Category Everyday Science

Although the helicopter in its present form is scarcely 50 years old, the principle of the rotary wing has been known for centuries. The Chinese used it some 2500 years ago for their flying top — a stick with propeller-like blades on top which was spun into the air. And Leonardo da Vinci actually sketched a helicopter in 1483. The English flight pioneer Sir George Cayley was among several people to design a model helicopter in the late 1700s, but the first man-carrying helicopter, which rose a few feet in the air, was not built until 1907 — by a Frenchman, Paul Cornu, at Lisieux. Problems with stability and other design aspects led to helicopters being abandoned for nearly 30 years in favour of fixed-wing aircraft. Many of the design problems were, however, solved by the Spanish inventor of the autogiro, Don Juan de la Cierva, in 1919. This aircraft had a large rotor that was not driven by the engine but turned freely in the airflow. It could not take off vertically — it had to taxi to get the rotor turning enough to lift it.

Not until 1936 did the German Professor Heinrich Focke, of the Focke-Wulf Company, design a practical helicopter with twin rotors. Three years later a Russian-born engineer, Igor Sikorsky, produced a successful single-rotor helicopter, the VS-300, in the USA. This was the true ancestor of the modern rotorcraft — the most versatile of aircraft.

The development of jet engines in the 1950s led to the adoption of turboshaft engines that have considerably increased the range and speeds possible. Today the helicopter is invaluable not only as a military transport, hedge-hopping patrol plane and sky crane — for lifting steeples onto churches, for example — but also for rescuing people from remote mountainsides, sinking ships and burning buildings.

 

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Submarines often travel in the ocean depths for weeks on end. They do not need to surface to check their position by the Sun, Moon or stars, because the latest navigation systems allow them to know where they are to within less than 320ft (100m) of their actual position while still submerged.

 These systems are known as inertial navigation systems and are computer-controlled. There are usually at least two on a submarine, operating independently. They are a modern version of ‘dead reckoning’ — calculating where you are by measuring exactly how far you have come from your starting point, and in what direction.

The inertial navigation system is held absolutely horizontal and pointing in a fixed direction by gyroscopes, whatever the attitude of the submarine.

 At the start of the voyage, the instruments are fed with the submarine’s exact position. An accelerometer then measures movement in every direction, and the computer works out the overall distance and direction travelled, thus establishing the present position.

Sonar is used to determine the water depth below the vessel to prevent it running aground. Inertial systems are on the whole accurate, but the small errors they do make gradually accumulate. They have to be realigned regularly. This is done by picking up radio signals from satellites in space, which form part of the American NAV-STAR Global Positioning System (GPS). The submarine has to partly surface.

 The satellites transmit a radio message which contains precise details about their orbit, and a time signal controlled by an atomic clock. In effect, the signal says ‘It is now time X’. The submarine uses its own clock to calculate how long it takes the signal to arrive. As radio waves travel at 186,000 miles (300,000km) per second, the navigators can calculate the sub-marine’s distance from the satellite by the time the signal takes. By calculating the distance from three GPS satellites, the ship’s position can be pinpointed on a chart.

During the 1990s, the last 04 18 satellites in the GPS system will be placed in orbit at a height of 12,500 miles ,20.000km), orbiting the Earth at 12-hourly intervals. They will ensure that at any time at least four satellites will be available for navigators to calculate their position to within 550yds (500m;

The GPS system has virtually replaced older forms of submarine navigation such as the OMEGA system, but submarines still carry it as a back-up. This system detects radio signals broadcast from eight stations dotted around the Earth’s surface — in Japan. Hawaii, Australia, Argentina, North Dakota. Norway. Liberia and Reunion Island. These stations broadcast at very long wavelengths, so their signals carry all around the world. The signals are synchronised, and by measuring the time differences in their reception, a sub-marine’s position can be estimated to within about miles (3.2km)

 Inertial navigation also mounted in long-range intercontinental launched from submarines .

 

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Medieval castles had all sorts of traps pitfalls to keep out intruders. Homes of today can have an equal number of defences, without having to resort boiling pitch. Modern defence devices include floodlights or alarms that are triggered when an intruder upsets a circuit monitored by hidden magnets or micro. chips, or by invisible beams.

The outer defences

The modern burglar might first have to face  a strategically placed invisible infrared detector that is affected by temperature changes caused by body heat. When anyone approaches the house, a sensor in When the detector switches on floodlights. If the caller is legitimate, the lights show the Way but anyone planning burglary will feel very exposed and less likely to continue.

The sensor is pyroelectric — that is, made from a ceramic material such as tourmaline, which, when heated, generates a voltage across it. The system is designed so that the sensor will respond to a temperature change caused by human body heat, but is less likely to be set off by changes in the weather.

 A burglar who dodges a floodlight – barrier may then face a door connected to a noisy alarm. A magnetic switch IL inserted between the door and its frame. When the door is shut, two contacts keep switch circuit closed. This switch is monitored electronically by an alarm circuit. If the door is opened arid switch circuit is broken, the alarm circuit triggers the alarm.

But a resolute burglar, out of sight of passers-by, might attack the door with a chisel or drill. This type of attack can be foiled by a vibration detector fitted to the door. This is a device in which a ball is disturbed by vibrations. The ball rests on sharp metal points wired to a microchip that is programmed to accept certain vibrations — such as those caused by wind or passing traffic — as normal. If the ball bouncing on the points sets up vibrations not in the program, it sets off the alarm.

