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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