lec 1 history of aeronautics and fundamental ideas

8/13/2019 LEC 1 History of Aeronautics and Fundamental Ideas

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History of Aeronautics and Fundamental Ideas Lecture 1

Introduction to Aerospace Engineering | Ing. Carlos Snchez

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1. The First Aeronautical Engineers

It is Kill Devil Hills, 4 miles south of Kitty Hawk, North Carolina, about 10:35 AM on

Thursday, December 17, 1903. Orville and Wilbur Wright are ready to make history. Near

the end of the starting rail, the machine lifts into the air. It is the most historic moment in

aviation history.

Above is a summary of the moment in which the Wright brothers accomplished what many

had failed before: to fly a heavier-than-air machine. It was the first genuine powered flight

of this kind. After this moment, the world of aviation took a whole new direction, since

many scientific and technical aspects of aviation were applied and controlled. However,

contrary to the common belief, the Wright brothers did not truly invent the airplane; rather,

they represent the milestone of a century of prior aeronautical research and development.

1.1 Very Early Developments

The desire to fly has always been an objective for man since history has a record. We can

witness the early Greek myth of Daedalus and his son Icarus. Imprisoned in the island of

Crete in the Mediterranean Sea, Daedalus is said to have made wings fastened with wax.

Using these wings they both flew and escaped from prison. However, Icarus, against his

fathers warnings, flew to close to the sun; the wax melted and Icarus fell to his death in the

sea.

There were also many ancient and medieval people who tried to fly by attaching wings into

their own arms, jumping from towers or roofs and flapping their arm-wings without success

and sometimes with fatal consequences.

The idea of flying took a slightly different path when people started to build wings that

flapped up and down by various mechanical mechanisms, powered by some type of human

arm, leg, or body movement. These machines are called ornithopters. Among these people

is Leonardo da Vinci, who designed many ornithopters and wrote about 500 sketches that

dealt with flight. However, human-powered flight by flapping wings was always doomed to

failure, and Da Vinci did not make important contributions to the technical advancement of

flight.

Human efforts to fly literally got off the ground on November 21, 1783, when a balloon

designed and built by the Montgolfiers in France, carrying Pilatre de Rozier and theMarquis dArlandes, ascended into the air and drifted 5 miles across Paris. The balloon was

inflated by hot air from an open fire burning in a large wicker basket underneath. This

flight, which became the first one with human passengers rose into the air and lasted for 25

minutes. However, balloons made no real technical contributions to human heavier-than-air

flight. They were the only means of human flight for almost 100 years.


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1.2 CayleyThe True Inventor of the Airplane

The modern airplane has its origin in a design created by George Cayley in 1799. This

design included a fixed wing for generating lift, another separate mechanism for propulsion

(paddles), and a combined horizontal and vertical tail for stability. Cayley engraved his

design in a silver disc, and on the other side he drew a diagram of the lift and drag forces onan inclined plane (the wing). On the past, people had been thinking that mechanical flight

had to do with flapping the wings of ornithopters, in which the flapping motion would

provide both lift and propulsion. However, Cayley is responsible for breaking with this line

of thought; he separated the concepts of lift from propulsion and started a new era of

aeronautical development that culminated with the Wright brothers success in 1903.

George Cayley is considered the father of modern aviation and the first true aeronautical

engineer.

After experimenting with model helicopters, Cayley engraved his revolutionary concept of

the fixed-wing concept. This was followed by an intense 10-year period of aerodynamicinvestigation and development. He built a whirling arm apparatus for testing airfoils; this

was simply a lifting surface (airfoil) mounted on the end of a long rod, which was rotated at

some speed to generate a flow of air over the airfoil. In Cayleys time, the whirling arm was

an important development, which allowed the measurement of aerodynamic forces and the

center of pressure of a lifting surface. However, these measurements were not very

accurate, because after a number of revolutions of the arm, the surrounding air would begin

to rotate with the device. In 1804, Cayley designed, built, and flew a small model glider.

This model glider represents the first modern-configuration airplane of history, with a fixed

wing, and a horizontal and vertical tail that could be adjusted.

