Elements of-aeronautics

KIT – KALAIGNAR KARUNANIDHI
INSTITUTE OF TECHNOLOGY
( Approved by AICTE, Affiliated to Anna University, Chennai )
KANNAMPALAYAM, COIMBATORE – 641 402.
Department of Aeronautical engineering
Course Material
AE 6302 – ELEMENTS OF AERONAUTICS

UNIT – I
Historical Evaluation
1. Biplanes:
Type of airplane in which two wings are placed one above the other to increase the lift
produced with minimum speed. (e.g) Wright Flyer – I
2. Monoplanes
Type of airplane in which only one wings will be there placed along the lateral axis of
aircraft.(e.g) most modern air crafts are monoplanes.
3. Biplane interference:
The condition in a biplane in which the high pressure on under surface of upper wing low
pressure on upper surface of lower using, results in interference between two wings. Thus lift is
reduced.
4. An ornithopter:-
The concepts of wings flapped up and down by various mechanical mechanisms, powered by
some type of human arm, leg or lady movement was given by Leonardo da vinci in late 15th
century. This is termed as ornithopter.
5. Triplane:
Type of airplane in which three wings are placed one above the other. The wings are called
as low wing, mid wing and shoulder wing.
6. Differentiate between Monoplanes and Biplanes.
Monoplanes Biplanes
a) Only one wing is present.
b) Lift produced will be loss compared to
biplane
c) Biplane interference will not occur
Two wings placed one above other. They are
a) Upper wing and
b) Lower wing lift produced will be high but
not exactly double the monoplane
Biplane interference will occur
7. Differentiate between Lighter than Aeroplanes and Heavier than Aeroplanes.
Lighter than Aeroplanes Heavier than Aeroplanes
Based on Archimedes principles.
Pay load is very less control and manocurve is
tedius
Based on lift produced by a moving body.
Payload is very high control and manocurve is
simple.

Engines are not used for propulsion Engines are used for propulsion.
8. What is the difference between Airmen and Chauffeurs?
Airmen Chauffeurs
a) Air man are those who recognized the need
to get up in the air, fly around with gliders
and obtain the feel of an airplane before
engine was used for powered flight.
b) They are interested in flight control in air
a) Chauffeurs are those who just makes
engine and fix, in air frame and gets into air.
b) They interested in thrust and light.
9. Whirling arm apparatus.
Whirling arm apparatus is the one which is used by cay by to test air foils. This is nothing
but a airfoil mounted on the end of a long rod, which was rotated at some speed to generate a flow
of air over airfoil, which allowed the measurement of aerodynamic forces and centre of pressure
on lifting surface.
10. Glider:
Gliders are un powered airframes, which has very large lift producing surfaces and less weight.
11. Four forces acting on an aero plane.
i) lift - Perpendicular to direction of relative wind
ii) Drag - Parallel to direction of relative wind
iii) Thrust - produces forward motion
iv) Weight - force of gravity
12. Lift:
A force on airplane which is perpendicular to the direction of relative wind and opposite in
the direction of weight in level flight.
13. Drag:
A force acting on aero plan, which is parallel to the direction of relative wind a opposite
to thrust direction under level flight.
14. Composition of aluminum alloy used in modern aircraft.
i) Duralumin ii) Jn Bocing 747
Al-93.5%
Cu-4.4%
Mn-1.5%
Mg-0.6%
Al-80%
Steel-17%
Titanium-3%
15. How aircrafts propelled during early days?
Some basic propulsion methods are
i) Paddle wheel mechanism

ii) Steam engine
iii) Flapper using type
iv) Reciprocating engine, etc.
PART - B
DEVELOPMENTS IN PROPULSION AND MATERIALS:-
Human effort to fly literally got off the ground on November 21, 1783, when a balloon
carrying Pilatre de Rozier and Marquis d‟ Arlandes ascended into the air and drifted 5 miles across
Paris. The balloon was inflated and buoyed up by hot air from an open fire burning in a large
wicker basket underneath. It was the first time humans had been lifted off the ground for a
sustained period of time.
In 1799, Sir George Cay by used a paddle wheel mechanism for the propulsion of his aero
plane. He also stated that lift is generated by a region of low pressure on the upper surface of
using.
In 1810, the first successful airship, propelled by a steam engine was built.
In 1849, he built and tested a full – size airplane of trip lane type called “The Boy carrier”
and the vertical and horizontal fail surfaces are made and propulsive mechanism is flapper wing
type.
William Samuel Hendon (1812-1888) was contemporary of cay by. In April 1843, he
published in England a design for a fixed using airplane powered by steam engine driving two
propelled called the aerial steam carriage. In this type the engine is inside a closed fuselage,
driving two propellers.
In 1857, Felix Du Temple made the first successful powered model airplane in monoplane
type swept. Forward wings and was powered by lock work.
In 1874, In Temple achieved the world first powered take off by a piloted, full size airplane;
it was powered by some type of hot air engined.
In 1884 Alexander F. Mozhaiski designed a steam powered monoplane,
In 1893, lilienthal build a powered machine; however, the prime mover was carbonic acid
gas motor that twisted six states at each using tip, obviously an ornithoptes type ideal to mimic the
natural mode of propulsion for birds.
In 1897, Hawk was designed with 4hp engine weighing about 40lt, driving a 5-ft diameter
propeller by pitcher.
In 1905 samuel Pierpont Langley designed and builded a series of powered aircraft which
finally culminated in two attempted piloted flights.

Cay lay build a large whirling arm, powered by a steam engine, with which he made force
test on airfoils. He then build nearly 100 different types of rubber – band – powered model
airplanes, graduating to steam – powered models in 1892.
It had two propellers between the wings, powered by a 1-hp steam engines of langley‟s own
design.
Departing from his earlier use of steam Langley correctly decided that the gasoline fueled
engine was the proper prime mover for air craft. The first commissioned Stephan Balzer of New
York to produce such an engine. The resulting engine produced 52.4 hp and yet weighted only
208 lt.
Using 1.5-hp gasoline fueled engine he made successful flight with quarter scale size.
In 1903, Willbar‟s build theirs own engine of 12 hp and 200 lp weight.
In Wright flyer I, the spectacular gasoline fueled Wright engine, driving two pushes
propellers. By means of bicycle type chains.
In 1905, the advanced propellers are used in flyer III
During 1905 to 1908, wright‟s atleast would have designed six new engines.
In 1909, the European designers were quick to adopt the long, slender shape wright‟s
propeller, different from wide paddle like shape
The efficiency of propeller used to 76%
DEVELOPMENTS IN STRUCTURE OVER THE YEARS:-
The idea of flying come to human from birds. The early greek myth of daedalus and his son
I carus. Imprisoned on the Island of crete. Daedalus and his son made flying model both escaped
from prison.
Leonards da vinci have designed many or nithopters during 15th
century it is a human
powered flight by flapping wing.
George cayley in 1799 gave concept of fixed using for generating lift, a paddles for a
propulsion and combined horizontal and vertical (cruciform) tail for stability. In 1804, he built a
whirling – arm apparatus for testing air foils similar to wind tunnels and also designed a model
glider. He represented first modern – configuration of air plane with a fixed wing and horizontal
and vertical tail.
In 1809 cayley explained that when 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.
For first time in history that lift is generated by a region of low pressure on the upper surface of the
using.

The first successful air ship, propelled by a steam by a steam engine, was built by Henri Gifford
in Paris in 1852 in 1849, he built and tested a full – size airplane.
The modulation are
i) A main using at an angle of incidence for lift, with a dihedral for lateral stability
ii) An adjustable cruciform tail for longitudinal directional stability.
iii) A pilot – operated elevator and rudder
iv) A fuselage in the form of a car, with a pilot‟s seat and three – wheel under carriage
v) A tubular beam and box beam construction.
vi) Tricycle landing gear
In 1857, Felix Du temple made a monoplane with swept- forward wings and in 1884 he made
steam powered plane
In 1866, Francis H. wenhem published paper, in that most of the lift of a wing was obtained
from the portion near the leading edge and using with high aspect ratio was the most efficient for
producing lift.
In 1891, otto lilienthal designed and flow the first successful controlled gliders in history with
birdlike platform of the using lilienthal used cambered (carried) airfoil shaped on the using and
incorporated vertical and horizontal tail planes in the back for stability.
In 1896, Chanute designed a hang gliders and biplane glider which introduced by the effective
platt truss method of structural rigging.
In 1903, Langley stepped directly to the full size airplane. He mounted this on tandem winged
aircraft on a catapult to provide an assisted take off.
In willur‟s model the use of using twist to control airplane in lateral (rolling) motion and aibrons
are used on modern airplanes for this purpose, willur wined the term using warping and led to their
first aircraft, a trip lane kite with using span of 5 ft in 1899.
A full size biplane glider was ready by September 1900, it had 17 ft using span and a horizontal
elevator in front of the wings, and was usually flows on strings from the ground.
In 1901, Glider 2 was made of larger using span of 22-ft using span.
In 1902, they made about 200 different airfoil shapes.
In September 20, 1902 number 3 glider of biplane type flow with wing span of 32-ft 1- inch, with
modification in vertical rudder behind the wings.
In 1903, they made wright flyer I of using span 40 feet 4 inch and used double rubber behind
the wings and a double elevator in front of the wings.

