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The University of Texas at Arlington

Department of Mechanical and Aerospace Engineering

MAE 1105: Introduction to Mechanical and Aerospace Engineering

Aero Lab # 1: Lift and Drag Measurement (30 Points)

OBJECTIVE:

The experiment is designed to introduce the student to some of the techniques and approaches

used in wind tunnel testing. It is also intended for the student to learn how to determine thevarious forces on an object surrounded by a moving fluid.

BACKGROUND:

A body immersed in a moving fluid, such as an airfoil, experiences a resultant force due to the

interaction between the body and the fluid surrounding it. In two dimensions, the resultant force

can be decomposed in two components. The component in the direction of the upstream velocityis named the Drag, and the component normal to the upstream velocity is named the Lift (see

Figure 1). (ote: - Angle of Attack)

Upstream velocity, V Airfoil (or body)

Figure 1 - Lift and Drag Force on an Airfoil

Description of the wind tunnel and measurement device:

The Aerolab wind tunnel is the device used for this experiment. A honeycomb with circular

elements and a carefully designed entrance section provide a flow in the test section, which is

steady in both magnitude and direction with a uniform transverse velocity. Models can bemounted in the test section, in order to record lift and drag forces. This lab will use a model of a

General Dynamics F-111 aircraft (variable swept wing). Lift and drag forces are measured using

a pyramidal balance system. The balance system measures lift and drag through load (force)measuring devices. These devices contain a beam with strain gauges that are connected to aWheatstone bridge circuit. When the model experiences a force, the beam deflects and the change

in resistance of the strain gauge is measured by the Wheatstone bridge circuit. The measured

resistance is then converted to a voltage output on the voltmeter. The voltage output correspondsto a calibrated force in pounds. The angle of attack on the model is varied with dials located on

the balance system.

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PROCEDURE:

1. Read and record the temperature and atmospheric pressure in the laboratory at the time of theexperiment.

2. An aircraft model is mounted on the pyramidal balance system in the test section of the windtunnel.

3. Turn on the wind tunnel and adjust the desired air speed by changing the motor frequencysetting.

4. Calibrate the balance such that the Lift and Drag voltage outputs are approximately zero forthe model at zero angle of attack.

5. Slowly vary the angle of attack ( ) of the model and record Lift and Drag voltage readingsfor each angle of attack considered.

6. Repeat the procedure for a different air speed.

Dimensions of the model:

Reference Surface Area:291 inS

Figure 2 - F-111 Reference Surface Area

OTE: Remember to convert reference area to the appropriate unit (e.g. in2

toft2)

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DEFINITION AND UNITS:

Lift force: L ( )lbf Drag force: D ( )lbf Air speed: V ( )sft

Reference Surface Area: S ( )2ft Density: ( )3ftslug Temperature: T ( )RO

Pressure: P ( )2ftlbf Drag coefficient: dC Lift coefficient: lC

Dynamic pressure: q ( )2sftslug

Gas constant: R = 1716 ( )Rsluglbfft O

ft

slbfslug2

11 =

FORMULAS:

= RTP

( )2

2

1

= Vq Sq

L

Cl = Sq

D

Cd =

CONVERSIONS:

Convert Temperature from (F) to (R): ___F = (___+ 460)R

Convert Pressure, Inches of Hg (mercury), to ( )2

ftlbf : ___ In of Hg = (___*2116/30)

2

ftlbf

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REPORT REQUIREMENTS:

Follow the Sample Report and answer all relevant bulleted items in each section. The

RESULTS AND DISCUSSION section in the report must also include the following:

Indicate the measured temperature and atmospheric pressure in the discussion. Put the lift and drag measurements ( V and lbf ) and the corresponding angles of attack ( )

into tables. (Similar to the tables used during the experiment).

For each Air Speed ( )21 VandV :

Calculate the lift and drag coefficient ( lC and dC ) for all angles of attack ( ) .o Put the lift and drag coefficient values into tables.o In the report only provide a sample calculation for both the lift and drag

coefficient calculations. Choose one and airspeed. Include all conversion calculations. Put the

sample calculation in the APPEDIX.

Plot the lift coefficient as a function of the angle of attack. ( lC vs. )

Plot the drag coefficient as a function of the angle of attack. ( dC vs. )

You must use Microsoft Equation 3.0 editor and Excel for the equations/calculations and

tables/plots.

Example Plot (FORMAT):

Figure 3 Lift Coefficient versus Angle of Attack

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Answer the following questions (discuss and do not label the questions in your report):

1. Analyze the lift and drag coefficient plots and the measurement (force) data from the tables.a. What can be said about the lift and drag on the model as the angle of attack varies?

Refer to the coefficients and measurement data.

b. What can be said about the lift and drag on the model as the airflow speed varies? Youneed to compare your results with other sources (e.g. textbooks, internet (ASA), etc.)

Remember that you are only comparing the plot trend and not the data points.

c. Include the reference plot in the report.Reference the source.2. What is the purpose of calculating lift and drag coefficients?

OTE:

1. The lift and drag coefficients are without dimensions. Make sure that you are using theappropriate conversion to ensure a dimensionless result.

2. Convert microvolt ( )V data to pound-force ( )lbf . Remember that the voltage outputcorresponds to a calibrated force in pounds. (Use ftrL and ftrD ).

3.

DO NOT COPY the lab manual.

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(deg) L ( V ) D ( V)

-20

-15

-10

-5

0

5

10

15

20

(deg) L ( V ) D ( V)

-20

-15

-10

-5

0

5

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P = _____ In of Hg T = _____ FV

lbfLftr

5.2=

V

lbfDftr

5.2=

=2V ______ ft/s

=1V ______ft/s