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A SEMINAR REPORT ON AIRCRAFT PROPULSION SYSTEM PRESENTED BY:- GUIDED BY:- PREETI DWIVEDI Mr. UC JHA
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Page 1: Aircraft Propulsion System

ASEMINAR REPORT ON

AIRCRAFT PROPULSION SYSTEM

PRESENTED BY:- GUIDED BY:-PREETI DWIVEDI Mr. UC JHACOURSE: B.TechCOURSE: Mechanical Engineering 3rd yearROLL No.: 0716540040

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Aircraft Propulsion System

A SeminarSubmitted to the

Department of Mechanical EngineeringKanpur Institute of Technology,(Kanpur)

U.P Technical University, LucknowIn partial fulfillment of requirements for the award of the degree of

“Bachelor of Technology in Mechanical Engineering”GUIDED BY: Mr. UC JHA

SUBMITTED BY:-PREETI DWIVEDIRoll No.: 0716540040

DEPARTMENT OF MECHANICAL ENGINEERINGKANPUR INSTITUTE OF TECHNOLOGY

A-1, UPSIDC Industrial Area, Rooma Kanpur-208001 U.P(INDIA)

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CERTIFICATE

This certify that “Neha Singh” has worked under supervision and guidance for the seminar entitled “AIRCRAFT PROPULSION SYTEM” in partial fulfillment of the requirements for the award of the degree of B.TECH in “MECHANICAL ENGINEEING” OF U.P.T.U LUCKNOW , during academic year 2009-2010.

It is further that to the best of my knowledge, this work has not been submitted to any University in fulfillment of requirement of any degree & has not been published elsewhere. His submission for the above mentioned course is here by approved.

Mr. UC JHA(Department of

Mechanical Engineering)Kanpur Institute of Technology

DATE:………………………….

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ACKNOWLEDGEMENT

I am on cloud nine to extend my thanks to our H.O.D, Mr. SHAKUN SRIVASTAVA for providing me such a great opportunity to work on this topic

I would also like to thanks to Mr. UC JHA for his kind cooperation and providing guidance to me related to thetopic.

I would also like to forward my thanks to all faculty members of Mechanical Department who directly or indirectly helped me a lot in completion of my project.

I would also like to include here my Parents who encouraged me at every step and provided me the useful information related to the topic.

At last but not the least I thank to all my friends without whose cooperation the completion of this project would not be an easy task.

PREETI DWIVEDI

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AN INTRODUCTION TO AIRCRAFTS

Aircrafts come in many different shapes and sizes depending on the mission of the aircraft, but all modern airplanes have certain components in common. These are the fuselage, wing, tail assembly and control surfaces, landing gear , and power plant(s).

For any aircraft to fly, it must be able to lift the weight of the aircraft, its fuel, the passengers, and the cargo. The wings generate most of the lift to hold the plane in the air. To generate lift, the aircraft must be pushed through the air. The engines, which are usually located beneath the wings, provide the thrust to push the aircraft forward through the air.

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The fuselage is the body of the airplane that holds all the pieces of the aircraft together and many of the other large components are attached to it. The fuselage is generally streamlined as much as possible to reduce drag. Designs for fuselages vary widely. The fuselage houses the cockpit where the pilot and flight crew sit and it provides areas for passengers and cargo. It may also carry armaments of various sorts. Some aircraft carry fuel in the fuselage; others carry the fuel in the wings. In addition, an engine may be housed in the fuselage.

The wing provides the principal lifting force of an aircraft. Lift is obtained from the dynamic action of the wing with respect to the air. The cross-sectional shape of the wing as viewed from the side is known as the airfoil section. The platform shape of the wing (the shape of the wing as viewed from above) and placement of the wing on the fuselage (including the angle of incidence) , as well as the airfoil section shape, depend upon the aircraft mission and the best compromise necessary in the overall aircraft design.

The control surfaces include all those moving surfaces of an aircraft used for attitude, lift, and drag control. They include the tail assembly, the structures at the rear of the aircraft that serve to control and maneuver the aircraft and structures forming part of and attached to the wing.

The tail usually has a fixed horizontal piece (called the horizontal stabilizer ) and a fixed vertical piece (called the vertical stabilizer). The stabilizers provide stability for the aircraft—they keep it flying straight. The vertical stabilizer keeps the nose of the plane from swinging from side to side (called yaw ), while the horizontal stabilizer prevents an up-and-down motion of the nose (called pitch). (On the Wright brothers' first successful aircraft, the horizontal stabilizer was placed in front of the wings. Such a configuration is called a canard after the French word for "duck").