In 1904, wright flyer II made with a smaller using camber (airfoil curvature) and a more
powerful and efficient engine.
In 1905, with more progress flyer III with slightly lower using area, increased airfoil camber,
large biplane elevator, double rubber and improved propellers was made.
In 1909, Henri Farman III introduced flap like ailerons at the trailing edge near wing tips,
ailerons quickly became the favored mechanical means for lateral control, continuing to present
day.
Thus the structure of air craft have attained several stages of improvements and made into a
fine structure with high rigid strength and very less drag for effective airborne of air craft.
MATERIALS:
Some of the materials commonly used in flight structures.
Aluminium:
It is the most widely used material in aircraft structures. Modern commercial transports such
as Boeing 749 use aluminum for about 80% of the structure. Al in reality formed and machined
has reasonable cost is corrosion – resistant, and has an excellent strength – to – weight ratio. In
its pure from Al in two self for aircraft use. Therefore alloys of Al are used, the most common being
Al 2024, an alloy consisting of 93.5%. Al, 4.4% cu, 1.5% Mn and 0.6% Mg. this alloy is also called
duralumin. The first metal covered airplanes were designed by Miyo Junkens. In 1914. He finet
used all steel, which proved to be too heavy, In 1915, he turned to the use of duralumin.
Steel:-
For a typical commercial transport, steel makes up about 17% of the structure. If in used in
those areas requiring very high strength, such as wing attachment fittings, landing gears, engines
fittings, and flap tracks steel in an alloy of iron and carbon, typical steel alloys have about 1%
carbon. Stainless steel is an alloy of steel and chromium that has good corrosion resistant
properties.
Titanium:
Titanium has a better strength- to – weight ratio than aluminum and retains its strength at
higher temperatures however it is hard to form and machine and in expensive, costing about 5 to
10 times more than Al. But some supersonic air craft have to use titanium because of the high skin
temperatures due to aerodynamic heating.
High temperature Nickel alloys:
The hypersonic airplanes require advanced, high – temperature materials to withstand the
high rates of aerodynamic heating at hypersonic speeds. Some nickel – based alloys are capable
of withstanding the temperatures associated with moderate hypersonic speeds.

The hypersonic aircraft X-15 made by usage of inconel, a nickel – based alloy.
Composites:
Composites materials can yield at least a 25% reduction in weight. Composites are quite
different from metals, in both their composition and physical properties.
Generally composites mean “made up of distinct components”.
For example, the nockhead – martin F-22 has 28% of its structure made up of composite
material with 33% Al, 24% Ti, 5% steel and 10% miscellaneous.
Biplanes:
Biplanes is plane using two aerofoils one placed above other. It is naturally come from birds
but the biplane idea seems to be a purely man made invention, though some naturalists claim that
there are biplane insects. At any rate of, the first plane to fly was a biplane, so the idea is at least
as old as the history of flight.
A very large wing areas are required for flight, and advantage of the biplane was that this
large area could arranged in a more compact fashion, making the finished aeroplane more
convenient to handle both on the ground and in the air. The biplane structure seemed more suited
than the monoplane to give as what we most required. Strength without weight so far the biplane
seemed to have all the advantages why then, has it proved the loser in the long run.
It is as a wing, as an aerofoil, that the monoplane has always been superior. Remembering
how the pressure is distributed round a wing section let us put two such section let us put two such
sections together, one above the other, and observe the effect. The increase pressure on the
under surface of the upper wing is not to so effective as it was when it was alone – still less is the
decreased pressure. Above the lower wing so effective; thus both upper and lower wings suffer.
There is in fact, an interference between the two wings and this is called bipolar interference.
Another way of thinking of it is to consider the induced drag, which is greater on a biplane – with
its four wing tips-than on a monoplane of the same wing area and so the overall lift 1 drag ratio of
the monoplane is better than that of the bipolar.

Fig.
The biplane enthusiasts full of confidence owing to the structural superiority of the bipolar
persistently endeavored to minimize this disadvantage.
To eliminate the interference by staggering the planes. That is separating them horizontally
rather than vertically.
 When the leading edge of the upper plane was infront of the leading edge of the lower
plane it was called forward (or) positive stagger.
 When behind it, it was called back ward (or) Negative stagger.
Wright Brothers contribution and their development in obtaining their successful flight
Willur and orille wright – Inventors of the first practical airplane they are called the premier
aeronautical engineers of history.
Willur look up the study of bird flight as a guide on the path toward mechanical flight. Willur
wrote to smithronian institution in May 1899 for papers and books on aeronautics in turn her
received a brief bibliography of flying. This led to their first air craft, a biplane kite with a using
spane of 5 ft in August 1899.
A full size biplane glider was ready by September 1900 and was flown in October of that year
at kity Hawk. It had a 17-ft using span and a horizontal elevator in front of the wings and was
usually flown on strings from the ground.
Willur and orbille preceded to build their number 2 glider moving their base of operations to kill
Devils Hills, 4 miles south of kitty Hawk, they tested number 2 during July and August of 1901.
This new glider was somewhat larger, with a 22-ft wing span. As with all wright machines, it has a
horizontal elevator in front of the wings.
The wrights were not loose to being satisfied with their results when they returned to Dayton
after their 1901 tests with the number 2 glider, both brothers began to suspect the existing data
that appeared in the aeronautical literature.
Between September 1901 and August 1902 the wrights under took a major program of
aeronautical research. They built a wind tunnel in their bicycle shop in Dayton and tested more
than 200 different airfoil shapes. They designed a force balance to measure accurately the lift a
drag.
The papers of Wilbur and orvile wright in 1901 led to their number 3 glider, which was flown in
1902. It was so successful. It first flew at kill Devil Hills on September 20, 1902. It was a biplane
glider with a 32 ft 1-inch wing span, the largest of wright gliders to data.
After several modifications, the wrightor added a vertical ladder behind the wings. During 1902,
they made more than 1000 perfect flights. They set a distance record of 622.5 ft and a duration

record of 26s. In the process, both Wilbur and orville become highly skilled and proficient pilots,
something‟s that would later be envied world wide.
They designed and burst their own engine during the winter months of 1903 It produced 12hp
and weighed about 200lt. moreover, they conducted their own research which allowed them to
design an effective propeller.
Wilbur and orville built their flyer I from scratch during the summer of 1903. After orville‟s first
flight on that December 17, three more flight were made during the morning, the last covering 852
if an remaining in the air for 59s the In may 1904, their second powered machine, the Wright flyer
II was ready this air craft had a smaller wing camber and more powerful and efficient engine. More
progress was made in 1905. The Wright flyer III was ready by June. The wing area was slightly
smaller than that of the flyer II, the airfoil camber was increased back to what it had been in 1903.
biplane elevators was made larger and was placed.
Composites and advanced materials in aircraft
The Lockheed F-22 uses composites for the atleast a third of its structure.
For many years, aircraft designers could propose theoretical designs that they could not
build because the materials needed to construct them did not exist (The term “unobtainium” is
sometimes used to identify materials that are desired but not yet available.) For instance, large
spaceplanes like the Space Shuttle would have proven extremely difficult, if not impossible, to
build without heat – resistant ceramic tiles to protect them during re – entry. And high – speed
forward-swept-wing airplanes like Grumman‟s experimental X-29 or the Russian Sukhoi S-27
Berkut would not have been possible without the development of composite materials to keep their
wings from bending out of shape.
Composites are the most important materials to be adapted for aviation since the use of
aluminium in the 1920s. composites are materials that are combinations of two or more organic or
inorganic components. One material serves as a “matrix,” which is the material that holds
everything together, while the other materials serves as a reinformcement, in the form of fibres
embedded in the matrix. until recently, the most common matrix materials were ”thermosetting”
materials such as epoxy, bismaleimide, or polymide. The reinforcing materials can be glass fibre,
boron fibre, carbon fibre, or other more exoitic mixtures.

Fiberglas is the most common composite material, and consists of glass fibres embedded
in a resin matrix. Fiberglas was first used widely in the 1950s for boats and automobiles, and
today most cars have fiberglass bumpers covering a steel frame Fiberglas was first used in the
boeing 707 passenger jet in the 1950s, where it comprised about two percent of the structure. By
the 1960s, other composite materials became available, in particular boron fibre and graphite,
embedded in epoxy resins. The U.S. Air Force and U.S. Navy began research into using these
materials for aircraft control surfaces like ailerons and rudders. The first major military production
use of boron fibre was for the horizontal stabilizers on the Navy‟s F-14 Tomcat interceptor. By
1981, the British Aerospace-McDonnell Douglas AV-8B Harrier flew with over 25 percent of its
structure made of composite materials.
Making composite structures is more complex than manufacturing most metal structures.
To make a composite structure, the composite material, in tape or fabric form, is laid out and put in
a mould under heat and pressure. The resin matrix material flows and when the heat is removed, it
solidifies. It can be formed into various shapes. In some cases, the fibres are wound tightly to
increase strength. One useful feature of composites is that they can be layered, with the fibres in
each layer running in a different direction. This allows materials engineers to design structures that
behave in certain ways. For instance, they can design a structure that will bend in one direction,
but not another. The designers of the Grumman X-29 experimental plane used this attribute of
composite materials to design forward – step wings that did not bend up at the tips like metal
wings of the same shape would have bent in flight.
The greatest value of composite materials is that they can be both lightweight and strong.
The heavier an aircraft weighs, the more fuel it burns, so reducing weight is important to
aeronautical engineers.
Despite their strength and low weight, composites have not been a miracle solution for
aircraft structures. Composites are hard to inspect for flaws. Some of them absorb moisture. Most
importantly, they can be expensive, primarily because they are labour intensive and often require
complex and expensive fabrication machines. Aluminium, by contrast, is easy to manufacture and
repair. Anyone who has ever gotten into a minor car accident has learned that dented metal can
be hammered back into shape, but a crunched fiberglass bumper has to be completely replaced.
The same is true for many composite materials used in aviation.
Modern airliners use significant amounts of composites to achieve lighter weight. About ten
percent of the structural weight of the Boeing 777, for instance, is composite material. Modern
military aircraft, such as the F-22, use composites for at least a third of their structures, and some
experts have predicted that future military aircraft will be more than two – thirds composite
materials. But for now, military aircraft use substantially greater percentages of composite
materials than commercial passenger aircraft primarily because of the different ways that
commercial and military aircraft are maintained.
Aluminum is a very tolerant material and can take a great deal of punishment before it fails.
It can be dented or punctured and still hold together. Composites are not like this. If they are
damaged, they require immediate repair, which is difficult and expensive. An airplane made
entirely from aluminium can be repaired almost anywhere. This is not the case for composite
materials, particularly as they use different and more exotic materials. Because of this, composites

