The History of the Jet Engine Sir Isaac Newton in the 18th century was the first to theorize that a rearward-channeled explosion could propel a machine forward at a great rate of speed. This theory was based on his third law of motion. As the hot air blasts backwards through the nozzle the plane moves forward. Henri Giffard built an airship which was powered by the first aircraft engine, a three-horse power steam engine. It was very heavy, too heavy to fly. In 1874, Felix de Temple, built a monoplane that flew just a short hop down a hill with the help of a coal fired steam engine. Otto Daimler, in the late 1800's invented the first gasoline engine. In 1894, American Hiram Maxim tried to power his triple biplane with two coal fired steam engines. It only flew for a few seconds. The early steam engines were powered by heated coal and were generally much too heavy for flight. American Samuel Langley made a model airplanes that were powered by steam engines. In 1896, he was successful in flying an unmanned airplane with a steam-powered engine, called the Aerodrome. It flew about 1 mile before it ran out of steam. He then tried to build a full sized plane, the Aerodrome A, with a gas powered engine. In 1903, it crashed immediately after being launched from a house boat. In 1903, the Wright Brothers flew, The Flyer, with a 12 horse power gas powered engine.

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study of jet engines & how they works1.History of jet engine 2. Introduction 3. Parts of jet engine 4. How a get engine works 5. Types of jet engine (i) Ramjet (ii) Turbojet (iii) Turbofan (iv) Turboprop (v) Turbo shaft 6.Comparison of Turbo Jet 7.Jet engines Vs Rockets 8.Difficulties 9.Suggestion for improvement 10. Merit and Demerits 11. Jet engine uses 12.Conclusion 13.Future vision

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Page 1: Report on jet engines

The History of the Jet Engine

Sir Isaac Newton in the 18th century was the first to theorize that a rearward-channeled explosion could propel a machine forward at a great rate of speed. This theory was based on his third law of motion. As the hot air blasts backwards through the nozzle the plane moves forward.

Henri Giffard built an airship which was powered by the first aircraft engine, a three-horse power steam engine. It was very heavy, too heavy to fly.

In 1874, Felix de Temple, built a monoplane that flew just a short hop down a hill with the help of a coal fired steam engine.

Otto Daimler, in the late 1800's invented the first gasoline engine.

In 1894, American Hiram Maxim tried to power his triple biplane with two coal fired steam engines. It only flew for a few seconds.

The early steam engines were powered by heated coal and were generally much too heavy for flight.

American Samuel Langley made a model airplanes that were powered by steam engines. In 1896, he was successful in flying an unmanned airplane with a steam-powered engine, called the Aerodrome. It flew about 1 mile before it ran out of steam. He then tried to build a full sized plane, the Aerodrome A, with a gas powered engine. In 1903, it crashed immediately after being launched from a house boat.

In 1903, the Wright Brothers flew, The Flyer, with a 12 horse power gas powered engine.

From 1903, the year of the Wright Brothers first flight, to the late 1930s the gas powered reciprocating internal-combustion engine with a propeller was the sole means used to propel aircraft.

It was Frank Whittle, a British pilot, who designed the first turbo jet engine in 1930. The first Whittle engine successfully flew in April, 1937. This engine featured a multistage compressor, and a combustion chamber, a single stage turbine and a nozzle.

The first jet airplane to successfully use this type of engine was the German Heinkel He 178. It was the world's first turbojet powered flight. General Electric for the US Army Air

Force built the first American jet plane. It was the XP-59A experimental aircraft.

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About inventors

Dr. Hans von Ohain and Sir Frank Whittle are both recognized as being the co-inventors of the jet engine. Each worked separately and knew nothing of the other's work. Hans von Ohain is considered the designer of the first operational turbojet engine. Frank Whittle was the first to register a patent for the turbojet engine in 1930. Hans von Ohain was granted a patent for his turbojet engine in 1936. However, Hans von Ohain's jet was the first to fly in 1939. Frank Whittle's jet first flew in in 1941.

Sir Frank Whittle was an English aviation engineer and pilot, the son of a mechanic, Frank Whittle joined the Royal Air Force or RAF as an apprentice. He joined an RAF fighter squadron in 1928 and became a test pilot in 1931. The young RAF officer was only 22 when he first thought to use a gas turbine engine to power an airplane. While often regarded as the father of modern jet propulsion systems, the young Frank Whittle tried without success to obtain official support for study and development of his ideas. He had to persist his research on his own initiative and received his first patent on turbojet propulsion in January 1930.

