscurrently used to power the Airbus 318. The engine uses less parts compared to its counterpartsmaking the maintenance costs lower. The emission of the engine complies with the regulations statedin ICAO Annex 16 (appendix VI.a). The sound emission of the Pratt & Whitney 6124 can be found intable 7.

P&W 6124 Noise emission (EPNdB) Stage

Take-off 79.73Side Line 90.4

Approach 89.7Table 7: Noise emissions of the P&W 6124

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2.3.2 CFM56-7B24

Following table 8 gives an overview of the specifications of CFMs 56-7B24 engine.

SpecificationsBypass ratio: 5.3:1Take-off thrust (lb): 24,200Specific fuel consumption at max. power (lb/lbs/h): 0.37Fan tip diameter (inch): 61.0Length, flange to flange (inch): 98.7Compressor stages: 3, 9Turbine stages: 1, 4Dry weight (lb): 5,216HC emission (g/kN): 6.0CO emission (g/kN): 45.6NOx emission (g/kN): 55.4Smoke number (g/kN): 16.2Table 8: Specifications CFM56-7B24

The CFM56-7B24 (figure 2.3) is a high bypass engine, one of the next engines in the CFM56 series,which is developed by CFM international. This engine is developed to provide engines with higherthrust, improved efficiency and lower maintenance cost than its predecessor CFM56 engines. Theengine has achieved outstanding reliability since its entry, this reliability made the CFM56-7B powered

737 the first aircraft the first to be granted with 180-minute ETOPS approval by the U.S. FederalAviation Administration. ETOPS is the number of minutes flying time from a suitable airport that a twinengine aircraft may operate in the event that one engine becomes inoperative. The approval givesgreat advantage airliners have a greater route-scheduling flexibility. The engine has a fan diameter of61.0 inches and a length of 98.7 inches.

The improvements of the CFM56-7B engines are mainly due to the new 61.0 inch fan, this fan consistof 24 solid titanium wide chord fan blades (figure 2.4, 1). The new core and low pressure turbomachinery, which are designed with the most advanced three-dimensional aerodynamic designmethods makes the engine better than its predecessors. The engine incorporates a three stage

booster(2) and a nine stage axial compressor(3). Furthermore, the engine incorporates a four stagelow pressure turbine (4). The CFM56-7B is equipped with a dual annular combustor which results in asignificant reduce of NOx emission.The CFM engine is also equipped with the new electronic engine control called the Full AuthorityDigital Engine Control (FADEC). This system makes sure that the engines operate at their maximumpotential. A new material is used in the turbine and is called the single-crystal. This material is used inthe high pressure turbine. By using this material, the CFM56-7, compared to its previous engines, hasa lower operation temperature with higher exhaust gas temperature. It also improves the significantfuel with eight percent. Maintenance has improved compared to its predecessors, because theremoval and replacement for line replaceable units (LRU) have been reduced by more than 80percent. Also, the engines can be replaced in a single shift. The emission of the engine complies withthe regulations stated in ICAO Annex 16 (appendix VI.B).

Figure 2.3: CFM56-7B

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The sound emission of the CFM56-7B can be found in table 9.

CFM56-7B Noise emission (EPNdB) Stage


Approach 96.5

Table 9: Noise emissions of the CFM56-7B

2.3.3 International Aero Engines V2528-D5

In table 10, specifications of the International Aero Engines V2528-D5 can be seen.

SpecificationsBypass ratio: 4.66:1Take-off thrust (lb): 28,000Specific fuel consumption at max. power (lb/lbs/h): 0.35Fan tip diameter (inch): 63.5Length, flange to flange (inch): 126Compressor stages: 4, 10Turbine stages: 2, 5Dry weight (lb): 5,720HC emission (g/kN): 0.4CO emission (g/kN): 26.4

NOx emission (g/kN): 62.2Smoke number (g/kN): 11.6Table 10: Specifications International Aero Engines V2528-D5

2

4

1

3

Figure 2.4: CFM56-7B engine

1. Fan blades2. Booster

3. Compressor4. Turbine

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Figure 2.5: V2500 Parts produced per shareholder

International Aero Engines AG is a consortium of four aircraft engine manufacturers, namely Pratt &Whitney, Rolls Royce, Japanese Aero Engines Company Corporation (JAEC) and Germanys MTU