will probably always be used more in military aircraft, which are constantly being maintained, than
in commercial aircraft, which have to require less maintenance.
Thermoplastics are a relatively new material that is replacing thermosets as the matrix
material for composites. They hold much promise for aviation applications. One of their big
advantages is that they are easy to produce. They are also more durable and tougher than
thermosets, particularly for light impacts, such as when a wrench dropped on a wing accidentally.
The wrench could easily crack a thermoset material but would bounce off a thermoplastic
composite material.
In addition to composites, other advance materials are under development for aviation.
During the 1980s, many aircraft designers became enthusiastic about ceramics, which seemed
particularly promising for lightweight jet engines, because they could tolerate hotter temperatures
than conventional metals. But their brittleness and difficulty to manufacture ewer major draw
backs, and research on ceramics for many aviation applications decreased by the 1990s.
Many modern light aircraft are constructed in composite material such as this Glasair
Aluminium still remains a remarkably useful material for aircraft structures and metallurgists
have worked hard to develop better aluminium alloys (a mixture of aluminium and other materials).
In particular, aluminium-lithium is the most successful of these alloys. It is approximately ten
percent lighter than standard aluminium. Beginning in the later 1990s it was used for the Space
Shuttle‟s large External Tank in order to reduce weight and enable the shuttle to carry more
payload. Its adoption by commercial aircraft manufacturers has been slower, however, due to the
expense of lithium and the greater difficulty of using aluminium lithium (in particular, it requires

much care during welding). But it is likely that aluminium lithium will eventually become a widely
used material for both commercial and military aircraft.
Aircraft Structural Design
Introduction
Although the major focus of structural design in the early development of aircraft was on
strength, now structural designers also deal with fail – safety, fatigue, corrosion, maintenance and
inspectablility, and producability.
EARLY DEVELOPMENTS IN AERODYNAMICS
Aerodynamics, literally “air in motion,” is the branch of the larger field of fluid dynamics that
deals with the motion of air and other gaseous fluids. It concerns the forces that these gaseous
fluids, and particularly air, exert on bodies moving through it. Without the science of
aerodynamics, modem flight would be impossible.
The word “aerodynamics” itself was not officially documented until 1837. However, the
observation of fluids and their effect on objects can be traced back to the Greek philosopher.
Aristotle in 350 B.C. Aristotle conceived the notion air has weight and observed that a body
moving through a fluid encounters resistance.
Archimedes another Greek philosopher, also has a place in the history of aerodynamics. A
hundred years later, in 250 B.C, her presented his law of floating bodies that formed a basic
principle of lighter-than-air vehicles. He stated that a fluid –either in liquid or a gaseous form – is
continuous, basically restating Aristotle‟s theory of a hundred years earlier. He comprehended that
every point on the surface of a body immersed in a fluid was subject to some force due to the fluid.
He stated that, in a fluid, “each part is always pressed by the whole weight of the column
perpendicularly above it. “He observed that the pressure exerted on an object immersed in a fluid
is directly proportional to its depth in the fluid. In other words, the deeper the objects is in the fluid,
the greater the pressure on it. Deep-sea divers, who have to accustom themselves to changes in
pressure both on the way does into the sea and again on the way up to the surface, directly
experience this phenomenon.
Leonardo da vinci sketched various flow fields over objects in a flowing stream.

A direct proportional relationship means that it one part increases, the other will increase by
the same factor. Physicists and mathematicians use the Greek letter alpha ( ) to denote such a
relationship. Applied to pressure and depth, if the depth of an object is doubled, the pressure
exerted on the object would double as well (Depth Pressure). The opposite would also be true.
As altitude increases (negative depth), pressure decreases. Archimedes also demonstrated that,
in order to set a stagnant fluid in motion, the pressure on the fluid must be increased or
decreased. The resultant movement will take place in the direction of the decreasing pressure.
The next contribution to aerodynamics did not occur until the end of the 1400s. In 1490, the
Italian painter, sculptor, and thinker Leonardo da vinci began documenting his aerodynamic
theories and ideas for flying machines in personal notebooks. An avid observer of birds and
nature, he first believed the birds fly by flapping their wings, and thought that this motion would
have to occur for manmade aircraft to rise. He later correctly concluded that the flapping of the
wings created forward motion, and this forward motion allowed air to pass across the bird‟s wings
to create lift. It was the movement of the wing relative to the air and the resulting reaction that
produced the lift necessary to fly. As a result of his studies, he designed several ornithopters –
machines that were intended to copy the action of a bird‟s wing with the muscle power being
supplied by man. But these designs did not leave the drawing board. His other designs included
those for the first helicopter and a parachute.
Leonardo da Vinci’s ornithoptger design
Leonardo noticed another phenomenon that would prove useful in the study of
aerodynamics. He noticed that water in a river moved faster- at a greater velocity- where the river
narrowed. In numerical terms, the area of a cross section of a river multiplied by the velocity of the
water flowing through that section equals the same number at any point in the river. This is known
as the law of continuity (Area Velocity=constant or AV=constant). The law of continuity
demonstrates the conservation of mass, which is a fundamental principal in modem
aerodynamics. He also observed the different ways in which a fluid flowed around and object-
called a flow field.
Leonardo also stated that the aerodynamic results are the same if an object moves through
the fluid at a given velocity or if the fluid flows past the object at rest at the same velocity. This
became known as the “wind tunnel principal.” For example, the results are the same
aerodynamically whether a runner moves at 10 miles per hour in calm air and if the wind is
blowing at 10 miles per hour past a stationary person. He also determined that drag on an object

is directly proportional to the area of the object. The greater the area of an object, the greater the
drag. Further, Leonardo pointed out the benefits of streamlining as a way to reduce an object‟s
drag.
However, Leonardo‟s notebooks were not discovered until centuries later, and his ideas
remained unknown until the 19th
century.
Scientists working in the 17th
century contributed several theories relating to drag. The
Italian mathematician and inventor Galileo Galilel built on Archimedes‟ work and discovered that
the drag exerted on a body from a moving fluid is directly proportional to density of the fluid.
Density describes the mass or an object per unit volume. A very dense fluid produces more drag
on objects passing through it than a less dense fluid. The density of air (a fluid) changes with its
distance from the Earth‟s surface, becoming less dense the farther it is above the Earth‟s surface
and, as such, exerting less pressure. Thus, an object passing through air high above the Earth‟s
surface will encounter less drag than the same object passing through air close to the Earth‟s
surface.
In 1673, the French scientist Edme Manotte demonstrated that drag is proportional to the
square of the velocity of an object (D V2
). Dutch mathematician Christiaan Huygens had been
testing this theory since 1669 and published his results with the same conclusion in 1690. The
English scientist and mathematician Sir Isaag Newton presented a derivation of the drag equation
of a body in 1687: Drag SV2
(where is density and S is cross – sectional area of the body.)
In 1738, the Dutch scientist Daniel Bemouli published his findings on the relationship
between pressure and velocity in flowing fluids. Other scientists used his research as a foundation
for further research. The French scientist Jean le Rond d‟Alembert, an associate of Benmouli‟s,
introduced a model for fluid flows and an equation for the principle of the conservation of mass. He
further presented the idea that velocity and acceleration can vary between different points in fluid
flow. (Remember that air is a fluid).
Benjamin Robins, the British mathematician, proved that air resistance was a critical factor
in the flight of projectiles in 1746. His apparatus consisted of a whirling arm device in which
weight (M) turned a drum and rotated the test object (P).
Swis mathematician Leonha.d Euler, also an associate of Bernoulli, derived equations from
Bemouili‟s and d‟Alembert‟s principles. The most famous of these became known us “Bemoulli‟s
Principle.” It states that, in a flowing fluid, as velocity increases, pressure decreases. This became

a key concept for understanding how lift is created. Euler also introduced equations for fluid flow,
though at the time they could not be solved and applied.
Italian mathematician Joseph Lagrange and French mathematician Pierre-Simon Laplace
studied Euler‟s findings and tried to solve his equations. In 1788, Lagrange introduced a new
model for fluid flow as well as new equations for calculating velocity and pressure. In 1789,
Laplace developed an equation that would help solve Euler‟s equations. It is still used in modem
aerodynamics and physics. Laplace also successfully calculated the speed of sound.
In addition to these theoretical advancements, experiments in aerodynamics were also
producing more practical results. In 1732, the French chemist Henri Pilot invented the Pilot tube, a
device that enables the calculation of velocity at a point in a flowing fluid. This would help explain
the behavior of fluid flow. The English engineer Benjamin Robins performed experiments in 1746
using a whirling arm device and a pendulum to measure drag at low and high speeds.
In 1759, the English engineer John Snmeaton also used a whirling arm device to measure
the drag exerted on a surface by moving air. He proposed the equation D=kSV2
, where D is the
drag, S is the surface area, V is the air velocity, and k is a constant, which Smeaton claimed was
necessary in the equation. This constant became known as Smeatorn‟s coefficient, and the value
of this constant was debated for years. Those making the first attempts at flight, including the
Wright brothers, used this coefficient. The French scientist Jean-charies Borda published the
results of his own whirling arm experiments in 1763. Borda verified and proposed modifications to
current aerodynamic theories and was able to show the effect that the movement of one object
had on another nearby object.
Sir George Cayley of England is generally recognized at the father of modem
aerodynamics. He understood the basic forces acting on a wing and built a glider with awing and a
tail unit that new successfully, he realized the importance of the wing angle of attack and that
curved surfaces (camber) would produced more limit than flat one. Stability in his designs came
with the use of dihedral – an important concept still used today He first made public the notion that
a fixed-wing aircraft was possible in 1804 in his major publication, “On Aerial Navigation,” which
described the theoretical problems of flight.
The contributions of all of these thinkers, mathematicians, and scientists are part of the
foundation of the science of aerodynamics. They paved the way for the aerodynamic
developments that would occur during the nineteenth century, as well as for those who would
eventually achieve heavier than air flight.