With private financial support, he began construction of his first engine in 1935. This engine, which had a single-stage centrifugal compressor coupled to a single-stage turbine, was successfully bench tested in April 1937; it was only a laboratory test rig, never intended for use in an aircraft, but it did demonstrate the feasibility of the turbojet concept. The modern turbojet engine used in many British and American aircraft is based on the prototype that Frank Whittle invented.

The firm of Power Jets Ltd., with which Whittle was associated, received a contract for a Whittle engine, known as the W1, on July 7, 1939. This engine was intended to power a small experimental aircraft. In February 1940, the Gloster Aircraft Company was chosen to develop the aircraft to be powered by the W1 engine - the Pioneer. The historic first flight of the Pioneer took place on May 15, 1941, with Flight Lieutenant P. E. G. Sayer as pilot.

born: June 1, 1907, Coventry, Warwickshire, Englanddied: Aug. 8, 1996, Columbia, Md., U.S.

Doctor Hans Von Ohain was a German airplane designer who invented an operational jet engine. Hans Von Ohain obtained his doctorate in Physics at the University of Göttingen in Germany and then became the junior assistant to Hugo Von Pohl, director of the Physical Institute at the University. German aircraft builder, Ernst Heinkel asked the university for assistance in new airplane propulsion designs and Pohl recommended his star pupil. Hans Von Ohain, was investigating a new type of aircraft engine that did not require a propeller. Only twenty-two years old when he first conceived the idea of a continuous cycle combustion engine in 1933, Hans Von Ohain patented a jet propulsion engine design similar in concept to that of Sir Frank Whittle but different in internal arrangement in 1934.

Hans Von Ohain joined Ernst Heinkel in 1936 and continued with the development of his concepts of jet propulsion. A successful bench test of one of his engines was accomplished in September 1937. A small aircraft was designed and constructed by Ernst Heinkel to serve

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as a test bed for the new type of propulsion system - the Heinkel He178. The Heinkel He178 flew for the first time on August 27, 1939. The pilot on this historic first flight of a jet-powered airplane was Flight Captain Erich Warsitz.

Hans Von Ohain developed a second improved jet engine, the He S.8A, which was first flown on April 2, 1941.

born: Dec. 14, 1911 , Dessau, Germanydied: March 13, 1998, Melbourne, Fla., U.S.

Introduction to Jet EnginesAn aircraft engine, or power plant, produces thrust to propel an aircraft. Reciprocating engines and turboprop engines work in combination with a propeller to produce thrust. Turbojet and turbofan engines produce thrust by increasing the velocity of air flowing through the engine. All of these power plants also drive the various systems that support the operation of an aircraft.

Turbine EnginesAn aircraft turbine engine consists of an air inlet, compressor, combustion chambers, a turbine section, and exhaust. Thrust is produced by increasing the velocity of the air flowing through the engine. Turbine engines are highly desirable aircraft power plants. They are characterized by Smooth operation

High power-to-weight ratio

Readily available jet fuel.

Types of Turbine EnginesTurbine engines are classified according to the type of compressors they use. There are

three types of compressors—centrifugal flow, axial flow, and centrifugal-axial flow. Compression of inlet air is achieved in a centrifugal flow engine by accelerating air outward perpendicular to the longitudinal axis of the machine. The axial-flow engine compresses air by a series of rotating and stationary airfoils moving the air parallel to the longitudinal axis.

The centrifugal-axial flow design uses both kinds of compressors to achieve the desired compression.

The path the air takes through the engine and how power is produced determines the type of engine. There are four types of aircraft turbine engines—turbojet, turboprop, turbofan,

and turboshaft.


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The turbojet is the oldest kind of general-purpose airbreathing jet engine. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.The turbojet engine consists of four sections: compressor, combustion chamber, turbine section, and exhaust. The compressor section passes inlet air at a high rate of speed to the combustion chamber. The combustion chamber contains the fuel inlet and igniter for combustion. The expanding air drives a turbine, which is connected by a shaft to the compressor, sustaining engine operation. The accelerated exhaust gases from the engine provide thrust. This is a basic application of compressing air, igniting the fuel-air mixture, producing power to self-sustain the engine operation, and exhaust for propulsion.

