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CHAPTER 1INTRODUCTION
1
INTRODUCTION
THORPEDO T211 – Even the name screams power and performance.
Affectionately named after its designer, John Thorp, the six cylinders Jabiru
3300 equipped T211 is not an ordinary aircraft. The combination of a light, yet
strong airframe with 120 horsepower provides a tremendous power to weight
ratio which creates short take off runs, strong climbs and impressive cruise
speeds. The Thorpedo is the first U.S. manufactured aircraft to earn the Special
Airworthiness certificate under the Light Sport Aircraft ruling. The FAA type
certified heritage ensures a proven design that has been tested to a higher
standard. With all its power, this nimble aircraft outperforms many in its class.
The available digital panel, luxurious interior and other options make this an
efficient or spirited recreational aircraft, suitable for both the seasoned pilot and
the new sport pilot alike.
Almost all the trainer and light sport aircraft have fixed landing gear
system. The landing gear system itself produces about 20 – 40% of the total
drag produced in an airplane. We know that the resultant power needed to
overcome this drag will vary as the cube of velocity, hence if the drag produced
in the aircraft is reduced, the total power consumed by the aircraft will be
reduced by a great extent. In order to do so, the perfect alternative would be the
retractable landing gear system, which will not only increase the performance of
the aircraft but will also enhance the maneuverability of the aircraft. We will
also be observing the various changes which will occur with respect to
aerodynamics and performance of the aircraft. The present wing of the aircraft
does not have the thickness to incorporate the landing gear of the aircraft, thus
we will have to change the wing of the aircraft keeping in mind the lift co-
efficient and the Reynolds no. at which the aircraft flies. Hence to check the
results we have made a prototype of the aircraft and tested the same in the wind
tunnel.
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The project is an industrial project sponsored by Taneja Aerospace and
Aviation Ltd., Hosur. Part of the Pune based Indian Seamless group, TAAL was
established in 1994 as the first private sector company in the country to
manufacture general aviation i.e. non-military aircraft. The company’s vision at
the time was to create a nucleus facility for the development of an aeronautical
industry in India, TAAL entered into collaboration with Partenavia of Italy to
manufacture the six-seat twin piston engine P68C aircraft and the eleven-seat
twin turbo-prop Viator aircraft. While TAAL continues to manufacture Light
Transport and Trainer Aircraft, the company has since diversified its activities
and has established a significant presence in many segments of the aviation and
aeronautical industries in India.
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CHAPTER 2DRAG
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DRAG
In fluid dynamics, drag (sometimes called air resistance or fluid resistance)
refers to forces that oppose the relative motion of an object through a fluid (a
liquid or gas). Drag forces act in a direction opposite to the oncoming flow
velocity. Unlike other resistive forces such as dry friction, which is nearly
independent of velocity, drag forces depend on velocity. For a solid object
moving through a fluid, the drag is the component of the net aerodynamic or
hydrodynamic force acting opposite to the direction of the movement. The
component perpendicular to this direction is considered lift. Therefore drag
opposes the motion of the object, and in a powered vehicle it is overcome by
thrust. In aerodynamics, and depending on the situation, atmospheric drag can
be regarded as an inefficiency requiring expense of additional energy during
launch of the space object or as a bonus simplifying return from orbit.
VARIOUS TYPES OF DRAG:
1) PARASITE DRAG:
i) FORM DRAG
ii) SKIN FRICTION DRAG
iii) INTERFERENCE DRAG
2) LIFT-INDUCED DRAG
3) WAVE DRAG
2.1 PARASITE DRAG:
Parasitic drag (also called parasite drag) is drag caused by moving a solid
object through a fluid. Parasitic drag is made up of multiple components
including viscous pressure drag (form drag), and drag due to surface roughness
(skin friction drag). Additionally, the presence of multiple bodies in relative
proximity may incur so called interference drag, which is sometimes described
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as a component of parasitic drag. In aviation, induced drag tends to be greater at
lower speeds because a high angle of attack is required to maintain lift, creating
more drag. However, as speed increases the induced drag becomes much less,
but parasitic drag increases because the fluid is flowing faster around protruding
objects increasing friction or drag. At even higher speeds in the transonic, wave
drag enters the picture. Each of these forms of drag changes in proportion to the
others based on speed. The combined overall drag curve therefore shows a
minimum at some airspeed - an aircraft flying at this speed will be at or close to
its optimal efficiency. Pilots will use this speed to maximize endurance
(minimum fuel consumption), or maximize gliding range in the event of an
engine failure.