Cayleys first outpouring of aeronautical results was documented in his triple paper of

1809-1810 called On Aerial Navigation,which was published in the November 1809,

February 1810, and March 1810 issues of NicholsonsJournal of Natural Philosophy. This

document is one of the most important aeronautical works in history. Cayley documented

many aspects of aerodynamics in his triple paper. It was the first published document on

theoretical and applied aerodynamics in history. In it, Cayley elaborates on his principle of

separation of lift and propulsion and his use of a fixed-wing to generate lift. He states that

the basic aspect of a flying machine is to make a surface support a given weight by the

appli cation of power to the resistance of air He notes that a surface inclined at some

angle to the direction of motion will generate lift and that a cambered surface will do this

more efficiently than a flat surface. He also states that lift is generated by a region of low

pressure on the upper surface of the wing. His triple paper also discussed flight control and

the role of horizontal and vertical tail planes in airplane stability. In 1849, he built and

tested a full-sized airplane called the boy carrier, which was a human-carrying glider that

lifted several meters off the ground when gliding down a hill. In 1852, in the Mechanics


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Magazine, Cayley published the design of a large human-carrying glider which

incorporated:

1. A main wing at an angle of incidence for lift, with a dihedral for lateral stability.2. An adjustable cruciform tail for longitudinal and directional stability.3. A pilot-operated elevator and rudder.4. A fuselage in the form of a car, with a pilots seat and a three-wheel undercarriage.5. A tabular beam and box beam construction.

These combined features were not seen until the Wright brothers designs in the 20th

century. George Cayley died in 1857. During his almost 84 years of life, he laid the basis

for all practical aviation. Unfortunately, the name of George Cayley retreated to the

background after his death. Many subsequent inventors did not make the effort to examine

the li terature before forging ahead on their own ideas (This is a problem for engineers

today).

The French aviation historian wrote: The aeroplane is a British invention: it was

conceivedby George Cayleythe greatest genus of aviationhe realized that the

problem of aviation had to be divided between theoretical researchand practical

tests


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1.3 LilienthalThe Glider

In 1891 was the year in which a human literally jumped into the air and flew with wings in

any type of controlled fashion. This person was Otto Lilienthal. He designed and flew the

first successful controlled gliders in history. Being a mechanical engineer, Lilienthal went

on to work on designing machinery in his own factory. From early childhood he wasinterested in flight and performed some youthful experiments on ornithopters of his own

design. Toward the late 1880s he became interested in fixed-wing gliders.

In 1889, Lilienthal published the book Der Vogelf lug als Grundlage der Fliegekunst

(Bird Flight as the Basis of Aviation). This is a classic in aeronautical engineering because

he studied the structure and types of birds wings and he applied the resulting aerodynamic

information to the design of mechanical flight. In 1889 Lilienthal came to the philosophical

conclusion that to learn practical aerodynamics, he had to get up in the air and experience it

himself. He wrote One can get a proper insight into the practice of f lying only by actual

flying experiments

Lilienthal used cambered airfoil shapes on the wing and incorporated vertical and

horizontal tail planes in the back for stability. Lilienthal made over 2500 successful glider

flights. The aerodynamic data he obtained were published in papers circulated around the

world. Such widespread dissemination of his results inspired other pioneers in aviation,

including the Wright brothers.

Lilienthal died after a temporary gust of wind brought Lilienthal monoplane glider to a

standstill; he stalled and crashed to the ground.


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1.4 The Wright BrothersInventors of the First Practical Airplane

The Wright brothers drew on an existing heritage that is part of every aerospace engineer

today. The Wright brothers had mechanical talents and set up a shop in which they started

fixing bicycles, and then designing and constructing their own.

Wilbur and Orville had been following Lilienthals progress intently since Lilienthals

gliders were shown in flight by photographs distributed around the world. His progress and

articles quickly made Wilbur Wright to be interested in human flight. Like several flight

thinkers before him, Wilbur approached mechanical flight by the study of bird flight. He

concluded that birds regain their lateral balance when partly overturned by a gust of

wind, by a torsion of the tips of the wings. With this, it emerged one of the most

important developments in aviation history: the use of wind twist to control airplanes in

lateral (rolling) motion. Ailerons are used on modern airplanes for this purpose. This lateral

motion was called wing warping.

