UIUC Low Speed Airfoil Test Program
Airfoil Testing for Model Aircraft
and Cameron Ninham
March 23, 1995
At last, success! And lots of it. During the first major test phase of the
UIUC Low Speed Airfoils Tests, over 300 hours of wind tunnel test time was
logged and over 80MB of data were taken. Airfoil performance data were
gathered on over 30 airfoils for free flight models, R/C sailplanes, sport
planes and more. Here's a snapshot of some of the results:
All of this and more will be published in an upcoming volume of
which we are now in the process of writing. In a worst case scenario (see
below regarding the coordinate measurement machine), we should have the
page proofs ready within 2 months. When the book becomes available, it
will be announced in the upcoming Bulletin No. 3 and you can send your
- The new S1223 (was S1214)
achieves over 30% more lift than the FX 63-137 -
a result that spells opportunity for those competing in the SAE Aero
Design (heavy lift) competition. Specifically, the airfoil maximum lift
coefficient is above 2.2.
A 1% chord Gurney flap and vortex generators increase
this to at least 2.3.
- The S7012 looks like it should be the next hot airfoil on
the scene. It has been used on the Mark Allen
2M and is reportedly
getting good field reviews from the pilots.
- Remember the Princeton wind tunnel test results on the
SD8020 as compared with other symmetrical airfoils? Near zero lift,
the SD8020 had a
negligible deadband, which made it attractive for
use on tail surfaces.
Well, to our
surprise there is a deadband near zero lift, although it is less
than other comparable symmetrical airfoils.
The implication is that the turbulence levels of the current
wind tunnel are lower than the tunnel used at Princeton.
- Besides taking performance measurements for use in design codes,
detailed wake measurements were taken to document the peculiar airfoil
wake behavior at low Reynolds numbers, in particular, the
spanwise variation in the drag along the model span. These tests will
be used to help determine the importance of the model leading edge
accuracy. Expect the conclusions to be surprising.
- The test capability has been expanded from the Reynolds number
range of 60k - 300k
to 40k - 500k. This means that we can better match the conditions for
free flight models (on the low end) and F3B/power models
(on the high end).
- An additional capability is that we can test airfoils as thin as
airfoil models had to be at least around 8% thick.
For this capability,
thanks go to Gil Morris of the National Free Flight Society
engineering a new 0.25 inch
balance sleeve that is inserted into the model.
- Four free flight airfoils were tested and the results have
application not only to free flight models but
R/C hand launch models as well.
SoarTech Aero Publications
1504 N. Horseshoe Circle
Virginia Beach, VA 23451
Photos of the Wind Tunnel
Appear here. These
gifs are a little bit too dark, and we are trying to fix that...
A Follow-Up on Bulletin No. 1
In reference to the last bulletin:
- We did upgrade from a 12-bit A/D converter (used in April 1994)
to a 16-bit, which
now provides ample resolution.
- A coordinate measuring machine (CMM)
has been found on campus, and we
plan to digitize all the models tested.
We feel that this is very important. It
will be time consuming to learn the system and consequently
it may delay having the results published in SoarTech Aero.
- We have located some flyers to help us define the needs for power
- Work related to the topic "Making the Best Use of Boundary Layer
Trips" has yet to begin. Expect more on this topic later.
Airfoil Data on the Web
If you are on the Internet and have access to the
World-Wide Web (WWW)
through a browser like NCSA Mosaic or Netscape, then
The address on the Web is:
- Keep abreast of the latest information on the wind tunnel tests
- Download airfoil coordinates on over 80 airfoils.
- Download airfoil performance data from the wind tunnel tests.