TurbopropA turboprop engine is a turbine engine that drives a propeller through a reduction gear. The exhaust gases drive a power turbine connected by a shaft that drives the reduction gear assembly. Reduction gearing is necessary in turboprop engines because optimum propeller performance is achieved at much slower speeds than the engine’s operating rpm. Turboprop engines are a compromise between turbojet engines and reciprocating power plants. Turboprop engines are most efficient at speeds between 250 and 400 mph and altitudes between 18,000 and 30,000 feet. They also perform well at the slow airspeeds required for takeoff and landing, and are fuel efficient.


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Schematic diagram showing the operation of a turboprop engine

An ATR-72, a typical turboprop aircraft.

A turboprop engine is a type of turbine engine which drives an aircraft propeller using

a reduction gear.[1]

The gas turbine is designed specifically for this application, with almost all of its output

being used to drive the propeller. The engine's exhaust gases contain little energy

compared to a jet engine and play only a minor role in the propulsion of the aircraft.[citation


The propeller is coupled to the turbine through a reduction gear that converts the high RPM,

low torque output to low RPM, high torque. The propeller itself is normally a constant speed

(variable pitch) type similar to that used with larger reciprocating aircraft engines.[citation needed]

Turboprop engines are generally used on small subsonic aircraft, but some aircraft outfitted

with turboprops have cruising speeds in excess of 500 kt (926 km/h, 575 mph).

Large military and civil aircraft, such as the Lockheed L-188 Electra and the Tupolev Tu-95,

have also used turboprop power. The Airbus A400M is powered by four Europrop

TP400 engines, which are the third most powerful turboprop engines ever produced, after

the Kuznetsov NK-12 and Progress D-27.[citation needed]

In its simplest form a turboprop consists of an intake, compressor, combustor, turbine, and

a propelling nozzle. Air is drawn into the intake and compressed by the compressor. Fuel is

then added to the compressed air in the combustor, where the fuel-air mixture

then combusts. The hot combustion gases expand through the turbine. Some of the power

generated by the turbine is used to drive the compressor. The rest is transmitted through

the reduction gearing to the propeller. Further expansion of the gases occurs in the

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propelling nozzle, where the gases exhaust to atmospheric pressure. The propelling nozzle

provides a relatively small proportion of the thrust generated by a turboprop.

Turboprops are very efficient at flight speeds below 450 mph because the jet velocity of the

propeller (and exhaust) is relatively low. Due to the high price of turboprop engines, they are

mostly used where high-performance short-takeoff and landing (STOL) capability and

efficiency at modest flight speeds are required. The most common application of turboprop

engines in civilian aviation is in small commuter aircraft, where their greater reliability

than reciprocating engines offsets their higher initial cost. Turboprop airliners now operate

at near the same speed as small turbofan-powered aircraft but burn two-thirds of the fuel

per passenger.[2] However, compared to a turbojet (which can fly at high altitude for

enhanced speed and fuel consumption) a propeller aircraft has a much lower ceiling.

Turboprop-powered aircraft have become popular for bush airplanes such as the Cessna

Caravan and Quest Kodiak as jet fuel is easier to obtain in remote areas than is aviation-

grade gasoline (avgas).[citation needed]

[edit]Technological aspects

Flow past a turboprop engine in operation

Much of the jet thrust in a turboprop is sacrificed in favor of shaft power, which is obtained

by extracting additional power (up to that necessary to drive the compressor) from turbine

expansion. While the power turbine may be integral with the gas generator section, many

turboprops today feature a free power turbine on a separate coaxial shaft. This enables the

propeller to rotate freely, independent of compressor speed. Owing to the additional

expansion in the turbine system, the residual energy in the exhaust jet is low. Consequently,

the exhaust jet produces (typically) less than 10% of the total thrust.[citation needed]

Propellers are not efficient when the tips reach or exceed supersonic speeds. For this

reason, a reduction gearbox is placed in the drive line between the power turbine and the

propeller to allow the turbine to operate at its most efficient speed while the propeller

operates at its most efficient speed. The gearbox is part of the engine and contains the

parts necessary to operate a constant speed propeller. This differs from

the turboshaft engines used in helicopters, where the gearbox is remote from the engine.[citation needed]

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Residual thrust on a turboshaft is avoided by further expansion in the turbine system and/or

truncating and turning the exhaust 180 degrees, to produce two opposing jets. Apart from

the above, there is very little difference between a turboprop and a turboshaft.[citation needed]