The hinged part found on the trailing edge of the wing is called the aileron . It is used to roll the wings from side to

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side. Flaps are hinged or pivoted parts of the leading and/or trailing edges of the wing used to increase lift at reduced airspeeds, primarily at landing and takeoff. Spoilers are devices used to disrupt the airflow over the wing so as to reduce the lift on an airplane wing quickly. By operating independently on each wing, they may provide an alternate form of roll control. Slats at the front part of the wing are used at takeoff and landing to produce additional lift.

At the rear of both the aileron surfaces and elevators and rudders are small moving sections called trim tabs that are attached by hinges. Their function is to (1) balance the airplane if it is too nose heavy, tail heavy, or wing heavy to fly in a stable cruise condition; (2) maintain the elevator, rudder, and ailerons at whatever setting the pilot wishes without the pilot maintaining pressure on the controls; and (3) help move the elevators, rudder, and ailerons and thus relieve the pilot of the effort necessary to move the surfaces.

The landing gear, or undercarriage, supports the aircraft when it is resting on the ground or in water and during the takeoff and landing. The gear may be fixed or retractable. The wheels of most aircraft are attached to shock-absorbing struts that use oil or air to cushion the blow of landing. Special types of landing gear include skis for snow and floats for water. For carrier landings, arrester hooks are used.

Forward motion, or thrust, is generated by a thrust-producing device or power plant to sustain flight. The power plant consists of the engine (and propeller, if present) and the related accessories. The main engine types are the reciprocating (or piston type), and the reaction, or jet, engine such as the ram jet, pulse jet, turbojet, turboprop, and rocket engine. The propeller converts the energy of a reciprocating engine's rotating crankshaft into a thrust force. Usually the engines are located in cowed pods hung beneath the wings, but some aircraft, like fighter aircraft, will have the engines buried in the fuselage.

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Other configurations have sometime been used. For instance, the Wright brothers' 1903 Flyer had pusher propellers (propellers at the rear of the plane) and the elevators at the front of the aircraft. Many fighter aircraft also combine the horizontal stabilizer and elevator into a single stipulator surface. There are many possible aircraft configurations, but any configuration must provide for the four forces needed for flight.

HISTORY OF AIRCRAFT

The ease with which birds roam the skies has always been envied by man. The dream to be able to take off to the skies is probably as old as mankind itself. However, the concept of the aircraft

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or airplane is fairly new. 

Just about 2 centuries ago man tried imitating birds by creating the omithopter. The omithopter was basically a machine with flapping wings. Unfortunately, it did not scale well. Flapping wings were great to lift light bodied birds. However, they simply did not have the power required to lift an entire machine and a human body as well. The concept was good but could not be executed.

In around 1783, another attempt at flying was made by a few daring aeronauts in lighter-than-air balloons. While this experiment succeeded in getting off the ground – literally – it did not go very far either. The aeronauts had no way to maneuver the balloon and were completely dependent on the strength and direction of the wind for their flight. The project was grounded soon after. 

It was only in 1799, that an Englishman named Sir George Clayey built the first true airplane. He conceptualized a flying machine that had fixed wings instead of flapping ones, a propulsion system and even movable control surfaces. Thus, the fundamental concept of airplanes came into existence. 

With his emphasis on lift, thrust and control Clayey designed the first glider in 1804. It had a single wing and a movable tail mounted on a universal joint. It also had an adjustable center of gravity and was the first ever aircraft of any size capable of

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flying. In 1809 Clayey expanded the glider concept and built a man-sized one with wings spanning 300 feet. A few hops were all it could manage. Around the same time Clayey also published a three part series ‘On Aerial Navigation’ in Nicholson’s Journal Of Natural Philosophy to propound his theory on flying as being a consequence of lift, propulsion and control.

While Clayey was working on his glider there were others too who were trying to fly. In 1831 Thomas Walker proposed the tandem-wing design airplane. It featured a wing whose camber was upside down. Had it been built it would have stayed firmly on the ground. In 1843 Samuel Henson proposed the first ever design for a propeller driven fixed-wing aircraft. A few years later Henson built his airplane with String fellow but it only managed brief glides.

It was after years of experimentation and research in 1849, that Clayey finally built a small glider that could lift about 80 pounds of weight. He called it the ‘boy-glider’ since it could lift a 10-year old boy for a few yards. And what followed changed the course of flying forever. In 1853, Clayey built an improved version of the boy-glider and convinced his coachman to pilot it. The coachman made a wavering and uncontrolled glide of a few hundred feet. This was the first ever truly manned flight in a fixed wing aircraft!

