wings design and application in flight theory

8/3/2019 Wings Design and Application in Flight Theory

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FACULTY OF ENGINEERING

DEPARTMENT OF MECHANICAL ENGINEERINGWind Engineering

RESEARCH PROJECT

WINGS DESIGN AND APPLICATION IN FLIGHT THEORY

PREPARED BY: IBUKUN OLUWOYE

ASSESSED BY: Dr Lida E. VAFAE

NICOSIA 2010


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Abstract

A wing has lots of applications. The popular wind turbine depends on wing

application; in fact it is generally known that the efficiency of the wind turbine

depends on the number of wings used. Applications of wing are also seen in

airplane. This term is generally known as flight theory.

In this report project, the effect of wings in flight will be studied and explain. In

general, how it helps in attaining lift for an aircraft, factors and conditions,

mathematical relation involve will all be critically discussed in this report.


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Table of Contents

1.0 Introduction .1

1.1 Aircrafts wings

1.2 types of wings

2.0 Theory of flight 4

2.1 effect of wings in flight2.2 wing shape

2.3 relative pressure difference

2.4 angle of attack and dihedral angle

2.5 wing vortices

2.6 ground effect

3.0 Calculations involved 153.1 general explanations

3.2 drag force and lift force

3.3 effect of angle of attack, aspect ratio and flaps

3.4 example and power concept

3.5 efficiency of flight wing

4.0 Conclusion and suggestion ..325.0 Reference .33


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1.0 Introduction

1.1 Aircrafts wings.

The wings are the airfoil that generates the lift necessary to get and

keep an aircraft off the ground. Like the fuselage to which they are

attached, they are made of aluminum alloy panels riveted together.

The point of attachment is the aircrafts center of gravity, or balance

point.

Most jet aircraft have, meaning the wings are angled back toward the

rear of the plane. Swept wings produce less lift than perpendicular

wings, but they are more efficient at high speed because they create

less drag.

Wings are mostly hollow inside, with large compartment for fuel. On

most of the aircraft in service today, the wings also support the

engines, which are attached to pylons hung beneath the wings.

Wings are designed and constructed with meticulous attention to

shape, contour, length, width and depth, and they are fitted with

many different kinds of control surface. [1]


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Now our days, the term wings had expanded into the world of

advanced engineering and technology. In wind turbine, the blades

are sometimes known as wings.

In aerodynamics, wings are one of the major parts of an aircraft. It is

a typical device designed to produce lift by generating a pressure

distribution that is different on the top and bottom surface. [2]

AIRPLANE PARTS WITH FUNCTION. [3]

1.2 Types of wings

There are different types of wing depending on their shapes. Aircraft

wings are built in many shapes and sizes for difference application. It

is depending on the desired flight characteristics of an aircraft. Also,

wing designed in difference configurations to achieve greater lift,

balance or stability in flight.


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Here shows a number of typical wing leading and trailing edge

shapes.

Delta wing: Thin triangular wing that is especially aerodynamic.

Variable geometry wing: Arrow-shaped wing found on combat

aircraft; the angle it forms with the fuselage can be changed in

flight.

Tapered wing: Wing that is perpendicular to the fuselage and

whose width decreases toward the tip.

Straight wing: Long wing of consistent width and perpendicular

to the fuselage; it is found on low-speed planes such as cargo

and light planes.

Swept-back wing: Arrow-shaped wing that is found on jet

planes. [4]


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2.0Theories of flight

2.1 Effect of wings in flight

To understand the effect of wings in flight we have to understand the

main forces acting on an aircraft. There are four forces acting on a

typical aircraft namely:

Weight

Lift

Drag

Thrust

The jet engine only creates thrust which opposes the drag force

thereby helping to move the plane forward.


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Our major objective is to create lift which will be opposite and

greater than the force of gravity (weight). The wing of a plane helps

to create lift. [5]

2.2 Wing shape

Wing shape is otherwise known as aerofoil.

