ContentsINTORDUCTION : Mankind’s journey towards powered flight...........................................................2

CHAPTER 1 : Reciprocating engines...................................................................................................4

1.1 Inline and V type engines.............................................................................................................4

1.2 Radial engines................................................................................................................................5

1.3 Carburators.....................................................................................................................................7

1.4 Fuel injection.................................................................................................................................8

1.5The Diesel Aero engine..................................................................................................................9

CHAPTER2 : Jet engines......................................................................................................................10

2.1The Turbojet Engine.....................................................................................................................10

2.1.1 Development of Centrifugal and Axial turbojet engines......................................................11

2.1.2Modern developments............................................................................................................12

2.2Turboprop Engines.......................................................................................................................13

2.3 Turbofan Engines.........................................................................................................................14

2.3The Turboshaft Engine.................................................................................................................16

2.4 Pulsejet Engines..........................................................................................................................17

2.5 Ramjet Engines............................................................................................................................18

2.5 The Scramjet................................................................................................................................19

CHAPTER 3 : A look into the future....................................................................................................20

3.1 Nuclear powered aircraft.............................................................................................................20

3.2 Fuel cell and Hydrogen powered aircraft....................................................................................22

3.4 Solar powered Aircraft.................................................................................................................23

3.5 Diesel and bio-fuels.....................................................................................................................23

CHAPTER 4 : Conclusion.....................................................................................................................24

List of figuresFigure 1 Mesopotamian winged god Anunnaki ……………………………………..2

Figure 2 Ravana’s flying machine…………………………………………………..2

Figure 3 Leonardo daVinci’s vision of a helicopter…………………………………2

Figure4 First flight of Montgolfier brothers………………………………………...3

Figure 5 First powered flight by the Wright Brothers……………………………….3

Figure 6 The Wright “Flyer” engine…………………………………………………3

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Figure7 The first powered flying machine used a steam engine……………………3

Figure8 The Merlin and a Supermarine Spitfire……………………………………4

Figure 8 The Bugatti U 16 water cooled U type engine……………………………..5

Figure 9 Napier cub X engine………………………………………………………..5

Figure 10 a modern four cylinder opposed engine…………………………………..5

Figure11 Wright J-5 whirlwind……………………………………………………..6

Figure12 Pratt& Whitney double Wasp 18 cylinder………………………………..6

Figure 13 Lockheed c-609 Constellation……………………………………………6

Figure 14 Le Rhone C-9 engine…………………………………………………….6

Figure 15 The cylinders rotate……………………………………………………….6

Figure 16 Internal arrangement of a radial engine…………………………………...7

Figure 17 Ford Trimotor……………………………………………………………..7

Figure 18 An updraft carburetor……………………………………………………..7

Figure 19 Antoinette V11…………………………………………………………….8

Figure 20 Focke Wolf 190D………………………………………………………….8

Figure 21 A modern Diesel aircraft………………………………………………….9

Figure 22 The first diesel aircraft……………………………………………………..9

Figure23 Hero’sEngine……………………………………………………………….10

Figure 24 Camprini…………………………………………………………………..10

Figure 25 Heinkel HE178…………………………………………………………….10

Figure 26 Messerschmitt Me 262……………………………………………………..11

Figure 27 Gloster meteor……………………………………………………………...11

Figure 28 a centrifugal flow jet engine………………………………………………..11

Figure 29 Junkers Jumo 004…………………………………………………………..11

Figure 30 Sir Frank Whittle…………………………………………………………...11

Figure 31 De Havilland Comet………………………………………………………..12

Figure 32 The CFM composite blade engine………………………………………….12

Figure 33 Rolls Royce RB50 Trent……………………………………………………13

Figure 34 An Axial flow turboprop …………………………………………………...13

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Figure 35 Kuznetsov NK-12 on a TU 95 ……………………………………………...13