- View photos of the wind tunnel setup
Next Test Phase and New Airfoils
Currently, our plans are to be in the tunnel in August 1995. Some of the
airfoils now being designed include: (3) thermal duration/F3J airfoils, (2)
R/C hand launch airfoils, (2) power airfoils (sport and Quickee 500). Part
of the focus of the next test series is to look at flap effects in detail
on the SD7037 and RG15. The idea about using trips on airfoils as
discussed in Bulletin No. 1 is still being explored. It still looks
Low Speed Airfoil Aerodynamics
In the last bulletin, a list of 20 topics in low speed airfoils
aerodynamics were posed as "things a knowledgeable modeler interested in
airfoils ought to know something about." The obvious happened. We received
requests to answer them! So we will. The list started with:
"What a bubble ramp is."
This discussion must first begin with an explanation of what a bubble is.
Airfoils at low Reynolds numbers (short chords flying at model like speeds)
do not behave like airfoils at higher Reynolds numbers such as those
typical of general aviation aircraft. As adapted from SoarTech 8 (with a
The flow behavior over an airfoil at high Reynolds
numbers -- greater than, say, 1-3 million -- is well known. The boundary
layer is laminar from the leading edge to a point typically near mid-chord
where it makes a transition to turbulent flow. This transition, as well as
the flow behind it, is generally well behaved.
The bubble can be reduced in size by destabilizing the laminar boundary
layer to promote a transition as early as possible. One method of
promoting transition is through the use of turbulators affixed to the upper
surface of the airfoil before the laminar separation point. (If
turbulators are immersed in the bubble downstream of the separation point
they have little effect.) Another approach used to destabilize the laminar
boundary is to employ a gradual upper surface pressure recovery so as to
gradually slow the flow down from its highest value. This gradual pressure
recovery which shortens the length of the bubble and thereby reduces the
bubble drag is called the "bubble ramp."
Unlike full-size airplanes, model sailplanes typically operate at chord
Reynolds numbers between 50k and 500k, often called the low Reynolds number
regime. At these low Reynolds numbers the flow is fundamentally different.
The transition process is neither abrupt nor does it usually take place
while the boundary layer is attached to the airfoil. Instead the laminar
boundary layer separates, that is, it physically detaches from the airfoil
surface. The flow then becomes unstable while separated, and makes a
transition to turbulent flow in `mid-air.' Only then does the flow reattach
to the airfoil. If the laminar separation point is sufficiently far aft or
if the Reynolds number is very low, the flow sometimes entirely fails to
return to the airfoil surface. In either case large energy losses are
associated with this process. This laminar separation, transition to
turbulence, and turbulent reattachment enclose a region of recirculation
flow aptly called the `laminar separation bubble' or `bubble' for short.
Problems with the bubble are greatest on the upper surface where the flow
is accelerated the most. Typically, the laminar separation bubble can
extend over 10-30% of the airfoil upper surface. The bubble on the lower
surface (if present at all) is much smaller under normal operating
conditions. The presence of the bubble is the principal reason for the
degradation in performance at low Reynolds numbers. Efforts towards drag
reduction, therefore, largely concentrate on reducing the size and extent
of the bubble.
One down, 19 to go. (They are not all this hard.)
A Word from Selig on the S9000 Airfoil Series
Several people have asked for coordinates (and performance data) for the
S9037 airfoil used on the OPUS 750 standard class and the S9000 on the
BLACKHAWK open class sailplanes. Both of these gliders and their airfoils
were designed while I was still at Penn State -- after the Princeton wind
tunnel tests and before the UIUC tests were even envisioned. The idea was,
of course, to apply my experience in aero engineering to generate some
income in case I found myself unemployed (like many of my fellow graduate
students and colleagues at the time). Fortunately, I did not have to
depend on that income. The upshot of all this is (1) the airfoils are
proprietary to the current manufacturers, (2) I am not able to release
them, (3) the airfoils will not be wind tunnel tested, and (4) your
donations did not subsidize that work done at Penn State. People are now
becoming aware of this work since the gliders are only recently being
produced -- some 3-4 years after they were designed. But for those patient
enough and should I decide to exercise a clause in the agreements, the
airfoils can be released after 10 years from the date that the sailplanes
were first made available. I will be very surprised if by that time
someone else has not figured out how to clone the S9000
S9037 (OPUS 750) airfoils.
