Category FLIGHT and M ОТІOIM

There are several ways of steering a rocket or rocket-powered spacecraft. One way is to use swiveling fins, like an airplane’s control surfaces, in the atmos­phere. A rocket must be traveling fast before its fins begin to work, because they only work when air is flowing over them very quickly. Other rockets have swiveling vanes in the rocket exhaust. When the vanes swivel, they deflect some of the engine’s exhaust jet. The entire jet can be deflected by swiveling the engine itself or just the nozzle. Most modern rockets have swiveling engines, also called gimbaled engines. The Space Shuttle’s main engines are gimbaled.

A rocket or spacecraft also can be turned or steered by means of thrusters.

When the Space Shuttle’s solid rocket boosters fall away, thrusters push them away from the spacecraft. The Space Shuttle uses forty-four thrusters in its nose and tail for attitude control when flying in space.

Rockets are used for braking as well as steering. Braking rockets also are called retro-rockets. When an orbiting spacecraft is ready to land, it fires off rockets in the direction in which it is traveling. The thrust slows the space­craft, and gravity begins to pull it down.

The Soyuz spacecraft uses retro-rock­ets for landing. It fires retro-rockets just before it touches down on the ground to cushion its landing.

United Aircraft discontinued the Clippers, but the company funded Sikorsky’s effort to achieve his long-

"I have never been in the air in a machine that was as pleasant to fly as the helicopter. It is a dream to feel the machine lift you gently up in the air, float smoothly over one spot for indefinite periods, move up or down under good control, as well as move not only forward or backward but in any direction."

Igor Sikorsky

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held dream of building a helicopter. This time, that effort succeeded, with the help of new, lightweight materials and a staff of engineers.

On September 14, 1939, Sikorsky climbed into the first helicopter model, the VS-300. He always insisted on tak­ing the first flight of any completely new design. The helicopter worked— it rose vertically, hovered, and returned to land. The flying machine had a single rotor with three blades driven by a 75-horsepower engine. Sikorsky’s heli­copter was not the first to reach the air, but it was the first successful flight of a helicopter with a single rotor. Because most helicopters follow that design, Sikorsky is considered the leading pioneer of the helicopter industry.

The design needed improvement, however. Sikorsky tried another version with two small rotor blades in the rear. On May 13, 1940, that machine rose into the air, but was difficult to move for-

ward. The next model had just one smaller rotor blade in the rear. This ver­sion flew smoothly and on May 6, 1941, it set a record by staying aloft for more than an hour.

erodynamics is a branch of sci­ence that deals with the behavior of moving gases and how they affect objects passing through them. Designers use their knowledge of aero­dynamics to make aircraft and rockets the right shape.

The word aerodynamics comes from two Greek words. The first word, aer, means “air.” The second, dunamis, means “force.” Aerodynamics, therefore, means “force from air.”

Aerodynamic Force

When an object moves through air, it generates aerodynamic force. The size and direction of the force depend on the size, shape, and speed of the object.

The level of force also depends on the physical properties of the air, such as its pressure and temperature.

It does not matter whether it is the object that is moving or the air that is moving. Air flowing around a stationary object generates aerodynamic force, too.

A kite flies because of the force gen­erated by the wind blowing around it. The aerodynamic force that acts on a kite has two parts. These parts are called lift and drag. Lift takes the kite upward, and drag pulls it backward in the direc­tion that the wind is blowing. The kite does not fly away because these forces

О Two aerodynamic forces operate on a kite as it moves through the air. The movement creates lift, which raises the kite up, and drag, which pulls the kite back.

are balanced by the tension in the kite string. Kites often have a long tail. The tail has a purpose-it is there for aero­dynamic reasons. The drag it creates keeps the kite facing in the right direction.

Airplanes also generate lift and drag when they move through air. Lift oper­ates at right angles to a plane’s direction of flight. When the plane is flying straight and level, the lift generated by its wings acts straight upward. Drag operates in the opposite direction to a plane’s motion. When the plane is flying straight and level, therefore, drag pulls backward.

