Oleo Hydraulics And Pneumatics

Parker Watts

How Do Airplanes Fly?

How do airplanes fly?

Rather than asking students who invented the airplane, it is important that Filipino educators begin explaining to their students what makes an airplane fly? We all know that Orville and Wilbur Wright developed a flying machine that first lifted from the grounds of Kitty Hawk, North Carolina and stayed on the air for 12 seconds on December 17, 1903. But it is time for both teachers and students to know how and why that machine flew in the first place.

Instead of using aerodynamics terms to explain the theory of flight, it will be useful to explain it in the simplest way possible. An airplane is able to fly because it applies a force created by a propeller, which is strong enough to make it move forward and uses wings or airfoil to deflect air pressures in such a way that the wind pushes back from underneath the wings to lift the whole airplane.

The propeller creates an aerodynamic force called thrust, which pulls the air past the blades. The movement of the wind around the wing creates a movement called "lift". The plane can fly higher or lower and faster or slower by adjusting the position of the wing to direct air pressures.

The angle of the wing determines how much air pressure it can get from underneath, and how high the airplane can fly. The greater the pressure under the wing, the greater the lift.

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How does the telephone work?
Alexander Graham Bell was credited for having invented the telephone on March 10, 1876. It was a magnificent invention, that helped us in so many ways. It is only proper that we give proper recognition to this device by trying to understand how it functions. But we would not go to the extent of explaining acoustics or the science of sound to make our point.

First let us define telephone as a device capable of replicating voice and transmitting it from one point to another in the fastest means possible. Imagine, we can now hear the replicated voice of our relatives on the other side of the planet in a matter of seconds through telephone wires. Yes, the voice we hear on the phone is a product of replication by devices.

Let us try to define some terms in simple language. Human voice is a sound, which is produced by the movement or vibration of our lips, tounge and mouth. Sound wave travels through the air, water or solid objects. It is important to realize that sound can be converted into electrical energy, which we will elaborate later. Telephone is a device that can transform sound into electrical energy and transmit it through copper wires to another point.

Remember that as grade school children, we had for a school project a basic telephone, composed of two cans connected by a string. When we pull the string to form a straight line and make it tight, we can actually communicate through the cans. This is possible because when one student talks into the can, the bottom of the can vibrates back and forth with sound waves that travel through the straight line of string, which the other student who puts his ear near the can hears. The telephone uses the same principle, but instead of string, it uses wire.

Instead of empty cans, the telephone uses a mouthpiece, composed of a transmitter, which is made up of a thin metal diaphragm. Inside the diaphragm is a small chamber filled with carbon granules. When we speak, sound waves cause the granules to compress, which allows a low-voltage electric current to pass. This current comes from batteries at the telephone company. The electric current then travels. The louder we speak, the more the granules are compressed, and the heavier voltage of electric current is released. When the carbon grains are compressed, electric currents pass through them more easily. If we don't make any sound, no sound waves will cause the grains to compress, which would not allow electric currents to pass.

By copying the pattern and loudness of our voice, the release of the electric current through the carbon grains serves as the same pattern when the current hits the diaphragm on the other line. In other words, the vibrations caused by our voice are converted into electrical impulses that travel through wires until they reach the receiver. The receiver (ear-piece), which also has an iron diaphragm, converts the electrical impulses back into sound. Once the electric current hits the electromagnetic field in the receiver, the diaphragm vibrates and produces sound waves almost exactly like the pattern of sound waves at the point of origin.

Simply put, the telephone set has transmitter, receiver, a connection and a switch, which allows us to dial a number and exchange replicated voices.

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Keeping Food Cold in Refrigerators
How do freezers produce ice? How do food items get cold inside refrigerators? And how do air-conditioning units release cool air? All these appliances use the same process to function - refrigeration. But to know what refrigeration is, we need to understand the science of thermodynamics in the simplest way possible.

Thermodynamics has something to do with heat? Yes, it is about heat, which is ironically the opposite of coldness, which is our topic. To make it simple, let us define the word "cold" as an adjective characterized by the low degree of heat. Also, let us define refrigeration as the process of removing heat from an object to make it cold. With these twin definitions, we assume that freezers, refrigerators and air-conditioning units are machines that take away heat from an object or a surface. In other words, these machines suck heat out of an enclosed space.

Taking away heat from an object is possible through the system of evaporation. Have you ever observed that it becomes cooler after it had rained. This is because the rain, the perfect result of evaporation, takes away the heat of the soil. Have you ever felt fresher after taking a bath. This is because the water on your body takes away some of the heat from your skin.

Freezers, refrigerators and air-con units follow the same principle of evaporation, but instead of using water, they use refrigerants that vaporize at much colder temperatures. These chemicals - like ammonia, freon, and Greenfreeze - are injected into a tube or evaporator coil inside the machine where they turn from liquid into gas into liquid through evaporation via compression. As they evaporize through compression, these refrigerants absorb and take away heat from the inside surface of the refrigerator and transfer the heat to the outside surface of the refrigerator as they become liquid again while traveling through a coil mostly located at the back or bottom of the machine. The inside surface of the refrigerator thus becomes cool and the outside, hot.

A compressor is responsible for the process of evaporation. Essentially, the compressor machine, powered by an electric motor, squeezes the refrigerants into the coil that extends to the outside part of the machine. It gathers the refrigerant vapor articles inside the coil and compresses them into liquid form again, which in effect releases heat outside the body of the freezer, refrigerator or air-con unit. When the compressed gas passes through the coil on the back or bottom of the machine, the hot gas can lose its heat to the atmosphere outside the machine. Because the refrigerants travel through the tube and the coil endlessly, the whole refrigeration process is repeated over and over again, without allowing the refrigerants to leak.

