Stephen Canham of Methven Primary School asks :-

Plane wings are curved at the top and flat at the bottom and are probably only made to work the right way up. So how can planes fly upside-down?

Jim Rankin, a physicist who is a flight instructor in the Royal New Zealand Air Force, responded.

You are quite correct. To generate lift to keep flying, aircraft wings are usually curved more on the top than the bottom. The bigger curve on top makes the air going over the top flow faster than the air flowing over the bottom. This speed change causes a reduction in the air pressure on top of the wing, which generates the lift that keeps the plane flying.

However, that is only part of the reason why wings produce lift. You can produce lift just by putting a flat surface in the airflow, at an angle to the flow (called the `angle of attack'). Everyone has tried putting their hand out of a car window as they drive along, and made their hand `fly' up or down by twisting their wrist. A flat wing, like your hand, is not as efficient at producing lift as a curved one, but will still do so because the air going over the top has further to travel than the air on the bottom, so it speeds up, reduces pressure and produces lift.

When a plane flys upside down, the angle of attack has to be increased enough to make the wing work even though the lower side of the wing is now more curved than the top. Have a look at a photograph of the Air Force Red Checkers `mirror' formation. The top aircraft (NZ1938) is pointing much higher up in the sky than the bottom one. It has a bigger angle of attack, so the wing still works, but not as efficiently as the right way up.