Two other forces act on every pow­ered airplane. First, thrust generated by its engines pushes the plane forward. Second, the plane’s weight pulls the plane downward. For an airplane flying straight and level at a steady speed, these forces are perfectly balanced.

A pilot begins a turn by operating the plane’s ailerons. The aileron panels work by tilting up and down. As the aileron in one of the wings tilts up, the aileron in the other wing tilts down. When an aileron is tilted up, it makes its wing lose
lift (the aerodynamic force that pulls it upward), and the wing tips down. In the other wing, the aileron that is tilted down creates more lift, and so the wing rises. The aircraft banks (rolls over to one side) like a bicycle leaning into a turn.

When an airplane flies straight and level, the lift produced by its wings acts straight upward. When an aircraft banks, the lift’s direction tilts with the plane. It acts upward and also to one side. It is this sideways part of the force that pulls the airplane around into a turn.

Using the ailerons alone, however, is not enough to make a smooth turn. The rudder has to be used, too.

Before takeoff a pilot completes a flight plan. This shows the flight as stages, or sectors. It lists details of aircraft type and registration, speed in knots (nautical miles per hour), height, wind speed, fuel consumption (in hours and minutes), number of passengers, and estimated
time for the flight. It indicates whether the pilot will be using visual flight rules (VFR) or instrument flight rules (IFR). The plan always allows for an aircraft to have some fuel in reserve, and it

includes details of alternate landing fields in case of emergency.

This flight plan goes to control cen­ters along the planned route. Flight plans are usually required for all flights using IFR. For VFR flights, they are optional (although recommended) unless an airplane is crossing national borders. Air traffic controllers enter flight plans into the FAA computer, which generates a flight progress strip. The strip is passed from center to center along the route and contains all the data needed to track the aircraft.

After an aircraft has been given clearance to take off, it is directed away from the airfield onto an outgoing route, safely clear of all other planes. A transponder on board picks up radar sig­nals from the ground and relays back flight details, which appear alongside a “blip” on the controller’s radar screen. During the flight, an airplane’s progress
is followed by a minimum of two traffic controllers in each sector of ARTCC air­space. Pilots and controllers exchange information during the flight, in case a change of plan is necessary to avoid bad weather, air turbulence, or possible congestion around an airport.

Most aircraft used by the U. S. military today are jet planes. There are super­fast spy planes-the Mach 3 SR-71A, for example-and enormous cargo planes designed to carry heavy loads, such as the C-5 Galaxy. Not all military aircraft need pilots. Drones, or unmanned air vehicles, are directed from the ground.

The main strike force of an air force is its bombers. The U. S. Air Force has the B-52, B-1B, and B-2 “stealth” bomber. Some planes designated as fighters, such as the F-117, are in fact ground attack aircraft that drop guided bombs and other weapons. Another effective air­craft is the A-10 Thunderbolt, which is heavily armed to support ground troops.

Electronic warfare planes can jam enemy communications and defense systems. Planes called Airborne Warning and Control Systems (AWACS) act as air­borne command centers.

The fastest planes now in service are multipurpose airplanes such as the F-15 Eagle, first flown in 1972 to combat the Soviet MiG-25. A recent version is the F-15E, which weighs 81,000 pounds (36,775 kilograms). The F-15 flies at 2.5 times the speed of sound and carries bombs, electronic jamming devices, guns, and guided missiles of various kinds.

Instead of weaving about the sky in dogfights like a World War II pilot, the modern pilot fights at long range. A mil­itary airplane is flown with the aid of computers. A visual display gives pilots a virtual reality image of the sky or battlefield and helps them detect and aim missiles at a target many miles away.

Most airplanes leave a radar trace, especially at very high speed. To evade radar, warplanes can fly at low levels to slip under the radar screen. Some high-tech aircraft, known as stealth planes, are designed to have a reduced radar profile, making them almost invis­ible to a hostile radar tracking system.

When their flight is announced, passen­gers make their way to one of the num­bered boarding gates. From the gate, most passengers walk directly to the air­plane doors along an enclosed bridge. At small airports, they may walk across the apron and climb steps to enter the cabin.