2.2 LIFT-INDUCED DRAG:
Lift-induced drag (also called induced drag) is drag which occurs as the result
of the creation of lift on a three-dimensional lifting body, such as the wing or
fuselage of an airplane. Induced drag consists of two primary components,
including drag due to the creation of vortices (vortex drag) and the presence of
additional viscous drag (lift-induced viscous drag). The vortices in the flow-
field, present in the wake of a lifting body, derive from the turbulent mixing of
air of varying pressure on the upper and lower surfaces of the body, which is a
necessary condition for the creation of lift. With other parameters remaining the
same; as the lift generated by a body increases, so does the lift-induced drag.
For an aircraft in flight, this means that as the angle of attack, and therefore the
lift coefficient, increases to the point of stall, so does the lift-induced drag. At
the onset of stall, lift is abruptly decreased, as is lift-induced drag, but viscous
pressure drag, a component of parasite drag, and increases due to the formation
of turbulent unattached flow on the surface of the body.
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FIG 2.1 INDUCED DRAG Vs LIFT
2.3WAVE DRAG:
Wave drag (also called compressibility drag) is drag which is created by the
presence of a body moving at high speed through a compressible fluid. In
aerodynamics, Wave drag consists of multiple components depending on the
speed regime of the flight. In transonic flight (Mach numbers greater than 0.5
and less than 1.0), wave drag is the result of the formation of shockwaves on the
body, formed when areas of local supersonic (Mach number greater than 1.0)
flow are created. In practice, supersonic flow occurs on bodies traveling well
below the speed of sound, as the local speed of air on a body increases when it
accelerates over the body, in this case above Mach 1.0. Therefore, aircraft flying
at transonic speed often incur wave drag through the normal course of
operation. In transonic flight, wave drag is commonly referred to as transonic
compressibility drag. Transonic compressibility drag increases significantly as
the speed of flight increases towards Mach 1.0, dominating other forms of drag
at these speeds. In supersonic flight (Mach numbers greater than 1.0), wave
drag is the result of shockwaves present on the body, typically oblique
shockwaves formed at the leading and trailing edges of the body. In highly
supersonic flows, or in bodies with turning angles sufficiently large, unattached
shockwaves, or bow waves will instead form. Additionally, local areas of
transonic flow behind the initial shockwave may occur at lower supersonic
speeds, and can lead to the development of additional, smaller shockwaves
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present on the surfaces of other lifting bodies, similar to those found in
transonic flows. In supersonic flow regimes, wave drag is commonly separated
into two components, supersonic lift-dependent wave drag and supersonic
volume -dependent wave drag.
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CHAPTER 3DRAG REDUCTION TECHNIQUES
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DRAG REDUTION TECHNIQUES
Drag reduction is one of the main objectives of the transport aircraft
manufacturers. The drag breakdown of a transport aircraft at cruise shows that
the skin friction drag and the lift-induced drag constitute the two main sources
of drag, approximately one half and one third of the total drag. Hybrid laminar
flow technology and innovative wing tip devices offer the greatest potential for
drag reduction. Aircraft performance improvement in off-design conditions can
also be obtained through trailing edge optimization, control of the shock
boundary layer interaction and of the boundary layer separation. The paper will
give an overview of the results obtained for the different mentioned topics and
will try to evaluate the potential gains offered by the different technologies.
Drag reduction of civil transport aircraft directly concerns performance, but also
indirectly, of course, cost, and environment. Fuel consumption represents about
22% of the Direct Operating Cost (DOC) which is of utmost importance for the
airlines, for a typical long range transport aircraft.
Drag reduction directly impacts on the DOC: a drag reduction of 1% can
lead to a DOC decrease of about 0.2% for a large transport aircraft. Other trade-
offs corresponding to a 1% drag reduction are 1.6 tons on the operating empty
weight or 10 passengers. The environmental factors, such as noise, air pollution
around airports and impact on climate change, which are well underlined in [1],
will also play an important role for future growth of the civil aviation. The
impact of air travel on the environment will then become an increasing powerful
factor on aircraft design. It is also important to recall the main goals of the
vision 2020 launched by the European commission: a 50% cut in CO2
emissions per passenger kilometer and an 80% cut in nitrogen oxide emissions.
These objectives cannot be reached without breakthrough in today technologies.