Figure 36 TP400 engines mounted on a Airbus A 400M………………………………14

Figure 37 Diagram of a turbofan engine……………………………………………….14

Figure 38 Afterburners operating………………………………………………………15

Figure 39 PW1000G engine……………………………………………………………15

Figure 39 a turboshaft helicopter engine……………………………………………….16

Figure 40 Sikorsky CH-35……………………………………………………………...16

Figure 41 Junkers E126 Pulse jet aircraft………………………………………………17

Figure 42 operation of a pulse jet………………………………………………………17

Figure 43 Boeing’s Light Arial Multi-purpose Vehicle (LMAV) concept……………17

Figure 44 Operation of a ramjet………………………………………………………18

Figure 45 Kostikov 302………………………………………………………………...18

Figure 46 Leduc 0.1……………………………………………………………………18

Figure 47 A surface to air missile……………………………………………………...19

Figure 49 X-43 being released from the underside of a B52………………………….19

Figure 50 Pratt and Whitney HTRE-3 direct nuclear engine…………………………..20

Figure 51 Artists impression of a nuclear aircraft circa 1950’s………………………..21

Figure 52 Boeing’s fuel cell aircraft …………………………………………………..22

Figure 53 Rendering of the Proposed DLR ‘Smartfish”……………………………..22

Figure 54 NASA’s Solar plane………………………………………………………...23

Figure 55 The Sunseeker 11 solar powered manned aircraft………………………….23

Figure 56 Airbus E-fan………………………………………………………………..23

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INTORDUCTION : Mankind’s journey towards powered flight.

Since the dawn of time, man has been forever fascinated by the heavens. The skies were the realms of the gods, for who’s attributes, many cultures added the power to sore among the birds. These divine beings had the power to come and leave as they wish, no mountain and ocean was an obstacle (Figure 1).

Man forever dreamed of taking to the skies and soaring among the birds. From ancient times many dreamt of devising elaborate machines to take them to the heavens, accounts of such fabulous creations are found throughout ancient mythology, one famous such is the flying machine of Ravana (Figure2).

It was not until the renaissance that the budding field of science that we find physical records of flying machine designs (Figure 3). Man carrying kites have been reported in ancient China and Japan, but physical evidence is yet to be found.

Man’s first recorded flight was not in an aircraft as we know now, but in a balloon. The Montgolfier brothers were the first recorded human beings to take into the skies in their hot air balloon on 19th October 1784.Prior their flight, a test flight was performed successfully with a Sheep, duck and a chicken on board in June the same year, marking the first established account of the flight of a species who evolution did not intend to leave solid ground (the sheep).However, the occupants were at the mercy of the winds. Steam engines were too heavy to be practical in a flying machine. However the first controlled powered flight was achieved using a

small steam engine in 1852.While lighter than air and heavier than air flying continued to develop, the lack of

a lightweight mode of propulsion to maintain flight and

control direction remained an unsolved problem.

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Figure 2Mesopotamian winged god Anunnaki

Figure 2 Ravana’s flying machine.

Figure 3 Leonardo daVinci’s vision of what appears to be a helicopter

The dawn of powered flight

The dream of powered flight did not materialize till the invention of the internal combustion engine. By the end of the 19th century, internal combustion engines had reached a level of development where the power to weight ratio was adequate enough to propel an aircraft. The Wright brothers are the first to record a powered flight in a heavier than air machine. Airships, preceded airplanes into service also powered by gasoline or diesel engines.

The following pages will follow the evolution of aircraft propulsion systems and future trends.

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Figure4 First flight of Montgolfier brothers.

Figure 5 First powered flight of a heavier than air flying machine by the Wright Brothers in 1903

Figure 6 The Wright “Flyer” engineFigure7 The first powered flying machine used a steam engine

CHAPTER 1 : Reciprocating enginesThis Chapter covers the evolution of reciprocating internal combustion engines in aircraft propulsion up to modern aircraft.

1.1 Inline and V type engines.

Prior to the development of gas turbine engines in the 1930’s reciprocating internal combustion engines was the sole mode of propulsion for aircraft. A wide range of configurations existed, and today, piston engines continue to be developed, albeit in smaller aircraft. The early aircraft engines were derivatives of automobile engines produced by automobile manufacturers, notable among them are Rolls Royce, Alfa Romeo, Hispano Suiza Bugatti and Packard.

Aircraft engines, in general are built to a higher level of durability than automobile engines. Furthermore, several redundancies are built into an engine.

Early engines were inline engines which resembled automobile engines of the time. These engines were narrow, reducing the frontal area of the aircraft. Inline engines could be vertical, inverted (crankshaft above pistons) or horizontal according to aircraft design. As power requirements increased the size of inline engines, crankshafts and crankcases increased in weight to withstand increasing bending moments and stresses, thus reducing the power to weight ratio.

Air cooled engines encountered difficulties in cooling cylinders at father away from the propellers, thus requiring heavy liquid cooing systems. Early engine failures were mainly due to cooling system malfunctions. It was not until the 1920’s that manufacturers truly understood air cooling.

V type engines offered the solution. V engines were produced far back as 1886 by Daimler. These engines provided far better power to weight ratios as well as being more compact. The wright brothers first used a V8 in 1910.By the dawn of world war 11 , vtype engines reached mamoth proportions, powering fast combat aircraft. One of the most succesfull V type aircraft engines is the Rolls Royce Merlin. Which was built from 1933 well into the 1950’s and is still operational in many aircraft. This 27litre V12 produced over 1000horspower. Supercharging was the norm in aircraft by this time,which not only incresed power, but enebled aircraft to attain higher altitudes.