Soon after attempts started being made by others

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as well to build power aircrafts. In 1857 Felix Due Temple and his brother Louis flew a model monoplane with steam engine driven propellers. This was the first ever, successful flying powered aircraft.

In 1871, Penned built the planophore. It was a 20-inch long monoplane with a pusher propeller powered by a rubber band and flew 131 feet in 11 seconds. Wenham and Browning in the same year demonstrated the wind tunnel to prove that cambered wings produce more lift than other types of wings. There were continued attempts by many inventors to build successful powered aircrafts. While many important discoveries were made, no one was able to build an aircraft capable of sustained flight.

In the last two decades of the nineteenth century many discoveries and attempts were made to build an airplane. Milliard of France pointed out the necessity of training pilots to fly the various aircrafts being built. Parsons in England used a small steam engine to propel a plane for almost 300 feet. This is the first ever account of a jet aircraft.

In 1884 a significant discovery was made by Horatio Philips. He worked with cambered wings in a wind tunnel, which is the scientific foundation for modern airfoil designs as well. He also discovered that when wind blows across a curved surface, it creates a low pressure area on top of the surface

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and high pressure area below it. This is what generates the much-required lift.

In 1891 Samuel Langley began experimenting with Aerodromes and even got funding from the government. The first five attempts however, were all miserable failures.

And finally, it was around the same time, the Wright brothers start building their airplane and getting recognized for their work at Kitty Hawk. The story of the Wright brothers’ airplane reads like a true American success story! All the above events seem to be leading up to the grand finale executed and performed by Orville and Wilbur Wright.

AN INTRODUCTION OF PROPULSION

What is propulsion? The word is derived from two Latin words: pro meaning before or forwards and peeler meaning to drive.

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Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward. On airplanes, thrust is usually generated through some application of Newton's third law of action and reaction. A gas, or working fluid, is accelerated by the engine, and the reaction to this acceleration produces a force on the engine.A general derivation of the thrust equation shows that the amount of thrust generated depends on the mass flow through the engine and the exit velocity of the gas. Different propulsion systems generate thrust in slightly different ways. We will discuss four principal propulsion systems: the propeller, the turbine (or jet) engine, the ramjet, and the rocket.

Why are there different types of engines? If we think about Newton's first law of motion, we realize that an airplane propulsion system must serve two purposes. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising. And second, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate. In fact, the greater the difference between the thrust and the drag, called the excess thrust , the faster the airplane will accelerate.

Some aircraft, like airliners and cargo planes, spend most of their life in a cruise condition. For these airplanes, excess thrust is not as important as high engine efficiency and low fuel usage. Since thrust depends on both the amount of gas moved and the velocity,

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we can generate high thrust by accelerating a large mass of gas by a small amount, or by accelerating a small mass of gas by a large amount. Because of the aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large mass by a small amount. That is why we find high bypass fans and turboprops on cargo planes and airliners.

Some aircraft, like fighter planes or experimental high speed aircraft require very high excess thrust to accelerate quickly and to overcome the high drag associated with high speeds. For these airplanes, engine efficiency is not as important as very high thrust. Modern military aircraft typically employ afterburners on a low bypass turbofan core. Future hypersonic aircraft will employ some type of ramjet or rocket propulsion.

CLASSIFICATIONS OF PROPULSION SYSTEM

Propulsion systems are classified into four parts:-

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1.) TURBOJET ENGINE

2.) TURBOPROP ENGINE

3.) TURBOFAN ENGINE

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4.) RAMJET ENGINE

AN OVERVIEW OF TURBOJET ENGINE

   The turbojet uses a series of fan-like compressor blades to bring air into the engine and compress it. An entire section of the turbojet engine performs this function, which can be compared to the compression stroke of the reciprocating engine. In this section, there is a series of rotor and stator blades. Rotor blades perform somewhat like propellers in that

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they gather and push air backward into the engine. The stator blades serve to straighten the flow of this air as it passes from one set of rotor blades.

   As the air continues to be forced further into the engine, it travels from the low-compression set of rotors and stators to the high-compression set. This last set puts what we might say is the final squeeze on the air.

   The combustion chamber receives the high-pressure air, mixes fuel with it, and burns the mixture. The hot, very high-velocity gases produced strike the blades of the turbine and cause it to spin rapidly. The turbine is mounted on a shaft which is connected to the compressor. Thus, the spinning is what causes the compressor sections to function. After passing the turbine blades, the hot, highly accelerated gases go into the engine's exhaust section.