Aero Engines. Each company produces one specific module of the successful V2500 jet enginesseries (figure 2.5), and continuously focuses on refining their specific part of the engine.The International Aero Engines V2500 two-shaft high bypass turbofan series entered service in 1982as an engine specifically developed for the 150-seater aircraft market. Various versions were designedin the 22,000 to 33,000 pound thrust range. International Aero Engines has powered more than 1,300aircraft with the V2500 engines, accumulating more than 40 million flight hours.Currently, different versions of the V2500 engine are in use on the Boeing MD-90 and Airbus A319,

A320 and A321 aircraft. Because the AWACS E-3A is based on a Boeing 707 jetliner, the MD-90engine will be most suitable as a replacement. A derated MD-90 version of the V2500 exists, it isnamed V2528-D5. This engine is compliant with the Federal Aviation Administration (FAA) Stage 4standards and therefore also compliant with the ICAO Chapter 4 minimum requirements for aircraftnoise. The NATO will probably prefer these quiet engines, because of the noise pollution aroundGeilenkirchen Airbase.The V2528-D5 is an advanced, efficient and reliable high bypass turbofan. It comprises, next to thewide chord fan, which is less vulnerable for FOD, four low-pressure compressor stages and ten high-pressure compressor stages manufactured by Rolls Royce. The engine has two-shafts, with a twostage high pressure- and five stage low pressure turbine powering the compressors and fan (figure2.6).

Figure 2.6: V2500 engine overview

The engine operability and maintenance diagnostics are made easier and more efficient with theFADEC. Furthermore, the V2500 series are designed with a balanced emissions approach, which

makes it the engine one of the lowest emission levels in its class (appendix VI.C). The soundemission of the V2500 can be found in table 11.

V2500 Noise emission (EPNdB) Stage


Approach 91.7

Table 11: Noise emissions of the V2500

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2.4 Pros and Cons

To make the right engine choice, several items have to be investigated. Some characteristics play animport role when making an engines decision. Most important demands are: fuel consumption, noiseand emissions produced and at last the compatibility with the E-3A. To get a good overview of thespecific engines the following table (table 12) is set up using the excel sheet (appendix VII).

Pratt & Whitney 6124 CFM56-7B24International AeroEngines V2528-D5

Take Off thrust 23.800 lb 24,200 lb 28,000 lb

TSFC Take Off 0.37 0.37 0.35

TSFC Cruise 0.0672 Kg/N * h 0.0615 Kg/N * h 0.0625 Kg/N * h

Range 5528 NM 5838 NM 5632 NM

Max endurance 14,2 Hours 15,0 Hours 14,5 hours

HC emission 0.0 g/kN 6.0 g/kN 0.4 g/kN

CO emission 56.7 g/kN 45.6 g/kN 26.4 g/kN

NOx emission 45.7 g/kN 55.4 g/kN 62.2 g/kN

Smoke number 6.7 g/kN 16.2 g/KN 11.6 g/kN

Noise Stage 2 Stage 3 Stage 4

Dry weight 5,050 lb 5,216 lb 5,720 lb

Fan Tip Diameter 56.5 inch 61.0 inch 63.5 inchTable 12: Pros and cons summary

The fuel consumption is one of the most important demands on the engine. The aircraft will have to flyat least ten hours without refuelling, to comply with the demands. The engine that is most efficient atcruise level is the CFM56-7B24. Due to the lower emissions the P&W is the most environmentalfriendly, but when the P&W runs at take-off thrust the slightly higher fuel consumption, in comparisonto the IAE engine makes the IAE more economical.The dimensions that are needed to install the engine and complying with the law will mean that certainmodifications will have to be done. These changes will have to be made in order to get the plane safeand running. Due to the slightly lower fuel consumption the range of the CFM is a bit larger. But theemissions made by the CFM is much more that the emissions of the P&W engine. The weight of theengine is also a point of consideration, the P&W weighs almost 200 pounds less than the CFM andthis will make the amount of weight added to the plane less than when the CFM engines are installed.

The weight of the engine will mean that there is less mass and therefore less fuel consumption.

