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.