# Air Planes (flight dynamics)

Air planes are generally recognized as one of the greatest inventions of all time. Air planes have engines that power their forward movement at high speed. However these engines are not the sole factor determining the flight of air planes. Gliders, birds, paper planes etc. fly without engines.

The wings of planes are shaped in such a way that air moves faster over the top when the plane moves at high speed. The pressure of air decreases when air moves faster. When planes move at top speed, the pressure on top of the wing decreases, compared to the air pressure at the bottom of the wing. The difference in pressure establishes a force (lift) on the wings. This force lifts the wings up into the air. The force of lift overcomes the plane’s weight and suspends the plane in the sky. A plane’s engine moves the plane forward, while the wings move it forward.

A plane makes three significant movements in determining its direction. These are roll, pitch and yaw.

A pilot uses the ‘roll’ to control the direction of the plane. A pilot can ‘roll’ the plane to the left or right. If a pilot lowers the ailerons  on one wing and raises the ailerons on the other, the wing with the lowered ailerons rises. The wing with the raised aileron drops.

The plane climbs or descends with the ‘pitch’ movement. A pilot lowers the elevators on the tail of the plane causing the nose of the plane to drop. This eventually sends the plane down. When the elevators are raised, the plane moves upward.

An airplane turns when it ‘yaws’. The plane turns either left or right depending on whether the rudder is turned left or right.

#### Control instruments

##### Throttle

It is used in controlling the engine power. When pulled, the engine power decreases. When pushed, the engine power increases.

##### Ailerons

The ailerons control the roll of the plan. A pilot lowers or raises either ailerons of either wing of the plane with a control wheel.

##### Rudder

The rudder controls the plane’s ‘yaw’. The pedals control the plane’s ‘rudder’. The rudder moves to the right when the right rudder pedal is pressed. The rudder moves left when the left rudder pedal is pressed.

Also, the top of the left rudder controls the plane’s left break while the top of the  right rudder controls the right break. The brakes are used to slow down the plane when it is on the ground.

##### Elevators

The elevators are found on the tail of the plain. They control the plane’s pitch. The elevators are raised or lowered through a control wheel. The plane goes down when the elevators are lowered. It goes up when the elevators are raised.

#### Breaking the Sound Barrier when air planes are in flight

Sound is comprised of air molecules. These molecules of air move. When they gather together, they form sound waves. When a plane is on top flight (speed of sound), air waves gather together in a compressed form in front of the plane. This compressed air slows down the plane through a shock wave formed in front of the plane. In order to move faster than the speed of sound, the plan needs to break through the shock wave. When it does this, the shock waves spread out creating a loud (sonic boom) sound. The sonic boom is caused by the instantaneous change in the air pressure. A plane travels at supersonic speed when it travels faster than the speed of sound.

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