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.

2

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.

3

CHAPTER 2DRAG

4

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

5

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.

6

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

7

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.

8

CHAPTER 3DRAG REDUCTION TECHNIQUES

9

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.

10

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.

11

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.

12

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.

13

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

14

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.

15

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.

16

CHAPTER 4LANDING GEAR

17

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.

18

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.

19

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

20

Fig 4.3 Courtesy: www.mooney.com

21

CHAPTER 5DESIGN

22

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

23

Fig 5.2: TOP VIEW

Fig 5.1 and 5.2 shows us the side view and the top view of the model aircraft.

24

CHAPTER 6WING SELECTION

25

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

26

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.

27

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

28

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).

29

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.

32

CHAPTER 8WIND TUNNEL

33

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.

36

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.

40

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.

51

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.

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