Finally, all of the results generated in the UIUC wind tunnel studies will
be publically available.
Publications: S1223 Airfoil and More
The high-lift S1223 (was S1214) airfoil was published as AIAA Paper
94-1866: M.S. Selig and J.J. Guglielmo, "High-Lift Low Reynolds Number
Airfoil Design," presented at the AIAA Applied Aerodynamics Conference,
Colorado Springs, CO, June 1994. Several of the SAE Aero Design Teams have
requested information on this airfoil. For now, this paper is the source.
Only predicted performance is included in the paper. To date no wind
tunnel test data have been released. SAE Teams: Watch the Web for more
data. We will announce the availability of the data under the What's New heading.
Also, the AIAA Paper 95-1783: J.J. Guglielmo and M.S. Selig, "Large
Spanwise Drag Variations in Wake Profiles for Airfoils at Low Reynolds
Numbers: Issues and Observations" will be presented at the Applied
Aerodynamics Conference this summer.
E-Mail Mailing List Instead
If you are currently receiving this bulletin and would rather receive an
electronic version, please let us know and we can help save some trees.
Your Snail Mail and E-Mail Received
No doubt about it, interest in the airfoil tests is pretty high. We have
received at least 1000 letters and e-mail messages combined since the start
of the program in December 1993. Now, on an average day there's a phone
call or two related to the airfoil tests and we receive between 3-6 pieces
of mail. These numbers go up when hot airfoils appear in Popular Science
(see February issue, p. 18) or when the model magazines publicize the
tests. We appreciate the attention, and we definitely appreciate your
comments, donations, and other forms of support. Unfortunately, it's
almost impossible to respond to everything, so please don't be offended if
we are slow to respond (if at all) or if we merely send a perfunctory
thank-you note. Rest assured, the airfoil tests go on -- that's the prime
Points of Contact
You can write, e-mail (preferred), fax or call any one of us. Use the fax
number and address later listed for Jim Guglielmo. To help you decide who
to write to, you might want to consider our profiles:
- Michael Selig, Ph.D.: Assistant Professor of Aeronautical
and Astronautical Engineering.
7 graduate students (gasp).
UIUC LSAT project initiator. Flys R/C sailplane (since 1976)
-- mostly in competition more recently.
include: airfoil design and wind tunnel testing,
wind turbine rotor aerodynamics, flight simulation, and unmanned
- Jim Guglielmo: Graduate student (M.S.) in Aero/Astro Engineering.
Scheduled to graduate in May 1995.
Co-founder and coordinator
of the project.
Interested in aerodynamics, flight mechanics, and aircraft
conceptual/advanced design. Currently looking for a job.
- Andy Broeren: Graduate student (M.S.) in Mechanical Engineering.
Participates in the SAE Aero Design competition. Interested in high-lift
low Reynolds number
airfoils, high-lift devices (flaps, slats, etc.)
and unsteady aerodynamics. firstname.lastname@example.org
- Philippe Giguere: Graduate student (Ph.D.) in Aero/Astro
Engineering. He arrived on campus from Quebec, Canada in August 1994.
Interested especially in (1) wind energy -- wind turbine performance and
field testing, (2) wind tunnel boundary corrections and (3) airfoil
performance enhancement through the use of simple devices such as the
Gurney flap. Participated for 4 years in the SAE Aero Design competition.
- Cameron Ninham: Graduate student (M.S.) in Aero/Astro
Engineering. New UIUC LSAT recruit from South Africa. In August 1995
will take over Jim
Guglielmo's present role in the project. Flys R/C sailplanes.
Interested in flight simulation. email@example.com
Your Letters Received
We like your mail. Besides a lot of juicy technical stuff, we get some
praise and here's a sample:
I received the T-shirt today. Thanks so much!