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Drag reduction is a great challenge but there is certainly room for
improvements. The drag breakdown of a civil transport aircraft shows that the
skin friction drag and the lift-induced drag constitute the two main sources of
drag, approximately one half and one third of the total drag for a typical long
range aircraft at cruise conditions. This is why specific research on these topics
has been initiated in European Research centers and it seems that Hybrid
Laminar Flow technology and innovative wing tip devices offer the greatest
potential. Aircraft performance improvement can also be obtained through
trailing edge optimization, control of the shock boundary layer interaction and
of boundary layer separation. In the following sections, the different
technologies which were investigated at ONERA will be presented and
illustrated by experimental results.
3.1 SKIN FRICTION DRAG REDUCTION
Two methods are generally considered for skin friction drag reduction.
The first one aims at reducing the turbulent skin friction while the second one
aims at delaying transition to maintain large extent of laminar flow.
3.1.1 Turbulent skin friction reduction
A skin friction drag reduction can be obtained with the use of passive
boundary layer manipulators. Among the various devices, V-groove rib-lets
have demonstrated substantial reductions (up to 8%) of the local skin friction.
An experimental verification in a large wind tunnel was carried out in 1988 on a
1/11 scale complete model of the Airbus A320. For the test, 2/3 of the wetted
model surface was covered with the rib-lets for which the previously mentioned
V-groove cross-section has been chosen. Viscous flow computations on the
wing and on the fuselage have shown that a rib-let depth of 0.023 mm can allow
a average value of h + w=8 to be obtained. Wind tunnel test was successful and
total drag reductions up to 1.6% have been demonstrated at corresponding
cruise Mach number conditions.
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With the guidelines of the previous wind tunnel investigations and the
recommendations coming from the structure, material and system teams, a flight
test was prepared with the Airbus A320 No 1. 600 m2 rib-let film covering 75%
of the wetted surface was installed on the aircraft and the tests took place in
1989. Overall performance and local data were measured with and without the
rib-lets, and drag reduction predictions based on the wind tunnel tests were
confirmed.
Operational aspect and maintenance problems have then been
investigated and in-service application has been decided by the Cathay Pacific
Airways airline on an A340.Significant fuel consumption has been obtained.
However, this in service application showed that the rib-let film has to be
replaced after 2-3 years. The applications of this technology depend now on the
quality improvement of the rib-let film: the characteristics of the film have to be
maintained at least for 5 years in order to obtain benefits.
3.1.2 Hybrid laminar flow technology
A substantial reduction in fuel consumption and in CO2 emissions will
certainly require the adoption of laminar flow control in order to reduce the skin
friction. For small aircraft with low swept wing, laminar flow can be maintained
by shaping the airfoil and this concept is currently considered for new small jet
aircraft. However for high Reynolds number and high sweep encountered on a
large transport aircraft, suction has to be applied.
In the Hybrid Laminar Flow concept, the laminar flow can be maintained
by the application of suction in the region of the leading edge to control the
development of cross flow instabilities combined with favorable pressure
gradients in the spar box region. It is first necessary to ensure that the
attachment line remains laminar and to avoid contamination phenomenon. Anti
contamination devices have to be used to avoid the contamination of the
attachment line by the turbulent structures coming from the fuselage.
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The suction system has to be designed according to various aerodynamic
and structure requirements. Main features of suction systems are laser drilled
titanium panel and suction chambers controlled by independent ducts. The
geometrical characteristics of perforated panel such as hole diameter, porosity
as well as chamber sizes are determined taking into account the suction velocity
range, computed by stability approach, and pressure distributions for various
aerodynamic conditions. With suction systems, premature transition can be
caused by outflow and by roughness effects due to high velocities in the suction
holes. Pressure drop methods and suction criteria have to be used to avoid these
premature transitions.
Surface imperfections such as isolated roughness, gaps, steps and
waviness can provoke premature transition. It is then necessary to study their
effects on transition and to develop calculation methods and criteria in order to
estimate these effects. Recent studies have shown that modern manufacturing
techniques can provide smooth surfaces, compatible with laminar flow.
Recent progress carried out towards the understanding of transition
characteristics of swept-wing flows would allow to control the transition by
passive means. Some experiments presented in have shown that transition
governed by cross flow instabilities can be delayed using artificial roughness. In
this concept, the artificial vortices interact nonlinearly with the natural vortices
in such a way that the natural vortices are strongly reduced. In this approach, the
drag reduction could be lower than the one expected with the HLF concept, but
the drawbacks are also very limited. It is worthwhile to investigate these passive
means through basic experiments and non-linear PSE computations, because
they can contribute to the system simplification needed for a future laminar
aircraft.
