Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
THE PRINCIPLES OF FLIGHT The Air Around You The 6 properties of air: • Air takes up space. • Air has weight. • Air can be compressed by applying pressure or squeezing. • Air can insulate. • Air can expand and create pressure when heated. • Air can contract when cooled. • Air is a mixture of 78% nitrogen, 21% oxygen and 1% a combination of carbon dioxide, helium, water vapour and other gases. • When air is heated, the molecules speed up and move farther apart. This heated air takes up more space. As the air is cooled, the molecules slow down and move closer together, causing the air to take up less space. Heated air, which has greater volume than cooler air with the same mass (the number of atoms that holds or clings together in an object), will naturally rise, since the pull of gravity workers harder on the denser air. Gravity • Gravity is a force. • For an object to fly, there must be enough lift (a force that causes something to rise) to overcome the force of gravity acting on the mass of an object. In a hot-air balloon, unbalanced forces work such that the force of lift must overcome the force of gravity. The lighter the object, the less lift is required to overcome the force of gravity. Thus a very light object, such as a dandelion seed, can use the wind to give it enough lift to be carried away. • Gravity is a force that results from the masses of objects being attracted to each other. Your mass is attracted to Earth’s surface. It is important to know that the force of gravity does not depend on air, it depends only on mass. Daniel Bernoulli The work of Swiss mathematician Daniel Bernoulli was instrumental in the study of flight. In 1738, he published his first article explaining his discovery of how moving fluids exert less pressure than still fluids. This discovery was found to be true for moving air as well. Today this discovery is called Bernoulli’s Principle. It means that the faster air moves over an object, the lower the pressure. Bernoulli’s Principle • Bernoulli’s Principle states that moving fluids (air is considered a fluid) creates less pressure than non-moving fluids. TRY THIS EXPERIEMENT: To show how to generate lift, hold one end of a strip of paper (5 by 20 cm) against your lower lip so that the strip sags down over your chin. Blow hard across the top of the paper. • how was the lift created? • When you blew air across the strip of paper, you lowered the air pressure by making the air above the strip move faster than the air below the strip. With lower pressure on top compared to below, lift was created and caused the paper to rise. • Moving air pushes on objects. • Moving air can move other objects. • Moving air can cause changes in pressure. Aerodynamics • Bernoulli’s Principle is used to explain properties of aerodynamics (The study of air in motion). This same principle explains how airplanes work. As a jet plane is thrust through the air by the hot exhaust gases expelled from its engines (or air being moved by propeller) the shape of the wing forces the air traveling over the top of the wing to move faster. This lowers the air pressure and gives it lift to the wing, allowing the plane to take off from the ground and increase altitude as it flies through the air. Airfoil The curved shape of the wing of a bird or an airplane is called an airfoil. It is important to understand how Bernoulli’s principle relates to an airfoil. 1. As an airfoil moves through the air, the air hits the front of the airfoil (leading edge) and separates. 2. The air flowing over the curved surface has a greater distance to travel than the air flowing over the flat surface. Airfoil 3. 4. 5. For the two streams of air to reach the back of the airfoil (trailing edge) at the same time, the air over the curved surface must travel at a faster speed. This quickens movement of air over the top of the airfoil. This creates a low pressure area above the airfoil and a high air pressure area below the airfoil. The difference in pressure causes the wing to lift. In other words, air below the wing pushes up more than air above the wing pushes down. This difference in pressure results in an upward force called lift. All winged aircraft, including gliders and helicopters, use airfoils to create lift. Airplanes and birds fly even though they are heavier than air. As mentioned, aerodynamics is the study of air which examines the forces of lift, weight, thrust, and drag. These forces affect every surface that moves through the air. A bird, for example, is aerodynamically designed. It’s curved wings create lift, and the streamlined shape allows it to move through the air with little resistance. Aerodynamics engineers try to design airplanes whose shape will create maximum speed and lift, while minimizing the effects of drag. The Four Forces of Flight • The four forces of flight are: Lift, Gravity (weight), Thrust and Drag. All flying devices must use thrust and lift to overcome the forces of drag and gravity (weight). When there is a balance of the four forces, a stable flight can occur. • Gravity/Weight A real downer, caused by gravity, pulls everything toward the ground. • Lift An upbeat kind of force, caused by air moving over the wings, acts upward against weight. • Drag A backward force, caused by air resistance, acts in the opposite direction to motion. • Thrust A very forward force, caused by an engine, overcomes the force of drag. • Thrust is the force that moves the plane forward. Thrust comes from the propellers or jet engine. And when you have thrust or moving air across a surface you get lift. This is how an airplane can fly. The thrust moves the plane forward and generates lift to keep the plane in the air. • Drag slows down or prevents the motion of an object in air or water. It is difficult to run in water because the water slows you down. You could say that the water is creating a drag on your movement. Air behaves in a similar way. Air creates drag on a plane and slows it down. The force has advantages and disadvantages. Advantage: It helps the pilot to steer the plane. Disadvantage: It needs more thrust (energy) than drag to fly. • Three terms describe the movements of an airplane. Pitch is the up-anddown movement of the nose of a plane. Roll is a motion where one wing tip moves up while the other wing tip moves down, causing the body of the plane to roll. Yaw is the side-to-side movement of the nose of a plane. Pilots maneuver planes through the air using combinations of pitch, roll, and yaw. The End