I Love the airfoil data on the net. I jumped on today and downloaded the
graphs from the S7012 and RG15 wind tunnel tests. What a way to publish
Special thanks to Mr. and Mrs. Hermann Andresen, who provided food,
lodging, and hospitality in their home for Jim and Phil during a recent
visit to California. The purpose of the trip was to meet with Hermann
Andresen and design new lift and pitching moment balances for the wind
tunnel. Thanks to Mr. Andresen's expertise, Mrs. Andresen's excellent
cooking, and some wonderful weather, the trip was both a success and very
enjoyable. As a result, both the lift and pitching moment balances will be
built and installed for the next test phase in August.
We would also like to thank Roger Morell and Norm Furutani, who helped
organize a talk on the UIUC Low-Speed Airfoil Tests. The talk was
sponsored by the Southern California Aero Team, and members of SULA were
also present. Overall, we received some excellent feedback concerning the
testing program and were extremely happy with the turnout. Thanks to
everyone who came.
To all old and new builders, please take a few minutes to fill out the
enclosed "Model Builder Information Form." The purpose of this form is to
provide us with a complete record on each builder involved with the testing
If anyone has any comments or suggestions, please fill out the enclosed
"General Information Form."
What's Old, But Still Important
Airfoil Coordinates for S1210, S1223, S4083, and S7012
Until the new airfoils are published through SoarTech Aero, the airfoil
coordinates and a brief description of the performance characteristics for
these designs can be obtained from the Web site or by sending a
self-addressed stamped envelope with your request to:
Prof. Michael Selig
Dept. of Aeronautical and Astronautical Eng.
University of Illinois at Urbana-Champaign
306 Talbot Laboratory, 104 S. Wright St.
Urbana, IL 61801-2935.
Support the Test Program: Make a Donation for a T-Shirt
Robertson of Flagstaff, AZ has designed a T-shirt exclusively for the UIUC
Low Speed Airfoil Test Program. You can receive this white short-sleeve
shirt for a suggested donation of $18 ($15 for the shirt and $3 for
mailing in US, Canada, and Mexico or $7 in other countries) to help
support the project by sending your check payable to "University of
Illinois, AAE Dept." Please write on the check "Selig -- Wind Tunnel
Testing/AAE Unrestricted Funds." The shirts are Hanes Beefy-T brand and
100% cotton. Shirts can be obtained from the graduate student
James J. Guglielmo, Coordinator
c/o Prof. Michael Selig
Dept. of Aeronautical and Astronautical Eng.
University of Illinois at Urbana-Champaign
306 Talbot Laboratory, 104 S. Wright St.
Urbana, IL 61801-2935
voice: (217) 244-0684
fax: (217) 244-0720
Offer to Build a Wind Tunnel Model
If you have an interest in building a wind tunnel model, please contact Jim
Guglielmo. Please give us some idea of your interests (sailplanes, power,
helicopters, etc.), and your method of construction (foam core or built-up
and full sheeted), your building skills -- we dream about the perfect
airfoil model, but don't expect to ever see one.
The wind tunnel models should be 33 5/8 inch in span with a 12 inch chord
and can either be built-up or foam core. To insure a uniform contour, the
built-up models need to be fully sheeted. For the foam core models, we
may be able to supply two 12 inch chord wing templates. The surface
finish can either be fiberglass or monokote; however, we are interested in
the effects of surface finish and will consider testing models with
non-smooth surfaces. The models are attached to the wind tunnel balance by
standard model wing rods. K&S tubing is installed in the model to adapt
to the wing rods. Details of the mounting system and airfoil model dimensions are
presented in Figure 1.
Standard model construction techniques should provide the necessary
strength (supporting 15-20 lb of lift when pinned at both ends). The K\&S
brass tubing and collars for the models are supplied along with full-scale
The airfoils are tested in the UIUC open-circuit 3 x 4 ft subsonic wind
tunnel (see Figure 2). The turbulence intensity
level is minimal and more than sufficient to ensure good flow integrity at
low Reynolds numbers. The experimental apparatus used at Princeton
modified for the UIUC tests. Lift and drag measurements for each airfoil
are taken at Reynolds numbers of 60k, 100k, 200k and 300k; however,
sometimes data is taken down to 40k and up to 500k.