Here, the common explanation is that when compressing refrigerants to a higher pressure, the temperature of the refrigerants will rise and release heat. By the time the chemicals cool off, significant amount of heat has been released from it. As the refrigerants cool down and condense into liquid form again, they flow through a device called an expansion valve, which has a small opening. The liquid refrigerants become very cold as they travel fast and pick up heat from the surface of the machine. Between the expansion valve and the compressor, there is a low-pressure area because the compressor is pulling the refrigerant gas out of that side. When the liquid refrigerants hit the low pressure area, they boil and changes into a gas. This is called vaporizing. The refrigerants then pass through the coil touching the inside surface of the machine where they cool and absorb heat at the same time, and in the process, pull the heat out of the compartment.

Cooling machines therefore are composed of a compressor, which compresses the refrigerant gas into liquid; expansion valve, where the liquid refrigerants move from a high-pressure zone to a low-pressure zone, so they can expand and evaporate; and the coils, which extend to the outside part of the machine. While evaporating, the refrigerants absorb heat from the inside surface and transfer the heat outside. The cycle repeats endlesslly until the inside surface of the refrigerator or the freezer becomes very cool. Freezers, which are more enclosed than refrigerators, allow their surface to cool to the extent of turning water into ice. In case of the air-conditioning unit, a blower pushes the cool air from the machine into the room.

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How is Electricity Produced?
In the Philippines, teachers focus more on the definition of electricity and the people who discovered it than on how it is produced in the first place. We know that Benjamin Fraklin, the greatest American statesman and inventor, was the one who discovered the nature of electricity through his experiments with lightning in 1740s. Thomas Edison applied electricity to light a bulb in 1879 while Nikola Tesla developed a system of generating and transmitting alternating current (AC) electricity in the 19th Century. James Watt, on the other hand, invented the steam engine, which remains the basic structure of most engines and power generators to this day.

But the real challenge for Filipino educators is to explain to their students how electricity is generated. Our crude interpretation is that electricity is a reaction from the process of rubbing two objects. Others call electricity as a form of energy or a force, but this remains debatable. The fact is we need to apply energy or force to release electricity. Lightning is electricity, which is produced by force - the violent movement of winds in the sky. When we rub two stones for a certain period, a spark is produced, and the two objects become hot. Electricity is released.

A more precise definition could be electricity is the surge of electrons. Every object is composed of atoms. In every atom there is the nucleus or the center which is surrounded by negatively charged particles called electrons. Inside the nucleus are positively charged particles called protons and uncharged particles called neutrons. Now, a balance between the number of protons and electrons exists in most atoms, but when this balance is disrupted by a force such as the rubbing of two objects, some electrons are released - a process called electric current.

To release electricity, we need to apply force first to drive electrons from an object. The most common force applied to achieve this is magnetism which is also known as electromotive force. Here, the spinning of a copper coil within a magnetic field will produce a force that will push the electrons through a circuit. This push is called voltage.

Most power generators are built this way, with a copper coil spinning within a magnetic field to generate electricity. A coil serves as a conductor. By rotating a magnetic field around the conductor or the conductor within the magnet, electricity is produced and each time the conductor travels through the magnetic field, a voltage is created. The mechanical energy of the spinning coil transforms to electrical energy in the wire. In other words, electricity generation is based on the relationship between magnetism and electricity. When a wire moves across a magnetic field, an electric current occurs in the wire. Put it simply, a power generator needs magnets, coiled copper wire and spinning motion to generate electric current.

But to enable the magnetic field to spin, a force is needed. Most power generators have turbines that are connected to the magnet, so that the spinning will be caused first by the blades of the turbine. What will cause the spinning motion depends on the type of energy source: coal-fired, diesel oil, wind-powered, hydroelectric, gas turbine, nuclear (uranium), geothermal, solar or others.

We can use actual motion or steam to spin the turbine. Wind-mills use the spinning motion to push the turbine blades and turn the copper coil in the generator and eventually generate electric current. The same principle applies to hydroelectric turbine or wheel, where water flows provide the force to move the turbine blades.

In case of fuel-powered plants, a boiler is set up to burn fuel and produce heat, which will transform water stored in long vertical tubes into steam. As the water begins to boil, the highly pressurized steam rises through the pipes and blows against the turbine blades, causing the spinning motion. Fuel includes natural gas, coal and diesel. The same principle of spinning the turbine blades through steam pressures applies to plants powered by nuclear, geothermal, solar and biomass energy. Steam turbines spin at about 3,600 revolutions per minute.

With the spinning motion of the turbine and the copper coil, electricity is generated and runs through the wires or electric circuit which is connected to our homes via transformers. When electricity flows through a light bulb's filament, the electricity appears as light. Power plants' transformers increase the voltage of the electricity to make it travel through the distribution lines more efficiently until the electricity reaches to substations where separate transformers reduce the voltage again for consumer use. Electricity travels at lightning speed.

Households regulate the use of electricity by switches, which open or close the electricity circuit. Basically, electricity consumption is measured by a unit of power called watts. A kilowatt is equal to 1,000 watts. The unit kilowatthour, on the other hand, represents the use of electricity for a certain number of hours.

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