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3.2 LIFT-INDUCED DRAG REDUCTION
The second major drag component is the lift-induced drag. The classical
way to decrease the lift-induced drag is to increase the aspect ratio of the wing.
Wing aspect ratio is a compromise between aerodynamic and structure
characteristics and it is clear that for a given technology there is not a great
possibility to increase aspect ratios. The alternative is to develop wing tip
devices acting on the tip vortex which is at the origin of the lift-induced drag.
Basic studies have shown that drag reduction can be obtained with variations in
plan form geometry along a small fraction of the wing-span and with aft-swept
configurations. Furthermore, the presents, as examples among the investigated
shapes, the wing tip turbine, the wing tip sails, the wing grid, the blended
winglet and the spiroid tip.
Fig 3.1 various wingtip devices
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The concept of the blended winglet is to modify a large part of the wing
tip together with the winglet itself in order to obtain a very smooth blended
shape. The blended winglet is expected to be more efficient than a narrow one
to reduce the flow acceleration that occurs in the cross flow curvature and to
decrease the vortex intensity as important chord variation is avoided. The
spiroid tip is a spiral loop obtained when joining by their tip a vertical winglet
and a horizontal one. This unconventional device seems promising to reduce the
tip vortex intensity but has a complex geometry difficult to optimize. Total drag
reduction of about 2% can be expected with such wing tip devices. However,
for industrial applications, wingtip devices have a strong influence on the wing
structure and aero- elastic effects have to be taken into account through a
multidisciplinary optimization approach.
3.3 WAVE DRAG REDUCTION
Even if the wave drag contribution to the total drag of a modern transport
aircraft is not high, there is room for some significant improvements through
adaptation of the aircraft to the variation of the flight conditions : an increase of
the cruise Mach number for example. This aerodynamic adaptation can be
realized with shock control or trailing edge devices.
3.3.1 Shock control devices
Among the different passive shock boundary layer control concepts
investigated, the bump concept seems promising. This concept is based on the
local modification of the airfoil surface in the shock region. The straight shock
is transformed into a lambda shock configuration and its strength is reduced by
the presence of the compression waves.
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3.3.2 Trailing edge devices
For wave drag reduction, the concept of the thick cambered trailing edge
which increases the rear loading and reduces the upper surface pressure
recovery seems also very promising. This concept has then been investigated on
a wing body configuration under a co-operation with Airbus France. Tests were
carried out on a half-model in the wind tunnel and the results have been
carefully analyzed through far-field drag extraction techniques. The computed
and measured drag reduction obtained when the thick cambered trailing edge is
installed in the outer part of the wing. It is clear that the thick cambered trailing
edge concept can be used by the designer as an additional degree of freedom. Its
effects can also be obtained through a trailing edge deflector. These results
show that characteristics of the flow can be strongly modified with the use of a
trailing edge device which allows drag reduction and greater buffet margin to be
obtained. Important investigations are currently carried out to adapt the wing
geometry to the different flight conditions: cruise, take-off and landing.
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CHAPTER 4LANDING GEAR
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LANDING GEAR
Landing gear is the structure under a plane's fuselage that allows it to land
safely. The earliest landing gear consisted of skids, but designers soon attached
wheels to the skids. Landing gear must have some mechanism for absorbing the
force of the landing in addition to the airplane's weight. Early gear used flexible
material for landing gear struts (the structure that connected the airframe and the
wheels). Some landing gear use a shock absorbing system called the oleo strut
that cushions the landing and keeps the plane level while landing. The Thorpedo
T211 Aircraft is currently equipped with the oleo strut type of landing gear. The
diagram below shows the typical configuration of the oleo strut type of landing
gear
Fig 4.1 Courtesy: www.pilotfriend.com
The above diagram also shows us how the landing gear works as a shock
absorber on sudden impact during landing. Landplanes are fitted with either a
nose wheel or tail wheel. The gear is always sprung. This can be by the use of
spring metal, rubber or by oleo. An oleo is in effect a spring and shock absorber
combined. Most modern aircraft have are fitted with a nosewheel (tricycle).
Earlier designs are most likely to have a tail wheel (taildragger). However, the
THORPEDO T211 Aircraft is fitted with tricycle type of landing gear.
