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Wing
shapes are designed to perform best over a selected range of airspeeds. The
table and lower diagram show the shape of the Lissaman 7769 airfoil that was
used for the Gossamer aircraft that won the Kremer prize. In terms of percent
chord, the leading edge radius is 1.84 centered 0.14 above the chord-line,
the upper trailing edge surface makes an angle of 4.50 with the chord-line
and the lower surface an angle of - 0.90 with the chord-line.
As the diagram indicates, the wing has a curved (concave down) camber-line.
The wing gave a high lift/drag ratio at the low anticipated airspeed (5
m/s) and the drag remained low over the range of angles of attack expected in
these record runs. The section shape also made for easy wing construction
and the modest curvatures permitted the mylar-film wing surface to follow the
profile. |
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