# What is an airfoil and How to Make an Airfoil?

## What is an airfoil?

When an airfoil moves through the air, it produces lift because the force of the air pushing down on its top surface is less than the force of the air from below.
The uneven pressure causes lift.
Balloons and airships stay up off the ground because the gas inside them is lighter, or less dense, than the air outside.

## But airplanes are heavier than air, so how can they stay in the air?

The shape of an airplane’s wings gives it upward movement, or lift. If you look at an airplane from the side, you’ll see that the upper surface of the wing is curved, and the lower surface is straighter.
This shape of wing is called an airfoil.
When the plane is in flight, the air which passes over the top of the airfoil has to travel faster than the air which passes underneath it.
This makes the air on the top push down on the airfoil less than the air pushing up from underneath. Therefore, the airplane is lifted up and stays in the air.

### Take-off and landing

When an airplane is taking off, it needs a great deal of lift.
If you look at a large airliner, you can see some movable flaps, or ailerons, at the rear, or trailing, edge of the wings.
These ailerons can be lowered.
The lowered flaps increase the top surface of the wing.
This makes air travel even farther over the top surface than over the bottom.
This increases the lift force during take-off. During flight, the ailerons are usually in a normal position, neither up nor down.
But when the aircraft is landing, the flaps are lowered again. Besides maintaining lift with reducing speeds, the lowered ailerons help to slow the plane down.

At take-off, the ailerons on the plane’s wings are lowered to provide additional lift. Once the plane is up in the air, the ailerons fit neatly against the wings.

## How to Make an Airfoil?

1. Fold the paper in half. Move the edge of the upper half of paper back a little from the edge of the lower half. It will bow upwards.
Carefully stick the edge down with adhesive tape.
2. You have made an airfoil.
Put your airfoil on the edge of a table.
Now place your mouth level with the edge of the table, and blow.
What happens?
Why?