Wilbur wrote to the Smithsonian Institution in 1899 to request books and materials in

aeronautics since he wanted to test his concept of wing warping. He received a vast set of

materials written by earlier pioneers of aviation. Both Wilbur and Orville digested all the

aeronautical literature, which led to the design of a biplane kite. This machine was designed

to test the concept of wing warping, which was accomplished by means of four controlling

strings from the ground. The concept worked!

The Wright brothers thought that by flying they could actually get a better feel of the air

and what needed to be done in order to design their airplanes more efficiently, with the goal

of building a heavier-than-air machine that could actually fly and be controlled. They found

an ideal spot in Kitty Hawk, North Carolina, where there were strong and constant winds.

They designed and built two gliders which were used to test the wing warping concept.

However, they started to doubt the science behind the literature they received from the

Smithsonian, and decided to embark in their own aeronautical research program. They built

a wind tunnel and tested over 200 different airfoil shapes. They designed a force balance to

measure accurately lift and drag. This period of aeronautical research and development led

the Wrights to design their glider No. 3, which was flown in 1902. It was so successful that

Orville wrote that our tables of air pressure which we made in our wind tunnel would

enable us to calculate in advance the performance of a machine. The glide r No. 3 was

designed with a vertical rudder behind the wings. This rudder was movable, and when

connected to move in unison with the wing warping, it enabled the glider to make a

smooth, banked turn. This combined use of rudder with wing warping (ailerons) was

another major contribution of the Wright brothers to flight control and aeronautics. Using

this glider the Wright brothers made over 1000 perfect flights and became highly skilled

pilots. Powered flight was the next step, and they were very close to achieve it. However,


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they faced the problem of propulsion. There was no commercial engine available for this

purpose, so they designed their own engine and propeller.

With all the major obstacles behind them, they designed and built their Wright Flyer 1

during the summer of 1903. It was similar to the glider No. 3, but included a double rudder

behind the wings and a double elevator in front of the wings. And there was the gasoline-fueled engine, driving two pusher propellers by means of bicycle-type chains.

The Wrights transported the Wright Flier 1 to Kill Devil Hills, North Carolina. On

December 17, 1903, Orville Wright was ready at the controls. A camera was adjusted to

take a picture of the machine as it reached the end of the rail. The engine was put on full

throttle, the holding rope was released, and the machine began to move. The rest is history.

On this date, the world of successful aeronautical engineering was born.

By their persistent efforts, their detailed research, and their superb engineering, the Wrights

had made the worlds first successful heavier-than-air flight, satisfying all the necessary

criteria laid down by aviation historians.


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2. Fundamental Physical Quantities of a Flowing Gas

The flow of air over the surface of an airplane is the basic source of the lifting force that

allows a heavier-than-air machine to fly. The shape of an airplane is designed to encourage

the airflow over the surface to produce a lifting force in the most efficient manner possible.

The science that deals with the flow of air is aerodynamics. Aerodynamics is applied inaircraft design, the design of rocket and jet engines, propellers, vehicles entering planetary

atmospheres from space, wind tunnels, and rocket and projectile configurations. Four

fundamental quantities in aerodynamics are pressure, density, temperature, and velocity.

2.1 Pressure

When you are inside a car in motion, if you take out your hand you can feel the air that

strikes your palm. What is happening is that air molecules are transferring some of their

momentum to the surface of your hand.

Pressure is the normal force per unit area exerted on a surface due to the time rate of

change of momentum of the gas molecules impacting on that surface.

Pressure is defined at a point in the gas or a point on a surface and can vary from one point

to another. Let

dA = an incremental area around B

dF = force on one side of dA due to pressure

()

The pressure P is the limiting form of the force per unit area where the area of interest has

shrunk to zero around the point B.


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2.2 Density

The density of a substance (including a gas) is the mass per unit volume.

