Announcements/Opportunities
• Next year’s Aircraft Design class:
– We will (again) have a joint team with ME to build and
fly a morphing airplane
– Send me email: whmason@vt.edu to apply
– We will have 4 AEs on this team
• Undergraduate research:
- lots of opportunities to help the design class software
and do student AIAA papers, see me if you are
interested.
Aerospace and
Ocean Engineering
slide 1
AOE 3054
Aerospace and Ocean Engineering
Instrumentation and Laboratory
A Lecture
on
Aerodynamic Testing
W.H. Mason
Aerospace and
Ocean Engineering
slide 2
Overview
• Where you test
• Why you test
• How you test
• Some specifics for your lab
Aerospace and
Ocean Engineering
slide 3
The NTF at NASA Langley
Hampton, VA
Performance:
Aerospace and
Ocean Engineering
M = 0.2 to 1.20
PT = 1 to 9 atm
TT = 77° to 350° Kelvin
Feb. 1982
slide 4
The Full Scale Tunnel at NASA Ames
40x80 Foot
Test Section
80x120 Foot
Test Section
Aerospace and
Ocean Engineering
Aviation Week & Space Technology, Dec. 7, 1987
slide 5
Information Sources
• Lot's of introductory material on
Aero Test in the manual: read it!
• The standard reference book:
Barlow, Rae and Pope,
Low Speed Wind Tunnel Testing
Aerospace and
Ocean Engineering
slide 6
Wind Tunnel Testing is Expensive
Preparation and planning are required to get into any tunnel:
• Make pre-test estimates
• Prepare a pre-test report including a Run Schedule
Aerospace and
Ocean Engineering
slide 7
So Will the Computer Eliminate the WT?
E.N. Tinoco, (Boeing) “The Impact of CFD in Aircraft Design,”
Canadian Aeronautics and Space Journal, Sept., 1998, pp. 132-144
Cost,
Flowtime
One complete airplane development requires
about 2.5 million aerodynamic simulations.
10
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Ocean Engineering
100
1,000
Number of Simulations
10,000
slide 8
Key Items
• Safety, accidents can happen
• Pretest Planning - the key to success
• Model Design
• The Run schedule
• Typical Tests:
- force and moment
both performance, stability, and control
- pressure distributions
- flow diagnostics
on and off surface flow visualization
Aerospace and
Ocean Engineering
slide 9
Test Hours, F-16 WT Test
general arrangement
wing planform,camber
LE & TE flaps
strake development
control deflections
stores
store loads
pressure loads
inlet
flutter
store separation
spin/stall
spillage and nozzle
miscellaneous
0
Aerospace and
Ocean Engineering
500
1000
1500
2000
slide 10
Research Fighter Configuration (RFC)
Visualization with a Tuft Grid
Small Model in Grumman Tunnel
Aerospace and
Ocean Engineering
slide 11
Another Way To Do Flow Diagnostics
Kurt Chankaya, Grumman (now Lockheed)
Aerospace and
Ocean Engineering
slide 12
Typical way to put tufts on the wing
From Pope and Harper’s text, taken in the Wichita State tunnel
Aerospace and
Ocean Engineering
slide 13
Oil Flows for Surface Visualization 1
Aerospace and
Ocean Engineering
SC3 Wing, M = 1.62, a = 8° (nominally attached)
slide 14
Oil Flows for Surface Visualization 2
Aerospace and
Ocean Engineering
SC3 Wing, M = 1.62, a = 12° (TE flow separation)
slide 15
Laser Light Sheet example
Light Sheet from an
argon laser, the flow
is seeded with an
standard smoke
generator.
Northrop IR & D
example of vortex
flow over a delta
wing configuration.
Exhibited at the
36th Paris air show.
Aerospace and
Ocean Engineering
Aviation Week & Space Technology, July 29, 1985
slide 16
Model Fabrication:
• Accuracy important!