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4.1 RETRACTABLE LANDING GEAR
Aircraft designers of the 1920s knew that reducing drag on an airplane in
flight was important to improving speed and fuel efficiency, as well as
maneuverability and controllability. But they still had relatively little
understanding of what actually caused drag on airplanes. Various structures
obviously caused drag, but they had first to identify the most important sources
before they could address them.
In 1927, the National Advisory Committee for Aeronautics (NACA)
opened its new Propeller Research Tunnel (PRT) at Langley Memorial
Aeronautical Laboratory in Virginia. The PRT was a very large wind tunnel for
the time, with a diameter of 20 feet (6.1 meters). It was designed to allow the
testing of an entire airplane fuselage with engine and propeller, as opposed to
simply a part of an airplane or a scale model. NACA aeronautical engineers
suspected that the aircraft landing gear contributed to much of the drag of an
airplane, and the PRT was the first wind tunnel that would allow them to test
this.
Landing gear consists of the wheels that stick out below the fuselage so
that an airplane can roll down the runway during landing and takeoff. In early
aircraft, they were fixed in an open position so that they protruded at all times,
even while the plane was flying and nowhere near the ground. Tests in the PRT
immediately demonstrated that landing gear contributed up to 40 percent of
fuselage drag, which shocked the researchers. They realized that reducing the
drag produced by the landing gear would significantly improve the performance
of the airplane in flight.
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The retractable landing gear system used in modern day aircrafts is
shown in the figure below:
Fig 4.2 Courtesy: www.google.com
Hydraulic pump is used to pressurize the hydraulic fluid. This fluid
pressure is used for retraction and release of landing gear. Few trainer aircrafts
are equipped with the retractable landing gear as the Mooney- Ovation GX
aircraft as shown in the diagram below
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Fig 4.3 Courtesy: www.mooney.com
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CHAPTER 5DESIGN
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AUTOCAD
AutoCAD is a CAD (Computer Aided Design or Computer Aided
Drafting) software application for 2D and 3D design and drafting, developed
and sold by Autodesk, Inc. Computer-aided design (CAD) is the use
of computer technology for the design of objects, real or virtual. CAD often
involves more than just shapes. As in the
manual drafting of technical and engineering drawings, the output of CAD often
must convey also symbolic information such as materials, processes,
dimensions, and tolerances, according to application-specific conventions.
Fig 5.1: SIDE VIEW
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Fig 5.2: TOP VIEW
Fig 5.1 and 5.2 shows us the side view and the top view of the model aircraft.
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CHAPTER 6WING SELECTION
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Following six terms are essential in determining the shape of a typical
airfoil:
(1) The leading edge
(2) The trailing edge
(3) The chord line
(4) The camber line (or mean line)
(5) The upper surface
(6) The lower surface
Fig 6.1
For Thorpedo T211 aircraft,
Wing Span, b = 7.62m
Wing Area, S = 9.75m2
S = b x Croot
Solving,
Croot = 1.28m
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Aspect Ratio, A.R = b2
S
= 5.953m
Wing loading, W 0
S = 576.607N/m2
Stall Velocity, Vstall = 39 knots
=20.063m/s
CLmax = 2(WS
)
ρV stall2
Density at sea level = 1.225kg/m3
Hence,
CLmax = 2.338746
Reynold’s number:
Reynolds's number, Re = ρ×V ×Lμ
µ0 = 1.667x10-5 Ns/m2
ρ0 = 1.225kg/m3
Re = 3.8318023 x 106
Hence it is transient flow.
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When a retractable landing gear is installed it needs provisions to be stored
within airplane body. In Thorpedo T211 aircraft fuel is stored within the
fuselage. Hence the wings are hollow. This space can be utilized for storing the
under carriage once it’s retracted. But, the existing airfoil NACA 1410 is a thin
airfoil and cannot accommodate it. So a new airfoil which is thicker and has
more CLmax, in order to counter the extra weight of landing gear mechanism, is
selected.
NACA 4415 airfoil meets all these requirements.
0 20 40 60 80 100 120
-6-4-202468
101214
NACA 4415
Fig 6.2
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National Advisory Committee for Aeronautics (NACA)
Mathematical theory has not, as yet, been applied to the discontinuous motion
past a cambered surface. For this reason, we are able to design aerofoil only by
consideration of those forms which have been successful, by applying general
rules learned by experience, and by then testing the airfoils in a reliable wind
tunnel.
