why 2 curve dont loft
 

I've 2 different curve with the same span in same position
but when I loft first to second (or second to first)
I dont have a clean loft

I think you have to reverse the direction of one of the curves. Can't remember where that is, but it should be under the create curve tool.

I tried but nothing

anyway tnx 4 support

i'd suggest trying a birail instead.