The leading edge: the portion that meets the air first. The shape of

the leading edge depends upon the function of the airfoil. If the

airfoil is designed to operate at high speed, its leading edge will be

very sharp, as on most current fighter aircraft. If the airfoil is

designed to produce a greater amount of lift at a relatively low rate

of speed, as in a Cessna 150 or a Cherokee 140, the leading edge will

be thick and fat. Actually, the supersonic fighter aircraft and the light

propeller-driven aircraft are virtually two ends of a spectrum. Most

other aircraft lie between these two.


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Upper camberand Lower camber:Upper camber refers to the curve

of the upper surface of the airfoil, while lower camber refers to the

curve of the lower surface of the airfoil. In the great majority of

airfoils, upper and lower cambers differ from one another.

Mean camber: is the characteristic curve of its upper or lower

surface. The camber determines the airfoil's thickness. But, more

important, the camber determines the amount of lift that a wing

produces as air flows around it. A high-speed, low-lift airfoil has very

little camber. A low-speed, high-lift airfoil, like that on the Cessna

150, has a very pronounced camber.

Chord: is an imaginary straight line drawn through the airfoil from its

leading edge to its trailing edge. We might think of this chord line as

the starting point for drawing or designing an airfoil in cross section.

It is from this baseline that we determine how much upper or lower

camber there is and how wide the wing is at any point along the

wingspan. The chord also provides a reference for certain other

measurements.

Trailing edge: is the back of the airfoil, the portion at which the

airflow over the upper surface joins the airflow over the lower


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surface. The design of this portion of the airfoil is just as important as

the design of the leading edge. This is because the air flowing over

the upper and lower surfaces of the airfoil must be directed to meet

with as little turbulence as possible, regardless of the position of the

airfoil in the air. [5]

How the wing is use to create lift is explained below.

2.3 Relative pressure difference

The wings create lift due to the external flow of wind on its surface.

Airplanes fly when the movement of air across their wings creates an

upward force on the wings (and thus the rest of the plane)

That is greater than the force of gravity pulling the plane toward the

earth.

The physics behind this is called THE BERNOULLI PRINCIPLE. It was

first introduced by Daniel Bernoulli, an 18th century Swiss

mathematician and scientist who studied the movement of fluid.

When fluid travels at higher velocity the pressure will reduced and

when fluid travels at lower velocity pressure increases. [6]


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The wind that travels at the upper camber of the wing is faster

relatively to the wind that travels at the lower camber.

2.4 Angle of attack

The angle of attack is the angle that the wing presents to oncoming

air, and it controls the thickness of the slice of air the wing is cutting

off. Because it controls the slice, the angle of attack also controls the

amount of lift that the wing generates (although it is not the only

factor).


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Zero angle of attack

Shallow angle of attack

steep angle of attack

How the degree angle of attack affects the flight is discussed in later

part of the report.

Dihedral Angle.

The purpose of dihedral is to improve the aircraft stability during

flight. Dihedral angle is added to the wings for later or rolls stability.

When the aircraft encounters a slight roll displacement caused by

distribute from air stream or a gust of wind. An aircraft wings with

some dihedral will naturally return to its original position.


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The front view of this wing shows that the left and right wing do not

lie in the same plane but meet at an angle. The aircrafts wing is

inclined upward an angle from root to tip. The angle that the wing

makes with the local horizontal is called the dihedral angle. [7]

2.5 Wing vortices

One might ask what the downwash from a wing looks like. The

downwash comes off the wing as a sheet and is related to the details

on the load distribution on the wing. Figure 14 shows, through

condensation, the distribution of lift on an airplane during a high-g

maneuver. From the figure one can see that the distribution of load

changes from the root of the wing to the tip. Thus, the amount of air

in the downwash must also change along the wing. The wing near the

root is "scooping" up much more air than the tip. Since the wing near


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the root is diverting so much air the net effect is that the downwash

sheet will begin to curl outward around itself, just as the air bends

around the top of the wing because of the change in the velocity of

the air. This is the wing vortex. The tightness of the curling of the

wing vortex is proportional to the rate of change in lift along the

wing. At the wing tip the lift must rapidly become zero causing the

tightest curl. This is the wing tip vortex and is just a small (though

often most visible) part of the wing vortex. Returning to figure 5 one

can clearly see the development of the wing vortices in the

downwash as well as the wing tip vortices. [8]