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   The exhaust section of the jet engine is designed to give additional acceleration to the gases and thereby increase thrust. The exhaust section also serves to straighten the flow of the gases as they come from the turbine. Basically, the exhaust section is a cone mounted in the exhaust duct. This duct is also referred to as the tailpipe. The shape of the tailpipe varies, depending on the design operating temperatures and the speed-performance range of the engine.

   With all the heat produced in the turbojet engine, you probably wonder how it is kept from overheating. Like most aircraft reciprocating engines, the jet is also air-cooled. Of all the air coming into the compressor section, only about 25 percent is used to produce thrust; the remaining 75 percent passes around the combustion chamber and turbine area to serve as a coolant.

AN OVERVIEW ON TURBOPROP ENGINE

The turboprop engine is an effort to combine the best features of turbojet and propeller aircraft. The first is more efficient at high speeds and high altitudes; the latter is more efficient at speeds under 400 mph and below 30,000 feet. The turboprop uses a gas turbine to turn a propeller. Its turbine uses almost all the engine's energy to turn its compressor and propeller, and it depends on the propeller for thrust, rather than on the high-velocity gases going out of the exhaust. Strictly speaking, it is not a jet. Study Figure 6-9 and note how the turbine turns the compressors and the propeller.

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The gas turbine can turn a propeller with twice the power of a reciprocating engine. Reduction gears slow the propeller below the turbine's rpm, and this must be done because of the limitations of propellers. That is, no propeller is capable of withstanding the forces generated when it is turned at the same rate as that of the gas turbine. Even so, the turboprop engine receives fairly extensive use in military and civilian aviation circles.

      In summary, aircraft turbine engines may be classified as turbojet, turbofan, or turboprop. As a group, the turbine engines have many advantages over reciprocating engines, the most obvious being the capability of higher-altitude and higher-speed performance. Vibration stress is relieved as a result of rotating rather than reciprocating parts. Control is simpler because one lever controls both speed and power. With the large airflow, cooling is less complicated. Spark plugs are used only for starting, and the continuous ignition system of reciprocating engines is not needed. A carburetor and mixture control are not needed.

   The major disadvantages have been the high fuel consumption and poor performance at low power setting, low

speeds, and low altitudes. Turboprop and turbofan developments have greatly improved aircraft turbine engines

in these areas

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AN OVERVIEW ON TURBOFAN ENGINE

The turbofan engine has gained popularity for a variety of reasons. As shown in Figure 6-8, one or more rows of compressor blades extend beyond the normal compressor blades. The result is that four times as much air is pulled into the turbofan engine as in the simple turbojet. However, most of this excess air is ducted through bypasses around the power section and out the rear with the exhaust gases. Also, a fan burner permits the burning of additional fuel in the fan airstreams. With the burner off, this engine can operate economically and efficiently at low altitudes and low speeds. With the burner on, the thrust is doubled by the burning fuel, and it can operate on high speeds and high altitudes fairly efficiently. The turbofan has greater thrust for takeoff, climbing, and cruising on the same amount of fuel than the conventional turbojet engine.

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   With better all-around performance at a lower ate of fuel consumption, plus less noise resulting from its operation, it is easy to understand why most new jet-powered airplanes are fitted with turbofan engines. This includes military and civilian types

JET ENGINE THRUST:-

   The force produced by a jet engine is expressed in terms of pounds of thrust. This is a measure of the mass or weight of air moved by an engine times the acceleration of the air as it goes through the engine. Technically, if the aircraft were to stand still and the pressure at the exit plane of the jet engine was the same as the atmospheric pressure, the formula for the jet engine thrust would be:

Weight of air in pounds per second X velocityThrust = -------------------------------------------------------------- 32.2 (normal acceleration due to gravity, in feet per second2)

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   Imagine an aircraft standing still, capable of handling 215 pounds of air per second. Assume the velocity of the exhaust gases to be 1,500 feet per second. The thrust would then be:

215 lbs of air per secondThrust = --------------------------- X 1,500 feet per second= 6.68 X 1,500 = 32.2 feet per second2

Thrust = 10,020 lbs

If the pressure at the exit plane is not the same as the atmospheric pressure and the aircraft were not standing still, the formula would be somewhat different.  

    It is not very practical to try to compare jet engine output in terms of horsepower. As a rule of thumb, however, you might remember that at 375 miles per hour (mph), one pound of thrust equals one horsepower; at 750 mph, one pound of thrust equals two horsepower.