Category FLIGHT and M ОТІOIM

Modern propeller planes have their pro­pellers at the front, pulling the plane through the air. These are called tractor
propellers. In the early days of aviation, it was just as common for planes to have their propellers at the back, pushing the aircraft. The first successful powered air­plane, the Wright brothers’ Flyer, had two pusher propellers behind the wings.

Pusher propellers were popular because they did not get in the way of the air flowing over the wings. Without an engine or propeller in the way, the pilot had a great view ahead. It also was eas­ier to fit guns in the nose of a fighter

PROPROTORS

The strangest propellers are called proprotors. They have this name because they work like helicopter rotors part of the time and like propellers the rest of the time. Compared to regular propellers, proprotors are enormous. The propellers of a C-130 Hercules cargo plane, for example, are 13.5 feet (4 meters) across. The V-22 Osprey’s proprotors are nearly three times as big: 38 feet (12 meters) across. When the Osprey is on the ground, its engines are tipped up, pointing straight up in the air. Its two propellers look like helicopter rotors, and they work in the same way-when they spin, they lift the Osprey straight up into the air. Then the engines swivel forward, and the rotors work like propellers.

C The Osprey’s engines and pro­pellers tilt up (top left) for vertical takeoff. The engines tilt down and the propellers face forward (bottom left) for level flight.

plane that had its engine and propeller mounted in back.

Pusher propellers had drawbacks, however. They made it harder for pilots to escape from planes in the air without hitting a propeller. Also, the heavy weight of an engine at the back of a plane could be dangerous in a crash. It could move forward and crush the cock­pit. The problem of fitting guns to fight­er planes with propellers at the front was solved during World War I (1914-1918) by a device called an interrupter gear. It stopped a machine gun from firing when a propeller blade was in front of the gun barrel. The gun was synchronized to fire through the spaces between the blades. By the end of the war, nearly all fighter planes had their propellers at the front.

The idea of “artificial moons” orbiting Earth was put forward by a few scien­tists and science-fiction writers in the early 1900s. In 1945, British science fic­tion writer Arthur C. Clarke suggested in a magazine article that three satellites orbiting Earth could act as relay trans­mitters for worldwide communications. The visionary Clarke now has a satellite orbit named after him.

By the 1950s, there were rockets capable of launching satellites, although these were being developed primarily as military missiles. The American Rocket Society and the National Science Foundation both suggested using satel­lites for the scientific study of space. These groups proposed that, to mark International Geophysical Year (1957­1958), the United States should launch a science satellite.

The Soviet Union announced that it also would launch a satellite, but few people in the West took this claim seriously. So it was a great surprise when, on October 4, 1957, the Russians launched the world’s first satellite, Sputnik 1. Orbiting Earth every 96 minutes, Sputnik 1 caused a sensation. An even greater surprise followed on November 3, 1957, with the launch of Sputnik 2, which was bigger still and carried a dog named Laika. The United

О The first satellite launched by the United States was Explorer 1, seen here being installed on its launch vehicle in January 1958.

States launched its first satellite, Explorer 1, early in 1958. The “space race” had begun in earnest.

The Soviet Union launched hundreds of Cosmos satellites and also Molniya communications satellites, but seldom released much information about them. U. S. space launches were more public, and satellites were usually designated by their function: scientific, weather, com­munications, navigation, or Earth obser­vation. Only satellites for military use were kept secret.

Since the 1960s, France, China, Japan, Britain, India, and Israel have launched satellites with their own launch vehicles. Other nations have hired launches to put satellites into space. Once front-page news, satellites are now routine, with many commercial and multinational launches each year.

The first parachutists usually fell “like a sack being hurled out of a window,” in the words of Leo Valentin, a parachute jumper. (Valentin wore suits with batlike wings in an attempt to imitate bird flight. Wing suits often broke in midair, and Valentin was killed in an accident in 1956.) Parachutists soon found, howev­er, that by adopting a box position as they fell-stomach-down, with arms and legs bent slightly backward-they could soar like a bird rather than drop like a sack until their parachute opened.

Modern skydivers are taught to fall in the box position, although experi­enced divers also adopt other positions. The spread-eagle body acts like a wing, so a skydiver can fly around, and teams can formate (group together). Groups of as many as 282 divers have achieved formation in free fall.

An amazing demonstration of free fall maneuvering took place in 1987, in the sky above Arizona, when skydiver Gregory Robertson saved the life of fel­low parachutist Debbie Williams. She was knocked unconscious after colliding with another jumper, and she fell for

6,0 feet (1,830 meters). Robertson dived alongside her and opened her parachute at 3,500 feet (1,070 meters) above the ground. Only then did he open his own parachute.