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Figure8 The Merlin and a Supermarine Spitfire

During the first half of the 20th century, several piston engine configurations were built and tested, despite not becoming commercial successes, these engines are most interesting(figures 8 &9).

The 2 cylinder Lawrence A3 was the first flat aircraft engine. Lycoming and continental were at the forefront of flat engine technology in the 1930’s and 40’s.The first modern opposed engine was the Continental A40 in1931 .Today opposed, air-cooled four- and six-cylinder

piston engines are by far the most common engines used in small general aviation aircraft requiring up to 400 horsepower (300 kW) per engine.

1.2 Radial enginesThe other major development in piston engines was the radial engine. Radial engines are universally regarded as air cooled. However the first such engine built in 1901 was water cooled. In 1903-4 Jacob Ellhammer constructed the first air cooled radial engine, which was later used to power a triplane of his own design. The radial engine Bleriot IX was the first aircraft to cross the English Channel. Radial engines posses several major advantages , appealing to aircraft manufacturers at the time, The radial design ensured adequate cooling of cylinders and eliminated liquid cooling systems, which were a liability especially in combat aircraft. Radial engines possess shorter crankshafts which reduce weight as well as vibration. Some notable radial engines are stated below.

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Figure 8 The Bugatti U 16 water cooled U type engine

Figure 9 Napier cub X engine with 4 banks of four cylinders each

Figure 10 a modern four cylinder opposed engine.

Between 1909 and 1919, radial engines, as we know today, fell out of favor and were replaced by a novel radial engine; the “Rotary” or “Rotating radial” (Not to be confused with Wankel engines). These engines gained wide acceptance during the short time during WW1.

The rotary engine was unique due to the cylinders rotating with crankshaft and crank case stationary. These unorthodox engines were seen as beneficial for their smooth operation, better cooling due to the cylinders rotating and higher power to weight ratio (due to the absence of a heavy flywheel) .Many early air speed records were set in aircraft powered by rotary engines. The end of WW1 saw the rotary radial fall out of favor, the engines produced prominent gyroscopic precession, and a significant component of the engines power was used to overcome its own aerodynamic drag. Therefore, the conventional radial engine was preferred.

However, radial engines had several drawbacks; the large frontal area resulted in excessive drag. The large front mounted engine hinders visibility, engine configuration makes multiple valve designs impractical, and thus most engines have two valves per cylinder actuated by pushrods. This limits the possible improvements. Multiple row engines suffer from cooling problems. Improvements on these issues continued and radials remained the choice engine in commercial and military applications until the advent of jet engines.

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Figure11 Wright J-5 whirlwind used for the first transatlantic flight

Figure12 Pratt& Whitney double Wasp 18 cylinder. The pinnacle of radial engine technology 1939-1960

Figure 13 Lockheed c-609 constellation powered by 4 double Wasp engines

Figure 14 Le Rhone C-9 engine. Used by the French during WW1.

Figure 15 The cylinders rotate, driving the propeller.

The largest radial engine produced was the 28cylinder Pratt & Whitney_R-4360which entered service in1944.

Large piston engines are virtually nonexistent in modern aircraft. However, manufacturers still produce small piston aero engines for light and medium applications. These engines are reliable and easy to maintain. Major reciprocating engine manufacturers include Continental, Lycoming and Rotax. Significant advancement has been made in the past decades in machining processes, improving the engines’ reliability. Advancements in engine management systems have eliminated the pilot’s interference in fuel air mixture adjusting. Despite initial appearance remaining unchanged, modern reciprocating engines have better reliability and fuel economy as a result of increasingly intelligent engine management systems.

1.3 CarburatorsThe engines discussed in the previous pages were gasoline powered spark ignition engines operating in the Otto cycle. Therefore delivery of proper air fuel mixture is required.

The first aircraft engine used in the Wright flyer did not have a carburetor. Fuel dripped into the combustion chamber and was vaporized by heat from the crankcase. Carburetors, a development form the auto industry was then used. The major disadvantage of using carburetors was that the aircraft’s maneuverability was significantly restricted. Steep dives, ascents, rolls or banking in short, any maneuver causing significant G force, would cut off or disrupt fuel delivery in a float type conventional carburetor. Float regulation will fail under negative G or turbulence.

Typically updraft carburetors are used so as to prevent flooding of the engine and enable a gravity feed lest fuel pumps fail as the updraft carburetor can be mounted low in

the engine block.