NACA 4415 is defined as a shape that has a maximum camber of 4 percent of
the chord (first digit); the maximum camber occurs at a position of 0.4 chord
from the leading edge (the second digit), and the maximum thickness is
15percent (the last two digits).
NACA 1410 is defined as a shape that has a maximum camber of 1percent of
the chord (first digit); the maximum camber occurs at a position of 0.4 chord
from the leading edge (the second digit), and the maximum thickness is 10
percent (the last two digits).
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CHAPTER 7FABRICATION OF MODEL
30
The fabrication process of the aircraft model can be sub-divided into 3
basic steps viz.
7.1 Carving :
Carving of the aircraft model means precise shaping the wood into the desired
without using any powered tools. The wood used for the fabrication of the
model is the Balsa wood, which are lightweight, simple to construct and
inexpensive to gather materials for. Extreme accuracy has to be maintained in
making the model as the whole success of the project depends on it. Various
tools that were used are wooden files, sand paper, hacksaw blade, bench knives,
straight chisels, skew chisels etc.
7.2 Fixing :
The second stage of the fabrication is to fix the various parts of the aircraft more
or less like assembly. The parts that were fixed to the fuselage were the wings,
propeller, vertical stabilizer and the horizontal stabilizer. Various adhesives
were used in this process like fevicol, anabond and m-seal.
7.3 Primer Coating / Artwork :
Once the adhesives have dried then comes the final stage in fabrication process
– the artwork. Before the model is painted primer coating has to be given to
model. A primer is a preparatory coating put on materials before painting.
Priming ensures better adhesion of paint to the surface, increases paint
31
durability, and provides additional protection for the material being painted.
Fig 7.1 FABRICATION OF MODEL
The above figure gives us a pictorial description as how the model looks with
primer coated over it. Once the primer has dried off the model has been painted
with the desired colors.
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CHAPTER 8WIND TUNNEL
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8.1WIND TUNNEL
The "Wind tunnel" is a facility, by artificially producing airflow relative
to a stationary body, that measures aerodynamic force and pressure distribution
to simulate the actual flight of airplane or orbiting plane in the air.
TYPES:
Wind tunnels are often denoted by the speed in the test section relative to
the speed of sound. The ratio of the air speed to the speed of sound is called the
Mach number.
Tunnels are classified as
• Subsonic (M < 0.8),
• Transonic (0.8 < M < 1.2) ,
• Supersonic (1.2 < M < 5.0) , or
• Hypersonic (M > 5.0).
8.2 OPEN CIRCUIT SUBSONIC WIND TUNNEL :
Fig 8.1 Open Circuit Wind Tunnel
34
8.2.1 Honey comb:
Honey comb along with the wire mesh protects the wind tunnel from
foreign objects. It also provides laminar flow for the wind tunnel test section.
8.2.2 Effuser:
It converts the available pressure energy to kinetic energy which is
located upstream of the test.
8.2.3 Test section:
The models to be tested are placed inside the test section by means of
supports and balances. The instruments necessary for recording the data are also
fixed in the wind tunnel.
8.2.4 Diffuser:
Diffuser is locates at the downstream of the test section, it converts the
kinetic energy to pressure energy.
8.2.5 Propeller driving unit:
A fan or a propeller is fitted with electric motor to drive airflow to the test
section.
8.3 Measurement of aerodynamic forces
Ways that air velocity and pressures are measured in wind tunnels:
Air velocity through the test section (called the throat) is determined
by Bernoulli's principle. Measurement of the dynamic pressure, the static
pressure, and (for compressible flow only) the temperature rise in the airflow
35
Direction of airflow around a model can be determined by tufts of yarn
attached to the aerodynamic surfaces
Direction of airflow approaching an aerodynamic surface can be visualized
by mounting threads in the airflow ahead of and aft of the test model
Dye, smoke, or bubbles of liquid can be introduced into the airflow upstream
of the test model, and their path around the model can be photographed
8.4 Force and moment measurements:
With the model mounted on a force balance, one can measure lift, drag, lateral
forces, yaw, roll, and pitching moments over a range of angle of attack. This
allows one to produce common curves such as lift coefficient versus angle of
attack.
The force balance itself creates drag and potential turbulence that will affect the
model and introduce errors into the measurements. The supporting structures
are therefore typically smoothly shaped to minimize turbulence.
