Physics

Flight Airplanes how Airplanes Fly Lift Drag Thrust Pitch Roll Yaw Rocket Science



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For millions of years humans have watched winged creatures soar high in the air above, and as many have themselves dreamed of one day escaping the bond of gravity to match this alluring aerial feat. Many with dubious fascination, binding feathers to their appendages, have tempted fate to float off yonder precipice; only then to find their bodies in a tangled and broken profusion at the bottom, should they have been so lucky enough to have survived the event. After centuries of dreaming and the process of trial and painful error, two brothers Orville and Wilbur Wright succeeded where others before them had failed. They first took to the air with winged craft in 1903, but how?

The Wright's had been experimenting for several years, and in 1902 made a key discovery. They found that an airfoil provided greater lift than a surface, in this case a wing, that is flat on top and bottom. An airfoil is essentially a geometric plane which is flat on one side and curved or convex on the other. The air passing over the top - convex side - of the airfoil, having to travel further to reach the trailing edge of the plane or wing, must travel farther to get there. Air traveling under the wing -on the flat side- reaches the back of the wing faster than air traveling over it. This relative differential of air velocity also represents a difference of air pressure; it being lower on the top of the wing and greater on the underside. This pressure differential produces a dynamic referred to by aeronautical engineers as "lift," and its how air plains fly, but there is a little bit more to it. Getting up there is one thing, staying up there an entirely different scenario; as the Wright brothers would learn.

As lift is generated by air passing over and under the wing, the force of gravity is overcome and the wing begins to ascend. But how do you get the wind moving over the wing or the wing moving through the air in the first place. Well, for one thing, this is why planes always take off into the wind. For another, it brings to mind a second dynamic of flight which is called "drag." Drag is essentially the aggregate force of gravity and air resistance which is always trying to slow an air craft down, and bring it back to earth. The force of gravity is of course overcome by the dynamic of lift. In fact, in the case of a glider, gravity actually creates lift by increasing the gliders downward motion and thus accelerating the velocity of air passing over the wing surface, generating lift. Even a glider has to get up there before it can use gravity and air currents to generate lift however, and there is another aspect of flight The Wright's learned about which solves this problem.

The final dynamic necessary for flight is called "thrust." Thrust can be provided in a number of ways. A glider uses a tow plane to hall it up to an altitude where the glider can fly on its own. In this case the tow plane provides the thrust. Powered aircraft use propellers or jet engines to force air over and under the planes wing. Rockets are another type of propulsion that provides thrust and which are used to promote flight. Thrust overcomes the drag on an air plain and also provides lift by moving the plains wing through the air.

By December of 1903, Wilbur and Orville Wright had developed a fundamental understanding of the dynamics of flight, and returned to Kitty Hawk North Carolina to have another go at soaring with the birds. On this occasion, they got the coefficients of lift, drag, and thrust dialed in just right, and indeed did take to the sky and fly. Manned flight was no longer a dream but a reality.

Once an airplane is airborne, there are a number of variables which will influence its direction (heading) speed and so on. There are three additional dynamics to consider here and they are "roll," "pitch," and "yaw," and they all have to do with the attitude of the aircraft as it flies. The simplest way to understand each of these dynamics is to think of a line passing through the center of the fuselage of an aircraft from front to back. Roll pertains to the rotation of the wing tips of the airplane in circular motion around this center line. Pitch refers to nose up or down with respect to the centerline in relation to the earths surface. Yaw relates to an offset between the centerline of the aircraft and actual compass heading of it's forward movement. Roll, pitch, and yaw, are measured in degrees, and a parameter of zero degrees for each of these dynamics represents an aircraft in level flight.

Controlling roll, pitch, and yaw maintains the stability of the aircraft for level flight, but these dynamics are also exploited to change the course and altitude of the plane. Most aircraft designs utilize a tail section which includes horizontal and vertical stabilizers to effect pitch and yaw. The vertical stabilizer controls yaw and the horizontal stabilizer effects pitch. To control these dynamics, the vertical stabilizer is outfitted with a movable surface called a rudder, and the horizontal stabilizer is equipped with a similar surface referred to as an elevator. Finally, out near the end and on the back side of the wings, there are movable surfaces called ailerons which control the roll attitude of the aircraft. Using the rudder, elevators, and ailerons, the pilot can turn and bank the air craft, as well as cause it to climb and descend. In the case of ascent and descent, the pilot also throttles the engines up or down to control the amount of lift generated by the wing.

Finally, most airplanes today have movable surfaces on the back of the wings, and some times on the front of the wings also, called flaps. Flaps are used to adjust the lift dynamic of the wings, and also to increase drag to slow the plane down. In addition, some propeller driven air craft can adjust the pitch of the propeller blades, to cause them to change or reverse the direction of air flow, a capability which is also used to slow the aircraft down during landing. Jet aircraft accomplish the same thing with thrust reversers that redirect the engine exhaust forward.

So as you can see, and as the Wright brothers surely found out, there is a little more to how an airplane flies than meets the eye. But at the same time, its' not rocket science although its pretty close.

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