How things fly
The forces of flight
There are 4 forces of flight through the air.
- Drag is is partly caused by the air rubbing against the aircraft as it flies (friction). It slows the aircraft.
- Thrust is the force that moves a flying machine forwards. Engines produce thrust.
- Weight is the force of gravity. It acts in a downward direction — toward the centre of the Earth.
- Lift is created by differences in air pressure above and below the wings.
How does a plane get lift?
Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air.
Air pressure
Air pressure is the force put on you by the weight of tiny particles of air (air molecules). Although air molecules are invisible, they still have weight and take up space.
How does a propeller make a plane fly forwards?
A propeller “lifts” a plane forward. Like a wing, it produces lift, but in a forward direction—a force we call thrust. A propeller is just like a wing - in fact, they are just a wing with a twist in them. When a propeller moves through the air, the air in front will speed up and decrease in pressure, while the air behind will stay slow. The air behind the propeller now has higher pressure. The high pressure air will push the propeller forward!
How do you keep a ball in the air? Use the Bernoulli principle!
Shooting fast-moving air under a Ping-Pong ball will send the ball flying into the air. The ball then hovers in the air because two forces are in balance, the lift from the air blowing up and gravity pulling it down.
If the ball moves away from being straight above the blower, it won't easily fall down. This is because the air around the side of the ball pushes it back. Why? The air to the side of the ball pushes the ball more than the air from the blower pushing it to the side. As the air from the blower is faster, it has less pressure, so pushes less on the ball's surface. The slower air around the side of the ball has more pressure, so it pushes more on the ball. The faster air goes, the less pressure it has. The slower the air goes, the more pressure it has.
How to control an aircraft
You need elevators on the tail fins, a rudder on the back of the tail and ailerons on the wings.