Flow past finite length wing: (a) the horse shoe vortex system produced by the bound vortex and

trailing vortex; (b) the leakage of air around the wing tips produces the trailing vortices. [9]


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Winglets (those small vertical extensions on the tips of some wings)

are used to improve the efficiency of the wing by increasing the

effective length, and thus area, of the wing. The lift of a normal wing

must go to zero at the tip because the bottom and the top

communicate around the end. The winglet blocks this

communication so the lift can extend farther out on the wing. Since

the efficiency of a wing increases with area, this gives increased

efficiency. One caveat is that winglet design is tricky and winglets can

actually be detrimental if not properly designed.

2.6 Ground effect

Another common phenomenon that is often misunderstood is that of

ground effect. That is the increased efficiency of a wing when flying

within a wing length of the ground. A low-wing airplane will

experience a reduction in drag by as much as 50% just before it

touches down. This reduction in drag just above a surface is used by

large birds, which can often be seen flying just above the surface of

the water. Pilots taking off from deep-grass or soft runways also use

ground effect. Many pilots mistakenly believe that ground effect is

the result of air being compressed between the wing and the ground.


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To understand ground effect it is necessary to look again at the

upwash. Notice in Figure 15 that the air bends up from its horizontal

flow to form the upwash. Newton's first law says that there must be

a force acting on the air to bend it. Since the air is bent up the force

must be up as shown by the arrow. Newton's third laws says that

there is an equal and opposite force on the wing which is down. The

result is that the upwash increases the load on the wing. To

compensate for this increased load, the wing must fly at a greater

angle of attack, and thus a greater induced power. As the wing

approaches the ground the circulation below the wing is inhibited. As

shown in Figure below, there is a reduction in the upwash and in the

additional loading on the wing caused by the upwash. To

compensate, the angle of attack is reduced and so is the induced

power. The wing becomes more efficient. [8]

Wing out of ground effect


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Wing in ground effect


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3.0Calculation involved

3.1 General explanation

Like every other scientifically proven theories and demonstrations,

there are mathematical prove behind the philosophy of flight. In

these section, detailed about the mathematic needed will be given.

In fluid mechanics, the main aspect involved is the flow of an

immersed body. External flow over an immersed body that involves

air is often termed aerodynamics in response to the important

external flows produced when an object such as an airplane flies

through the atmosphere. [10]

Recall: when anybody moves through a fluid, an interaction between

the body and the fluid occurs; this effect can de described in term of

the force at the fluid-body interface. This can be described n term of

the stresseswall shear stresses, w , due to viscous effect and

normal stresses due to the pressure, p. Typical shear stress and

pressure distributions are shown in figure a & b below. Both w and p

vary in magnitude and direction along the surface.


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3.2 Drag force and Lift force

The resultant force in the direction of the upstream velocity is term

the drag, D, and the resultant force normal to the upstream velocity

is termed the lift, L, as is indicated in the figure c.[11]

The resultant of the shear stress and pressure distributions can be

obtained by integrating the effect of these two quantities on the

body surface as is indicated in figure c. the x and y component of the

fluid force on the small area element dA are


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Pressure and shear forces on a small element of the surface of a body.

Although these two equation above, the difficulties in their use lies in

obtaining the appropriate shear stress and pressure distribution on

the body surface.

Without the detailed information concerning the shear stress and

pressure distributions on a body those equations cannot be used.


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The widely used alternative is to define dimensionless lift and drag

coefficient and determine their approximate values by means of

either a simplified analysis, some numerical technique, or an

appropriate experiment. The lift coefficient, CL, and the drag

coefficient. CD, are defined as

A: characteristic area, projected area seen by a person looking

toward from a direction parallel to the upstream velocity

U: upstream velocity

: density of air

L: lift force

D: drag force

CD and CL are function of shape, Reynolds Number, Mach

number, Froude number, Relative roughness of the surface. It will

be given depending on the standard of wing design to be

followed.

Most lift-producing objects are not symmetrical.


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Symmetrical and nonsymmetrical airfoils.

