UIUC Low-Speed Airfoil Tests Manifesto 

The UIUC Low-Speed Airfoil Tests Manifesto which appears below is a modified
version of the initial announcement of the wind-tunnel test program written
in December 1993. At the risk of being redundant with respect to what was
included in the Preface, most of the original content of the announcement is
retained. For recent information on the UIUC LSATs, please see the latest
bulletin available from either the coordinator at the address given or from
http://uxh.cso.uiuc.edu/~selig/uiuc_lsat.html on the World Wide Web.

We are searching for a group of experienced modelers to build a variety of
airfoil wind-tunnel models for tests at the University of Illinois at
Urbana-Champaign (UIUC). A low-speed, low-turbulence wind tunnel has been
instrumented to take lift and drag measurements on airfoils at low speeds
over the Reynolds number range from 40,000 to 500,000 (40k to 500k). The
scope of the airfoil wind-tunnel tests will be limited only by the number of
wind-tunnel models provided and the amount of funding received. Hopefully,
the proposed modeler-supported airfoil test program will become
self-sustaining. Your support and help of any kind will be acknowledged in
reports on the project to be published through SoarTech Publications (Herk
Stokely). We plan to publish the results through SoarTech frequently -
possibly twice per year.

A similar undertaking (with substantial support from modelers) was started
by Michael Selig, John Donovan and the late David Fraser in 1987 at
Princeton University. In a two year period, over 60 various low-speed
airfoils were wind-tunnel tested, involving over 1200 hours of wind-tunnel
test time. The results were published in SoarTech 8 in 1989, and many of the
new airfoil designs produced and tested during the program are now widely
used on R/C sailplanes. As of November 1993, over 2200 copies of SoarTech 8
are in circulation worldwide. SoarTech 8 is available from

SoarTech Publications 
c/o Herk Stokely 
1504 N. Horseshoe Circle 
Virginia Beach, VA 23451 
herkstok@aol.com 

At the present time, there is a need for new airfoils for R/C
sailplanes. For example, R/C handlaunch soaring is booming, but few good
airfoils (e.g., E387 and SD7037) presently exist for such
sailplanes. Sailplanes for the new F3J competition are just beginning to
evolve, and new airfoils will probably be required. What will they look
like? In the past, only a few airfoils (e.g., HQ 1.5/8.5, RG15 and SD7003)
have been favored for F3B competition. In shape, handling and performance
the SD7003 is quite different from the other airfoils mentioned. These
significant differences suggest that it may be possible to design new
airfoils that have better overall characteristics for F3B competition. In
addition to the design and wind-tunnel testing of new airfoils, several
existing airfoils should be tested. The SD7037 and RG15 are quite popular
and often used with flaps. The flap effectiveness of these airfoils should
be quantified through wind-tunnel tests, and the results should be used in
the design of new airfoils.

There is also a need for new airfoils for R/C sport, aerobatic, and electric
planes, as well as R/C helicopters.  Often, NACA airfoils are used for these
applications, but as compared with airfoils that could be designed today,
many of the NACA airfoils (which were designed decades ago mostly by trial
and error) are inferior. At the time the NACA airfoils were designed, little
was known about the complex aerodynamics of airfoils operating at low
Reynolds numbers. (Airfoils with small chords at low speeds, such as those
on model aircraft, are said to operate in the low Reynolds number flight
regime). In recent years, much has been learned about low Reynolds number
aerodynamics, and this knowledge has successfully been applied to the design
of new airfoils for R/C sailplanes, ushering in a new era in R/C
soaring. Overall, R/C sailplane performance has improved dramatically.
Older airfoils are no longer used. R/C power aircraft performance could
likewise be dramatically improved through the use of newly designed,
specially tailored airfoils.

Unique airfoil design requirements also exist for other categories of model
aircraft. For example, FAI free flight aircraft (which incorporate both a
powered launch segment and gliding flight) operate over a wide range of
speeds. In the past, many airfoils with good performance characteristics
have been designed for FAI free flight.  These airfoils should be
wind-tunnel tested to quantify their performance. The results gleaned from
the tests could then be applied in the design process in an effort to
develop new airfoils with improved performance.  Also, the Society of
Automotive Engineers (SAE) sponsors an annual model airplane design
competition in which university student teams design, build and fly an R/C
cargo aircraft. The record cargo weight that has been carried now stands at
24 3/4 lb for a model with a 60-size engine and 1200 in^2 total projected
area.  Conceivably, this record could be broken by an aircraft with an
airfoil (or airfoils) specifically designed for the competition. Clearly,
the need for new airfoils and data on existing airfoils is not limited just
to R/C sailplanes, but applies to any type of model aircraft where better
handling qualities and overall performance are desired.