- drag, under all conditions
- low speed near max lift
- transonic cruise condition
Aerospace and
Ocean Engineering
slide 17
WT model with high LE accuracy Req’ts.
Supercritical Conical Camber (SC3)
Wing, developed using CFD.
The leading edge contour accuracy is
critical.
Note the arc of the wing
along the trailing edge,
a sort of “gull shape”
Aerospace and
Ocean Engineering
slide 18
Inspecting the Model Leading Edge
Aerospace and
Ocean Engineering
slide 19
Fab agrees with designed contour!
Aerospace and
Ocean Engineering
slide 20
Simulation Issues
• Fundamental: Mach number and Reynolds number
- Match Mach, do your best on Reynolds, leads to:
- transition fixing
• Test issues:
- wall interference, flow angularity, nonuniformity
• Adjustment from model scale to full scale
Aerospace and
Ocean Engineering
slide 21
Tunnel/Mounting Interference
Walls restrict airflow around mode
l
L mea s
L tru e
Tunnel and Balance Centerlin
aup
e
V
Flow angularity causes
causes true forces to be
in a direction different than
the reference
Aerospace and
Ocean Engineering
Dtru e
Dmea s
Exposed strut senses addtional drag
on external balanc e
slide 22
Sue Grafton with RFC at NASA Langley
Aerospace and
Ocean Engineering
slide 23
RFC in the 30x60 at Langley: static tests
Aerospace and
Ocean Engineering
slide 24
Free Flight Setup: A complicated activity
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Ocean Engineering
slide 25
RFC Model in Free Flight at Langley
Aerospace and
Ocean Engineering
slide 26
The Tunnel
Aerospace and
Ocean Engineering
slide 27
The Virginia Tech Stability Tunnel
• A high quality flowfield
- uniform mean flow
- low turbulence level
- low flow angularity
• came from NASA in 1958
• 6'x6' test section, 24 ' long
• 600 hp motor/14' fan
• 275 fps max speed
Aerospace and
Ocean Engineering
slide 28
Virginia Tech Stability Tunnel Layout
Aerospace and
Ocean Engineering
slide 29
Velocity Variation in the Test Section
Virginia Tech Stability Wind Tunnel
Mean Flow Calibration Characteristics
V/Vref,
V/Vref,
V/Vref,
V/Vref,
1.04
U = 125 fps,
U = 125 fps,
U = 200 fps,
U = 200 fps,
Z = 0 ft
Z = 0.5 ft
Z = 0.0 ft
Z = 0.5 ft
1.02
V/Vref
1.00
0.98
VPI Aero-161, Dec. 1987
0.96
-2.0
Aerospace and
Ocean Engineering
-1.5
-1.0
-0.5
0.0
y, ft
0.5
1.0
1.5
2.0
slide 30
Upwash Variation in the Test Section
Alpha,
Alpha,
Alpha,
Alpha,
Virginia Tech Stability Wind Tunnel
Mean Flow Calibration Characteristics
1.50°
U = 125 fps,
U = 125 fps,
U = 200 fps,
U = 200 fps,
Z = 0 ft
Z = 0.5 ft
Z = 0.0 ft
Z = 0.5 ft
1.00°
a
0.50°
0.00°
-0.50°
-1.00°
VPI Aero-161, Dec. 1987
-1.50°
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
y, ft
Aerospace and
Ocean Engineering
slide 31
Sidewash Variation in the Test Section
Virginia Tech Stability Wind Tunnel
Mean Flow Calibration Characteristics
1.00°

Beta, U = 125 fps, Z = 0 ft
Beta, U = 125 fps, Z = 0.5 ft
Beta, U = 200 fps, Z = 0.0 ft
Beta, U = 200 fps, Z = 0.5 ft
0.50°
0.00°
-0.50°
-1.00°
-1.50°
VPI Aero-161, Dec. 1987
-2.00°
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
y, ft
Aerospace and
Ocean Engineering
slide 32
Use a Strain Gage Force Balance
to Measure Loads
Tension change in wire changes resistance
You used one before?