2.5 Engine choice

The engine that will be chosen is the CFM56-7B24. This engine is chosen because of the higherrange and endurance. Also the TSFC at cruise is lower, which means fewer emissions. All the threeengines comply to ICAO chapter three or four (noise regulations) so this is no point to decide on. Alsonamed before, the maintenance will be outsourced and this will have the consequence that no peoplehave to be trained and hired for maintenance. Companies like KLM make use of the CFM-56 engines,and also maintenance is supported by their own personnel. By example, mechanics of their companycan by used for maintaining the E3As new CFM engine. All these things will make the CFM the bestcontestant to replace the current engine.

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3 Modification Aspect

The CFM56-7B24 engines are the best choice for the engine refit of the AWACS E-3A. To make agood decision about the re-engining of the aircraft, the benefits of the new engine compared to the oldone need to be known (3.1). The total costs of this modification are the second big influence on thedecision (3.2). The NATO must make a decision about the modification concerning all the costs andbenefits, using the conclusions found during this project (3.3).

3.1 Old versus New

To see if it is rewarding to buy and install the new engine, the new engine must be compared with theold engine. In order to see the advantages the new engine brings in the following table is made (table13). The table contains the most relevant values of the engine.

Pratt & WhitneyJT3D / TF-33

CFM56-7B24

Weight 4150 lb (1884 kg) 5216 lb (2365 kg)Maximum TSFC 0,52 lb/lbs/h 0,37 lb/lbs/hLegal Noise Emission No YesTable 13: Pros and cons summary

Although the CFM56-7B24 is heavier, it has a much lower TSFC. This results in a lower and moreefficient fuel usage. The chosen engine also complies with the emission standards set by ICAO. After

all, the CFM56-7B24 has an overall advantage over the JT3D.The new engine is however larger thanits predecessor. The P&W JT3D has a diameter of 1,35m and a length of 3,40m compared with 1.55mand 2.50m of the CFM56-7B24.

The new E3-A (equipped with CF56M-7B24) must be able to depart, to a TAS of 200 kts, under certaincircumstances. These circumstances are considered as hot day conditions. This includes anatmospheric temperature of 30. Another precondition is the ability to depart from an airport with analtitude of 6000ft AMSL. At this height, the atmospheric pressure is 0.812 bar and the density is0.8359 kg/m

3.

Under the previous circumstances, the engine will produce 200,744 kN of thrust. So the aircraft willhave a propulsion of 4 x 200,744 = 802,*967 kN.

3.2 Costs

The main costs of the engine replacement are the purchase costs (3.2.1). The modification costs arethe costs to adept the aircraft to the new CFM engine (3.2.2). Maintenance costs of the new enginewill be lower than the maintenance costs of the old engine (3.2.3). The operation costs will also belower with the new engine since the new engines TSFC is much lower compared to the TF-33 (3.2.4).Personnel costs will not change much since the same amount of engines will be operational.Personnel will have to be trained for the new maintenance procedures (3.2.5).

3.2.1 Purchase

The main costs of the engine are the purchase costs. Since the NATO has seventeen AWACS aircraftwith four engines each a minimum of 68 engines need to be bought. But there is also the need of extraspare engines in case of maintenance or failures. So there will be an extra of four engines whichbrings the total to 72 engines. The CFM56-7B24 engine costs 3.93 million euro each, so the grandtotal of purchase costs will be 283 million euro.

3.2.2 Modification

When the CFM-56 engines are bought the modification can start. Personnel are needed to perform themodification and replace all the old engines with the new engines. There are seventeen airplaneseach have four engines so there are 68 engines to replace. To replace one engine it cost 65 manhours, so to change all the engines it will sum up to 4420 man hours. This will take about 27 weeksbefore the modification is complete. To prepare the modification there are two men needed for 48hours for each airplane. For all the seventeen airplanes it means that it will cost 1632 man hours. Thepylons of the aircraft must be adapted for the wiring and the mounts of the engine. The ground

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engineers need a modification training to make sure that the modification is correct performed. Thereis at least one ground engineer needed for each engine and that is four ground engineers for eachplane. There are three kinds of shifts, each shifts needs four ground engineers that will assume in atotal of twelve ground engineers for each day. But in case of sickness there must be spare personnelthat are licensed to work on a CFM-56. So, sixteen ground engineers need a modification training tomake sure that the modification is correct performed.