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Figure 16 internal arrangement of a radial engine

Figure 17 Ford Trimotor

Figure 18 An updraft carburetor, common among early aircraft.

The pressure carburetor, designed by the Bendix Corporation USA, was introduced in 1940. This can be considered an early form of throttle body fuel injection.

After WW11 Bendix further developed this technology into its RSA multiport continuous flow fuel injection.

1.4 Fuel injectionThe 1902 Antoinette8V was the first aircraft engine to sport fuel injection. Fuel injection eliminated fuel delivery issues previously mentioned with regard to carburetors.

While carburetors were the norm in the US and Great Britain, almost all German aircraft of WW11 had gasoline direct fuel injection as standard. Junkers Jumo series, BMW 801,Daimler _Benz DB-601 are a few examples.

Fuel injection became the norm in piston driven aircraft after WW11, improved efficiency, reliability, smooth operation, as well as independence of G forces are only a few advantages.

Modern aircraft are equipped with electronic fuel injection, the first of which was introduced during the Korean war by the Bendix corporation. Electronic fuel injection has proven to be more efficient and than mechanical fuel injection for spark ignition engines. Fuel delivery can be controlled according to operating conditions to ensure optimum performance via the Electronic Control Unit. EFI is more reliable than mechanical fuel injection. All modern aircraft make use of EFI.

1.5The Diesel Aero engineWhile we outlined the development of reciprocating engines, our focus was spark ignition engines which operated on the Otto cycle. A brief overview of Diesel engines is also needed.

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Figure 19 Antoinette V11 powered by the fuel injected Antoinette 8V engine

Figure 20 Focke Wolf 190D powered by a BMW 801 direct injection Diesel engine

Diesel aero engines are nothing new. The first diesel aircraft engines appeared in the 1920’s . Diesel engines did not suffer fuel delivery issues as did gasoline engines of the day and the Diesel cycle is more efficient than the Otto cycle. The first successful Diesel powered aircraft took to the skies in 1928 (figure16).Interest in diesel power died after WW11. Only in the recent past has a renewed interest in diesels immerged. Environmental concerns as well as increasing avgas prices have made diesel engines a good alternative to spark ignition engines.

Today, reciprocating engines are confined to small lightweight aircraft. Radial as well as horizontally opposed engines are used. However we cannot say that the era of reciprocating aero engines is over, as we shall see in further chapters.

CHAPTER2 : Jet enginesThis chapter covers the development of jet propulsion up to the present day.

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Figure 22 first diesel aircraft: A StinsonSM –IDX with a Packard diesel radial engine.Figure 21 a modern Diesel aircraft

2.1The Turbojet EngineThe idea of jet propulsion was conceptualized many millennia ago, before any means of mechanical transportation, let alone flight was devised. Hero of Alexandria’s “Aeolipile” engine (150B.C) in ancient Egypt is said to be the first account of the reaction engine concept. This simple device, converted steam into a high pressure jet to rotate a sphere. It was, however, just a toy.

However, reaction engine concepts began to emerge only in the late 19th and early 20th century. Several concepts were put forward, notable among them, the 1913 design by Rene Lorin is noteworthy. The deisgn while not a pure jet engine, used a conventional piston engine to

compress air, and ignite the air fuel mixture later. This provided more thrust than propeller aircraft. But manufacture of such an engine

remained beyond the capabilities of the day. Known as motorjets, these type of engines flew in a few aircraft during WW11. The Caproni Camprini N1 which flew in 1940 was the first motorjet aircraft (Figure

24) and was considered by many to be the first jet aircraft due to the secrecy which surrounded Nazi military development at the time. Motorjets (or pulse jets as some refer to them), did not gain popularity and development was halted after WW11, in

favor of modern jet engines.

Sir Frank Whittle is credited with the invention of the jet engine. He file a patent for a turbojet engine in 1930. By 1937,Whittle succeeded in producing a working engine. Unknown to Whittle, a German team headed by Hans Von

Ohain, produced the world’s first aircraft to flu under turbojet power, the Heinkel HE 178 in 1939.Whittles jet first flew in 1941 in a Gloster Meteor.

Both Whittle and Ohain pursued the design of centrifugal flow turbojets. They worked independently and it is established that they were unaware of each other’s work. Whittle engines were more durable due to availability of advanced materials that could withstand high pressures and temperatures.