• Assume that the balance is adequately
calibrated - we will not check it this year
Aerospace and
Ocean Engineering
slide 33
Strain Gages
simple strain gage balance
Load
strain gage element
Strain
Gages
true force balance
circuit for balance
Load (D)
l2
l
1
11
3
M2
M1 = Dx l1
M2 = D x l 2
l
2
5 Volts
3
4
Output
Voltage
M1 - M 2= D(l1 - l 2 )
M
22
= Dl
1
4
D=
Aerospace and
Ocean Engineering
1
M1- M2
l
slide 34
Mechanics for this lab:
• two weeks
• 1st week - get ready
- check out tunnel, make pretest estimates
• 2nd week: test!
- run the model
Aerospace and
Ocean Engineering
slide 35
The Tests!
New this year: we have 2 possibilities:
1. The “standard” rectangular wing
2. The Pelikan Tail (from a senior design project)
Your choice!
Aerospace and
Ocean Engineering
slide 36
Objective:
Use Experimental techniques to find aero characteristics of:
1. A rectangular, unswept wing
• with and w/o transition strips
or
2. A novel tail concept almost used on the Boeing JSF,
and subsequently adopted by our senior UCAV-N team
Aerospace and
Ocean Engineering
slide 37
The Rectangular Wing Model
34.0 "
3.667"
Wing Mounting Holes
(.98" between holes)
6.0 "
Trailing Edge
The airfoil: originally a Clark Y, recently modified
(thickened) to strengthen the model How does this change the test estimates?
Aerospace and
Ocean Engineering
slide 38
Rectangular Wing
Model Airfoil Section
CLARK Y Airfoil for Aero Lab Test
Theoretical Coordinates and Coordinates after Wing reinforcement
0.20
y/c upper
y/c lower
y/c measured
0.15
y/c
0.10
0.05
0.00
Not to scale
-0.05
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
x/c
Aerospace and
Ocean Engineering
slide 39
Expected Lift Coefficient Variation:
Rectangular Wing Model
2.50
Clark Y Airfoil
AR = 5.6 Rectangular Wing
2.00
1.50
CL
Estimate,
(Inviscid Theory)
VPI data,
Re = .3x10 6
1.00
0.50
NACA data
Re = 1.0x10 6
0.00
-0.50
-15° -10°
Aerospace and
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-5°
0°
5° 10°
a, deg.
15°
20°
25°
slide 40
Expected Pitching Moment:
Rectangular Wing Model
2.50
Clark Y Airfoil
AR = 5.6 Rectangular Wing
2.00
1.50
CL
1.00
0.50
0.00
-0.50
0.05
NACA data,
Re = 1.0x10 6
-0.00
-0.05
Cm
-0.10
-0.15
Cm
Aerospace and
Ocean Engineering
slide 41
Expected Drag Coefficient Variation:
Rectangular Wing Model
1.50
Theoretical 100%
Suction Polar, e = .98
1.20
Wind tunnel test data
0.90
CL
0.60
Theoretical 0% Suction Polar
0.30
-0.00
-0.30
0.00
Aerospace and
Ocean Engineering
6
NACA Data, Clark Y airfoil, rectangular wing, AR = 5.6, Re = 1x10
Note: Theoretical polars shifted to match experimental zero lift drag
0.05
0.10
CD
0.15
0.20
slide 42
The Pelikan Tail
= HINGE LINE
Aerospace and
Ocean Engineering
slide 43
Pelikan Tail Plan View
Aerospace and
Ocean Engineering
slide 44
Let those seniors talk?
• Why should you do this?
Aerospace and
Ocean Engineering
slide 45
Wind Tunnel Testing
is
Fun!
Good Luck
Aerospace and
Ocean Engineering
slide 46