3.3 Effect of Angle of attack, Aspect ratio and Flaps

Effect of angle of attack: typically lift and drag force coefficient data

as a function of angle of attack, , and aspect ratio, A, are indicated

n figure below. The aspect ratio is defined as the ratio of the square

of the wing length to the planform area, A= b2 / A. if the chord

length, c, is constant along the length of the wing (a rectangular

planform wing), this reduces to A= b/c

in general, the lift coefficient increases and the drag coefficient

decrease with an increase in aspect ratio. Long wings are more

efficient because their wing tip losses are relatively more minor

than for short wings. [12]


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In many lift-generating devices the important quantity is the ratio

of the lift to drag develop, L/D = CL/CD. Such information is often

presented in terms of CL/CD versus , as is shown in figure below,

or in a lift-drag polar of CL versus CD with as a parameter, as

shown in the figure. The most efficient angle of attack (i.e., largest


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CL/CD) can be found by drawing a line tangent to the CL CD curve

form the origin, as is shown in figure. [13]

Lift and drag coefficient vs. angle of attack. [14]


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Lift-drag polar for two airfoil section of 15 percent ratio.

Effect of angle of attack can also be explained by the

phenomenon of circulation. It explain inviscid flow analysis which

can be used to obtain ideal flow past airfoil.


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Inviscid flow past an airfoil: (a) symmetrical flow past the

symmetrical airfoil at a zero angle of attack. (b) same airfoil at a

nonzero angle of attack no lift, flow near trailing edge not

realistic, (c) same airfoil as for (b) except circulation has been

added to the flow-nonzero lift, realistic flow, (d) superposition of

flow to produce the final flow past the airfoil. [15]


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Furthermore, the performance of wing can be greatly altered by

the availability of flaps.

Typical lift and drag alterations possible with the use of various

types of flap design.


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3.4 Example and Power concept

EXAMPLE

In 1977 the Gossamer Condor won the Kremer prize by being the first

human-powered aircraft to complete a prescribed figure-of-eight

course around two turning points 0.5 mi apart. The following data

pertin to this aircraft: [16]

Flight speed = U = 15ft/s

Wing size = b = 96ft, c = 7.5ft (average)

Weight (including pilot) = W 210lb

Drag coefficient = CD = 0.046 (based on planform area)

Power train efficiency = = power to overcome drag/pilot= 0.8

Determine the lift coefficient, CL, and the power,P, requird by the

pilot.

SOLUTION

For steady flight condition the lift must be exactly balanced by the

weight, or

Where A= bc = 96ft 7.5ft = 720ft2, W= 210lb, and = 2.38 slug/ft

3

for standard air. This gives


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ANS

A reasonable number. The overall-lift-to drag ratio for the aircraft is

CL/CD = 1.09/0.046 = 23.7

The product of the power that the pilot supplies and the power train

efficiency equals the useful power needed to overcome the drag, D.

That is

P = DU

where

ANS


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POWER REQUIRED FOR LIFT: As we can see from the example, the

power required for a lift can be determined. When a plane passes

overhead the formally still air gains a downward velocity. Thus, the

air is left in motion after the plane leaves. The air has been given

energy. Power is energy, or work, per time. So, lift requires power.

This power is supplied by the airplanes engine (or by gravity and

thermals for a sailplane).

How much power will we need to fly? If one fires a bullet with a

mass, m, and a velocity, v, the energy given to the bullet is simply

mv2. Likewise, the energy given to the air by the wing is

proportional to the amount of air diverted down times the vertical

velocity squared of that diverted air. We have already stated that the

lift of a wing is proportional to the amount of air diverted times the

vertical velocity of that air. Thus, the power needed to lift the

airplane is proportional to the load (or weight) times the vertical

velocity of the air. If the speed of the plane is doubled the amount of

air diverted down doubles. Thus to maintain a constant lift, the angle

of attack must be reduced to give a vertical velocity that is half the

original. The power required for lift has been cut in half. This shows


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that the power required for lift becomes less as the airplane's speed

increases. In fact, we have shown that this power to create lift is

proportional to 1/speed of the plane.