Density () is a point property and can be defined as follows. Let

dv = an elemental volume around B

dm = the mass of gas inside dv

( )

2.3 Temperature

Temperature is a measure of the average kinetic energy of the particles in the gas. If KE is

the mean molecular kinetic energy, then temperature if given by KE = 3/2 kT, where k is

the Boltzmann constant.

We can visualize a high temperature gas as one in which the particles are moving randomly

at high speeds, and a low-temperature gas as one in which the motion of its particles isrelatively low.

2.4 Flow Velocity and Streamlines

Velocity is a vector quantity and has direction and speed. For a flowing gas we can note

that each region of the gas does not necessarily have the same velocity. Therefore, velocity,

like pressure, density, and temperature, is a point property.


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We can imagine an infinitesimally small particle of flow and tracing its path as it moves

with time. This traced path is called s streamline of the flow.

2.5 The Source of All Aerodynamic Forces

The previously defined aerodynamic flow quantities will help to define a flow field.

Knowledge of P, , T, and V at each point of a flow fully defines the flow field.

How can these four quantities that define a flow field can help in the design of a newairplane or the shape of a rocket engine? This is defined as follows.

The most practical consequence of the flow of air on an object such as an airplane is that it

exerts an aerodynamic force composed of two sources:

1. Pressure distribution on the surface

2. Shear stress (friction) on the surface

The force exerted by pressure on the surface acts normal to the surface, and the force

exerted by the shear stress acts tangentially to the surface and is due to the frictional effectof the flow rubbing against the surface as it moves around the body.

A primary function of aerodynamics is to predict and measure the aerodynamic forces on abody, which includes prediction and measurement of P and w(w means wing).


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2.6 Equation of State for a Perfect Gas

In the regular flight of subsonic and supersonic airplanes the air in the atmosphere behaves

very much like a perfect gas. Looking closely at the molecular level, a gas is a collection

of particles in random motion, where each particle is separated a long distance away from

its neighboring particles. Each molecule has an intermolecular force field, which comesfrom the complex interactions of the electromagnetic properties of the electrons and

nucleus. The intermolecular force field of a particle extends a long distance and

changes from a strong repulsive force at close range to a weak attractive force at long

range.If the molecules are close (high densities), their motion can be greatly affected by

the intermolecular force field. If they are separated a long distance, the neighboring

particles only feel the tail of the weak attractive force. Therefore,

A perfect gas is one in which intermolecular forces are negligible.

The particles of air in a room are separated an average of 10 molecular diameters from any

other. The same applies to the air around ordinary subsonic and supersonic vehicles.

The equation of state is P = *R*T

Where R is the specific gas constant and its value varies from one type of gas to another.

For normal air it is R = 287 J/kg*K

To measure the deviation of an actual gas in nature from perfect gas behavior the modified

Berthelot equation of state is used:

Where aand bare constants of the gas. Therefore, the deviation from a perfect gas behavior

becomes smaller when pressure decreases and temperature increases. If pressure is high, the

intermolecular forces become important and the gas behaves less like a perfect gas.

However, if the temperature increases, the molecules move faster and their distance from

each other is larger, which make the gas behave more like a perfect gas. Furthermore, if air

is heated to above 2500K, oxygen begins to dissociate into oxygen atoms; if it is heated to

above 4000K, nitrogen begins to dissociate and air becomes a chemically reacting gas,

where its chemical composition becomes a function of pressure and temperature. In such a

case, the specific gas constant R becomes a variable, R = R(P, T). The equation of state is

still valid, but it is no longer a constant. This behavior occurs in very high speed flight such

as atmospheric reentry.


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2.7 Units

For units it will be used both the SI system and the English system. However, the majority

of the problems in homework and exams will be in SI units.

Unit SI System English System

P N/m2 lb/ft

2 1 atm = 2116 lb/ft

2

kg/m3 slugs/ft

3

T K R

R (for air) 287 J/kg*K 1716 ft*lb/slug R

2.8 Specific Volume

Specific volume is the inverse of density. It is volume per unit mass. By definition,

v = 1/

From the equation of state,

P = *R*T = (1/v)*R*T

Units for specific volume are m3/kg and ft

3/slug.

lec 1 history of aeronautics and fundamental ideas

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