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INTRODUCTION

Aerofoil Nomenclature

Aeroplane nomenclature

Aerofoil Pressure Distributions

Aerodynamic forces

Aerodynamic drags

Downwash

Coefficient of Lift

Coefficient of Drag

Boundary Layer

Aspect ratio

Cl vs Angle Of Attack

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Aerofoil Terminology

1. The leading edgeis the point at the front of the airfoil that has maximum curvature2. The trailing edgeis defined similarly as the point of maximum curvature at the rear of the airfoil.3. The chord lineis a straight line connecting the leading and trailing edges of the airfoil.4. The chord length, or simply chord, , is the length of the chord line and is the characteristic dimension

of the airfoil section.

5. The mean camber line is the locus of points midway between the upper and lower surfaces. Its exactshape depends on how the thickness is defined;

6. The thickness of an airfoil varies along the chord. It may be measured in either of two ways:a. Thickness measured perpendicular to the camber line. This is sometimes described as the

"American convention"

b. Thickness measured perpendicular to the chord line. This is sometimes described as the "Britishconvention".

Finally, important concepts used to describe the aerofoils behaviour when moving through a fluid are:

7. The aerodynamic centre, which is the chord-wise length about which the pitching moment isindependent of the lift coefficient and the angle of attack.

8. The centre of pressure,which is the chord-wise location about which the pitching moment is zero.

Aeroplane Terminolgy

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Aileronsare mounted on the trailing edge of each wing near the wingtips and move in opposite

directions. When the pilot moves the stickleft, or turns the wheel counter-clockwise, the left aileron goes up

and the right aileron goes down. A raised aileron reduces lift on that wing and a lowered one increases lift, so

moving the stick left causes the left wing to drop and the right wing to rise. This causes the aircraft to roll to the

left and begin to turn to the left. Centering the stick returns the ailerons to neutral maintaining the bank angle.

The aircraft will continue to turn until opposite aileron motion returns the bank angle to zero to fly straight

An elevatoris a moveable part of the horizontal stabilizer, hinged to the back of the fixed part of the

horizontal tail. They move up and down together. When the pilot pulls the stick backward, the elevators go up.

Pushing the stick forward causes the elevators to go down. Raised elevators push down on the tail and cause

the nose to pitch up. This makes the wings fly at a higher angle of attack, which generates more lift and

more drag. Centering the stick returns the elevators to neutral and stops the change of pitch. Many aircraft use

a fully moveable horizontal stabilizer called stabilator or all-moving tail. Some aircraft, such as an MD-80, use

a servo tab within the elevator surface to aerodynamically move the main surface into position. The direction of

travel of the control tab will thus be in a direction opposite to the main control surface. It is for this reason that

an MD-80 tail looks like it has a 'split' elevator system.

The rudderis typically mounted on the trailing edge of the vertical stabilizer, part of the empennage.

When the pilot pushes the left pedal, the rudder deflects left. Pushing the right pedal causes the rudder to

deflect right. Deflecting the rudder right pushes the tail left and causes the nose to yaw to the right. Centering

the rudder pedals returns the rudder to neutral and stops the yaw.

On low drag aircraft likesailplanes,spoilersare used to disrupt airflow over the wing and greatly

increase the amount of drag. This allows a glider pilot to lose altitude without gaining excessive airspeed.

Spoilers are sometimes called "lift dumpers". Spoilers that can be used asymmetrically are called spoilers and

are able to affect an aircraft's roll.

Flapsare mounted on the trailing edge on the inboard section of each wing (near the wing roots). They

are deflected down to increase the effective curvature of the wing. Flaps raise the Maximum Lift Coefficientof

the aircraft and therefore reduce its stalling speed. They are used during low speed, high angle of attack flight

including take-off and descent for landing. Some aircraft are equipped with "flapperons", which are more

commonly called "inboard ailerons". These devices function primarily as ailerons, but on some aircraft, will

"droop" when the flaps are deployed, thus acting as both a flap and a roll-control inboard aileron.

