lol. I grew up on the 70's and 80's FF comics, and there is a good chance I have read many more than you, but no big deal.
Actually. I have read all of them from FF #1 until the Civil War storyline they're getting into today. So, I think I have read just as many, if not more than you. And that's not even counting that I've read the Ultimate FF issues 1-5 and a few Human Torch issues.
So, don't talk down to me just because I'm younger than thou.
And, okay, I'm willing to admit that technically you could say it's flying, according to the dictionary descriptions generously provided by TripleF. But, all the same, Sue's been doing that in the comics. Since you claim to have read so many issues yourself, then you should know fully-well that she can do whatever she can put her mind to that applies to the properties of her powers.
Her powers are described as follows...
"The Invisible Girl/Woman possesses the psionic ability to manipulate ambient cosmic energy for the following effects. Can mentally bend light around herself without distortion to render herself invisible. Somehow, she enables light to penetrate her eyes so she can see while invisible.
Her body cells produce an unknown form of energy that she can mentally project around other persons or objects to render them invisible. Can use this energy to render visible persons and objects rendered invisible by other means, and energy that is normally invisible.
Her brain cells produce psionic force that she can project in relatively simple forms (rectangular planes, globes, cylinders, cones, domes, etc). Can mentally project protective force fields that are highly resistant to concussive force. Can travel through the air by projecting columns or disks of psionic force beneath her."
But, sure, if you'd like to think it's lame. That's fine by me. But Marvel came up with the idea long before this show was created. So, you can't pin the "lameness" on the cartoon.