8.5 Flow visualization :
In general, flow visualization is an experimental means of
examining the flow pattern around a body or over its surface. The flow is
"visualized" by introducing Yarn Tufts, smoke or pigment to the flow in the
area under investigation. The primary advantage of such a method is the ability
to provide a description of a flow over a model without complicated data
reduction and analysis. Smoke flow visualization involves the injection of
streams of vapor into the flow. The vapor follows filament lines (lines made up
of all the fluid particles passing through the injection point). In steady flow the
filament lines are identical to streamlines (lines everywhere tangent to the
velocity vector). Flow visualization can thus reveal the entire flow pattern
around a body.
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8.6 TUFT WANDS:
The least expensive method for flow visualization is a tuft wand. This method is
very much versatile and at the same time the flow pattern around the test object
is visible. A long tuft on a pole is useful for tracking the flow near the object.
Flow visualization foe the moment is possible if the trace particles location can
be identified at any time in the flow field.
Fig 8.2 Courtesy: www.nasa.gov
37
8.7 Three component balancing:
The Three-Component Balance provides an easy-to-use support system
for wind tunnel models. It measures lift, drag and pitching moment exerted on
the model. The balance attaches to the vertical wall of the wind tunnel working
section. It is designed for air flows from right to left when the balance is viewed
from the front. The balance comprises a mounting plate secured to the wind
tunnel working section. A triangular force plate is held on the mounting plate by
a mechanism that constrains it to move in a plane parallel to the mounting plate
only, while leaving it free to rotate about a horizontal axis. This arrangement
provides the necessary three degrees of freedom. Models used with the
equipment will need a mounting stem. The forces acting on the model are
transmitted by cables to three strain gauged load cells. The output from each
load cell is taken via an amplifier to a microprocessor-controlled display
module. The display module mounts onto the wind tunnel control and
instrumentation frame and includes a digital display to show the lift, drag and
pitching moment directly.
Fig 8.3 Three component balancing system
Courtesy: www.google.com
38
CHAPTER 9MODEL TESTING
39
9.1MODEL TESTING IN WIND TUNNEL
The wind tunnel is calibrated initially. The model is mounted in the wind
tunnel force balance with the help of a strut fixed at its center of gravity. After
ensuring that all the connections are proper the tunnel is started with an initial
velocity. The velocity is increased gradually; the lift and drag values are noted
simultaneously for corresponding velocities. The model is tested with landing
gear and then without the landing gear. In order to fix a retractable landing gear
mechanism we have proposed another wing with a thicker airfoil. The model
with a newly proposed wing is tested in the wind tunnel and the corresponding
values are noted. From the tabulations it is observed that the drag in the airplane
is reduced to a certain percentage without the landing gear. The flow over the
wings is observed in all the three cases by tuft flow visualization technique.
9.2 DIFFICULTIES FACED DURING TESTING
The propeller in the airplane did not run during the testing due to its
misalignment during fabrication. We used a white tape to tighten and hence we
could rectify the problem. The strut fixed to the airplane was slightly improper
causing certain vibrations; hence we welded the strut to a plate and then fixed
the model.
