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Home > Flying the Plane > How airplanes fly?
How airplanes fly?
Flying - Flying the Plane
Tuesday, 11 December 2007 21:33


Orville and Wilbur Wright would not have believed that, over the span of 99 years, their world's first flight on the Kitty Hawk has progressed so much since then. The distance of the first flight was shorter than the length of a Boeing 747. Today, a Boeing 777 can fly about half way round the globe without refueling!

The Boeing 777 is the latest of the Boeing family that started with the first commercial model, the Boeing 707. Although the Boeing 777 is slightly smaller than the Boeing 747, it is more fuel efficient and has only two engines.

A Boeing 777 weights about 287 tons or 632,500 lbs. To imagine how heavy 287 tons is, just think of the combined weight of 3250 passengers weighing about 88 kilograms each. The Boeing 777 can carry up to 400 passengers depending on the configuration of the seating. For comfort, most airlines reduce the seating to 300 or below.

How it flies?

How is it able to fly at a speed of about 550 miles per hour (480 knots/900 kph) in the air?

The ability of a plane to fly depends on the shape of the wings. Looking at the cross-section of a wing, the shape is similar to a curved elongated tear drop placed horizontally. The upper surface is more curved than at the bottom. When air flows across this aerofoil shape, the pressure at the top of the wing is lower than the pressure at the bottom. This create an upward force on the wing. That force is greater than the force of gravity pulling the plane toward the earth. The result is a wing with a lifting force. All you need now is an engine to pull the wing forward and you get a flying plane!

The science behind this can be attributed to an 18th century Swiss named Bernoulli. He discovered that the pressure exerted by moving fluid is inversely proportional to the speed of the fluid. In other words, fluid pressure decreases as speed of fluid increase and vice versa.

His principle also applies to moving air. The faster the air moves over the wing, the lower the air pressure is created, and the slower the air moves, the higher the pressure. This pressure differential creates a force known as lift.

The theory of lift can be quite mind boggling to some. Try this experiment. When someone is driving a car, get him to maintain a speed of about 100 mph. Wind down the side screen and with your hand steady, hold your palm flat and cut into the air flow at zero angle. You find that you could probably hold your hand into the air flow but the moment you increase the angle from zero to some positive value, your hand will gradually rise due to lift being created. So your palm is almost similar to the cross section of an aircraft wing.

The faster the wing moves through the air, the greater the lift becomes, eventually overcoming the force of gravity.

A Boeing 777 takes off at about 180 miles per hour. At this speed, the wings would have created a lifting force greater than the weight of the airplane (287 tons or 632,500 lbs) and the plane gets airborne. It will continue to accelerate as it climbs to its cruising altitude of about 35,000 feet (about 7 miles high).

During cruise, the weight of the aircraft would be about 275 tons due to some of the fuel being burnt off during the climb. The lifting force generated by the wings now is also about 275 tons, creating an equilibrium. The plane would no longer climb but continues to move forward because of thrust forces generated by the jet engines.

What makes the aircraft move forward?

Most airlines today have airplanes that are outfitted with jet rather than propeller engines. The engines propel the airplane to move forward through the air. The motion forward generate the lifting force. As above, this force has to be greater than the weight of the aircraft before it can lift off and fly away.

How a jet engine works?

A jet engine takes in air at the front, compresses it and then pull it through a series of compressor blades. It then adds fuel to the hot compressed air and ignites the mixtures in a hot combustion chamber. This produces an explosion of extremely hot gases out of the rear of the engines and create a force known as thrust. The thrust then propels the engine, attached to the wings, forward.

To put it very simply, the principle of a jet engine can be described in just five simple words. They are "suck, squeeze, blow and go". That is good enough if you have some problem understanding how the turbines and compressors work.

The most important product of the jet engine is the 'go' or thrust at the back. Remember, when you blew the balloon and the released it after it was fully inflated. What happened? The balloon flew away. What cause it to fly away? Well, when the air escaped, it is similar to thrust being generated by a jet engine.

To recapitulate, with the thrust pushing the aircraft forward, the speed would increase and cause lift to be generated on the aircraft wings. When the force of the lift increases to such an extend that it would overcome the weight of the aircraft, the airplane would take off and climb away.

That is how a Boeing 777 is able to fly into the air


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How a jet engine works
Here is a great video on how a jet engine or a gas turbine works!! Enjoy,

Alex M. , 07 May, 2010
Why be a pilot
Could you tell me some reasons why a person will want to be a pilot
Ib , 11 May, 2010

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