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 http://www.ae.illinois.edu/m-selig.

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
e-mail: m-selig@illinois.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  $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
e-mail: m-selig@illinois.edu
ph:  (217) 244-5757
fax: (217) 244-0720

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.