Attached is another update for PropDesignGeo script, which includes mirror of the curve.

The mirror code is very similar to the arccenter code.

One peculiarity is that the Base pt / End pt line appears on the screen, until Done or Cancel are selected. ?????

// To Mirror curve, using the CoordinateFrame:
// Create a point Object list, of the Curve points.
var CurvePtList = factory.calculate();
// The same Coordinate leFrame with same Base pt, pt_leArccenter, can be used.
var factoryMirror = moi.command.createFactory( 'mirror' );
factoryMirror.setInput( 0, CurvePtList );
factoryMirror.setInput( 1, leFrame );
// Set End pt. (pt on y axis works fine.)
factoryMirror.setInput( 2, pt_teArccenter );
// Save the current curve pt mirror.
AirFoilfactories.push( factoryMirror );