About Curve Tangents
Curve tangents can change the curve shape, and they can create connections with another curve or surface. You can constrain the tangents of control points and of interpolation points.
There is no tangency control on the endpoints of periodic curves.
A Natural tangent is calculated using the natural mathematical tangent for the defining points. This is the default for newly created curves. The tangent may change direction as you modify the defining points. A Free tangent is user-defined. A Natural tangent becomes a Free tangent as soon as you manipulate it.
When you create a tangent connection, you can select Fix Length or Relax Length. When you apply a fixed length, the Length value you set is preserved during changes to the curve, and a length parameter is created that can be edited outside Style mode. Tangent connections created before Pro/ENGINEER Wildfire 5.0 are Fix Length.
When you select Relax Length, the proportion between the curve length and the tangent length is maintained. The tangent updates when the curve is regenerated. This option is the default setting for new tangent curve connections, but you can fix the length during curve editing. A relaxed tangent length can only be edited within its Style feature.
You cannot select the Relax length option in Control Point mode.