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: firstname.lastname@example.org 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: email@example.com 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.