(beginner) Boundary surface with 3 splines

Hi there,

I started playing with surfaces (so i started an aircraft project), and i can't figure out how to do a simple looking surface. There are only 3 splines, and I want to do the surface with "Boundary surface". (is it the right option ?)
The problem is that its not defined enough, or that i didn't figured out how to use that tool correctly ?

I hope that itsn't a dumb question, my researches didn't lead to a response so i came to this forum.
Thank you for your time.

EDIT: at the beginning it worked nicely with arcs, and then i started again with splines.

2 Answers

EDIT: if i cut the down spline so that it don't exceed anymore, it works perfectly, but if i let the spline long and i just reduce it in the fonction, it doesn't work anymore. Is it a bug, or is it something that i didn't understand ?

Thanks to cmalco i understand my mistake, it was because of the order of choice, so i will close this topic by accepting the response of "SolidTweaks"