The main objective of this unit will be to discuss examine, and appreciate the science of flight. Also to give students hands on experience through speakers, field trips and a trip on an aircraft. The unit will attempt to teach about airplanes through an electric approach.
Airplanes
The airplane is one of the newest and fastest means of transportation. Only spacecraft travel faster than airplanes. A modern jet transport plane can carry a heavy load of passengers and cargo across the United States in less than 5 hours. It can fly nonstop halfway around the world—from Chicago to Calcutta, India in about 15 hours. Passengers can ride in comfort 30,000 to 45,000 feet (9,100 to 13,700 meters) above the ground. On many long flights, they can watch a movie or listen to music. The largest jets can hold nearly 500 passengers.
Rocket planes, the world’s fastest airplanes, have been flown at speeds faster than 4,500 miles per hour (mph). However, rocket planes are used for research only.
Most airplanes are not so large or powerful as jets. About 80 percent of all the planes in the United States have only one engine and can carry only a few passengers at a time. Many people use these light airplanes for short business or pleasure trips.
An airplane is a heavier-than-air machine. The largest transport planes weigh more than 350 short tons (320 metric tons) when fully loaded. A plane’s engines, wings and control surfaces enable it to fly. The engine or engines move the plane forward through the air. As the plane moves, the air that flows over the wings moves faster and therefore has less pressure—than the air under the wings. This difference in air pressure, called lift, keeps the plane in the air. The pilot keeps the plane balanced in flight by adjusting the control surfaces, which are movable sections of the wings tail.
Today’s airplanes can be divided into five main groups: (1) commercial transport planes, (2) light planes, (3) military planes, (4) seaplanes, and (5) special-purpose planes. This section discusses some of the different kinds of planes in each group and describes how they are used.
Commercial transport planes are large planes owned by airline companies. Most of these planes are designed specially to carry passengers and some cargo. Such transports are called airliners. Other commercial transports are designed to carry cargo only.
Supersonic transport planes are the fastest airliners. They can soar through the air at 1,330 mph with more than 100 passengers. Currently Supersonic transport planes can fly from Paris to New York City in less than four hours. However, their number is very limited and they play a minor role.
Most large airliners carry from 100 to 250 passengers. However, some carry many more. The Boeing 747 has room for nearly 300 passengers. It has 12 washrooms and 6 galleys and carries more than 47,000 gallons of fuel.
Four-engine jets, such as the Boeing 747 and the McDonnell Douglas DC-8, are designed for long-distance flights. Most of these planes can fly nonstop 6,000 miles or more—farther than the distance from New York City to Toyko. Four-engine transports cruise at an altitude of 30,000 to 45,000 feet (5.7 to 8.5) miles.
Some three-engine jetliners, such as the Boeing 727 and the McDonnell Douglas DC-10 can carry as many passengers as most four-engine jets can. But most three-engine jets are designed for shorter flights. They can also use shorter runways. The Soviet Yak-40 and some other three-engine jet airliners carry only about 40 passengers. These planes can land and take off at small air fields.
Most twin-engine commercial airliners carry fewer than 100 passengers. These planes serve many small and medium-size cities. Twin-engine, propeller-driven planes travel at less than 400 mph (640 kph) and make most short flights. But twin-engine jets can travel faster and farther. The McDonnell Douglas DC-9 and the Boeing 767 can fly at speeds faster than 575 mph and can make nonstop flights of 2,000 miles or more. They can carry as many passengers as most four-engine jets.
Many large airliners are designed so that their seats can be removed to make room for a full load of cargo. These planes have extra-large doors, and they may also have built-in machinery for loading and unloading.
Transport planes that carry only cargo look much like airliners except that they have no passenger windows. The largest of them, such as the Lockheed C-5A Galaxy and the all-cargo model of the Boeing 747, can carry 100 short tons of cargo more than 4,000 miles nonstop.
Most transport planes carry expensive, lightweight goods, such as electronic equipment and machine parts. These planes also transport goods that must be delivered quickly, including fresh flowers, fruits, and vegetables. The largest transport planes carry heavier loads such as building materials and military equipment. Some cargo planes carry goods in large metal boxes called containers. Special equipment easily and quickly lifts the containers on or off these planes.
Light planes are much smaller than commercial transport and can land and take off at small airfields. Most of these are single-engine, propeller-driven planes and are privately owned. There are more than 100,000 single light planes in the United States. Some of these planes weigh more than a few hundred pounds and have room for only the pilot. Other single-engine light planes can carry up to 12 passengers.