UNIT – II
Aircraft and Rocket Configurations
1. List out the different classifications of flight vehicles.
2. Differentiate between a gyroplane and a helicopter.
Helicopter Gyroplane
Rotor power driven Rotor not power driven
3. Explain how an airship or balloon is kept in the air.
By Archimedes principle, when a body is immersed in a fluid, a force acts upwards upon if
helping to support its weight, and this upwards force is equal to the weight of the fluid which is
displaced by body.
4. State the two kinds of aircraft.
5. What are the basic instruments of flying?
1. Altimeter
AIRCRAFT
LIGATER – THAN – AIR HEAVIER – THAN – AIR
Power – Driven Non-power – Driven Man-power – Driven
AIRCRAFT
LIGHTER – THAN – AIR HEAVIER – THAN – AIR

2. Air speed indicator
3. Mach Indicator
4. Turn and slip indicator
5. Artificial horizon.
6. What are the three main control surfaces used in an aircraft?
Elevator
Rudder
Aileron
7. What is the purpose of elevator?
The elevators are control surfaces that control the nose up – and – down pitching motion.
When the deflected downward the cost on the tail is increased, pulling the tail up and the nose of
the airplane down.
8. Name the secondary control surfaces used in an aircraft.
 Slats
 Flaps
 Spoilers
 Trim tab
9. What is the purpose of rudder and ailerons?
Rudder:
The rudder is a control surface that control surface that can turn the nose of the airplane to
the right or left (called yawing).
Ailerons:
The ailerons are control surfaces that control the rolling motion of the airplane around the
fuselage.
Example:
When left aileron is deflected downward and the right aileron is deflect upwards, lift is
increased on the left wing and decreased on the right wing, causing the airplane to roll to the rich.
Auxiliary airfoil surface, mounted forward of a main airfoil, to maintain a smooth airflow over
the main airfoil upper surface.
10. What are called Slats and what is its function?
Auxiliary air foil surface, mounted forward of a main air foil, to maintain a smooth air flow
over the main air foil upper surface.

Briefly explain about the Altimeter and air speed indicator.
The Altimeter
The word “altimeter” means “height measurer.” Would that the instrument were true to its
name! The so-called altimeter which is used in aero planes is nothing more or less than an
aneroid barometer, such as is used to measure the pressure of the atmosphere for the purpose of
forecasting the weather. The only real modification is that the dial is marked in thousands of feet
instead of in inches or millimeters of mercury, and this makes it just about as capable of
measuring the height as the barometer is of foretelling the weather. What it does do is to record
the pressure. As we go up, the pressure goes down, because there is less weight of air on top of
us; but unfortunately the rate at which the pressure goes down varies from day to day, depending
chiefly on the temperature and other effects, which also vary from day to day. Thus it is
impossible to mark off or calibrate the scale of an altimeter so that each pressure corresponds to a
definite height; the best that can be done is to assume some average set of conditions of
temperature and pressure, to mark the scale of the instrument to suit these conditions, and then
correct the readings for any large departure from such standard conditions.
This set of average conditions has been laid down, and, as mentioned in Section 4, is
called the International Standard Atmosphere (fig). When an aeroplane makes a test flight, or
some attempt on an altitude record, the height which counts is not the height reached according to
the altimeter, nor is it the actual height above the ground; it is the height which we estimate it
would have reached had the conditions of the atmosphere all the way up corresponded to those of
the Standard Atmosphere. It is not a very satisfactory state of affairs, but we cannot do any better
until we can devise an instrument which will really measure height, instead of just pressure.
Not only does an altimeter fail to record the correct height when flying, but it does not
necessarily read zero when at sea level, since the atmospheric pressure varies considerably from
time to the at the earth‟s surface. After all, that is how a bareometer works, and the altimeter is
only a barometer. For this reason, altimeters are fitted with an adjustment so that they can be
made to read zero (or the height of the aerodrome) before starting on a flight. It does onto by any
means follow that they will read zero on return to earth. In a flight of a few hours there may be
considerable change in atmospheric pressure, and there is also a certain amount of lag in the
instrument. For these reasons it is very important when flying over high ground or mountainous
districts in foggy weather not to put too much faith in the altimeter. Although this is usually
impressed upon pilots, accidents have occurred from this cause.
Modern altimeters are very much more sensitive than the old types. Some of them have
three hands, one making a complete revolution every 1,000 ft, the next one every 10,000 it, and
the third in 100, 000 ft. There is hardly any lag in such an instrument; in fact, such sensitivity
would be of no advantage if there were any serious lag. Another refinement is that, instead of
turning the dial to set the zero, the pointers are moved, and when they read zero a little window at

the bottom of the instrument gives the reading of the barometer. A great advantage of this method
is that if one can find out, by radio or other means, the reading of the barometer at any aerodrome
at which one wishes to land, one has only to set this reading on the altimeter and, one has only to
set this reading on the altimeter and, whatever may be the altitude of the aerodrome, the hands
will all point to zero or, by an alternative setting, to the correct height of the airfield, when the
aircraft touches the ground. This is a great help in instrument flying.
But, however sensitive the barometric type of altimeter may be, it still cannot measure true
height in the atmosphere, except under a very unlikely set of standardized conditions.
Is it possible, then, to measure the true height of an aircraft above sea level? In certain
instances it can be done by taking three simultaneous sight from the ground, or by various radio
and radar devices, or by some echo system such as is used for submarines.
But, for most purposes, the altimeter, the aneroid barometer, with all its faults still holds its
own, and though we never know how high we are flying we can either assume ignorance and
hope that the altimeter is right, or we can try to be very clever and work out how high we ought to
be. Special “computers” are provided for this purpose.
The Air-Speed Indicator
Throughout the book we have talked of air speed, and we have repeatedly noticed the
close connection with angle of attack. In taking off, climbing, straight and level flight, turning,
gliding, and landing, there is a best speed for each, while for the purpose of flying from one place
to another the navigator must known both the air speed of the aeroplane and the velocity of the
wind. It is true that he would prefer to know the ground speed, but no instrument can be devised
to measure this directly, and the pilot much prefers to know his air speed.
The usual type of air-speed indicator consists of a thin corrugated metal box very like that
used in an aneroid barometer. At some convenient place on the aeorplane, where it will be
exposed to the wind yet not affected by slipstream or other interference, is placed the pitoot-static
head Fig.
Figure: Pilot-static head
This consists of two tubes, one of which has an open end facing the air flow-called a pilot
tube. The other is closed at the end, but along the sides are several small holes which allow the

atmospheric pressure to enter, and this tube is called the static tube. In modern types the two
tubes are often combined into one, the static tube concentric with the pitot tube, and outside it
(fig).
Figure: Concentric pitot-static tube
Sometimes the pressure near the pitot tube is by no means atmospheric, and the static
pressure is taken from some other part of the aeroplane altogether. But wherever the pitot head,
and the static vent, may be, metal tubing is used to communicate the pressures to the instrument
in the pilot‟s cockpit, the pitot tube being connected to one side of the metal box and the static to
the other. When the aeroplane is at rest relative to the air, the ordinary atmospheric pressure will
be communicated by the tubes to both sides of the box and the instrument needle will be at “o”,
but when traveling through the air the pitot, or open, tube will record a higher pressure, depending
on the air speed, while the static tube will still record the atmospheric pressure. The instrument
then reads the difference between these two pressure which is automatically translated by the dial
into miles per hour or knots.
The pressure on the pitoto tube, just like all air resistances, will go up in proportion to the
square of the speed, e.g. at twice the speed to pressure will be four times as much, and thus we
can understand why the numbers round the dial of the instrument, 50, 60, 70, m.p.h., and so on,
are not equally spaced.
When we fly higher, the density of the air will become less, and since the difference
between the two pressures depends on the density as well as on the air speed, the indicator will
read incorrectly, we call the speed recorded by the instrument the indicated air speed, and the
real air speed the true air speed. The error is quite appreciable; for instance, when the indicator
reads 100 m.p.h. at 30,000 ft, the true air speed is about 160 m.p.h., and at 40,000 ft a reading of
100 m.p.h. on the instrument means that we are really traveling at more than 200 m.p.h.
There is, however, rather an interesting point about this incorrect reading of the air-speed
indicator at height. Just in the same proportion as the pressure on the metal box is reduced by the
smaller air density, so is the lift on the wings correspondingly reduced, and thus a higher speed is
necessary to support the aeroplane in flight. Therefore the stalling speed of the aeroplane will
increase with height, but at this increased speed the air-speed indicator will continue to read, when
the aeroplane is about to stall, the same stalling speed as when near the ground. The error, in
other words, has a distinct advantage from the pilot‟s point of view in that, whatever the height the
aeroplane stalls at the same indicated speed. Other speeds of flight, such as the speed for
maximum range, are affected in the same way.

True air speed can be measured by a system of rotating vanes or cups called an
anemometer. This instrument is used at meteorological stations for measuring wind velocity, but it
is not very satisfactory for use on aircraft. For navigational purposes elaborate instruments have
been devised for measuring true speed, but they are outside the scope of this book.
Describe about the primary control surface in detail.
There are three basic control on an airplane ailerons, elevator and rudder
These are hinged surfaces usually at the trailing edge of the wings and tail that can be
rotated up and down.
Ailerons and Elevators:
Figure:
The ailerons are control surfaces that control of the rolling motion of airplane around the
fuselage
Example:
When left aileron is deflected downward the right aileron is deflected upward, lift is
increased on the left wing deflected upward, lift is increased on the left wing decreased on the
right wing causing the airplane to roll to the right.
The elevators are control surfaces that controls nose up and down pitching motion.
Aileron
Elevator

When a elevator is deflected down wards the lift on the tail is increased, pulling the tail up and
nose of airplane down.
Rudder:
Figure:
Rudder is control surface can turn nose of airplane to the right or left. It is called yawing
1. 215 & 218
3. 114
Write short notes on Lateral control and longitudinal control.
Lateral control
The usual method of obtaining lateral control is by means of ailerons hinged at the rear of
each main plane near the wing tips.
Figure:

Plate 5: Here seen with landing gear extended, the Boeing YC-14 was the first to large aircraft to
use USB (uperr-surface blowing), one of the most potent forms of powered lift. The two 25-tonne
thrust turbofans blow their jets across the top of the wing. The Coanda effect keeps the transonic
jets attached to the metal surface, so with flaps depressed (as here) they end up deflected sharply
down, enormously increasing lift. The huge tail is needed for control at the very speeds that can
safely be reached.
Figure:
Plate 6: Here seen in service with the Royal Thai Navy, the Canadair CL-215 proves that large
piston-engined aircraft are not obsolete! Powered by 2,500-hp Pratt&Whitney R-2800 engines, this
amphibian is used mainly as a water bomber to fight forest fires, having the ability to scoop up
fresh loads many times in a single mission. Other mission include anti-smuggling patrols, air-sea
rescue, medevac and utility transport.
The ailerons are connected to the control column by a complete system of control wires
(figure) by a rigid system of rods, by torque tubes inside the wings, or again by some power-
operated system. This time it is a sideways movement of the control column which moves the
ailerons and does so in such a way that once again the control is instinctive, i.e. if the control
column is moved to the left the right-hand ailerons will go down, increasing the lift on the right-
hand wings, thus banking the aeroplane to the left; at the same time the left ailerons will have
been raised, decreasing the lift on the left wing and thus adding to the effect.

