Category FLIGHT and M ОТІOIM

avigation is the steering or directing of a course. Migrating birds, animals, and even insects seem able to navigate across the world with ease. People have developed ways of using nature, science, and technology to do the same thing—to figure out their position and find their way across land, sea, sky, and even in space.

Following Instinct and Landmarks

Monarch butterflies fly more than 1,500 miles (2,400 kilometers) on their annual migration across North America. One seabird, the Arctic tern, makes the longest migration journeys of any living creature. Every year, it flies up to 22,000 miles (35,400 kilometers) between the Arctic and Antarctic. Some animals are born with an instinct for migrating in a particular direction. Birds may navigate by recognizing familiar landmarks such as rivers and mountains. They also may use the position of the Sun and stars. Yet others seem to be able to sense the Earth’s magnetism, as if they have a nat­ural compass that directs them.

The first pilots relied on navigation methods similar to those used by birds. Planes flew low so that pilots could nav­igate visually by following landmarks such as roads, rivers, and railroads. For longer flights and for flights over oceans, a method called dead reckoning was used. A pilot used a map to figure out which direction to fly and then

measured the distance to the destination. Knowing how fast a plane flew, a pilot could figure out the journey time. If the plane was flown in the right direction (using a compass) at the correct average speed for the calculated length of time, it should arrive at its destination. In the real world however, an aircraft could be blown off course by wind, so pilots had to allow for this when plotting their course. Today, pilots of small aircraft still can navigate using dead reckoning and by looking out for landmarks.

THE STARDUST MYSTERY,

In 1947, an airliner called Stardust was flying from Buenos Aires, Argentina, across the Andes moun­tain range to Santiago, Chile. Just before it was due to land, it van­ished. Searchers found nothing. In 2000, the wreckage was found, and an explanation to the old mystery was pieced together. Because of bad weather, the airliner had flown so high that it reached the high-speed air current of the jet stream and was flying against it. The crew’s naviga­tion calculations indicated that they had crossed the mountains, but the jet stream had slowed them down so much that they were still over the mountains. Thick clouds prevented them from seeing the ground. As they descended to land, the plane crashed into a mountainside and fell onto a glacier, a slow-moving river of ice. The wreck was soon covered with snow and then sank into the glacier. It took fifty-three years for the wreckage to travel downhill inside the glacier and appear at the bottom.

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The basic principle of radar is very sim­ple. It sends out radio waves and then picks up any waves that are reflected back. Most radar systems are more com­plex, however, and they can tell much more about an object than just the fact that it is there. They can show its loca­tion, bearing (direction), range (dis­tance), velocity, and altitude.

A radar system has four main parts. A transmitter produces radar signals.

An antenna sends signals in the form of electromagnetic waves and picks up any reflections that return. A receiver ampli­fies the weak radar reflections and ana­lyzes them. A display shows the received information on a screen.

Radar uses short radio waves called microwaves. The simplest type of radar is pulse radar. It sends out short bursts, or pulses, of radio waves and listens for any reflections that bounce back from a target, such as an aircraft. The direction from which the reflection comes shows the aircraft’s bearing. The time the pulse takes to bounce back gives its range.

Antennae

A dish-shaped antenna can be steered to scan a particular area of the sky. It may swing back and forth, or it may rotate so that it scans the whole sky in all direc­tions. The most modern radar systems use a flat antenna that stays fixed in one place. A flat antenna is constructed from

О A simple radar has an antenna that sends out signals in the form of pulses of radio waves. It picks up any echo pulses that come back and uses them to measure an object’s distance and movement.

DOPPLER RADAR

When a police car races past sound­ing its siren, the sound rises in pitch as the car approaches and falls as it goes away. This is called the Doppler effect, and it happens with all kinds of waves, including microwaves. Radar equipment can be designed to make use of this effect. It can show if something is flying toward the radar antenna or away from it, and how fast. A type of radar called Doppler radar was developed in the 1960s. It uses continuous radar waves instead of pulses. Pulse – Doppler radar systems combine basic pulse radar systems with Doppler radar.

At first, Doppler radar was used mainly for weather forecasting. By the 1980s, Doppler weather radars were able to measure the speed and direction of raindrops inside clouds and storms. Portable Doppler radars carried on the back of trucks are used to study the most extreme weather systems, especially thun­derstorms and tornadoes.

thousands of small, electronic transmit – and-receive modules, and the radar beam is steered electronically. These radars are called electronically scanned arrays, or phased arrays. They can scan far faster than a rotating dish antenna, they can track many more targets, and – with fewer moving parts-they are more reliable.

Advanced combat aircraft, such as the F-22, are equipped with electronically scanned array radar. They can locate and track multiple high-speed targets and pass on the target information to the air­craft’s weapons systems.

Although accidents do happen, skydiv­ing and parachute sports have a good safety record. Accidents are most com­mon when people jump in poor weather conditions, such as unpredictable winds. Jumping from buildings, cliffs, or other high structures (known as BASE jump­ing) is especially dangerous. Because the modern parachute can be steered, there is little chance of the parachutist landing accidentally in a lake or a tree, as was often the fate of parachutists in the past.

Drop zones in the United States and Canada are required to have an experi­enced person who acts as a safety offi­cer. In most countries, skydivers are required to carry a reserve parachute that has been packed and inspected by a certified parachute rigger. In the United States, certification is provided by the Federal Aviation Administration (FAA).

Many countries have national para­chuting associations, affiliated to the Federation Aeronautique Internationale (FAI). In the United States, skydiving permits and ratings are issued by the United States Parachute Association.

EXTREME SKYDIVING

Specialized forms of skydiving and parachuting include:

• Accuracy landing: Aiming to land on or very near a drop zone target.

• Blade running: Like slalom skiing with a parachute.

• Formation skydiving: Also called relative work (RW).

• Paraskiing: Landing on a snowy mountain on skis.

• Skysurfing: Landing with a surfboard strapped to the feet.

• Stuff jumping: Jumping with

an object, such as a bicycle, which is ridden through the air before the sky – diver lets go and opens the parachute.