While most modern turbojet and turbofan engines use axial-flow compressors, turboprop

engines usually contain at least one stage of centrifugal compression. Centrifugal

compressors have the advantage of being simple and lightweight, at the expense of a

streamlined shape.[citation needed]

Propellers lose efficiency as aircraft speed increases, so turboprops are normally not used

on high-speed aircraft. However, propfan engines, which are very similar to turboprop

engines, can cruise at flight speeds approaching Mach 0.75. To increase the efficiency of

the propellers, a mechanism can be used to alter the pitch, thus adjusting the pitch to the

airspeed. A variable pitch propeller, also called a controllable pitch propeller, can also be

used to generate negative thrust while decelerating on the runway. Additionally, in the event

of an engine outage, the pitch can be adjusted to a vaning pitch (called feathering), thus

minimizing the drag of the non-functioning propeller.[citation needed]

Some commercial aircraft with turboprop engines include the Bombardier Dash 8, ATR

42, ATR 72, BAe Jetstream 31, Embraer EMB 120 Brasilia, Fairchild Swearingen

Metroliner, Saab 340 and 2000,Xian MA60, Xian MA600, and Xian MA700.[citation needed]



The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. The turbofan is

basically the combination of two engines, the turbo portion which is a conventional gas turbine engine,

[1] and the fan, a propeller-like ducted fan. The engine produces thrust through a combination of these two

portions working in concert; engines that use more jet thrust relative to fan thrust are known as low

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bypass turbofans, while those that have considerably more fan thrust than jet are known as high bypass.

Most commercial aviation jet engines in use today are of the high-bypass type, and most modern military

engines are low-bypass,

The fan serves two duties. Part of the airstream from the fan passes through the core, providing oxygen

to burn fuel to create power. However, the rest of the air flow bypasses the engine core and mixes with

the faster stream from the core at the back of the engine. As engine noise is a function of exhaust

temperature, turbofan engines are significantly quieter than a pure-jet of the same thrust. Additionally, the

efficiency of propulsion is a function of the relative airspeed of the exhaust to the surrounding air;

propellers are most efficient for low speed, pure jets for high speeds, and ducted fans in the middle.

Turbofans are thus the most efficient engines in the range of speeds from about 500 to 1000 km/h, the

speed at which most commercial aircraft operate.[2][3] Turbofans retain an efficiency edge over pure jets at

low supersonic speeds up to roughlyMach 1.6, but have also been found to be efficient when used with

continuous afterburner at Mach 3 and above. However, the lower exhaust speed also reduces thrust at

high vehicle speeds.

The vast majority of turbofans follow the same basic design with a large fan at the front of the engine with

a relatively small jet engine behind it. There have been a number of variations on this theme, however,

including rear-mounted fans where they can be easily added to an existing pure-jet design, or designs

that combine a low-pressure turbine and a fan stage in a single rear-mounted unit

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.

The inlet air that passes through a turbofan engine is usually divided into two separate streams of air. One stream passes through the engine core, while a second stream bypasses the engine core. It is this bypass stream of air that is responsible for the term “bypass engine.” A turbofan’s bypass ratio refers to the ratio of the mass airflow that passes through the fan divided by the mass airflow that passes through the engine core.

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TurboshaftThe fourth common type of jet engine is the turboshaft. It delivers power to a shaft that drives something other than a propeller. The biggest difference between a turbojet and turboshaft engine is that on a turboshaft engine, most of the energy produced by the expanding gases is used to drive a turbine rather than produce thrust. Many helicopters use a turboshaft gas turbine engine. In addition, turboshaft engines are widely used as auxiliary power units on large aircraft.

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A turboshaft engine is made up of two major parts assemblies: the gas generator and the power section.

The gas generator consists of thecompressor, combustion chambers with ignitors and fuel nozzles, and

one or more stages of turbine. The power section consists of additional stages of turbines, a gear

reduction system, and the shaft output. The gas generator creates the hot expanding gases to drive the

power section. Depending on the design, the engine accessories may be driven either by the gas

generator or by the power section.

In most designs the gas generator and power section are mechanically separate so that they may each

rotate at different speeds appropriate for the conditions. This is referred to as a free power turbine. A free

power turbine can be an extremely useful design feature for vehicles, as it allows the design to forego the

weight and cost of complex multi-ratio transmissions and clutches.