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Figure23 Hero’sEngine

Figure 24 Camprini

Figure 25 Heinkel HE178

2.1.1 Development of Centrifugal and Axial turbojet engines

As aforementioned, the first jet engines were of centrifugal compressor design. Here a centrifugal impeller would compress incoming air and force to the outer perimeter of the engine where it is compressed by a divergent duct setup and ignited in a combustion

chamber. The overall construction was simple and robust. Debris sucked into the engine, for instance, did not result in catastrophic failure. Manufacturers of the day were able to produce these engines in significant numbers. The impeller could be machined from a single billet. The working principle of the centrifugal

impeller was well known at the time and perfected by automotive manufacturers in

the form of supercharges. Future generations of Rolls Royce, General electric, Allison, Pratt & Whitney and other British and American engines followed Whittles ‘model. However, as manufacturing methods advanced, the disadvantages of centrifugal flow jet engines began to overweigh its advantages. The impeller was large and heavy. Prevalent material constraints limited the operational speed of the

engine, thus reducing efficiency and requiring a larger diameter impeller. This increased frontal area and thereby increasing drag.. The gasses had to be ducted through the combustion chamber to the rear which also resulted in losses.

Development of axial flow jet engines were carried out more are less at the same time as Whittle and Ohain. Germany was in the forefront of axial compressor jet engines. The axial compressor is in essence a turbine in reverse.

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Figure 27 Gloster meteor

Figure 28 a centrifugal flow jet engine

Figure 30 Sir Frank Whittle with one of his prototype jet engines.

Figure 29 Junkers Jumo 004

Figure 26 Messerschmitt Me 262

Unlike centrifugal compressors, axial flow compressors could not produce required pressure in a single stage, several successive impeller sets have to be installed.

The world’s first jet fighter , the Messerschmitt Me 262, which was introduced in 1944 was powered by the Junkers Jumo 004 axial flow turbojet engine. Junkers produced 8000 examples of this pioneering engine to wide success. After WW11, allied forces acquired many German aircraft and studied their technology extensively.

The end of WW11 saw the emergence of jet powered aircraft into wide use. Today, axial flow turbojets are almost universal in modern large and medium fixed wing airliners and combat aircraft. Centrifugal engines have also improved greatly and can be found in many small aircraft as well as helicopters, due to their compact dimensions.

2.1.2Modern developmentsAlthough remaining similar in working principle, turbojet engines have improved vastly in terms of efficiency, power to weight ratio, emissions and noise levels. Advancements in material sciences has provided stronger, more lightweight materials which can withstand higher temperatures, pressures and speeds, all contributing to more powerful and efficient engines.

Single crystal growing of turbine blades is a well established method of manufacture. New 3D printing of parts and the use of composite ceramic matrixes has already been announced.

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Figure 31 De Havilland Comet. first flown in 1949, ushered in the age of passenger jet travel.

Figure 32 The CFM composite blade engine set to improve fuel economy by 15% has 4500 standing orders as of 2013

2.2Turboprop EnginesA turbo prop engine combines the light weight of a jet engine with the low speed efficiency of propellers. A turbo prop engine generally weighs around half that of a similar powered piston engine. The power of the turbine is directed to drive a propeller via a reduction gear to maintain propeller tip speed below the speed of sound (Propellers do not efficiently operate beyond mach 1). Little useful thrust is produced.

The first design of a turboprop was patented in 1929. by Hungarian  György Jendrassik. Jendrassik later succeeded in constructing a working prototype in 1938.A full sized working engine was produced in 1940. It was of axial compressor design. No further development was carried out .

Rolls Royce produced the first British turboprop engine, the “Trent”. This engine had a centrifugal flow turbojet engine which was geared to a 7 foot propeller. A retrofitted Gloster Meteor was the first turboprop aircraft to fly, in 1945.The Rolls Royce RB53 “Dart” turboprop engine, which was introduced in 1946, remains one of the most successful and reliable turboprop engines to date, was continuously produced until 1987.

Despite the first turboprop engine being an advanced axial flow turbojet, production engines remained centrifugal flow, as we observed in section 2.1 the reason behind this was that the British and Americans who pioneered turboprop technology did not have knowledge of axial flow engines.

The next development in turboprop technology was the Soviet built Kuznetsov NK-12 the most powerful turboprop engine to date. The NK-12 is attached to an 8 bladed counter rotating rotor 18 feet in diameter. The most famous application being the Tupolev TU 95 nuclear bomber, capable of speeds over 575mph (figure 28 ).

Turbopor engines continue to be developed, especially in small civilian aircraft as well as large cargo aircraft such as the C-130 Hercules. The latest development is the Europrop

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Figure 33 Rolls Royce RB50 Trent

Figure 34 An Axial flow turboprop Figure 35 Kuznetsov NK-12 on a TU 95

TP400 D6 an 11,000horsepower turboprop engine. The design consists of three coaxial shafts, two of which drive several stages of low, intermediate and high pressure turbines to generate a high pressure ratio.