Figure: Lateral control-general arrangement
Sometimes the control column has no sideways movement, and lateral control is effected
by a type of handlebars, or by a wheel similar to the steering wheel on a car.
Longitudinal Control
Longitudinal control of an aeroplane is nearly always provided by elevators attached to the
rear of the tail plane. The principle is best illustrated by the old-fashioned system in which the
elevators were connected by control wires and levers to the control column in the pilot‟s cockpit.
The control is instinctive, i.e. when the column is pushed forward, the elevators are lowered and
the upward force on the tail is increased, thus causing the nose of the aeroplane to drop Fig.
Figure: Longitudinal control-direction of movements
In order to achieve this result it will be seen that in an ordinary simple control system the
wires must be crossed between the control column and the elevators. In modern practice,
however, instead of employing two wires which will tend to become slack, causing a certain
amount of backlash in the system, more positive controls are nearly always used; these may take
the form of a rigid rod serving both to push and to pull the elevators from top or bottom only, or
they may rely simply on the torsion of a rod or tube, or the whole control system may be power-
operated, hydraulic, pneumatic or electric.

Explain with a neat sketch components of an aero plane and their functions.

Figure: Basic components of an aircraft
Fuselage:
The fuselage is that portion of the aircraft that usually contains the crew and payload, either
passengers, cargo, or weapons. Most fuselages are long, cylindrical tubes or sometimes
rectangular box shapes. All of the other major components of the aircraft are attached to the
fuselage. Empennage is another term sometimes used to refer to the aft portion of the fuselage
plus the horizontal and vertical tails.
Wing:
The wing is the most important part of an aircraft since it produces the lift that allows a
plane to fly. The wing is made up of two halves, left and right, when viewed from behind. These
halves are connected to each other by means of the fuselage. A wing produces lift because of its
special shape, a shape called an airfoil. If we were to cult through a wing and look at its cross –
section, as illustrated below, we would see that a traditional airfoil has a rounded leading edge and
a sharp trailing edge.

Figure: Definition of an airfoil
Engine:
The other key component that makes an airplane go is its engine, or engines. Aircraft use
several different kinds of engines, but they can all be classified in two major categories. Early
aircraft from the Wright Flyer until World War II used propeller – driven piston engines, and these
are still common today on light general aviation planes. But most modern aircraft now use some
form of a jet engine. Many aircraft house the engine(s) within the fuselage itself. Most larger
planes, however, have their engines mounted in separate pods hanging below the wing or
sometimes attached to the fuselage. These pods are called nacelles.
Horizontal stabilizer:
If an aircraft consists of only a wing or a wing and fuselage, it is inherently unstable.
Stability is defined as the tendency of an aircraft to return to its initial state following a disturbance
from that state. The horizontal stabilizer, also known as the horizontal tail, performs this function
when an aircraft is disturbed in pitch. In other words, if some disturbance forces the nose up or
down, the horizontal stabilizer produces a counteracting force to push the nose in the opposite
direction and restore equilibrium. When in equilibrium, we say that an aircraft is in its trim
condition. The horizontal tail is essentially a miniature wing since it is also made up of an airfoil
cross – section. The tail produces a force similar to lift that balances out the lift of the wing to keep
the plane in equilibrium. To do so, the tail usually needs to produce a force pointed downward, a
quantity called down force.

Vertical stabilizer:
The vertical stabilizer, or vertical tail, functions in the same way as the horizontal tail, except
that it provides stability for a disturbance in yaw. Yaw is the side – to – side motion of the nose, so
if a disturbance causes the nose to deflect to one side, the vertical tail produces a counteracting
force that pushes the nose in the opposite direction to restore equilibrium. The vertical tail is also
made of an airfoil cross – section and produces forces just like a wing or horizontal tail. The
difference is that a wing or horizontal tail produces lift or down force, forces that are pointed up or
down from the aircraft. Mean while the vertical tail produces a force pointed to one side of the
aircraft. This force is called side – force.
Basic control surfaces:
In addition to the wing and tail surfaces, aircraft need some additional components that give
the pilot the ability to control the direction of the plane. we call these items control surfaces.
Figure: Aircraft control surfaces and axes of motion
Elevator:
The elevator is located on the horizontal stabilizer. It can be deflected up or down to
produce a change in the down force produced by the horizontal tail. The angle of deflection is
considered positive when the trailing edge of the elevator is deflected upward. Such a deflection
increases the down force produced by the horizontal tail causing the nose to pitch upward.

Rudder:
The rudder is located on the vertical stabilizer. It can be deflected to either side to produce
a change in the side – force produced by the vertical tail. The angle of deflection is usually
considered positive when the trailing edge of the rudder is deflected towards the right wing. Such
a deflection creates a side – force to the left which causes the nose to yaw to the right.
Aileron:
Ailerons are located on the tips of each wing. They are deflected in opposite direction (one
goes trailing edge up, the other trailing edge down) to produce a change in the lift produced by
each wing. On the wing with the aileron deflected down ward, the lift increases whereas the lift
decreases on the other wing whose aileron is deflected upward. The wing with more lift rolls
upward causing the aircraft to go into a bank. The angle of deflection is usually considered
positive when the aileron on the left wing deflects downward and that on the right wing deflects
upward. The greater lift generated on the left wing causes the aircraft to roll to the right.
The effects of these control surfaces and the conventions for positive deflection angles are
summarized in the following diagram.
Figure: Aircraft control surfaces and positive deflection angles
3. Additional components:
We‟ve already seen the major parts of a typical plane, but a few important items were left
out for simplicity. Let‟s go back and discuss a few of these items.

Figure: Components of an aircraft
Flap:
Flaps are usually located along the trailing edge of both the left and right wing, typically
inboard of the ailerons and close to the fuselage. Flaps are similar to ailerons in that they affect
the amount of lift created by the wings. However, flaps only deflect down ward to increase the lift
produced by both wings simultaneously. Flaps are most often used during takeoff and landing to
increase the lift the wings generate at a given speed. This effect allows a plane to takeoff or land
at a slower speed than would be possible with out the flaps. In addition to flaps on the trailing
edge of a wing, a second major category is flaps on the leading edge. These leading – edge flaps,
more often called slats, are also used to increase life. More information on slats and flaps is
available here.

Cabin & cockpit:
Sometimes these two terms are used synonymously, but most of the time the term cockpit
is applied to a compartment at the front of the fuselage where the pilots and flight crew sit. This
compartment contains the control yolks (or sticks) and equipment the crew use to sent commands
to the control surfaces and engines as well as to monitor the operation of the vehicle. Meanwhile,
a cabin is typically a compartment within the fuselage where passengers are seated.
Nose & main gear:
The landing gear is used during takeoff, landing, and to taxi on the ground. Most planes
today use what is called a tricycle landing gear arrangement. This system has two large main
gear units located near the middle of the plane and a single smaller nose gear unit near the nose
of the aircraft.
Trim tab:
The above diagram illustrates a “trim tab” located on the elevator. These control tabs may
be located on other surfaces as well, such as a rudder control tab or a balance tab on the aileron.
Nonetheless, the purpose of all these tabs is the same. In the previous section, we discussed that
the horizontal stabilizer and elevator are used to provide stability and control in pitch. In order to
keep a plane in a steady, level orientation, the elevator usually has to be deflected by some small
amount. Since it would be very tiring for a pilot to physically hold the control stick in position to
keep the elevator at that deflection angle for an entire flight, the elevator is fitted with a small “tab”
that creates that elevator deflection automatically. The trim tab can be through of almost as a
“mini – elevator”. By deflecting the tab up or down, it increases or decreases the down force
created by the elevator and forces the elevator to a certain position. The pilot can set the
deflection of the trim tab which will cause the elevator to remain at the deflection required to
remain trimmed.
Summary:
This discussion has provided an overview of the basic parts and control surfaces of a
typical aircraft. Yet there are still many more features related to control surfaces that we have not
seen. In a future installment, we will add further detail and complexity to illustrate the complex
nature of modern control surfaces.

How the air planes are classified? Discuss about various types of flight vehicles with
schematic sketches wherever possible.
Lighter than air aircraft:
The name itself indicates, that the aircraft is lighter than air. These depend for their lift on a
well – known scientific fact usually called „Archimedes principle‟. The principles states that „when
a body is immersed in a fluid, a force acts upwards upon it., helping to support its weight and this
upward fore is equal to the weight of the fluid which is displaced by the body.
Air ships, free balloons or kite balloons obtains its lift in precisely the same way (ie) By
Archimedes Principle.
Airship:
A power driven aircraft that is light than air. An airship can carry a maximum up to 2 to 3
persons.
Free balloons:
Free balloons are also comes under this category that means the balloons one flown in the
air with the help of gases such as a helium, hydrogen etc.,
Aircraft
Lighter than air Heavier than air
Airships Free balloons Captive balloons Power driven Non - Power driven Man - Power
driven
Gliders Kites
Sailplanes
Aero plane Rotorcraft Ornithopter
Land plane Sea plane Amphibian Helicopter
(rotor power
driven )
Gyroplane
(rotor not
power driven)
Cyclogyro
(paddle – wheel
type motor)
Float plane Flying boat

Heavier than air aircraft:
Here in the aircraft solid metals are used. So that it could not fly in air without any definite
shape. In order to fly such aircraft, aerofoil shapes should be maintained for such aircrafts. Since,
there is steady flow of air over such aircrafts, these types of aircrafts are found to be airborne (ie, it
can stay in air for a long time).
Power driven:
Under the heavier than aircrafts, power driven aircrafts play a dominant role today. Power
driven aircrafts are nothing but aircrafts which are provided with external power supply. (ie) the
aircraft can be flown with the help of certain factors like engines, etc.,
Aero plane:
The aero plane must be given some power, so that it can fly. So as in aero plane, the
power is provided mainly by engines and as well as propulsion systems.
Figure:
Rotor craft:
Here, the power provided to the craft is by means of rotor (ie) a rotating member that can
take off the aircraft to a specified height and it can be flown.
The rotor craft designs are
1. Helicopter
2. Gyroplane
3. Cyclogyro

Helicopter:
Here in the helicopter, the power is driven by a rotor, which is having blades that rotates up
to a certain speed, that makes the helicopter to lift up and so it can fly.
Ornithopter
Here in the ornithopters, the power is given mainly by the mechanism of flapping wings up
and down.
Figure: Orinithopler
Non – Power driven:
Non – power driven aircrafts are those crafts which can flown without the help of any
external power supply (ie) there is no presence of engines.
Gliders:
Gliders are those aircrafts which comes under non – power driven such that it can fly
without engines and also it should be start to fly from some elevated places like maintains etc.

