3 Curves
The curve drawing commands, \curve, \closecurve and \tagcurve, draw parabola segments between coordinate points in the argument. The segments' tangents at these points are parallel to each other and to straight lines through the points either side. Segments at curve ends are from parabolas through the last three points. \closecurve adds a parabola between end points to close the curve. \tagcurve omits the first and last segments drawing curves with end tangents specified. The following table shows these features.
Example Curve
\curve(0,0, 50,100, 100,0)
\closecurve(0,0, 50,100, 100,0)
_\tagcurve(100,0, 0,0, 50,100, 100,0, 0,0)
Axial flow fans often use the RAF 6E aerofoil section. The section coordinates in the following macro come directly from aerodynamic tables
. The \arc commands draw the leading and trailing radii and the two coordinate \curve the flat chord.
___\scaleput(0,0){\curve(0.366,2.133, 1.25,3.19, 2.5,4.42,
_____5.0,6.10, 7.5,7.24, 10,8.09, 15,9.28, 20,9.90, 30,10.3,
_____40,10.22, 50,9.80, 60,8.98, 70,7.70, 80,5.91, 90,3.79,
_____95,2.58, 99.24,1.52)}
___\scaleput(0,0){\curve(1.25,0, 99.24,0)}
In a picture environment like:
this macro draws: __

The RAF 6E has a flat undersurface.
The drawing command
\bigcircle works similarly to \circle except there is no \circle* equivalent. The following section scales it to an ellipse.

R.A. Wallis, Axial Flow Fans, Academic Press, 1961, p.335