Figure 36 TP400 engines mounted on a Airbus A 400M

2.3 Turbofan Engines Turbofans were developed to combine some of the best features of the turbojet and the turboprop. Turbofan engines are designed to create additional thrust by diverting a secondary airflow around the combustion chamber. The turbofan bypass air generates increased thrust, cools the engine, and aids in exhaust noise suppression. This provides turbojet-type cruise speed and lower fuel consumption. Most modern airliners use turbofan engines.

Figure 37 Diagram of a turbofan engine

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The turbofan is a derivative of the axial flow turbojet engine. The first operational turbofan was the Daimler-Benz DB 670 in 1943. Low bypass engines were developed, to reduce the speed of the exhaust gas exiting the engine to a value closer to the aircrafts forward speed, the

first among these engines was the Rolls Royce Conway. By the 1970’s afterburners were installed in turbofan powered jet fighter aircraft. Afterburners injected a prodigious amount fuel upstream of the turbine blades, thereby bypassing the temperature constraints which are imposed to protect turbine blades. These are used to provide a quick boost of power.

The mid 1960’s saw the entry of the high bypass turbofan engine. These engines produce less noise and have better fuel economy. The first high bypass turbofan was the General electric TF39, which powered the Lockheed C-5 Galaxy.

The latest development is the geared turbofan, which connects the fan and low pressure turbine via a reduction gearbox (in conventional designs this is a single shaft). This enables the compressor shafts to be rotated at a higher speed than the turbo fan shafts. This will reduce the number of stages in both the LP turbine and compressor. However the gearbox is an added complexity. Pratt and Whitney first ran their PW1000G geared turbofan engine in 2008.This new engine is set to power several commercial jet aircraft in the near future.

Figure 39 PW1000G engine

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Figure 38 Afterburners operating

2.3The Turboshaft EngineThe main difference between a turbojet and turboshaft engine, is that unlike a turbojet where the exhaust gas is used to produce thrust, the turbo shaft engine uses a free turbine to extract energy from the exhaust gas and rotate a shaft. Many turboprop engines can be purchased in turbo shaft configuration as well.

First developed in Germany during WW11 as a power plant for Panzer tanks, turboshaft engines gained popularity as the choice engine for helicopters.

Today, larger helicopters use multiple turboshaft engines.

Figure 40 Sikorsky CH-35 is powered by three turboshaft engines

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Figure 39 a turboshaft helicopter engine

2.4 Pulsejet EnginesPulse jets, as their namesake suggest are a type of engine where combustion take place in pulses. The “engine” itself is extremely simple with little or no moving parts. The pulsing action results in high noise levels and vibration, which have prevented their use in manned aircraft. Today, pulsejets are mainly used in model aircraft and unmanned drones.

Pulsejets are extremely simple .The absence of an external compressor stage reduces the engines’ pre combustion pressure ratio to 1.2 or 1.1.

Figure 41 Junkers E126 Pulse jet aircraft

Apart from their simplicity, pulse jets do not apply torque on the airframe as do other jet engines and reciprocating engines. Several studies are underway to develop a pulse jet

suitable for manned aircraft. One such design is the pulse ejector thrust augmenter or PETA developed by Boeing. The augmenter channels surrounding air to the pulse jet exhaust to improve cooling and propulsion. One application is on vertical takeoff aircraft. The jets can be assembled in series according to the size of the aircraft.

2.5 Ramjet Engines The ramjet, in principle is similar to the pulse jet, but is a continuously operating engine. The major drawback being that it requires high airspeed to operate (above 900kmh). A ramjet

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Figure 42 operation of a pulse jet

Figure 43 Boeing’s Light Arial Multi-purpose Vehicle (LMAV) concept, powered by pulsejets

engine operates efficiently above mach3 and can attain speeds upto mach6. A ramjet powered aircraft requires assistance from another engine or rocket to attain a speed where the ram jet will begin operating.

French inventor Rene Lorin first presented the concept in 1913, (as mentioned in 2.1), but such phenomenal airspeeds were not attainable at the time, to test the concept in practice. It was in 1933 that the first operational ramjet engine, the GRD-04 fueled by hydrogen was tested. The engine was stationary, and air compressed to 200atm was blown into the engine to simulate forward speed. Later, the phosphorous fueled GRD-08 was launched using a cannon to attain operational airspeed. This was the first projectile to reach the speed of sound.

During WW11, two ramjet engines were attached to a YAK-7 aircraft for testing. In 1940, the Kostikov-302 experimental aircraft was constructed. It was launched by a liquid fueled rocket booster.

Germany also tested ramjet designs during WW11. Shortages of gasoline towards the end of the war prompted German scientists to use compressed coal dust, which was not successful.