3.2.3 Maintenance

By replacing the engine, a lot can be saved on maintenance costs. Naturally in the beginning,maintenance costs will be lower, concerning the replacement of the engine. Later on, there will be anincreasing of the maintenance costs. The maintenance is divided into on-wing maintenance andoverhaul maintenance. On-wing can be scheduled and unscheduled. Scheduled on-wing maintenanceis maintenance that is performed during A, B, C and D checks. Unscheduled on-wing maintenance isperformed when the engine has a failure or during trouble shooting an error has been found in theengine. Overhaul maintenance is performed every 4-5 years, an overhaul maintenance takes 35040men hour. This is performed by twenty men and will approximately take 70 days.

3.2.4 Fuel

Due to lower fuel consumption of the new engine, the airplane will be much more efficient during flight.There will be less fuel burned because of the lower TSFC at cruise altitude. This will mean that theairplane can stay longer in flight and will have a range of approximately 15 hours (5800 NM). The

engine will be lighter, this will mean that less mass has to be moved and therefore the range will alsobe greater. The thrust that is produced is higher, so the engine does not have to make as much RPMto have the same thrust as the TF-33, this will also result in lower fuel consumption.

3.2.5 Personnel

Some financial disadvantages can be expected because the CFM-56 is not of the same brand as theTF-33. Maintenance engineers and other maintenance crew will not be familiar with the CFM approachto manuals and support. Moreover, a big part of the tools and supportive equipment will not besuitable for the new engine, anymore. These factors altogether will make that the transition from theTF-33 to the CFM-56 will require a high effort of the supporting crew.On the positive side, CFM engines hold almost half of the market share of aircraft engines for aircraftcarrying more than 100 passengers. Although the E-3A is a military jet, scale profits could be madewhen maintenance is boarded out to large CFM engine maintenance facilities, like KLM Maintenance

and Engineering at Amsterdam Airport Schiphol. In the case that the NATO does not want to board outmaintenance services, CFM engineers will be the easiest to train or recruit.

3.3 Conclusion

A complete analysis of the engine replacement for the E-3A has been made. The basics of jet enginepropulsion have been investigated, three alternative engines have been compared and themodification aspects have been discussed. On each of these points, the following is concluded:

The NATO is an alliance of 26 countries with supporting forces on land, sea and air. The NATOowns 17 AWACS E-3A aircraft that are used as airborne support and surveillance units.

The thermodynamic process in a gas turbine engine is called the Brayton process. In practice,losses always occur during this process, for this reason the efficiency of a jet engine is alwayssmaller than one. A gas turbine engine is built up out of at least the following components:compressor, combustion chamber, turbine and exhaust. Using these components, the layout ofthe engine can be of the turbojet, turbofan or turboprop type. Turbofans have the highestefficiency and therefore the lowest fuel consumption.Next to the primary intention of the engine, providing thrust, the engine also powers the hydraulic,pneumatic, electric and fuel systems and the engine lubrication and thrust reverser systems. In theengine, extremely durable materials as titanium and nickel are used to withstand the hightemperatures. The other elements that affect the materials in the engine are the various forcessuch as pressure differences, centrifugal forces and thrust and drag.Noise, other emissions and engines specification certification procedures can be found inrespectively ICAO Annex 16 Volume 1 and 2 and ICAO CS-E.

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Currently, the E-3A is fitted with Pratt & Whitney TF-33 turbofans. The downsides of these agedengines are their high fuel consumption and high noise levels. A turbofan with a higher bypassratio would take away these downsides. The Pratt & Whitney 6124, CFM56-7B24 andInternational Aero Engines V2528-D5 are more modern engines with a high bypass ratio in thesame thrust range as the TF-33. After a comparison, the CFM56-7B24 is the most suitable for theE-3A.

When fitted with four CFM engines, the improvement of the E-3A will be recognizable in a lowerfuel consumption, higher thrust, lower emissions and a lower noise level. Total amount ofpurchase and modification and fitting of the new CFM56-7B24 engines will be between 482 million

euro 690 million euro.

As the project assignment requires, the new CFM56-7B24 engines will be able to operate under hotconditions, have a low TSFC, so that the endurance will meet the demand of 10 hours non-stop flyingat a speed of 380

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