Hydraulic Actuator and Electronic actuator system:
Brief summary of the invention:
[0014] According to principles of the present invention, a backup system is provided that
has a local electric motor and pump for some or all of the hydraulic actuators. A local back up
hydraulic actuator (LBHA) has two power sources, central hydraulic as primary and electrical as
backup. During normal operation, the hydraulic actuator receives pressurized fluid from one of the
central hydraulic systems and the fluid flow to the chambers is controlled by a servo valve. Failure
of the hydraulic system is detected by the local electronic controller that monitors the output signal
of a pressure sensor. When this observed pressure falls below a certain threshold, the local
electronic controller determines that this central hydraulic system has failed and t urns on the
electrical motor, which powers the local hydraulic pump to provide high pressure hydraulic fluid to
the hydraulic actuator via the servo value. The local electronic controller also uses the pressure
reading for closed – loop feedback control, and the pressure is maintained at the normal level.
Other types of monitoring and control schemes may also be used instead. In this manner, the
LBHA remains functional with electrical power following a partial or complete failure of the central
hydraulic system.
[0015] By coupling the LBHAs to appropriate flight control surfaces, the airplane remains
controllable with loss of all central hydraulic systems; therefore, the number of central hydraulic
systems can be reduced compared to using only conventional hydraulic actuators.
[0016] As explained in the background of the invention, some prior art approaches provide
a reduction in the number of hydraulic systems, namely EHA and EBHA, for example. A major
advantage that the LBHA offers over these prior art actuators is that it enables this reduction in the
central hydraulic system for airplanes with flight control surfaces which are controlled in an active
– active fashion. This is accomplished by overcoming both of the two major difficulties that have
been cited herein for the electric and hybrid actuators of the prior art, namely that of reduced
reliability and force fight.
[0017] The LBHA overcomes the reduced reliability problem by using the low – reliability
components only as backup following the failure of a central hydraulic system or during specific
phases of flight. The electrical part of the LBHA can be switched of during much of flight so the life
of the motor and pump is greatly extended. Therefore, even when the LBHA is used continuously
during normal operation, such as on an active- active surface, the operation is more reliable and
the life of the motor and pump are extended.
[0018] The force fight problem associated with coupling dissimilar actuators on a surface
and using them in an active – active fashion is resolved according to this invention by continuously
controlling the actuator in the same manner as a conventional hydraulic actuator and providing as
backup only alternate power source. The local motor and pump are upstream of the servo valve
and in parallel with the central hydraulic lines. A common servo value for the hydraulic actuator is
used under a unified electrical control system for both the central hydraulic system and the backup
system. This ensures that there is no substantial force fight when LBHA is used in an active –
active fashion with a hydraulic actuator or another LBHA on the same surface. This is because
during normal operation and operation following the failure of the central hydraulic system, the

LBHA is controlled in the same manner through the servo valve, with the only difference being the
source of hydraulic power, central or local.
[0019] In addition to enabling the reduction of hydraulic systems and resolving the problems
associated with applying electric or hybrid actuators of prior art in an active – active fashion, the
LBHA also offers other advantages. With the LBHA, the local pump can be a one – way pump
rather than a two – way pump, which, together with the motor and controller, is lower in weight and
cost, while having higher reliability. The local pump‟s role is to provide increased local pressure,
rather than also provide servo control of the system, thus simplifying the motor, the motor driver
and control device, and increasing the reliability of operation.
[0020] The inventive system also provides the advantage that during critical flight phases,
such as takeoff and landing, both the main system and the backup system can be in operation. In
the event of failure of the main system, the backup; system is already under power and is assisting
in the operation, so that there is no time lost for control while the backup system comes on. Check
values are provided between the central hydraulic system and the local backup system, permitting
both to operate at the same time when appropriate.
[0021] A further advantage is that the backup system has a separate power source, namely
electric power, so that increased availability of power is provided to the actuator. Because of this,
providing one LBHA in conjunction with at least one hydraulic actuator for a particular surface is
able to ensure that the likelihood of a complete loss of the power to position the surface correctly
is negligible. This may, for example, enable reduction in the number of actuators coupled to a
surface compared to only using conventional hydraulic actuators, while achieving and equivalent
or better level of safety. This may also enable smaller, lighter, and simpler individual actuators
than otherwise would have been possible.
Flight instruments:
From Wikipedia, the free encyclopedia
Most aircraft are equipped with a standard set of flight instruments which give the pilot information
about the aircraft‟s attitude, airspeed and altitude.
Figure: Six basic instruments in a light twin – engine airplane arranged in the basic – T.
From top left airspeed indicator, attitude indicator, altimeter, turn coordinator, beading
indicator, and vertical speed indicator.

Most aircraft have these seven basic flight instruments:
Figure:
Altimeter:
Gives the aircraft‟s height (usually in feet or meters) above some reference level (usually
sea – level) by measuring the local air pressure. It is adjustable for local barometric pressure
(referenced to sea level) which must be set correctly to obtain accurate altitude readings.
Figure: Attitude indicator (also known as an artificial horizon)
Shows the aircraft‟s relative to the horizon. From this the pilot can tell whether are level
and if the aircraft nose is pointing above or below the horizon. This is a primary instrument flight
and is also useful in conditions of poor visibility. Pilots are trained to use other instruments in
combination should this instrument or its power fail.
Figure: Airspeed indicator
Shows the aircraft‟s speed (usually in knots) relative to the surrounding air. It works by
measuring the ram – air pressure in the aircraft‟s pitot tube. The indicated airspeed must be
corrected for air density (which varies with altitude, temperature and humidity) in order to obtain
the true airspeed, and for wind conditions in order to obtain the speed over the ground.

Figure: The flight instruments of a Slings by T – 67 Firefly two – seat light airplane. The
basic T is present on the left side primary pilot station.
Magnetic compass:
Shows the aircraft‟s heading relative to magnetic north. While reliable in steady level flight
it can give confusion indications when turning, climbing, descending, or accelerating due to the
inclination of the earth‟s magnetic field. For this reason, the heading indicator is also used for
aircraft operation. For purposes of navigation it may be necessary to correct the direction
indicated (which points to a magnetic pole) in order to obtain direction of true north or south (which
points to the earth‟s axis of rotation).
Figure: Heading indicator
Also know as the directional gyro, or DG. Sometimes also called the gyrocompass, though
usually not in aviation applications. Displays the aircraft‟s heading with respect to magnetic north.
Principle of operation is a spinning gyroscope, and is therefore subject to drift errors (called
precession) which must be periodically corrected by calibrating the instrument to the magnetic
compass. In many advanced aircraft, the heading indicator is replaced by a Horizontal Situation
Indicator (HIS) which provides the same heading information, but also assists with navigation.

Figure: Turn and bank indicator or turn coordinator
The turn and bank indicator, also called the turn and slip indicator, displays of turn and rate
of turn. Internally mounted inclinometer displays „quality‟ of turn, i.e. whether the turn is correctly
coordinated, as opposed to an uncoordinated turn, where in the aircraft would be in either a slip or
a skid. Replaced in the late sixties and early seventies by the newer turn coordinator, the turn and
bank is typically only seen in aircraft manufactured prior to that time, or in Gliders manufactured in
Europe.
A turn coordinator displays rate and direction of roll while the aircraft is rolling; displays rate
and direction of turn while the aircraft is not rolling. Internally mounted inclinometer also displays
quality of turn. Replaced the older turn and bank indicator.
Figure: Vertical speed indicator
Also sometimes called a variometer Senses changing air pressure and displays that
information to the pilot as a rate of climb or descent, usually in feet per minute or meters per
second.