The US navy in collaboration with the University of Southern California produced the “Gorgon” series of air to air missiles, beginning in 1948.

The Leduc 0.1 designed by Frenchman Rene Leduc was the world’s first aircraft solely powered by ramjets. It was carried by a larger aircraft and released at high altitude (figure39).

The Nord 1500-Griffon, built by the then state owned Nord Aviation , was the next step in ramjet technology. This aircraft was powered by a turbojet and ramjet combined power plant.

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Figure 45 Kostikov 302

Figure 44 Operation of a ramjet

Figure 46 Leduc 0.1

While, the aircraft proved to be a success, its added complexity and lack of material suitable to withstand kinetic heating. First flown in 1955, the project was ended. Today, ramjets are used to power long distance missiles.

2.5 The ScramjetA variation of the ramjet, the Supersonic Combusting Ramjet , enables combustion of airflow at supersonic speeds whereas , in a ramjet, the air is decelerated to subsonic speeds before acceleration.

The first scramjet to fly was produced in Russia in 1991.The hydrogen fueled engine was mounted on a SA-5 surface to air missile.

In 2004 the NASA X-43A was the first scramjet powered aircraft. This unmanned carft was released at high altitude form a B52 Stratofotress. In 2013 another unmanned scramjet aircraft the Boeing X-51 “Waverider” successfully reached mach 5.1 (4828km/h) .On January 9th 2014 the Chinese government tested its first scramjet propelled aircraft ,the WU-14 marking China’s entry into hypersonic technology. The design appears to be mainly focused on carrying warheads and not passenger transport.

CHAPTER 3 : A look into the futureThis chapter covers the future of aircraft propulsion.

3.1 Nuclear powered aircraftThe idea of propelling an aircraft using nuclear power is not novel. During the 1950’s and 60’s the United Sates and Soviet Union were locked in a race to develop the first nuclear powered aircraft.

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Figure 47 A surface to air missileFigure 49 X-43 being released from the underside of a B52

The idea of nuclear propulsion in quite appealing; Aircraft consume vast quantities of fuel and have to compromise between speed, altitude and range. A nuclear powered aircraft, like modern nuclear submarines and ships, will be limited in range only by the need for supplies to sustain its crew. A nuclear aircraft has the ability to be air born for an indefinite period of time.

Two approaches to nuclear propulsion were initially proposed;

Direct propulsion: Here atmospheric air is channeled through the reactor to be heated. The heated air is then used to propel a jet engine.

Indirect propulsion: Molten metal (Sodium in most cases) is used to convey heat from the reactor core. Atmospheric air is heated in an external heat exchanger.

Working models of both designs were constructed, as well as a small lightweight reactor which was installed in a large aircraft. (Convair NB36 US, and Tupolev TU 95 USSR)

These were the first airborn nuclear reactors. However neither were actually propelled by nuclear power.

Several obstacles hindered progress;

Direct propulsion resulted in severe radiation being expelled from the exhaust gas. Indirect propulsion was more heavy and complex. Neither engine had sufficient power to weight ration to propel an aircraft. Shielding the aircraft’s occupants form nuclear radiation proved to be impractical

at the time due to excessive weight of insulating material. Possibility of catastrophic damage if such an aircraft would crash in a populated

area.

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Figure 51 Artists impression of a nuclear aircraft circa 1950’s

Figure 50 Pratt and Whitney HTRE-3 direct nuclear engine

The programs were cancelled in the 1960’s before any flying aircraft were produced.

However, the future might make nuclear aircraft a reality. Modern advancements in lightweight alloys and composite materials as well as manufacturing techniques will continue to progress.

As of now, research of nuclear powered aircraft is at a standstill. NASA continues to develop small nuclear reactors for deep space operation.

Thorium powered reactors have been proposed by researches as an alternative to uranium. General motors unveiled a Thorium powered concept car in2012 to mark the 100 th

anniversary of Cadillac. However, it did not possess a working power plant. Thorium still requires a fissile material to irradiate and does produce radioactive isotopes albeit in lesser numbers than conventional reactors. But the issue of safety during a crash remains unresolved. Future developments might lead to nuclear aircraft in the next 100 years. These aircraft could be stationed in the sky indefinitely as reconnaissance or even flying hotels and military bases

3.2 Fuel cell and Hydrogen powered aircraftWith increasing environmental concerns as well as the cost of fossil fuels, researches are focusing on alternative means of propelling aircraft. Hydrogen, has been used to fuel aero engines since the turn of the century. However, the scarcity of hydrogen discouraged its use.There are two main approaches of hydrogen powered aircraft that we will be seeing in the future;

Aircrafts which burn hydrogen in a similar manner to burning fossil fuels

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Fuel cell powered aircraft.

