Airfoils at Low Speeds
Selig, Donovan and Fraser
The work presented deals with the development of efficient low Reynolds number airfoils for model aircraft, although the airfoils are not limited to this application. Both experimental and computational techniques were used. The experimental facility and measurement technique are discussed in detail, and turbulence measurements in the tunnel freestream are presented. Lift and Drag data were taken at chord Reynolds numbers between 60,000 and 300,000. Comparisons of data obtained in the Princeton facility with that in several others are presented and show good agreement. Based on the results of over 60 models tested during the program (including models of the DAE51, FX63-137, E205, E374, E214, E387, Miley, NACA 0009, S3021, S2091, S4233), several new airfoils were designed using the Eppler and Somers code and screened using the Drela and Giles ISES code. Seventeen of the most promising designs were actually wind tunnel tested. The design philosophy is discussed and verified experimentally. Several of the new airfoils show significant performance improvements over previous airfoils. Boundary layer trips were also investigated as a means of reducing drag. Several types of trips were compared (zig-zag trips, bump tape, blowing, and two-dimensional trips), and the simple two-dimensional trip was found to yield the greatest improvement. The effects of model inaccuracies are also discussed, as well as the importance of a thin trailing edge in achieving low drag.