Slats, also known as leading edge devices, are extensions to the front of a wing for lift augmentation,

and are intended to reduce the stalling speed by altering the airflow over the wing. Slats may be fixed or

retractable - fixed slats (e.g. as on the Fieseler Fi 156 Storch) give excellent slow speed and STOL capabilities,

but compromise higher speed performance. Retractable slats, as seen on most airliners, provide reduced

stalling speed for take-off and landing, but are retracted for cruising.

http://en.wikipedia.org/wiki/Aileronshttp://en.wikipedia.org/wiki/Aileronshttp://en.wikipedia.org/wiki/Joystickhttp://en.wikipedia.org/wiki/Banked_turn#Aviationhttp://en.wikipedia.org/wiki/Elevator_(aircraft)http://en.wikipedia.org/wiki/Elevator_(aircraft)http://en.wikipedia.org/wiki/Horizontal_stabilizerhttp://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Stabilatorhttp://en.wikipedia.org/wiki/MD-80http://en.wikipedia.org/wiki/Servo_tabhttp://en.wikipedia.org/wiki/MD-80http://en.wikipedia.org/wiki/Rudderhttp://en.wikipedia.org/wiki/Rudderhttp://en.wikipedia.org/wiki/Empennagehttp://en.wikipedia.org/wiki/Sailplaneshttp://en.wikipedia.org/wiki/Sailplaneshttp://en.wikipedia.org/wiki/Spoiler_(aeronautics)http://en.wikipedia.org/wiki/Spoiler_(aeronautics)http://en.wikipedia.org/wiki/Spoiler_(aeronautics)http://en.wikipedia.org/wiki/Spoileronhttp://en.wikipedia.org/wiki/Flap_(aircraft)http://en.wikipedia.org/wiki/Flap_(aircraft)http://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Leading_edge_slatshttp://en.wikipedia.org/wiki/Fieseler_Fi_156http://en.wikipedia.org/wiki/STOLhttp://en.wikipedia.org/wiki/STOLhttp://en.wikipedia.org/wiki/Fieseler_Fi_156http://en.wikipedia.org/wiki/Leading_edge_slatshttp://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Flap_(aircraft)http://en.wikipedia.org/wiki/Spoileronhttp://en.wikipedia.org/wiki/Spoiler_(aeronautics)http://en.wikipedia.org/wiki/Sailplaneshttp://en.wikipedia.org/wiki/Empennagehttp://en.wikipedia.org/wiki/Rudderhttp://en.wikipedia.org/wiki/MD-80http://en.wikipedia.org/wiki/Servo_tabhttp://en.wikipedia.org/wiki/MD-80http://en.wikipedia.org/wiki/Stabilatorhttp://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Horizontal_stabilizerhttp://en.wikipedia.org/wiki/Elevator_(aircraft)http://en.wikipedia.org/wiki/Banked_turn#Aviationhttp://en.wikipedia.org/wiki/Joystickhttp://en.wikipedia.org/wiki/Ailerons

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Aerodynamic Forces

When anairfoil(or awing) is moving relative to the air it generates an aerodynamic force, in a

rearward direction at an angle with the direction of relative motion. This aerodynamic force is commonly

resolved into two components

dragis the force component parallel to the direction of relative motion, liftis the force component perpendicular to the direction of relative motion The force created by apropelleror ajet engineis calledthrustand it is also an aerodynamic force (since

it also acts on the surrounding air)

The force created by apropelleror ajet engineis calledthrustand it is also an aerodynamic force (sinceit also acts on the surrounding air)

The KuttaJoukowski theorem

The KuttaJoukowski theorem is a fundamental theorem ofaerodynamics. The theorem relates

theliftgenerated by a rightcylinderto the speed of the cylinder through the fluid, the density of the fluid, and

thecirculation. The circulation is defined as the line integral, around a closed loop enclosing the cylinder or

airfoil, of the component of the velocity of the fluidtangentto the loop.[1]

The magnitude and direction of thefluid velocity change along the path.

The theorem refers to two-dimensional flow around a cylinder (or a cylinder of infinite span) and

determines the lift generated by one unit of span. When the circulation is known, the lift per unit span

(or ) of the cylinder can be calculated using the following equation

where and are the fluid density and the fluid velocity far upstream of the cylinder, and is the

(anticlockwise positive) circulation defined as the line integral,

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Aerodynamic Drags

There are two main types of drag

1. Induced2. Parasitic:

a. Form dragb. Skin frictionc. Interference drag

1. Induced DragThis type of drag is based upon efficiency. Because no machine is 100% efficient, induced drag exists. With an

increase in efficiency, there will be a decrease in induced drag.It is the drag due to lift

Drag is defined in pounds

2. Parasitic Drag typesi. Form Drag: Due to the shape of an aircraft, form drag is a result of airflow going around it.

Consider a flat plate vs. a sphere when being thrown

ii. Interference Drag: This occurs a the intersection of air currents. For example, the wing rootconnected to the fuselage.

iii. Skin friction: This drag is the aerodynamic resistance from the contact of air with the surface ofthe airplane.