The largest light planes have two reciprocating engines and can carry up to 19 people. These planes are really small airliners. Air taxi services and commuter lines use such planes to transfer passengers between small airports and the large airports that serve commercial transports. Many business firms also own single twin-engine light planes. Such businesses use the planes to fly their executives, managers, salespeople and other employees to out-of-town assignments or meetings. A few of these business, or executive planes are three or four-engine transports powered by reciprocating engines.
Light planes have hundreds of other uses.
An airplane is a mechanical device that obeys mechanical laws. To fly a plane, a person must know these laws and the laws of aerodynamics. Flying an airplane differs from driving an automobile. The driver of an automobile simply turns the steering wheel when making a turn, but to make a turn in an airplane, the pilot must operate several controls at once. The plane has three basic movements: pitch, roll and yaw. (see figure 2).
Pitch is the motion of a plane axes as its nose moves up or down, a roll is when one wing tips down lower than the other. Yaw is a planes motion as the nose turns right or left. A plane has many controls, but four of them are basic. They are: the elevator and rudder parts of the tail assembly, the ailerons, located on the wings and throttle. A system of cables, rods, and pulleys leads from the outside controls to the pilots controls in the cockpit. The pilots yoke or stick controls the ailerons and elevator. The rudder pedals control the rudder. The pilot uses the throttle to control the engine’s speed and power. (see figure 3).
The two major principles that relate to aerodynamics forces are lift and drag.
Lift is the aerodynamic force produced by the motion of an airfoil (wing) through the air. The lift force acts at a right angle to the direction of motion. Lift gives an airplane the ability to climb into the air and holds it up during flight.
A typical airfoil has a rounded leading edge and a sharp trailing edge. As the flow of air approaches the leading edge, it splits to go around the airfoil. To produce lift, the flows along the upper surface and the lower surface must be unsymmetrical. An unsymmetrical flow can be created by the curved shape of the airfoil, called the camber. Such a flow also occurs when the airfoil meets the air at an angle. Furthermore, the two flows must merge smoothly as they leave the trailing edge. The Kutta condition, in combination with the unsymmetrical flow of air, produces a faster flow along the upper surface, thus reducing the air pressure on that surface. As a result, the airfoil is lifted into the air.
Lift can also be explained by an airfoil’s ability to deflect air downward. An airfoil deflects air by its camber and by meeting the air at an angle.
The amount of lift produced by a wing depends mainly on its angle of attack and high-lift devices. The density of the air and the area and speed of the wing also affect the amount of lift.
Angle of attack is the angle that a wing makes with the air flowing past it. A pilot can change this angle by changing the plane’s pitch. Up to a certain point, increasing the angle of attack increases the lift force produced by the wing. An increase in lift means the plane can climb faster or fly slower. (see figure 4)
The angle of attack plays an important part in safe flying. Air cannot flow smoothly over the wing if the angle becomes too steep. Instead, the air stream suddenly breaks up into small whirlpools called eddies on top of the wing. The eddies sharply decrease the lift and let the plane drop toward the ground. This condition is called a stall. The aircraft may crash unless the angle of attack is quickly reduced. Planes fly at an angle ranging from 3 to 4 degrees. Most planes will stall if the angle becomes larger than 15 or 20 degrees.
The lift produced by an airfoil depends on the wing’s speed through the air. If the wing does not move fast enough, the difference in pressure above and below the wing will not produce enough lift to keep the plane in the air. During landings and take-offs, however, pilots want to fly as slowly as possible.
Planes have special parts which provide enough added lift for the plane to fly at minimum speeds. These devices include (1) the flap, (2) the slat, and (3) the slot.
The flap is a hinged section at the back of each wing. The pilot lowers the flaps for a landing and sometimes for take-off. When lowered the flaps increase the camber of the wing, furnishing extra lift. They also help slow the plane when landing.
The slat is hinged section near the front tip of each wing. When a plane slows down, the slats automatically move forward to increase the wings’ camber and lift.
The slot is an opening along the front edge of the wing. It helps air flow smoothly over the top of the wing so the plane can fly at a large angle of attack without stalling. Such an angle increase the lift.
