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The principles of flight
Lift, thrust, weight and drag aerodynamic forces Flight is the result of four basic forces: lift, weight, thrust and drag. Lift lifts you up. Weight pulls you down. Drag slows you down. Thrust thrusts you forward. If you're flying straight and level at a constant speed, thrust equals drag and lift equals weight. If thrust is bigger than drag, you speed up. If thrust is smaller, you slow down. If lift exceeds weight, you climb. If lift is less, down you go.
Thrust The thrust moving the plane comes from the propeller. It is like a special, spinning wing which pulls air past its blades. Drag Hold a sheet of paper vertically in front of an electric fan (at a safe distance). Drag is the force pushing the paper backwards. Skateboarders speed up by crouching, to reduce drag. Modern planes retract landing gear to reduce drag. On a modern jet at full speed, there is enough drag to tear off the undercarriage if it is not retracted. Early Q.A.N.T.A.S. planes flew too slowly for this to matter. Drag only occurs in a moving fluid. Stop the fan and the force on the paper vanishes. Weight You experience your own weight all day every day. Unless you're an astronaut in space. Lift Lift is the force keeping a plane in the air. Most lift is created by the wings. Like drag, lift only exists in a moving fluid, such as air. How lift and drag are created When air moves over curved surfaces, some speeds up. Some slows down. Some crowds together. Some spreads out thinly. This causes changes in pressure all over the surface. Lift or drag comes from adding together all of these small changes. Air approaching the top surface of a wing is compressed upwards. As the wing curves down and away from the airstream, a low-pressure area develops. Air above is pulled down toward the back of the wing. Air approaching the bottom surface is slowed, compressed and directed downward. Wing shape helps determine how much pressure change occurs and thus the amount of lift or drag. Roll, pitch and yaw aircraft control The tail controls a planes direction by two small wings horizontal and vertical stabilisers. The horizontal tail wing controls whether the plane goes up or down. The vertical tail wing controls turning left or right. On the outer ends, ailerons turn the plane and keep it level. And that takes us into roll, pitch and yaw.
Imagine an axis runs nose to tail. Rotation about this axis dipping a wing is called roll. Another runs wingtip to wingtip. Rotation about this axis moving the nose up and down is pitch. The third is vertical through the centre of gravity. Rotation about this axis is yaw. If a plane is flying straight and level, then turns its nose left, or right, it is yawing on its vertical axis not moving forward in the direction its nose is pointing. An aircraft may move about one or all of these axes at once. Dip a wing and roll 180 degrees. You are flying upside down. Roll another 180 degrees back, straight and level. Congratulations, you just executed a barrel roll. Change pitch 90 degrees downward: you are diving towards the ground. Rotate another 90 degrees: you have reversed your direction. And you are also upside down. Continue rotating another 90 degrees. Now you are climbing straight up. Complete a 360-degree circle, and you are again flying straight and level. You just did an outside loop. For an inside loop, change pitch upward and again do a full circle.
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