Sources of Induced Drag

When producing lift, air below the wing is generally at a higher pressure than the air pressure above the

wing, while air above the wing is generally at a lower than atmospheric pressure. On a wing of finite span, this

pressure difference causes air to flow from the lower surface wing root, around the wingtip, towards the upper

surface wing root. This spanwise flow of air combines with chordwise flowing air, causing a change in speed

and direction, which twists the airflow and produces vortices along the wing trailing edge. The vortices created

are unstable, and they quickly combine to produce wingtip vortices. The resulting vortices change the speed

and direction of the airflow behind the trailing edge, deflecting it downwards, and thus inducing downwash

behind the wing.

Wingtip vortices modify the airflow around a wing. Compared to a wing of infinite span, vortices reduce

the effectiveness of the wing to generate lift, thus requiring a higher angle of attack to compensate, which tilts

the total aerodynamic force rearwards. The angular deflection is small and has little effect on the lift. However,

there is an increase in the drag equal to the product of the lift force and the angle through which it is deflected.

Since the deflection is itself a function of the lift, the additional drag is proportional to the square of the lift.

Reducing Induced drag

Theoretically a wing of infinitespanand constantairfoilsection would produce no induced drag. The

characteristics of such a wing can be measured on a section of wing spanning the width of awind tunnel, since

the walls block spanwise flow and create what is effectively two-dimensional flow.

A rectangular wing produces much more severe wingtip vortices than a tapered orelliptical wing,

therefore many modern wings are tapered. However, an elliptical planform is more efficient as the induced

downwash (and therefore the effective angle of attack) is constant across the whole of the wingspan. Few

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aircraft have this planform because of manufacturing complications the most famous examples being

theWorld War IISpitfireandThunderbolt. Tapered wings with straight leading and trailing edges can

approximate to elliptical lift distribution. Typically, straight wings produce between 515% more induced drag

than an elliptical wing.

Similarly, a highaspect ratiowing will produce less induced drag than a wing of low aspect ratio because the

size of the wing vortices will be much reduced on a longer, thinner wing. Induced drag can therefore be said to

be inversely proportional to aspect ratio. The lift distribution may also be modified by the use ofwashout, a

spanwise twist of the wing to reduce the incidence towards the wingtips, and by changing theairfoilsectionnear the wingtips. This allows more lift to be generated at the wing root and less towards the wingtip, which

causes a reduction in the strength of the wingtip vortices.

Some early aircraft had fins mounted on the tips of the tailplane which served as endplates. More recent

aircraft have wingtip mountedwingletsor wing fences to oppose the formation of vortices. Wingtip mounted

fuel tanks may also provide some benefit, by preventing the spanwise flow of air around the wingtip.

What are wingtip vortices?

This is the wake that is generated from the wingtips. They are counter-rotating vortices that arecaused from air spilling over the end of the wing.

This pressure differential triggers the rollup of the airflow aft of the wing resulting in swirlingair masses trailing downstream of the wingtips (PHAK 12-13)

http://www.youtube.com/watch?v=E1ESmvyAmOs Wingtips generate induced drag. Therefore if an infinite wing does not have wingtips, it would

not generate induced drag.

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Introduction

One of the primary obstacles limiting the performance of aircraft is the drag that the aircraft produces.

This drag stems out from the vortices shed by an aircrafts wings, which causes the local relative wind

downward (an effect known as downward) and generated a component of the local lift force in the direction ofthe free stream called induced drag. The strength of this induced drag is proportional to the spacing and radii of

these vortices. By designing wings which force the vortices farther apart and at the same time create vortices

with large core radii, one may significantly reduce the amount of the drag the aircraft induces. Airplanes which

experience less drag require less power and therefore less fuel to fly an arbitrary distance, thus making flight,

commercial and otherwise, more efficient and less costly. Vortices at the wing tip can cause crash in aircraft.

This is when a big aircraft goes in front of a small aircraft; this big aircraft which has larger vortices can cause

the small aircraft to lose control and crash.

In airport to minimize the separation rule, an aircraft of a lower wake vortex category must not be

allowed to take off less than two minutes behind an aircraft of a higher wake vortex category. If the following

aircraft does not start its take off roll from the same point as the preceding aircraft, this is increased to three

minutes. One promising drag reduction device is winglet. For a number of years many investigations have been

carried out to prove the possible benefits of modifying wing tip flow. Tip devices have become a popular

technique to increase the aerodynamic performances of lifting wings. The present demand on fuel consumption

has emphasized to improve aerodynamic efficiency of an aircraft through a wingtip device which diffuses the

strong vortices produced at the tip and thereby optimise the span wise lift distribution, while maintaining the

additional moments on the wing within certain limits.