katyzzzAirplanes and working
August 26th 2006 23:44
airplane-rear gear
airplanes are one of the most amazing things that I see on a daily basis. When I get on a 747, I am boarding a gigantic vehicle capable of carrying 500 or 600 people. A 747 weighs up to 870,000 pounds at takeoff. Yet it rolls down the runway and, as though by magic, lifts itself into the air and can fly up to 7,000 nautical miles without stopping. It is truly incredible when you think about it!
Aerodynamic Forces :
Before we dive into how wings keep airplanes up in the air, it's important that we take a look at four basic aerodynamic forces: lift, weight, thrust and drag.
Thrust :
Thrust is an aerodynamic force that must be created by an airplane in order to overcome the drag (notice that thrust and drag act in opposite directions in the figure above). Airplanes create thrust using propellers, jet engines or rockets. In the figure above, the thrust is being created with a propeller, which acts like a very powerful version of a household fan, pulling air past the blades.
Drag :
Drag is an aerodynamic force that resists the motion of an object moving through a fluid (air and water are both fluids). If you stick your hand out of a car window while moving, you will experience a very simple demonstration of this effect. The amount of drag that your hand creates depends on a few factors, such as the size of your hand, the speed of the car and the density of the air. If you were to slow down, you would notice that the drag on your hand would decrease.
We see another example of drag reduction when we watch downhill skiers in the Olympics. You'll notice that, whenever they get the chance, they will squeeze down into a tight crouch. By making themselves "smaller," they decrease the drag they create, which allows them to move faster down the hill.
The Newtonian Explanation
What is it?
Isaac Newton stated that for every action there is an equal, and opposite, reaction (Newton's Third Law). You can see a good example of this by watching two skaters at an ice rink. If one pushes on the other, both move -- one due to the action force and the other due to the reaction force.
The Newtonian explanation provides a pretty intuitive picture of how the wing turns the air flowing past it, with a couple of exceptions:
The top surface of the wing is left completely out of the picture. The top surface of a wing contributes greatly to turning the fluid flow. When only the bottom surface of the wing is considered, the resulting lift calculations are very inaccurate.
Almost a hundred years after Newton's theory of ship hulls, a man named Leonhard Euler noticed that fluid moving toward an object will actually deflect before it even hits the surface, so it doesn't get a chance to bounce off the surface at all. It seemed that air did not behave like individual shotgun pellets after all. Instead, air molecules interact and influence each other in a way that is difficult to predict using simplified methods. This influence also extends far beyond the air immediately surrounding the wing.
More Airplane Parts :
The wing is obviously the most important part of an airplane -- it's what gets the airplane in the air. But airplanes have a lot of other characteristic parts designed to control the plane or get it moving. Let's examine the parts you find in a typical airplane by looking at a Cessna 152.
Horizontal and Vertical Stabilizers :
The tail of the airplane has two small wings, called the horizontal and vertical stabilizers, that the pilot uses to control the direction of the plane. Both are symmetrical airfoils, and both have large flaps on them that the pilot controls with the control stick to change their lift characteristics.
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