How Flight Takes Off ??

TAKING OFF A FLIGHT 

The THRUST force makes the aircraft speed up along the runway.Why doesn't it take off?

 

The WEIGHT force is bigger than the LIFT force. What happens as the aircraft goes faster?

 

Now the LIFT force is bigger than the WEIGHT force. The forces are unbalanced, and the aircraft starts to rise. How does the pilot get back down safely?

 

The spoilers increase the DRAG force, to slow down the aircraft. As it goes slower, the LIFT force gets less and the aircraft starts to descend. As the aircraft slows down, the pilot extends the flaps at the back of the wings. This increases the lift so that the aircraft does not fall out of the air. How can the pilot stop the aircraft quickly when it has touched down on the runway? Deflect the exhaust air forwards (on many aircraft this can be done to slow them down when they have landed). Now the THRUST force is forwards, and helps to stop the aircraft. Of course, pulling on the brakes helps as well!

 

Deflect the exhaust air forwards (on many aircraft this can be done to slow them down when they have landed). Now the THRUST force is forwards, and helps to stop the aircraft. Of course, putting on the brakes helps as well!

Forces of Flight

Use these pages to explore the science behind flight. Just click on the links round the diagram to find out about the four forces: lift, thrust, weight and drag. Click on the links below the diagram to find out more about balanced forces and the control of aircraft.

	LIFT
DRAG		THRUST
	WEIGHT

Forces of Flight - Drag

The drag of the air makes it hard for the plane to move quickly. Another name for drag is air resistance. What's a good shape for getting through the air?

 

A streamlined shape slips smoothly through the air. A wind tunnel can be used to show how the air moves. Who needs a lot of drag?

Drag can be a useful force for slowing things down. A big area gives more drag. Have you ever felt the force of drag?

You don't notice the air's drag when you walk or run. But you feel the force of drag when you try to move through water. Fish and dolphins must have a streamlined shape to reduce their drag. (There's more drag in water than in air, because it is denser). Why is the force of drag important to insects?

A large insect, like a dragonfly, moves easily through the air. Life is much harder for small insects. Drag has a much bigger effect if you are small. For a gnat, flying might feel a bit like swimming. Drag is more of a problem if you are small, and if you want to move fast. Forces of Flight - Thrust An aircraft can use propellers to make it go forwards. It speeds up along the runway. When it is going fast enough, it takes off. How does a propeller make the aircraft move forward?   The engine turns the propeller. The propeller is specially shaped to push the air backwards. This results in a reaction force on the propeller that moves the aircraft forwards. (Swimmers move forwards through the water in a similar way, by pushing water backwards). The force moving the aircraft forwards is called the thrust. How does a helicopter move forwards?    The helicopter's blades are like a propeller. They tilt forwards so that the blades push the air backwards.A jet aircraft can go faster than a propeller aircraft. Where does its thrust come from?    A jet engine burns fuel, like a piston engine. Hot exhaust gases are forced backwards at great speed. Pushing gases backwards makes the plane go forwards.

Forces of Flight - Weight

People can't fly. If we jump up in the air, gravity pulls us back down. Our weight is caused by the pull of the Earth's gravity. Weight is the force with which gravity presses us against the ground. (We feel our weight in the reaction force of the ground pushing up against our feet). How can a balloon help us get off the ground?

 

A balloon can lift a person off the ground. But the balloon must be less dense than air. (The balloon must be filled with a gas that is lighter than the same volume of air). Fill the balloon with hot air or helium. Then you can make it float upwards. How can you float?

 

You can float in water. The water around you pushes back on you to balance the force of your weight. You float because you are less dense than water. (You are lighter than the same volume of water). An aircraft is much denser than air. So what force keeps it up?

 

An aircraft can't float in the air like a balloon. It needs an extra force to keep it up. Its wings are tilted and specially designed to give the extra force. The force is called lift. Forces of Flight - Lift As the aircraft moves forward into a stream of air, the wing deflects the air. Some of the air moves to flow above the wing while some of the air moves to flow below the wing. The wing is curved to help the air that flows above the wing move more quickly than the air that was able to flow below the non-curved bottom of the wing.     The air that is moving more quickly above the curved wing starts to put less pressure on the wing while it adjusts to its new stream. Meanwhile, the air that is moving at a consistent speed below the wing maintains its rate of pressure. This quick differential produces lift. The higher air pressure pushes the wing upward into the space where the air pressure is lower. This difference in air pressures is a result of Bernoulli's Principle which states that as the speed of a moving fluid (like air) increases, the pressure within that fluid decreases. The curve of a wing, therefore, effects how much lift force is generated when an aircraft moves through a stream of air.