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How Do Airplanes Fly?What are the Principles that Allow an Aeroplane to Stay in the Air?
Lift, Drag, Thrust, Weight - these are the physical forces which are involved in aircraft flight. A flying instructor explains how they work to enable a plane to fly.
Some people learn about the principles of flight at school, but to others flight seems like magic. How does an aircraft manage to overcome gravity and remain in the sky? It is actually quite simple… Lift, Thrust, Drag, and WeightThe force needed to keep an airplane in the air is called ‘Lift’. Lift is produced by forcing air to flow over the wings. The construction of the wings is such that the air flowing over the top surface has to travel further, and it therefore travels faster, than the air under the wing. This causes the pressure of the air on the top of the wing to be lower, and so effectively the wing is sucked up by this lower pressure, and flies. Lift is produced independently of power from the engine. The engine produces ‘Thrust’, which gets the aircraft moving along the runway, so that air flows over the wings. Thrust also overcomes ‘Drag’, which is the force which tries to oppose the motion of the aeroplane through the air. The presence of the airplane – or any other object – causes friction; and this is a type of drag. The other force involved is ’Weight’, and the weight of the airplane determines how much lift is required to get it into the air. As long as there is enough lift to overcome the aircraft’s weight, and enough thrust from the engine to overcome the drag, then the plane will fly. Even if the engine stops, if the aeroplane is allowed to descend in a glide, the air over the wings will generate enough lift to keep it airborne, while the pilot prepares for a landing. Aircraft ControlsThe aircraft stays airborne because of lift, but the plane's controls are what enables the pilot to move it in a particular direction. On aeroplanes such as the Cessna 152, the ‘Elevator’ is a hinged surface on the rear of the fixed tailplane. If forward pressure is applied to the control column, the elevator causes the lift over the tail to increase, so that the nose of the airplane pitches down. Conversely, back pressure causes the nose to pitch up. The ‘Ailerons’ on the wings alter the lift on each wing, causing one wing to drop, which results in the airplane turning. The ‘Rudder Pedals’, connected to the rudder on the tail, cause the aircraft to yaw to right or left, working in much the same way as the rudder on a boat. Using the ailerons and rudder together means the plane can be turned in a balanced and comfortable fashion. That’s about it - now the flying student has to learn to use all the controls together to take off, and fly at a given height, and in a direction that he or she wants, before landing the aircraft. There is always more to learn about flying… SourceTrial Flight Guide, Dorothy Pooley, Pooley’s Flight Equipment Ltd 2002 Related Articles
The copyright of the article How Do Airplanes Fly? in Aviation is owned by Helen Krasner. Permission to republish How Do Airplanes Fly? in print or online must be granted by the author in writing.
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