when i jump, while I'm in the air ( no air friction), my weight would be zero, right? but the equation W=mg doesn't consider that. g and m would be constant so my weight would be the same. am i missing something?
When you stand on a scale, the scale is not measuring w=mg. It is actually measuring N, the normal force with which the ground is pushing back up on you.
If you are standing on a scale and you jump out of an airplane with the scale under your feet, the scale will read 0 because there is no normal force N acting upward on you--the only force acting on you is w=mg downward (which is why you are falling!).
So, in freefall, your weight would be the same as when you're standing on the ground. The thing that makes you feel weightless is the fact that there is no normal force from the ground acting on you, so you are accelerating downward with an acceleration g.