But, we all know that to go faster (in cruise) we must apply more

power. So there must be more to power than the power required for

lift. The power associated with lift is often called the "induced"

power. Power is also needed to overcome what is called "parasitic"

drag, which is the drag associated with moving the wheels, struts,

antenna, etc. through the air. The energy the airplane imparts to an

air molecule on impact is proportional to the speed2

(form mv2) .

The number of molecules struck per time is proportional to the

speed. The faster one goes the higher the rate of impacts. Thus the

parasitic power required to overcome parasitic drag increases as the

speed3.

Figure below shows the "power curves" for induced power, parasitic

power, and total power (the sum of induced power and parasitic

power). Again, the induced power goes as 1/speed and the parasitic

power goes as the speed3. At low speed the power requirements of

flight are dominated by the induced power. The slower one flies the


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less air is diverted and thus the angle of attack must be increased to

increase the vertical velocity of that air. Pilots practice flying on the

"backside of the power curve" so that they recognize that the angle

of attack and the power required to stay in the air at very low speeds

are considerable.

Power requirements versus speed.

At cruise, the power requirement is dominated by parasitic power.

Since this goes as the speed3

an increase in engine size gives one a

faster rate of climb but does little to improve the cruise speed of the

plane. Doubling the size of the engine will only increase the cruise

speed by about 25%.


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Since we now know how the power requirements vary with speed,

we can understand drag, which is a force. Drag is simply power

divided by speed. Figure 11 shows the induced, parasitic, and total

drag as a function of speed. Here the induced drag varies as

1/speed2

and parasitic drag varies as the speed2. Taking a look at

these figures one can deduce a few things about how airplanes are

designed. Slower airplanes, such as gliders, are designed to minimize

induced power, which dominates at lower speeds. Faster propeller-

driven airplanes are more concerned with parasite power, and jets

are dominated by parasitic drag. (This distinction is outside of the

scope of this article.). [8]

Drag versus speed.


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3.5 Efficiency of Flight wing.

Efficiency of a wing is the ratio of input to output power

consumption. To have highly effective wing, all the factors that affect

the efficiency of flight that have been discuss must be critically

consider.

Useful simplicities;

The amount of airdiverted by the wing is proportional to

the speed of the wing and the air density.

The vertical velocityof the diverted air is proportional to

the speed of the wing and the angle of attack.

The liftis proportional to the amount of air diverted times

the vertical velocity of the air.

Thepowerneeded for lift is proportional to the lift times

the vertical velocity of the air.


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4.0Conclusion and Suggestion

Conclusively, wings and it effect in flight had been discussed. It has been

shown that wing plays the major and the most important role in

aerodynamics analysis of flight.

Furthermore, the other minor but vital properties are also important. This

includes; angle of attack, aspect ratio, flaps, etc.

As a suggestion, I strongly suggest an additional chapter five to this project

report. The chapter will contain a simple scaled design of a flight wing. It

will be done by drawing our own new scaled dimension of wing from a

NACA standard, then actualizing it.


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5.0References

[1]: http://www.avjobs.com/history/how-aircraft-fly.asp

[2]: Fundamentals off fluid mechanics, Munson Young Okiishi, third edition, page 616,

[3]: national aeronautics and space agency; http://www.grc.nasa.gov/WWW/K-

12/airplane/airplane.html

[4]: http://visual.merriam-webster.com/transport-machinery/air-transport/examples-

wing-shapes.php

[5]: http://www.esparacing.com/sport_pilot/fxd_wing_fly.htm

[6]: Advanced Physics, Steve Adams and Jonathan Allday, oxford.

[7]: http://simbahzezen-simbah.blogspot.com/2010/05/configuration-wing.html

[8]: http://home.comcast.net/~clipper-108/lift.htm

[9]: see [2], page 622

[10]: see [2]. Page551

[11]: see [2]. Page 553

[12]: see [2]. Page 617

[13]: see [2]. Page 618

[14]: Introduction to Fluid Mechanics, Robert W. Fox and Alan T. McDonald, Fourth

Edition, page 433

[15]: see [2]. Page 621

[16]: see [2]. Page 620

wings design and application in flight theory

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