Other topics of interest include the effects of turbulators and contour
accuracy. Are boundary layer trips simply "repairs" to otherwise bad
airfoils, or can trips be integrated with the airfoil and result in
improvements over, say, the SD7037? The Princeton tests began to address
this issue, but many questions still remain. For example, what is the best
trip height for a given airfoil? Also, what is the best trip geometry, where
should the trip be located for best performance, and what type of airfoils
respond best to trips? The Princeton tests also shed some light on how
accurate airfoils must be in order to achieve expected performance, but a
more systematic effort should be made to test the best airfoils for
sensitivity to contour accuracy. Also, we are interested in designing and
testing families of airfoils for use in, say, transitioning from one airfoil
at the root to a different airfoil at the tip. It is unlikely that the best
performance can be obtained from a single airfoil used along the entire wing
span.  This is especially true for flying wings. Companion airfoils for
blending should be designed for use with the most popular existing airfoils,
e.g., SD7037 and RG15. It is expected that the practice of blending airfoils
along the span will become much more popular than it is today. In an effort
to maximize low Reynolds number airfoil performance for model aircraft, all
of these topics should be addressed.

Overall, the UIUC test objectives will be to design and wind-tunnel test new
airfoils for each category of aircraft listed above and also to examine the
effects of flaps, turbulators and contour accuracy. We are especially
interested in testing existing airfoils that are known to have superior
performance. Wind-tunnel data on such airfoils will be used during the
design of new and better airfoils. If you believe that we have overlooked an
important area, we would be interested in your input and may consider
expanding the scope of the project. The number of airfoil models to be
tested has not been predefined; rather, it will be depend on the level of
interest and support from the modeling community.

The wind-tunnel models should have a 33 5/8 in span with a 12 in 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 will be attached to the wind-tunnel balance by standard
model wing rods. Standard model construction techniques should provide the
necessary strength (supporting 15-20 lb of lift when pinned at both
ends). The brass tubing and collars for the models will be supplied along
with full-scale plots and/or coordinates of the airfoil, if
requested. (Please contact us before starting any construction on a
wind-tunnel model.)

The airfoils will be tested in the UIUC open-circuit 3x4 ft subsonic wind
tunnel. 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 will be modified for the UIUC tests. Lift and
drag measurements for each airfoil will be taken at Reynolds numbers of 60k,
100k, 200k and 300k. In some instances, it may be possible to take limited
data over an expanded range (40k-500k). The lift characteristics will be
determined through force-balance measurements, while the drag will be
evaluated by the momentum method through the use of pitot-static probes
traversed through the airfoil wake at several spanwise locations. We are
also interested in airfoil pitching moment measurements, but the current
apparatus does not have such a capability. However, a pitching moment
balance has been recently designed and should provide pitching moment data
in the near future.

If you are interested in building wind-tunnel models for the tests or wish
to request information, please write, fax or send e-mail to the coordinator

UIUC LSATs Coordinator 
c/o Prof. Michael Selig 
Dept. of Aeronautical and Astronautical Engineering 
University of Illinois at Urbana-Champaign 
306 Talbot Laboratory 
104 S. Wright St. 
Urbana, IL 61801-2935 
uiuclsat@opus.aae.uiuc.edu 
fax: (217) 244-0720 

The program will be self-sustaining so long as funds are made available for
equipment maintenance/upgrades and graduate student stipend support and
tuition and fees (approximately $16,000/yr per student). The initial goal is
to raise enough money to support at least two graduate students for a three
year period. It is envisioned that a small level of support from a large
number of modeling enthusiasts could sustain the airfoil design wind-tunnel
test program indefinitely. The impact on model aviation could be
tremendous. Donations can be mailed to

Prof. Michael Selig 
Dept. of Aeronautical and Astronautical Engineering 
University of Illinois at Urbana-Champaign 
306 Talbot Laboratory 
104 S. Wright St. 
Urbana, IL 61801-2935 
m-selig@uiuc.edu 

Please make checks payable to "University of Illinois, AAE Dept." Also,
please write on the check "Selig - Wind Tunnel Testing/AAE Unrestricted
Funds," and provide a letter stating that your contribution is to be used by
Prof. Selig and his group of students (both undergraduate and graduate) in
support of the airfoil wind-tunnel tests. Finally, for a suggested donation
of $18 in US, Canada, and Mexico (or $22 in other countries) you can receive
a UIUC LSATs white short-sleeve shirt. All proceeds will go toward the
continuation of the project.