Future advancements in material sciences shall enable hydrogen to be stored at high pressure onboard aircraft. Today, carbon fiber tanks are being tested, however high pressure storage is not possible. Hydrogen has high energy density per mass, but low energy density per volume. Therefore high pressure storage tanks are required to store sufficient amounts of hydrogen.

The first liquid hydrogen powered aircraft was a modified Russian TU-154 in 1989.

Fuel cell technology, unlike nuclear power is being developed for automotive use in the present day. Several working examples of fuel cell vehicles exist. An experimental light aircraft has been already made by the Boeing research division. Launched in 2008, the fuel cell powered an electric motor supplemented by a Li ion battery.

Leading manufacturers such as Airbus and Boeing are already planning for hydrogen fueled aircraft of the future. While fuel cell technology might not be sufficient to power large aircraft, hydrogen burning engines will become the norm in air travel of the future.

3.4 Solar powered AircraftThe enthusiasm regarding solar powered vehicles has diminished lately, as solar panels still fail to provide adequate energy per square meter to warrant practical human and cargo applications. Even so, solar power, coupled with advancements in battery technology, might prove to be a viable solution in the future.

Aircrafts in the future shall probably have a combination, of Fuel cell, battery, as well as solar power combined with other jet engines or internal combustion engines. A solar powered aircraft could remain in the air indefinitely .

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Figure 52 Boeing’s fuel cell aircraft

Figure 53 Rendering of a the Proposed DLR ‘Smartfish” a two passenger fuel cell aircraft

In march 2014, Airbus unveiled its “E-Fan “fully electric aircraft. Although not solar powered and with a 1hour flight time, it is a significant leap in aircraft technology. Agusta

Westland have also unveiled a vertical take off electric aircraft concept.

3.5 Diesel and bio-fuelsDiesel engine development was mentioned in section 1.3. We shall see an increasing number of diesel light aircraft in the near future. Bio fuels are already beginning to take hold in the aircraft industry.Gas turbine engines have the ability to burn a variety of different fuels. In short any volatile liquid can be used to power a jet airliner. Aviation biofuels were approved for commercial use in July 2011. Sustainable bio fuels are seen as a major means to reduce the carbon footprint of aircraft in the near future. Bio fuels can be used in existing engines; therefore bio fuels are a stepping stone towards more eco friendly aircraft in the future. On June, 2011 KLM flew a Boeing 737 fueled by used cooking oil. A study by Yale University suggests the use of bio fuel will reduce 85%of green house gas emissions if agricultural land were used for bio fuel cultivation and by 60% if natural woodland were to be used.

CHAPTER 4 : ConclusionAircrafts have advance in an exponential manner during the past century. We observed that many concepts of propulsion were first formulated during the industry’s infancy. However, material and manufacturing constraints needed to be overcome in order to make these concepts a reality.

As technology progressed, we observed more emphasis on speed, range, altitude, reliability and power. Little attention was paid towards the environmental impact of aircraft. However, as the 20th century came to a close, more and more emphasis was on making aircraft more environmentally friendly.

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Figure 54 NASA’s Solar plane Figure 55 The Sunseeker 11 solar powered manned aircraft

Figure 56 Airbus E-fan

We saw that the basic designs of aero engines had changed little since WW11, but what has improved are materials and manufacturing techniques, which have made aero engines, lighter, more durable and more efficient.

We also observed some interesting research in the past such as nuclear aircraft. These concepts were ahead of their time, but the future might bring new discoveries that will make these concepts a reality.

Finally we saw that the aircraft industry and major aircraft manufacturers have already established that alternative energy sources are a must to ensure the industry’s survival in a world where fossil fuels are a diminishing resource.

We can conclude that the future of aircraft propulsion shall bring exiting new technologies that will border on the realms of science fiction and bring flight even closer to the masses.

Refereneces

1. “Rolls Royce :The Jet Engine” 5th edition ISBN 0 902121 2 35.2. www.Airbus .com/ innovation/eco efficiency/design/fuel-cells3. MIT Technology review ; www.technologyreview.com/news/516576/once-a-joke-

battery-powered-airplanes-are-nearing-reality/4. “Airbus unveils plans to fly battery-powered PLANES within the next 20 years”

www.dailymail.uk (25/04/2014)5. www.frankwhittle.com

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6. Smithsonian “ Air and space” magazine : www.airandspace.com7. “Future Aero Engine Designs: An Evolving Vision” Konstantinos G. Kyprianidis

Chalmers University of Technology ,Sweden 8. “Centrifugal and Axial compressors” General electric corporation 2005

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