UIUC Low-Speed Airfoil Tests Manifesto
Michael S. Selig, et al
The UIUC LSATs Manifesto which appears below is a modified version of
the initial announcement of the wind-tunnel test program written in
December 1993. For recent information on the UIUC LSATs, please see
the latest bulletin available from either the coordinator at the
address given at the end of this Manifesto or from the world wide web
at https://m-selig.ae.illinois.edu/.
The University of Illinois at Urbana-Champaign Low-Speed Airfoil Tests
(UIUC LSATs) team is continuing its search for experienced modelers to
build a variety of airfoil wind-tunnel models to be tested in the UIUC
Department of Aerospace Engineering Subsonic Aerodynamics Research
Laboratory. A low-speed, low-turbulence wind tunnel has been
instrumented to take lift, moment, and drag measurements on airfoils
at low speeds over the Reynolds number range from 40,000 to
500,000. The scope of the airfoil wind-tunnel tests is limited only by
the number of wind-tunnel models provided and the amount of funding
received. While the LSATs program has been self-sustaining since its
inception, additional support is needed to continue these tests. If
you choose to support the program, your help will be acknowledged in
subsequent project reports to be published through SoarTech
Publications (Herk Stokely).
At the present time, there is a need for new airfoils for R/C
sailplanes. For example, R/C hand launch 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.
Other topics of interest include the effects of contour accuracy and
blended airfoils. While previous tests have shed some light on how
accurate airfoils must be in order to achieve expected performance, a
more systematic effort should be made to test the best airfoils for
sensitivity to contour accuracy. We are also interested in designing
and testing families of airfoils for use in "blending" 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.
Overall, the LSATs test objectives are to design and wind-tunnel test
new airfoils for each category of aircraft listed above and 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. We will supply 12-in.
chord wing templates to ensure the construction of accurate
models. The surface finish should preferably be smooth (fiberglass or
heat-shrinkable mylar covering); 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.)
As previously mentioned, the airfoils will be tested in the UIUC
open-circuit 3 x 4 ft subsonic wind tunnel. The turbulence intensity
level is minimal and more than sufficient to ensure good flow
integrity at low Reynolds numbers. Lift and pitching moment
characteristics will be determined through force-balance measurements,
while drag will be evaluated by the momentum method through the use of
total-head probes traversed through the airfoil wake at several
spanwise locations.
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 Aerospace Eng.
University of Illinois at Urbana-Champaign
306 Talbot Laboratory, 104 S. Wright St.
Urbana, IL 61801-2935
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 $22,000/yr per
student). 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 Aerospace Eng.
University of Illinois at Urbana-Champaign
Talbot Laboratory, 104 S. Wright St.
Urbana, IL 61801-2935
Please make checks payable to "University of Illinois, AE Dept."
Also, please write on the check "Selig --- Wind Tunnel Testing/AE
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.