The general layout of a turboshaft is similar to that of a turboprop. The main difference is that a turboprop

is structurally designed to support the loads created by a rotating propeller, as the propeller is not

attached to anything but the engine itself. In contrast, turboshaft engines usually drive a transmission

which is not structurally attached to the engine. The transmission is attached to the vehicle structure and

supports the loads created instead of the engine. However, in practice many of the same engines are built

in both turboprop and turboshaft versions, with only minor differences.

An unusual example of the turboshaft principle is the Pratt & Whitney F135-PW-600 engine for

the STOVL F-35B - in conventional mode it operates as a turbofan, but when powering the LiftFan it

switches partially to turboshaft mode to send power forward through a shaft (like a turboprop) and partially

to turbojet mode to continue to send thrust to the rear nozzle.

Parts of a Jet Engine

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Fan - The fan is the first component in a turbofan. The large spinning fan sucks in large quantities of air. Most blades of the fan are made of titanium. It then speeds this air up and splits it into two parts. One part continues through the "core" or center of the jet engine, where it is acted upon by the other jet engine components.

The second part "bypasses" the core of the jet engine. It goes through a duct that surrounds the core to the back of the jet engine where it produces much of the force that propels the airplane forward. This cooler air helps to quiet the jet engine as well as adding thrust to the jet engine.

Compressor - The compressor is the first component in the jet engine core. The compressor is made up of fans with many blades and attached to a shaft. The compressor squeezes the air that enters it into progressively smaller areas, resulting in an increase in the air pressure. This results in an increase in the energy potential of the air. The squashed air is forced into the combustion chamber.

Combustor - In the combustor the air is mixed with fuel and then ignited. There are as many as 20 nozzles to spray fuel into the airstream. The mixture of air and fuel catches fire. This provides a high temperature, high-energy airflow. The fuel burns with the oxygen in the compressed air, producing hot expanding gases. The inside of the combustor is often made of ceramic materials to provide a heat-resistant chamber. The heat can reach 2700°.

Turbine - The high-energy airflow coming out of the combustor goes into the turbine, causing the turbine blades to rotate. The turbines are linked by a shaft to turn the blades in the compressor and to spin the intake fan at the front. This rotation takes some energy from the high-energy flow that is used to drive the fan and the compressor. The gases produced in the combustion chamber move through the turbine and spin its blades. The turbines of the jet spin around thousands of times. They are fixed on shafts which have several sets of ball-bearing in between them.

Nozzle - The nozzle is the exhaust duct of the jet engine. This is the jet engine part which actually produces the thrust for the plane. The energy depleted airflow that passed the turbine, in addition to the colder air that bypassed the engine core, produces a force when exiting the nozzle that acts to propel the engine, and therefore the airplane, forward. The combination of the hot air and cold air are expelled and produce an exhaust, which causes a forward thrust. The nozzle may be preceded by a mixer, which combines the high temperature air coming from the jet engine core with the lower temperature air that was bypassed in the fan. The mixer helps to make the jet engine quieter.

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This is a picture of how the air flows through a jet engine.

Jet engines move the airplane forward with a great force that is produced by a tremendous thrust and causes the plane to fly very fast.

All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. A compressor raises the pressure of the air. The compressor is made up of fans with many blades and attached to a shaft. The blades compress the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward.

The image above shows how the air flows through the engine. The air goes through the core of the engine as well as around the core. This causes some of the air to be very hot and some to be cooler. The cooler air then mixes with the hot air at the engine exit area.

A jet engine operates on the application of Sir Isaac Newton's third law of physics: for every action there is an equal and opposite reaction. This is called thrust. This law is demonstrated in simple terms by releasing an inflated balloon and watching the escaping air propel the balloon in the opposite direction. In the basic turbojet engine, air enters the front intake and is compressed, then forced into combustion chambers where fuel is sprayed into it and the mixture is ignited. Gases which form expand rapidly and are exhausted through the rear of the combustion chambers. These gases exert equal force in all directions, providing forward thrust as they escape to the rear. As the gases leave the engine, they pass through a fan-like set of blades (turbine) which rotates the turbine shaft. This shaft, in turn, rotates the compressor, thereby bringing in a fresh supply of air through the intake. Engine thrust may be increased by the addition of an afterburner section in which extra fuel is sprayed into the exhausting gases which burn to give the added thrust. At approximately 400 mph, one pound of thrust equals one horsepower, but at higher speeds this ratio increases and a pound of thrust is greater than one horsepower. At speeds of less than 400 mph, this ratio decreases.In a turboprop engine, the exhaust gases are also used to rotate a propeller attached to the turbine shaft for increased fuel economy at lower altitudes. A turbofan engine incorporates a fan to produce additional thrust, supplementing that created by the basic turbojet engine, for greater efficiency at high altitudes. The advantages of jet engines over piston engines include lighter weight with greater power, simpler construction and maintenance with fewer moving parts, and efficient operation with cheaper fuel


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A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet

engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets

cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill. Ramjets

require considerable forward speed to operate well, and as a class work most efficiently at speeds

around Mach 3. This type of jet can operate up to speeds of Mach 6.

