If the airflow over a wing moves faster than below it to produce a
lower pressure over the wing and creating lift, then how can a plane
continue to fly while inverted?

Hi babuness,

Good question, one that I must admit I didn't know the answer to
either until I started researching this.  Obviously you are not the
first person to wonder this as I managed to find the exact explanation
as to how inverted flight is possible at the following site:

Lift and Inverted Flight
http://quest.arc.nasa.gov/aero/question/aerotheory/Lift_and_inverted_flight__.txt


A further explanation of the problems and possibilities of flying
upside down is available from:

How Things Work: Flying Upside Down
http://www.airspacemag.com/asm/Mag/Index/2002/AM/fusd.html


Additional links:

R/C Helicopter Fever : Flying a radio control helicopter upside down
http://www.helifever.com/advanced/lesson4.cfm

Pilots' Guide to Inverted Flying
http://www.slams.freeserve.co.uk/Q&A/Flying%20Info/Inverted%20Flying.htm


I hope this answers your question satisfactorily; if you would like
any further detail, explanation or clarification please do not
hesitate to ask.

mcfly-ga :)

---------------------

Search terms:

"inverted flying"
"flying upside down"

The answer doesn't require any links:

The reason airplanes can fly upside down is because the bottom of the
wing is now the top of the wing, and vice versa.  So what you said
initially still holds true.

Enjoy

That comment isn't strictly true, a conventional areofoil is curved at
the top and flat on the bottom, in order to create the pressure
difference required for lift. If this was inverted, the force would
still be created, but would be pointed towards the ground.

In order for a conventional areofoil to work inverted, the pilot will
have to fly with the nose of the plane slightly more upwards than
usual in order to get the required angle of airflow over the wing. 
Ask any pilot, and they will tell you that this works, but not really
well.  The answer is symmetrical wing design, and I'm sure those links
will tell you about that.

This page http://www.monmouth.com/~jsd/how/ has a phenomenal
explanation of
how wings work including why they'll fly upside down.     Go down to
the Airfoils
section and read away.   It's not dry reading either.    The
fascinating part is learning
about circulation, bound and unbound vortexes.    All wings create
circulation of the
air which causes it to displace air downwards behind  the plane.   
Basically a wing is
curved on top only because it increases the effective camber and
allows the wing to fly
at a greater angle of attack at lower speeds before it stalls.
No wing must be curved on top and flat on bottom to work.   Aerobatic
planes have
symetrical airfoils and control lift through angle of attack.    

     ian