Cruisingfoiler, "The devil ain't in the detail. It's plain to see.

It's the total drag package.  All that drag above and below the water must be overcome.  And you need lift to overcome it.  Your single element will either have to be so tall that you must depower before you generate much lift, or so squat that its draggy anyway.  

Aircraft don't use symmetric foils.  They don't fly upside down, at least not much better than a bucket of bricks when they try :)."

That is really funny.  Let me give you a quick tutorial.

When I am flying along and pull the flaps the airplane starts climbing (increased lift) and slowing down (increased drag). It doesn't take too long before the airplane slows down to where the wing stalls and I have to point the nose down to gain more airspeed. I can stabilize the airplane to where the elevation and airspeed are constant like before except that I am flying slower, a lot slower.

Increased lift means less speed....  

Now about flying upside down.  If you are flying with me you can put your cup of coffee on the dash board in front of you and close your eyes and I can do a barrel roll and you can't tell, your coffee won't spill either.

So yeah, you are right, an airplane can't fly upside down.

Talador