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CHAPTER 10OBSERVATIONS
41
LIFT(N) DRAG(N) VELOCITY(m/sec) L/D
1.5 0.2 5 7.5
2.8 0.3 10 9.33
3.2 0.4 15 8
4.4 0.5 20 8.8
5.8 0.7 25 8.28
6.6 0.8 30 8.25
7.2 0.9 35 8
WING 1: WITH PROPELLER AND LANDING GEAR
Table 10.1
0 1 2 3 4 5 6 7 80.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
LIFT vs DRAG
Graph 10.1
42
WING 1: WITHOUT LANDING GEAR
LIFT(N) DRAG(N) VELOCITY(m/sec)
L/D
1.6 0.1 5 16
2.9 0.2 10 14.5
4.1 0.3 15 13.6
5.5 0.4 20 13.75
6.8 0.5 25 13.6
7.3 0.6 30 12.16
8.2 0.7 35 11.71
Table 10.2
0 1 2 3 4 5 6 7 8 90
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
LIFT vs DRAG
Graph 10.2
43
WING 2: WITHOUT LANDING GEAR
LIFT(N) DRAG(N) VELOCITY(m/sec) L/D
1.7 0.1 5 17
3 0.2 10 15
4.3 0.3 15 14.23
5.6 0.11 20 14
7.1 0.5 25 14.2
9.4 0.7 30 13.42
11.6 0.8 35 14.5
Table 10.3
44
0 2 4 6 8 10 12 140
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
LIFT vs DRAG
Graph 10.3
DRAG DIFFERENCE:
00.10.20.30.40.50.60.70.80.9
1
Wing 1 with landing gear
Wing 2 Without landing gear
Graph 10.4
45
CHAPTER 11COMPARISON
46
COMPARISON
COMPARISON OF DRAG PRODUCED FOR EXISTING WING WITH
AND WITHOUT LANDING GEAR:
DRAG PRODUCED WITH LANDING
GEAR EXTENDED
DRAG PRODUCED WITH NO
LANDING GEAR
0.2 0.1
0.3 0.2
0.4 0.3
0.5 0.4
0.7 0.5
0.8 0.6
0.9 0.7
Table 11.1
Average drag produced with landing gear
Extended for existing wing = 0.5428714
Average drag produced with no landing gear
For new wing section = 0.4
Therefore,
Net percentage reduction in drag = 35.72%
47
COMPARISON OF DRAG PRODUCED FOR EXISTING AND NEW
SITUATIONS:
DRAG PRODUCED WITH LANDING
GEAR EXTENDED FOR EXISTING
WING
DRAG PRODUCED WITH NO
LANDING GEAR
FOR NEW WING SECTION
0.2 0.1
0.3 0.2
0.4 0.3
0.5 0.4
0.7 0.5
0.8 0.7
0.9 0.8
Table 11.2
Average drag produced with landing gear
Extended for existing wing = 0.5428714
Average drag produced with no landing gear
For new wing section = 0.42857143
Therefore,
Net percentage reduction in drag = 21.05%
48
COMPARISON OF LIFT PRODUCED FOR EXISTING AND NEW
SITUATION:
LIFT PRODUCED WITH LANDING
GEAR EXTENDED FOR EXISTING
WING
LIFT PRODUCED WITH NO
LANDING GEAR
FOR NEW WING
1.5 1.7
2.8 3.0
3.2 4.3
4.4 5.6
5.8 7.1
6.6 9.4
7.2 11.6
Table 11.3
Average lift produced with landing gear
` Extended for existing wing = 4.5
Average lift produced with no landing gear
For new wing section = 6.1
Therefore,
Net percentage increase in lift = 35.5%
49
CHAPTER 12CONCLUSION
50
CONCLUSION
Thus, the wind tunnel experiments were carried out with scaled down
model in allowed speed in an open type suction wind tunnel.
For various speeds drag and lift acting on the model were noted down.
L/D ratio for all the readings was calculated. Its value was in confirmation with
historical trend line. The entire L/D values lies between 8 and 15.
Tests were carried out with model having landing gear extended and
retracted. The drags produced in each case were noted. When the landing gears
were removed, a drastic reduction in drag of 21.05% was observed.
Thus it may be concluded that if the Thorpedo T211 aircraft is provided
with provisions for retractable landing gear, drag reduction occurs. The
reduction would directly affect the fuel consumption, carbon emission and the
range of aircraft. Fuel consumption will be reduced which would help to
improve the range. CO2 emissions are also reduced thus good for environment.
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CHAPTER 13FUTURE WORKS
52
FUTURE WORKS
From the calculations it’s observed that for the same wing section (naca 1401)
(ref. Chapter no.11), if provided with a retractable landing gear system a drag
reduction of 35.72% is observed.
While for the new wing section (NACA 4415) the percentage drag reduction is
just 21.05%. this is mainly due to the increased profile drag of thicker wing.
By formulating new methods to contain the lading gear within the available
volume a drastic reduction in drag can be achieved. Some suggestions for future
works are:
Mono wheel with out riggers:
A small number of aircraft use a single central landing wheel and are
laterally supported by outriggers.
Collapsible landing gear:
A landing gear whose strut retracts within one another would help in
reducing the net area required for the landing gear. If such a system
which is also fail proof, is developed net drag force acting on the aircraft
can be reduced.
53
CHAPTER 13BIBLIOGRAPHY
54
www.google.com
www.wikipedia.com
www.ad-holdings.co.uk
www.pilotmix.com
www.indusav.com
Introduction to flight- John. d. Anderson
Theory of wing section – Ira Abbott
Overview on drag reduction technologies for civil transport aircrafts -
Author J. Reneaux
Reymer.
55
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