Figure: Schempp – Hirth Janus – C glider Instrument panel equipped for “cloud flying”.
The turn and bank indicator is top center. The heading indicator is replaced by a GPS –
driven computer with wind and glide data, driving two electronic variometer displays to the
right.
Arrangement in instrument panel:
Most aircraft built since about 1953 have four of the flight instruments located in a
standardized arrangement known as the “basic T”. The attitude indicator is in top center, airspeed
to the left, altitude to the right and heading indicator under the attitude indicator. The other two,
turn – coordinator and vertical – speed, are usually found under the airspeed and altitude, but are
given more latitude in placement. The magnetic compass will be above the instrument panel,
often on the windscreen center post. In newer aircraft with glass cockpit instruments the layout of
the displays conform to the basic T arrangement.
Flight instrument
Pitot – static instrument: Altimeter: Airspeed indicator – Machmeter – Vertical speed indicator
Gyroscople instruments: Attitude indicator – Heading indicator – Horizontal Situation Indicator –
Turn and back indicator – Turn coordinator
Navigation: Horizontal Situation Indicator – Course Deviation Indicator – Inertial Navigation
System – GPS Other magnetic compass – Yaw string.
Figure: Tabs fitted on elevators and rudder of an old Catalina flying boat
Powered servo controls:
Powered controls may take two forms, servo – assisted, or fully power operated. In the
former type, hydraulic pressure is transmitted via pipes to a servo – actuator which helps the

mechanical linkage to move the surface. The mechanical linkage can be used to operate the
control surface, even if power is lost, although the controls will then feel very heavy. The system is
similar to the servo – assisted steering and braking system of car.
Power control, fly – by – wire and fly – by – light:
In pure power operation, no mechanical override is provided. Control signals may be
transmitted hydraulically, directly from valves attached to the control column, or electrically to
actuators, which move the control surfaces. The latter system is known as fly – by – wire. The
actuators are electrically or hydraulically operated rams motors.
As an alternative to electrical signal transmission, modulated light signals may be
transmitted along optical fibres. This system is known as fly – by – light and over comes problems
due to electromagnetic interference. The detonation of nuclear weapons would cause very strong
electromagnetic signals capable of upsetting, if not destroying, conventional electronic circuits.
The deliberate jamming of electronic circuitry by means of powerful electromagnetic beams is also
a possibility, and some military aircraft have been found to be very vulnerable in this respect.
Once control by electrical signals is accepted, it becomes convenient to incorporate
sophisticate electronic processing into the circuit, with increasing emphasis on digital systems.
Such processing can be used to alter the response to control inputs, and can follow for
manoeuvres such as flying in a stalled or an unstable condition, or approaching very close to the
stall on landing.
Fly – by – wire can thus dramatically improve the performance, efficiency and even safety
of aircraft. It also allows for coordinated control surface movement that would be too complex for
a pilot to manage unaided. Such systems have demonstrated a high level of reliability and are
being increasingly used. On military aircraft, the flight control, autostabilisation, navigation, radar
ad weapons control system are all integrated in varying degrees.
Feedback or feel:
One problem with power – operated controls is that the pilot has no direct feel for the
amount of force that the control surface is producing. Therefore, some form of artificial feel has to
be introduced.
Generally, mechanical controls feed heavier the further they are pulled, so a crude form of
feel could be provided by attaching springs to the control column. This system is inadequate,
however, because the control loads should also increase as the flight speed increase.
The force actually required at the control surface, depends on the dynamic pressure
2
1
V
2
, rather than just the speed. At constant altitude, the controls will, for example, require
sixteen times more force to operate them at 800 km /h than at 200 km/h. To over come this
problem, also –called q – feel device can be added. (q is the symbol conventionally used to denote
dynamic pressure). The q – feel unit is a device which is attached to the mechanical control
linkage to increase its stiffness in proportion to increases n dynamic pressure. Nowadays, much

more sophisticated feedback systems are used, in which the force required to move the control
surface is sensed, and the force required to move the pilot‟s control stick is increased
appropriately.
By using the electronic processing of the feedback signal, it is possible to make a small
aircraft feel and handle like a large one. Reversing the procedure might be unwise, as trying to
throw a 747 around like a Pitts Special could cause problems. The handling of new untested
aircraft types is often simulated by artificially modifying the control of an existing different aircraft
type.
Early aircraft and small modern types use a direct mechanical linkage between the control
surface and the pilot control stick. The linkage normally consists of an arrangement of multi –
stranded wires and pulleys. Figure shows the complex system used on an executive jet. The
rudder actuating wire may just be seen under the tailplane on the Auster shown in figure.
Alternatively push – pull rods and twisting torque – tubes may be used, and are in some ways
preferred, since they produce a stiffer system, less prone to vibration problems.
As the speed and size of aircraft increased, so did the control forces required, and some
considerable ingenuity went into devising means of reducing these loads. The position of the
hinge line can be arranged so that the resultant force acts just behind it, thus producing only a
small moment. A typical arrangement, used on many aircraft up to the 1950s, is seen in figure.
The top of the rudder projects forward, in front of the hinge line, thereby moving the centre of
pressure of the rudder forwards, towards the hinge line.
Unfortunately, the position of the resultant force changes with angle of attack, speed, and
deflection angle, so that it is difficult to devise an arrangement that produces small forces under all
conditions. It is particularly important that the resultant force should not be in front of the hinge
line, as this would cause the control surface to be unstable, and run away in the direction of the
ever – increasing force.
In addition to such aerodynamic balancing the control surface mass should also be
balanced so that gravity forces do not pull it down in level flight, and inertia does not cause it to
move relative to the aircraft during manoeuvres. A rather crude external form of mass balancing
may be seen figure. As described later, masses may also be added to the control surfaces to alter
the natural frequency of oscillation.
Servo – tabs and trim tabs:
Another means of reducing the load required is to use a servo – tab, as illustrated in figure.
Deflection of the tab downwards causes the trailing edge of the surface of lift, producing a large
turning moment in the primary control surface. Various means of coupling the tab and primary
surface were devised, but such arrangements are now largely obsolete. Kermode (1996)
describes the historical development of tabs.
Nowadays tabs are normally used primarily for trimming the control surfaces; that is, setting
them so that the control surface produces just the right amount of force to keep the aircraft flying
steadily, hands – off. Such trim tabs are controlled by a separate trim wheel in the cockpit or flight
deck, and are actuated independently of the main surface actuating system.

Figure: External mass balance weights were used on the tail of the Venom
Figure: A servo – tab
Downward deflection of the tab increases the lift on the main control surface causing it to deflect
upwards
The force required to operate the tab is considerably less than that which would be needed to
operate the main control surface directly
Trim tabs allow an aircraft to be flown virtually, or even literally, hands – off, for much of the time.
Tabs may be seen in figure. Fixed trim tabs, in the form of small strips of metal affixed to the
trailing edge, may sometimes be used, their purpose being to „tune‟ the control surfaces to give a
good balance.
Movable trim tabs can provide restricted emergency control in the case of a failure in the
primary control surface system. On recent aircraft designs, they may provide the only manual
means of control.
Cockpit Instruments:
Altimeter

The word “altimeter” means “height measurer.” Would that the instrument were true to its
name! The so-called altimeter which is used in aero planes is nothing more or less than an
aneroid barometer, such as is used to measure the pressure of the atmosphere for the purpose of
forecasting the weather. The only real modification is that the dial is marked in thousands of feet
instead of in inches or millimeters of mercury, and this makes it just about as capable of
measuring the height as the barometer is of foretelling the weather. What it does do is to record
the pressure. As we go up, the pressure goes down, because there is less weight of air on top of
us; but unfortunately the rate at which the pressure goes down varies from day to day, depending
chiefly on the temperature and other effects, which also vary from day to day. Thus it is
impossible to mark off or calibrate the scale of an altimeter so that each pressure corresponds to a
definite height; the best that can be done is to assume some average set of conditions of
temperature and pressure, to mark the scale of the instrument to suit these conditions, and then
correct the readings for any large departure from such standard conditions.
This set of average conditions has been laid down, and, as mentioned in Section 4, is
called the International Standard Atmosphere (fig). When an aeroplane makes a test flight, or
some attempt on an altitude record, the height which counts is not the height reached according to
the altimeter, nor is it the actual height above the ground; it is the height which we estimate it
would have reached had the conditions of the atmosphere all the way up corresponded to those of
the Standard Atmosphere. It is not a very satisfactory state of affairs, but we cannot do any better
until we can devise an instrument which will really measure height, instead of just pressure.
Not only does an altimeter fail to record the correct height when flying, but it does not
necessarily read zero when at sea level, since the atmospheric pressure varies considerably from
time to the at the earth‟s surface. After all, that is how a bareometer works, and the altimeter is
only a barometer. For this reason, altimeters are fitted with an adjustment so that they can be
made to read zero (or the height of the aerodrome) before starting on a flight. It does onto by any
means follow that they will read zero on return to earth. In a flight of a few hours there may be
considerable change in atmospheric pressure, and there is also a certain amount of lag in the
instrument. For these reasons it is very important when flying over high ground or mountainous
districts in foggy weather not to put too much faith in the altimeter. Although this is usually
impressed upon pilots, accidents have occurred from this cause.
Modern altimeters are very much more sensitive than the old types. Some of them have
three hands, one making a complete revolution every 1,000 ft, the next one every 10,000 it, and
the third in 100, 000 ft. There is hardly any lag in such an instrument; in fact, such sensitivity
would be of no advantage if there were any serious lag. Another refinement is that, instead of
turning the dial to set the zero, the pointers are moved, and when they read zero a little window at
the bottom of the instrument gives the reading of the barometer. A great advantage of this method
is that if one can find out, by radio or other means, the reading of the barometer at any aerodrome
at which one wishes to land, one has only to set this reading on the altimeter and, one has only to
set this reading on the altimeter and, whatever may be the altitude of the aerodrome, the hands
will all point to zero or, by an alternative setting, to the correct height of the airfield, when the
aircraft touches the ground. This is a great help in instrument flying.
But, however sensitive the barometric type of altimeter may be, it still cannot measure true
height in the atmosphere, except under a very unlikely set of standardized conditions.

Is it possible, then, to measure the true height of an aircraft above sea level? In certain
instances it can be done by taking three simultaneous sight from the ground, or by various radio
and radar devices, or by some echo system such as is used for submarines.
But, for most purposes, the altimeter, the aneroid barometer, with all its faults still holds its
own, and though we never know how high we are flying we can either assume ignorance and
hope that the altimeter is right, or we can try to be very clever and work out how high we ought to
be. Special “computers” are provided for this purpose.
Air Speed Indicator
Throughout the book we have talked of air speed, and we have repeatedly noticed the
close connection with angle of attack. In taking off, climbing, straight and level flight, turning,
gliding, and landing, there is a best speed for each, while for the purpose of flying from one place
to another the navigator must known both the air speed of the aeroplane and the velocity of the
wind. It is true that he would prefer to know the ground speed, but no instrument can be devised
to measure this directly, and the pilot much prefers to know his air speed.
The usual type of air-speed indicator consists of a thin corrugated metal box very like that
used in an aneroid barometer. At some convenient place on the aeorplane, where it will be
exposed to the wind yet not affected by slipstream or other interference, is placed the pitoot-static
head Fig.
Figure: Pilot-static head
This consists of two tubes, one of which has an open end facing the air flow-called a pilot
tube. The other is closed at the end, but along the sides are several small holes which allow the
atmospheric pressure to enter, and this tube is called the static tube. In modern types the two
tubes are often combined into one, the static tube concentric with the pitot tube, and outside it
(fig).

