It doesn't seem to take off. I put the flaps around 0.15 and the throttle and rps to max but even when I reach 40 m/s, it won't take off. Am I doing something wrong?

You're not doing anything wrong! It probably just doesn't work right now, due to the last couple of updates changing jet engines. I plan on completely rebuilding this plane; I'm unhappy with the design overall and I think I could do a lot better. I'm sorry it doesn't seem to work!