ACAD/C3D won't read an angle from a curve. A curve has a constantly changing angle to other objects. A work around is to draw a line tangent to the curve where you want to catch an angle. To get the line needed to angle you can use tangent osnap on the curve and point, end, etc, or tangent on the other. If there are no suitable targets, draw a line from the center of the curve perpendicular to the line and rotate it 90 degrees from the point it intersects the curve, put it on a non plotting layer and get the angle of the 2 lines.
