Hi Andrei:

here is an example about "mantain tangency" making a simple bike's saddle.
Both sweep examples (-B-C-) using same splines
Also Burr's suggestion with rail revolve instead of sweep.(magenta line is rail revolve axis)



you can see three different results
have a try with my file attached,if not clear

M

(..oopss..forgive me for grammar error..is MAINTAIN..)