What is SoarTech 8?
Airfoils at Low Speeds by M.S. Selig, J.F. Donovan and D.B.
Fraser -- a book with results on over 60 airfoil models tested over the
Reynolds number range 60k-300k at Princeton University. It has become a
popular source of airfoil data for R/C sailplanes. It's almost 400 pages
and a bargain at $20 in the US ($22 in Canada and Mexico, $25 / $35 in US
dollars for Surface/Airmail in other countries).
for more information. The book is only
available direct from:
SoarTech Aero Publications
1504 N. Horseshoe Circle
Virginia Beach, VA 23451
When ordering, please provide a check or money order in US Dollars which
can be paid at a US bank. US cash is also accepted. Residents of Virginia
should add the state 4-1/2 percent sales tax to the above rates. Sorry no
credit card or COD orders at this time.
Get on the Mailing List
To receive the next bulletin, send a self-addressed stamped envelope to
Michael Selig at the address listed previously. If you have made a
donation, you are automatically placed on the mailing list.
The airfoil testing (and the book that is now in the works) would not
exist without your financial support. If you like what we are doing, your
contributions are welcome. Here is a sampling of what some people have
done to support the airfoil testing.
- Robert Webster of Websoft, Inc., (918) 825-2220, markets Wingmaster
-- PC software for laying out wing plans.
In April 1994, he wrote that he would donate $10
per copy of Wingmaster sold in June and July. Sales must have been good
since we recently received a large donation from Mr.Webster. See
Websoft ad in Model Airplane News, January 1995, p. 142.
- Bob Matheson of Cloud-9, (619) 754-2657,
is starting to manufacture his new
VELVET 60 in Sport Racer. He has offered to
donate a percentage of sales on the kit to the wind tunnel tests.
- The Portland Area Sailplane Society (PASS) recently sponsored
a benefit/fun fly in support of the airfoil test program.
They made a donation of $140, which included some orders for t-shirts.
- Malvern Soaring Association,
U.K. (thanks to the efforts of
Nick Neve) will be making a donation in exchange
for a plywood wing-rib
which they are supplying to Selig for his autograph. (MSS: Sounds simple
enough.) The rib will then
be sealed and made into a contest trophy.
- Don Edberg has been helping to distribute the UIUC LSAT t-shirt
designed by Cody Robertson. If you see him on the contest circuit be
sure to ask for a t-shirt if you do not already have one,
and give him your name so that we put you on the mailing list and
record you as making a donation. Dr. Alan Schwerin also distributed the
t-shirts at some contests in the south.
- Northeast Sailplane Products
(Sal DeFrancesco) made a large donation to the wind tunnel tests and
is also a distributing t-shirts for the program.
- Slegers International (Ed Slegers) also
made a large donation to the wind tunnel tests.
- Several people have requested the club presentation on the test
program. Those that have received the presentation are listed later.
How to Wire Us Money
If you would like to wire money directly to the University of Illinois in
support of the wind tunnel testing, you will need the following:
Bank: Bank One N.A.
Address: One Bank One Plaza, Chicago, IL 60670
SWIFT Code: FNBCUS44
ABA Number: 0710 000 13
University Account Number: 11-12201
Account Title: Univ of Illinois Operating Account
Reference: "Selig -- Wind Tunnel Testing, 1-6-41784"
Banking info updated 8-4-00
In order for the university accounting department to identify where the
funds should be deposited once it has arrived, please reference
"Selig -- Wind Tunnel Testing, 1-6-41784." Also, send a fax to Michael Selig
indicating your support. If you need further information, please feel free
to contact the Aero/Astro business office (Ms. Lori Ballinger ) at (217)
Any portion of this bulletin can be reproduced.
List of Contributors
(as of March 1, 1995:
% -- percent of total support received)
[UIUC Applied Aerodynamics Group]