Drag is an aerodynamic force that resists the forward motion of an object. The shape of the object influences the amount of drag. Objects shaped to produce as little drag as possible are called streamlined or aerodynamically clean. Aircraft designers build planes to reduce drag to a minimum. Planes with low drag need less engine power to fly, and reduced drag also improves airplane’s performance. Automobiles, trains, trucks, and other vehicles also encounter drag.
Two types of drag—friction drag and form drag—act on all moving objects. A third type, induced drag, affect only objects with lift. Still another kind of drag results when a plane flies faster than the speed of sound.
Friction drag occurs next to the surface of an object. It is produced in a thin layer of air called the boundary layer. Friction results whenever one layer of a fluid slides over another layer. The air in the boundary layer move in either (1) orderly paths parallel to the surface or (2) irregular paths. Engineers call an orderly motion of the molecules laminar flow and an irregular motion turbulent flow which increases friction drag.
The boundary layer is laminar at the front of an object. The flow of air can become turbulent at some point as the air moves along the object. Aircraft designers try to delay this change from laminar to turbulent as long as possible to keep friction drag to a minimum. One way they do so is to make the surface of the object as smooth as they can.
Form drag results when the air flow past an object breaks away from the object. This type of drag produces swirling eddies of air that take energy from the object and slow it down. Form drag occurs with non-streamlined objects. For example, a motorist following a large truck at high speed may feel the car shaken by the eddies behind the nonstreamlined truck.
Engineers reduce form drag by streamlining the object. They also put vortex generators on airplane wings. These devices are small airfoils that stick up in long rows on top of a main wing. Vortex generators produce small disturbances in the boundary layer that keep it from breaking away from the wing.
Here are only a few of the more important instruments which a pilot uses to help operate the plane.
Oil Pressure Gauge indicates the pressure of the oil in the engine. The dial is colored so that it is easier for the pilot to instantly spot any danger.
Oil Temperature Gauge tells the temperature of the oil in the engine.
Rate-of-Climb Indicator tells the pilot the speed at which his plane is climbing or dropping. The indicator is at zero when the plane is flying level.
Air Speed Indicator notes how fast the plane is moving through the air. Four colors are used for greater safety. Red is used to show maximum speed at which the plane can fly. Yellow shows a caution range—speeds approaching maximum speed. Heavy blue is used for normal cruising speeds. Light blue is used to show landing speed.
Turn-and-Bank Indicator is actually two separate instruments. The curved glass tube with a metal ball in liquid, the bank indicator, located near the bottom of the instruments shows whether the plane is tilted to the right or left. The turn indicator show the direction in which the nose of the plane is headed to the left, straight ahead or to the right.
Instruments Landing System Indicator helps the pilot land his plane when the airfield is covered by fog or very low clouds. When the two pointers line up with the white circles on the dial, the plane is directly on path approaching the runway for a perfect landing.
Fuel Gauge indicates how much gasoline the plane has in its tank.
Tachometer tells the pilot how his motor is doing. It indicates the number of revolutions of the engine or the speed at which the propellers are turning.
Altimeter shows the height of the plane above the ground. There are three pointers—the smallest shows height in tens of thousands of feet above the ground; the medium-sized pointer shows height in thousands of feet; and the longest pointer shows height in hundreds and parts of hundreds of feet. The altimeter pictured here shows an altitude of height of 14,750 feet. (see figure 5).
Directional Gyro and Magnetic compass are used to guide the plane. The magnetic Compass acts like any regular compass you have seen; it points to the north. The directional gyro is used by the pilot to set his course. If the plane changes direction, the gyro shows this to the pilot.
Artificial Horizon helps a pilot when he is flying at night, in a cloud or in fog. During a clear day, a pilot keeps his plane straight and level by watching the horizon. At other times, he must use this instrument.
Drift Indicator is usually installed level with the floor. It shows the pilot how the wind might be blowing him off course.
In multi-engine, conventional aircraft, there is a separate oil pressure and oil temperature indicator and a tachometer for each engine. In addition, there is generally a separate fuel gauge for each tank in the plane. Thus, if you were to look at the panel of a large four-engine airliner which has six fuel tanks, you would see seventeen more instruments than you see here. Furthermore, there is an identical set of dials for the co-pilot in addition to the pilot, and on some planes a third set of dials is used for the navigator-engineer. (see figure 5).
All airplanes, except a few experimental planes, have the same basic parts and they have progressed tremendously (see figures 6 and 7).