The inner defences

If the burglar succeeds in getting through a door or window, he may face a battery of inner defences. These include pressure Dads concealed under the carpet and inked to an alarm circuit. They have two metal plates or foil sheets separated by a layer of spongy plastic. The two plates are pressed together if anyone treads on them, and this sets off the alarm.

Anyone who prowls around inside the house may be caught by a ‘magic eye’. This is a photoelectric cell with an invisible infrared beam shining onto it. If the beam is interrupted, the photocell triggers an alarm.

Other types of indoor detector use either ultrasonic waves (too high pitched for humans to hear) or microwaves (high-frequency radio waves) transmitted by

devices called transducers. They transmit the waves at a certain frequency (a given number per second), and the waves are reflected back to the unit from objects in the room. If anyone moves through the room, the reflected waves get bunched up or pulled apart, so their frequency is altered. The sensor detects the frequency change and feeds signals to a microchip which assesses the speed and bulk of the intruder. Anything assessed as typically man-sized makes it set off the alarm.

A commoner type of indoor detector uses an infrared system similar to the outdoor floodlight type. in the detector. a many-faced mirror or special lens creates a number of sensitive zones. If anything moving in and out of these zones is at a different temperature to the room surroundings, it generates a voltage. The detector electronically monitors the voltage, and is designed to set off the alarm if the temperature increase is likely to be caused by human body heat.

 

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When lightning struck the roof of York Minster, one of Britain’s finest medieval cathedrals, in 1984, it started a fire that was if trapped between the ceiling and the wooden roof. Firefighters could not get into the area, and the enormous heat that built up destroyed most of the roof.

If lightning should strike York Minster twice, space-age science has ensured that the same type of damage will not happen again. The new roof is fitted with trap doors to let the heat out and the firefighters in, and the doors have latches operated by springs made from memory metals, which will open automatically if they get hot.

Memory metals have two different shapes they can ‘remember’, and will switch from one to the other under certain conditions. The York Minster trap-door springs are made to remember a certain temperature, at which they will expand and withdraw the bolt, releasing the door.

One of the first uses of memory metals has been for hydraulic pipe couplings in aircraft, which came into use in 1971. The couplings are made too small to fit at a certain temperature, and are then cooled to well below room temperature and stretched to fit. When they warm up to their normal operating temperature, they shrink to the first shape, forming a tight joint. The same idea is used in surgery, with metal couplings to bind together broken bones. Body heat keeps them constantly tight.

Metals that change their shape under heat now have all kinds of uses, such as operating switches and valves in automatic coffee machines, and opening greenhouse windows when it is hot and closing them when it is cold. Most metals are made up of crystals (arrangements of atoms). When two or more metals are combined into an alloy, the alloy can form different crystal structures under different conditions.

Some alloys, if they are cooled rapidly, will undergo an abrupt change to a different alignment of crystals at a certain temperature. This transition temperature varies with the make-up of the alloy. The changed structure it brings about is called martensite, after the German metallurgist Adolph Martens who first identified it.

If such an alloy is shaped by heat treatment so that it becomes martensite at, for example, 122°F (50°C), it will change its shape at that martensitic temperature, but revert again at a different temperature.

Shaped for shaping

A Japanese company has found an unusual use for memory metals — as a super-elastic wire frame in brassieres. The alloys used will stretch up to ten times more than ordinary metals. When stretched in use, the bra wire gradually returns to its original bust-supporting shape.

Another use for super-elastic wire is in straightening teeth. Conventional stain-less-steel wires have to be regularly tightened, often by turning a tiny key. Super-elastic alloy wires exert a continuous gentle pressure ideal for coaxing teeth in the right direction.

 

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When someone blows into a breathalyzer bag, any alcohol in their breath is turned into acetic acid (vinegar). This chemical reaction changes the colour of the crystals in the blowing tube. The more crystals that change colour, the more alcohol they have in the body.

The first breathalyzer was developed by an American doctor, Rolla N. Harger (he called it a ‘Drunkometer’), and it was introduced by the Indianapolis police in 1939. Similar breathalyzers began to be widely used by the police in many Countries in the 1960s, as a yardstick for judging a driver’s ability to drive. A high Intake of alcohol dulls the nervous system and slows up coordination.

To begin with, the commonest type of breathalyzer was a plastic bag, similar to a balloon, with the crystals in the blowing tube. and the driver was asked to inflate the

bag. If the crystals changed colour as far as a level marked on the tube, the driver was possibly ‘over the limit’, and needed further tests. The crystals used were an orange-yellow mixture of sulphuric acid and potassium dichromate. They turned the alcohol into acetic acid (vinegar), and in doing so they were changed into colourless potassium sulphate and blue-green chromium sulphate.

The breathalyzers used by the police today, however, are usually electronic, and much more accurate than the inflatable-bag type. They use the alcohol blown in through the tube as fuel to produce electric current. The more alcohol the breath contains, the stronger the current. If it lights up a green light, the driver is below the legal limit and has passed the test. An amber light means the alcohol level is near the limit, a red light above the limit, and in both cases  the driver has failed the breath test and needs further testing.

This type of breathalyzer is about the size of a TV remote control, and contains a fuel cell that works like a battery. Breath from the tube is drawn into the cell through a valve, and meets a platinum anode (a positive plate). which is against a spongy disc impregnated with sulphuric acid. The platinum causes any alcohol in the breath to oxidise into acetic acid — that is, its molecules lose some of their electrons. This sets up an electric current through the disc, and it flows to a cathode (a negative plate) on the other side.

 

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