How do you control a spline to make the end points perpendicular to a surface?
I'm assuming that you want a vector from the end point (on the surface) to the second control point on the curve to be normal to the surface? Probably the easiest way is to create a line normal to the surface (Line>Normal) from the curve end point, then use an "on curve" osnap to snap the second control point to somewhere on the line segment... Or did I not get what you want to do?
Your method is to draw two straight lines, each normal (perpundicular) (is there no spell check to this site?) to the surfaces at the end of this line, then add a spline (in 3D) connecting those two normal lines. I believe this will work, but now I need to know how to make the connecting line tangent to the normal lines.
Also, is there a more straight forward way to do this?
I assumed that the end points were already on the surface. Perhaps that was incorrect... In any case - NURBS geometry rules say that the tangent at the end of a curve lies along a line between the end point and the next control point in. So, if both the end point and the next control point in both lie along a line that is normal (perpendicular) to a surface, the end of the curve will be guaranteed to be perpendicular.
I was simply suggesting that you draw the normal line and drag/snap the end two control points to it (somewhere along it). That will guarantee perpendicularity to the surface. However as you can imagine, there are an infinite number of solutions possible based on where along the line you place the control points - there is no one "right answer".
If you're only going to do this occasionally, the manual method is probably fine. I don't think there's a more automatic way to do this without getting into a scripted solution.