Figure: Concentric pitot-static tube
Sometimes the pressure near the pitot tube is by no means atmospheric, and the static
pressure is taken from some other part of the aeroplane altogether. But wherever the pitot head,
and the static vent, may be, metal tubing is used to communicate the pressures to the instrument
in the pilot‟s cockpit, the pitot tube being connected to one side of the metal box and the static to
the other. When the aeroplane is at rest relative to the air, the ordinary atmospheric pressure will
be communicated by the tubes to both sides of the box and the instrument needle will be at “o”,
but when traveling through the air the pitot, or open, tube will record a higher pressure, depending
on the air speed, while the static tube will still record the atmospheric pressure. The instrument
then reads the difference between these two pressure which is automatically translated by the dial
into miles per hour or knots.
The pressure on the pitoto tube, just like all air resistances, will go up in proportion to the
square of the speed, e.g. at twice the speed to pressure will be four times as much, and thus we
can understand why the numbers round the dial of the instrument, 50, 60, 70, m.p.h., and so on,
are not equally spaced.
When we fly higher, the density of the air will become less, and since the difference
between the two pressures depends on the density as well as on the air speed, the indicator will
read incorrectly, we call the speed recorded by the instrument the indicated air speed, and the
real air speed the true air speed. The error is quite appreciable; for instance, when the indicator
reads 100 m.p.h. at 30,000 ft, the true air speed is about 160 m.p.h., and at 40,000 ft a reading of
100 m.p.h. on the instrument means that we are really traveling at more than 200 m.p.h.
There is, however, rather an interesting point about this incorrect reading of the air-speed
indicator at height. Just in the same proportion as the pressure on the metal box is reduced by the
smaller air density, so is the lift on the wings correspondingly reduced, and thus a higher speed is
necessary to support the aeroplane in flight. Therefore the stalling speed of the aeroplane will
increase with height, but at this increased speed the air-speed indicator will continue to read, when
the aeroplane is about to stall, the same stalling speed as when near the ground. The error, in
other words, has a distinct advantage from the pilot‟s point of view in that, whatever the height the
aeroplane stalls at the same indicated speed. Other speeds of flight, such as the speed for
maximum range, are affected in the same way.

True air speed can be measured by a system of rotating vanes or cups called an
anemometer. This instrument is used at meteorological stations for measuring wind velocity, but it
is not very satisfactory for use on aircraft. For navigational purposes elaborate instruments have
been devised for measuring true speed, but they are outside the scope of this book.
Mach Numbers
Since the speed of sound is so important it is sometimes convenient to speak of the speed
of aeroplanes in relation to the speed of sound and to say that they are traveling at half, or three-
quarters, or nine-tenths of the speed of sound, or even at the speed of sound itself or at two or
three times that speed. This is expressed in terms of Mach numbers, a Mach number of 0.5
simply meaning that the aeoplane is traveling at half the speed of sound. Thus the Mach numbers
in the examples given above would be, respectively, 0.5, 0.75, 0.9, 1, 2 and 3. Here, at least, is a
highbrow term which anyone can understand. It is so simple, in fact, that the reader may well ask
why it is necessary at all-if the speed of sound is 760 m.p.h., we know that when an aeroplane is
traveling at 380 m.p.h. it is traveling at half the speed of sound; why wrap the thing in mystery by
saying that it is traveling at a Mach number of 0.5?
Well, as it happens, it ins‟t-in this case-just an attempt to blind people with science. An
observant reader-especially if he has already fallen into some of our traps-may have noticed that
we have been rather careful throughout this argument not to give the actual speeds of rifle bullets
and so on, but just to compare them with the speed of sound-and that when we first said that the
speed of sound, was as near as matters, 760 m.p.h., we specified under normal atmospheric
conditions. That is the clue. The rate at which sound travels in air depends on the temperature is
the controlling factors); the lower the temperature the lower the speed of sound. Thus at the
temperature of ground level conditions of the International Standard Atmosphere (conditions which
rarely apply in practice) the speed of sound is about 760 m.p.h.; while at the temperature of the
stratosphere an aeroplane may be traveling below the speed of sound, at the speed of sound, or
above the speed of sound, according to the temperature at the time. What matters is not that it is
going at 700 m.p.h. but at what fraction of the particular speed of sound it is traveling-in other
words what matters is, not its speed, but its Mach number.
When there is no need to specify the actual Mach number and we only wish to indicate that
a body, or the air flow, is traveling at less than the speed of sound, at the speed of sound or above
it, it is usual and convenient to use the Latin words and to speak of subsonic, sonic, and
supersonic speeds.
As we shall soon se, it isn‟t just at the speed of sound that curious things happen, but over
quite a range of speeds which include that speed, and it is useful, therefore, to introduce the word
transonic. Our subject then falls into there quite distinct parts, i.e. flight at subsonic speeds which
is what we have so far considered, flight at transonic speeds which ahs problems all of its own,
and flight at supersonic speeds in which we are in a new world altogether and all the rules are so
much the opposite from what we have already learnt that it reminds us of Alice Through the
Looking-glass.

Turn and slip indicator
These two instruments together-the artificial horizon and the directional gyro-are the basis
of “George,” the robot or automatic pilot, which not only detects any tendency of the aeroplane to
yaw, pitch or roll but, having done so, moves the controls until it is once more flying correctly. That
sounds wonderful indeed; but it is no longer fantastic to imagine that in the future aeroplanes will
be flying about, carrying and dropping bombs, and perhaps even fighting each other, without any
pilots at all-indeed guided missiles are already doing just this.
This third gyroscopic instrument in common use is the turn and side-slip indicator, which
has already been mentioned. The lower needle on this indicates the rate of turn and is worked by
the precession of a gyroscope; the upper needle indicates side-slip and is worked by a pendulum.
There are not many other instruments concerned with the actual flight of the aeroplene.
The air temperature is needed for various corrections to speed, height, and so on in record or test
flights, and for this purpose an ordinary thermometer may be fitted on some exposed part. A rate-
of-climb indicator or, to be more exact, an instrument which shows either rate of ascent or rate of
descent, is usually fitted to modern aircraft, and, like so many of these modern luxury instruments,
is of great value in instrument flying. A machmeter, which will be mentioned in the following
paragraphs, is indispensable in high-speed aircraft.
Apart from the aircraft itself the engine or engine will need revolution indicators, oil-pressure
gauges, oil-temperature gauges, air-pressure gauges, fuel-pressure gauges, boost gauges for
superchargers, water thermometers for water cooled engines, fuel flowmeters, fuel-contents
gauges, and so on.
On the electrical side there may be anything varying from the simple switch used for the
engine ignition to a complete system of lighting and heating, dynamos and motors, and full radio
and radar installation with all its attendant instruments.
For high flying, oxygen apparatus must be installed, and this needs special instruments all
to itself as does the pressurization of cabins.
Incidentally, we must not forget what is perhaps the most useful of all man-made
instruments-the clock or watch. For any kind of serious flying it is indispensable.
Artificial horizon
An instrument panel in a modern aeroplane may contain at least three instruments which
depend on gyroscopes. They are usually driven by suction from an engine-driven pump or from
double venture tubes exposed to the air stream, and may revolve at 10,000 r.p.m.
Perhaps the most striking of all such instruments is the artificial horizon, which shows the
position of a small model aeroplane relative to a horizon marked on the instrument. If the nose of
the real aeroplane goes down, the model goes below the horizon; if the nose goes up, the model
moves above the horizon. If the aeroplane banks to right or left, so does the model. even if the
pilot cannot see the real horizon at all, if he is flying on the darkest on the darkest of nights, or

“under the hood”, he can always tell the attitude of his aeroplane. Only those who have tried to fly
“blind” can possibly conceive the value of such an instrument. It is worked by a gyroscope which
is so mounted that its axis does not move even though the aeroplane (and with it the case of the
instrument) may pitch or roll.
Simpler in principle, but no less useful in practice, is the directional gyro. This detects any
turn of the aeroplane, just as the artificial horizon shows pitch or roll. It is very like a compass
except that, instead of possessing the property of pointing towards the north, it will remain in any
position in which the pilot likes to set it. Actually it is marked off in degrees just like a compass,
and the pilot usually sets it to correspond to the compass course. The reader may well ask what
its justification may be, seeing that it seems to act like a compass, though lacking the chief
attribute of the latter. The answer is simple. The directional gyro responds more quickly to the
slights turn, it settle down at once after at turn, it is unaffected by acceleration and the various
magnetic errors of the compass.
Controls:
a) Longitudinal control
b) Lateral control and
c) Directional control
Longitudinal control
Longitudinal control of an aeroplane is nearly always provided by elevators attached to the
rear of the tail plane. The principle is best illustrated by the old-fashioned system in which the
elevators were connected by control wires and levers to the control column in the pilot‟s cockpit.
The control is instinctive, i.e. when the column is pushed forward, the elevators are lowered and
the upward force on the tail is increased, thus causing the nose of the aeroplane to drop Fig.
Figure: Longitudinal control-direction of movements
In order to achieve this result it will be seen that in an ordinary simple control system the
wires must be crossed between the control column and the elevators. In modern practice,
however, instead of employing two wires which will tend to become slack, causing a certain
amount of backlash in the system, more positive controls are nearly always used; these may take
the form of a rigid rod serving both to push and to pull the elevators from top or bottom only, or

they may rely simply on the torsion of a rod or tube, or the whole control system may be power-
operated, hydraulic, pneumatic or electric.
Lateral control
The usual method of obtaining lateral control is by means of ailerons hinged at the rear of
each main plane near the wing tips.
Figure:
Plate 5: Here seen with landing gear extended, the Boeing YC-14 was the first to large aircraft to
use USB (upper-surface blowing), one of the most potent forms of powered lift. The two 25-tonne
thrust turbofans blow their jets across the top of the wing. The Coanda effect keeps the transonic
jets attached to the metal surface, so with flaps depressed (as here) they end up deflected sharply
down, enormously increasing lift. The huge tail is needed for control at the very speeds that can
safely be reached.

Elements of-aeronautics

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