Minor Project12

8/7/2019 Minor Project12

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A STUDY OF THE EXPERIMENTALDETERMINATION OF LIFT AND DRAG

FORCES FOR DIFFERENT ANGLES OF

ATTACK ON AN AEROPLANE MODEL

UNDER THE GUIDANCE OF

PROF. RAJESH GUPTA

PERFORMED BYP.T.PRASANNA (081116076)

GAUTHAM C (081116065)

K.T.RAO (081116026)


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ACKNOWLEDGEMENT

We are immensely thankful to Prof.

Rajesh Gupta for guiding us in this

project. We also thank the Director, all

Deans and the HOD, mechanical

department, for providing us with a

good and healthy environment for performing this project.


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OBJECTIVE

To study the measurement of the

different forces i.e. lift and drag for

different angles of attack on an aero-

plane model.

This experiment is done in an open

cycle wind tunnel. The plot of the various coefficients of

lift and drag versus angle of attack is

to be studied.


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INTRODUCTION

Airplanes are one of the most amazing things that

we see on a daily basis.

An airplane rolls down the runway ,lifts itself into theair and can fly up to 7,000 nautical miles without

stopping.

Bernoulli's principle states that for an in viscid

flow, an increase in the speed of the fluid occurs

simultaneously with a decrease in pressure.

Hence, due to the pressure difference at a high

speed, the airplane is lifted from the ground.

The basic aerodynamic forces: lift, weight, thrust

and drag.


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Drag is an aerodynamic force that resists the motion of an objectmoving through a fluid (air and water are both fluids).

Lift is the aerodynamic force that holds an airplane in the air.

Weight is the force of attraction between the plane and earth.

Thrust is an aerodynamic force that must be created by an airplane in

order to overcome the drag.


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APPARATUS USED

An open-cycle type wind tunnel

Aero plane model with a wingspan of 45cm

A calibrated sting-balance

Angle of attack indicator with LSR of 0.1

degrees

Data Precision Multimeter 3600 with LSR ofone microvolt

Common Mercury Thermometer/ Barometer

A 40HE35 model slant manometer


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ANAERO PLANE MODEL

The above model is then assembled by mounting the

wings and the tail on the fuselage using dowels and

adhesive. It then becomes ready for testing.


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STING BALANCE

An internal balance is a carefully designed and

precisely machined cantilever beam of complicated

cross-section equipped with electrical-resistancestrain-gage sensors.

This type of internal balance is most commonly

known in the aerodynamic field as a sting balance.

Wind tunnel testing requires a balance system

capable of accurately measuring the forces on the

model.

Some important factors that must be taken into

consideration during this selection process are the

number and arrangement of the strain gages on the


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STING BALANCE


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Airplane mounted on a sting balance


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WORKING OF A STING

BALANCE The electrical resistance strain gage is a strain-sensitive

component bonded to the surface of a balance to

measure strain.

When the strain gage is stretched (or strained), itsresistance changes in direct proportion to the strain.

The gage factor, K, of a strain gage, relates the change

in resistance (DR) to the change in length (DL). The

gage factor is constant for a given strain gage, and R is

the non deformed resistance of the strain gage, so the

equation is

K = (DR/R)/ (DL/L)= (DR/R)/e

where e is the strain.


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ANGLE OF ATTACK INDICATOR

Angle of attack is defined as the angle between the chord line of

the wing and the direction of the relative wind. The angle of

indicator is used to measure the angle of attack.


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DATA PRECISION MULTIMETER

Data precision multimeter displays the

output voltages from the sting balance.


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SLANT MANOMETER

Dynamic pressure is the component of fluid pressure

that represents fluid kinetic energy.

It can be measured using a slant manometer.

The slant tube manometer contains some type of liquidthat is contained in a reservoir.

The liquid is displaced up a slanted tube, which is

calibrated using a ruler.

The ruler reads the liquid displacement in inches ofwhatever fluid that is inside the tube.

where P= density , u = flow speed.


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SLANT MANOMETER


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A MERCURY THERMOMETER

A thermometer is a device that

measures temperature or temperature

gradient using a variety of different

principles


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MERCURYBAROMETER

A barometeris a scientific instrument used in

meteorology to measure atmospheric

pressure. It can measure the pressure exerted

by the atmosphere by using water, air, or


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INITIAL SETUP

The sting balance is calibrated.

The test-model is mounted on the sting balance and

is taken to the wind tunnel. The sting balance is connected to the angle of

attack indicator and the data precision multimeter.

The atmospheric temperature and pressure is

measured by the thermometer and barometer.

The slant manometer is used to measure the flow

speed.

The wind tunnel is made clear of any obstructions


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THE PROCESS

1. Known weights are added to the calibrated sting balance and their

corresponding voltages are recorded in the data precision

multimeter.

2. Next, the calibration is removed from the sting balance and the

strut attaching the aircraft is now attached to the sting balancewithout the air-craft.

3. The normal and axial forces for various angles of attack ranging

from -8 degrees to 18 degrees, in increments of 2 degrees up to

10 degrees and one degree from 10 to 18 degrees is measured.

4. The wind tunnel is turned on with the wind speed at 30mps, which

is verified by the slant manometer with a dynamic pressure of

2.77 inches of water and step 3 is repeated.

5. Now the aircraft is attached to the sting balance and the step 3

and step 4 are repeated.


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WIND TUNNEL ANALYSIS

The data is collected and transferred into an excel

spread sheet.

A calibration curve between the forces added on the

sting balance and the voltages is plotted.

The following equation converts voltages into directforces.

Similarly,axial forces are also found.

The drag and lift are calculated by the followingequations.

where

ais the angle of attack, N is normal force, A is

axial force D is dra and L is lift.


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COEFFICIENTS OF LIFT AND

DRAG

Using the measured temperature and pressure,

density of air is calculated.

The dynamic pressure is calculated by the equationgiven below using the flow speed.

The coefficients of lift and drag are then found using

the equations:


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RESULTS The sting balance was calibrated to find a conversion

factor between volts and pounds for normal and axial

forces. The conversion factor is based on the slope of the

resulting curve of the voltage plotted against calibration

load.

The resulting lift and drag coefficients versus angle of

attack found from the wind tunnel experiment is shown in

the graph.

As lift increases with angle of attack, the induced drag ofthe aircraft also increases.

A comparison of CFD and wind tunnel yields that error in

case of wind tunnel analysis has more errors.


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Sting balance calibration plot


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Lift Coefficient versus Angle of

Attack


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Wind Tunnel andCFDLift CurveComparison for lift coefficient


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Wind Tunnel andCFDDrag CurveComparison fordrag coefficient


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CONCLUSION The work presented in this project

provides a method for using industry

practices to populate a flight simulatordatabase with accurate lift, drag, and

moment coefficients.

Future studies could utilize the programs

used in this study and develop many new

methods for updating flight simulator data

bases.


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REFERENCES

1. Introduction to fluid mechanics by Fox and

McDonald.

2. A thesis on Flight Simulator Database Populationfrom Wind Tunnel and CFD Analysis of a

Homebuilt Aircraft by Robert P. Little.

3. Comparison of Strain Gage and Fibre Optic

Sensors On A Sting Balance In A Supersonic Wind

Tunnel by Alex T.Edwards.

4. A video on Alpha systems AOA indicator,

Youtube.com.

5. Wikipedia and Howstuffworks.com.

6. Mechanical engineering labs, MANIT.


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THANK

YOU

Minor Project12

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