Ramjets can be particularly useful in applications requiring a small and simple engine for high speed use,

such as missiles, while weapon designers are looking to use ramjet technology in artillery shells to give

added range: it is anticipated that a 120-mm mortar shell, if assisted by a ramjet, could attain a range of

22 mi (35 km).[1] They have also been used successfully, though not efficiently, as tip

jets on helicopterrotors.[2]

Ramjets are frequently confused with pulsejets, which use an intermittent combustion, but ramjets employ

a continuous combustion process, and are a quite distinct type of jet engine.


A ramjet is designed around its inlet. An object moving at high speed through air generates a high

pressure region in front and a low pressure region to the rear. A ramjet uses this high pressure in front of

the engine to force air through the tube, where it is heated by combusting some of it with fuel. It is then

passed through a nozzle to accelerate it to supersonic speeds. This acceleration gives the ramjet

forward thrust.

A ramjet is sometimes referred to as a 'flying stovepipe', a very simple device comprising an air intake, a

combustor, and a nozzle. Normally the only moving parts are those within the turbopump, which pumps

the fuel to the combustor in a liquid-fuel ramjet. Solid-fuel ramjets are even simpler.

By way of contrast, a turbojet uses a gas turbine driven fan to compress the air further. This gives greater

compression and efficiency and far more power at low speeds, where the ram effect is weak, but is also

more complex, heavier and expensive, and the temperature limits of the turbine section limit the top

speed and thrust at high speed

What is Thrust?

Thrust is the forward force that pushes the engine and, therefore, the airplane forward. Sir Isaac Newton discovered that for "every action there is an equal and opposite reaction." An engine uses this principle. The engine takes in a large volume of air. The air is heated and compressed and slowed down. The air is forced through many

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spinning blades. By mixing this air with jet fuel, the temperature of the air can be as high as three thousand degrees. The power of the air is used to turn the turbine. Finally, when the air leaves, it pushes backward out of the engine. This causes the plane to move forward.


A rocket engine, or simply "rocket", is a jet engine [1]  that uses only propellant mass for forming its high

speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's

third law. Since they need no external material to form their jet, rocket engines can be used forspacecraft

propulsion as well as terrestrial uses, such as missiles. Most rocket engines are internal combustion

engines, although non combusting forms also exist.

Rocket engines as a group have the highest exhaust velocities, are by far the lightest, but are the least

propellant efficient of all types of jet engines.

Rocket engines produce thrust by the expulsion of a high-speed fluid exhaust. This fluid is nearly always

a gas which is created by high pressure (10-200 bar) combustion of solid or liquid propellants, consisting

of fuel and oxidiser components, within a combustion chamber.

The fluid exhaust is then passed through a supersonic propelling nozzle which uses heat energy of the

gas to accelerate the exhaust to very high speed, and the reaction to this pushes the engine in the

opposite direction.

In rocket engines, high temperatures and pressures are highly desirable for good performance as this

permits a longer nozzle to be fitted to the engine, which gives higher exhaust speeds, as well as giving

better thermodynamic efficiency.

Uses of jet engines

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A JT9D turbofan jet engine undergoing maintenance on a Boeing 747 aircraft

Jet engines are usually used as aircraft engines for jet aircraft. They are also used for cruise

missiles and unmanned aerial vehicles.

In the form of rocket engines they are used for fireworks, model rocketry, spaceflight, and

military missiles.

Jet engines have also been used to propel high speed cars, particularly drag racers, with the all-time

record held by a rocket car. A turbofan powered carThrustSSC currently holds the land speed record.

Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines. These

are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing

propulsion for ships and locomotives. Industrial gas turbines can create up to 50,000 shaft horsepower.

Many of these engines are derived from older military turbojets such as the Pratt & Whitney J57 and J75

models. There is also a derivative of the P&W JT8D low-bypass turbofan that creates up to 35,000 HP.