After all the passengers are seated on board, the pilot waits for air traffic control to give the signal for takeoff. When told to move into position, the pilot uses lanes called taxiways to move the plane from the airport terminal onto the runway.

As one aircraft takes off, another is usually preparing to land. Once a plane has landed, it moves off the runway onto the loading apron to unload its passengers and cargo. Passengers collect their bags from a baggage reclaim area, where the bags from each flight are delivered on conveyor belts.

Before leaving the airport, passengers who enter a country on an international flight must go through the additional step of being cleared through immigra­tion and customs. These government departments control the movement of people and goods into their countries.

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SEE ALSO:

• Air Traffic Control • Aircraft,

Commercial • Pilot

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Everything had been tried and tested for the Moon landing. It was time for the actual mission to take place. The astro­nauts selected for the crew of Apollo 11

Florida. Nearly one million people gath­ered to watch from the surrounding beaches. Within minutes, the rocket’s first stage was out of fuel and dropped off, as the other stages would do when their jobs were done.

During the flight from Earth, the spacecraft reached a speed of 24,300 miles per hour (39,100 kilometers per hour). After the initial acceleration to break free of Earth’s gravity, the speed

Braking rockets slowed the spacecraft and sent it into lunar orbit. As their spacecraft traveled in orbit around the Moon, Armstrong and Aldrin prepared for their descent to the surface. They entered the Eagle, the lunar module, and separated it from the command module Columbia, leaving Collins in orbit in Columbia to await their return.

allistics is the scientific study of projectiles. A projectile is an object flying without engine power after it has been fired or launched. Baseballs and golf balls are projectiles. Cannonballs, bullets, and artillery shells are also projectiles. Rockets and certain types of spacecraft can be projectiles, too.

Ballistic Science

The science of ballistics was developed hundreds of years ago to help gunners figure out where their cannonballs would land. When a cannonball is fired from a cannon tilted up at an angle, it rises as it flies away from the cannon. Its upward motion is slowed down by grav­ity until it stops rising and falls back to the ground. The flight path of a projec­tile is called its trajectory.

If gravity were the only force acting on a cannonball, its path would follow a curving shape called a parabola. In fact, it falls short, because the air pushes back against it. This air resistance, called drag, slows the cannonball.

The first person to make a scientific study of ballistics was Italian mathe­matician and engineer Niccolo Fontana Tartaglia (1499-1557). Tartaglia was the first person to notice that a cannonball followed a curved path. Until he pointed this out in the 1530s, people thought a cannonball flew in a straight line.

A pointed projectile causes less drag than a ball. For this reason bullets, artillery shells, and rockets have pointed noses. A pointed projectile, however, tends to tumble as it flies through the air. Bullets and artillery shells are made to spin to stop them from tumbling and to keep them flying point first. This action is called spin stabilization. Some rockets are also spin stabilized. Large rockets, like arrows, are stabilized by tail fins.

Many of the planes that fought in World War I (1914-1918) were biplanes. There were fighters and bombers built by man­ufacturers such as Nieuport-Delage in France, Fokker in Germany, and Sopwith in the United Kingdom. The first four – engine bomber was a biplane-Igor Sikorsky’s giant Ilya Mourometz-that could carry sixteen people at 80 miles per hour (129 kilometers per hour). The Vickers Vimy airplane that made the first nonstop flight across the Atlantic

Ocean (June 14-15, 1919) was a biplane. So was the U. S. Army Air Service Martin MB-1 plane that made a “round the rim” flight, traveling the perimeter of the United States in November 1919.

In the 1920s, biplanes were used by barnstormers for aerobatic displays. Biplanes also carried mail and passen­gers when commercial airlines started running regular services. They were widely used by the military, both as land-based planes and as naval aircraft on the first aircraft carriers.

Biplanes and monoplanes competed on equal terms for the first thirty years of powered flight history. No airplane of the period could fly much faster than around 200 miles per hour (320 kilome­ters per hour). The fastest biplane fight­ers of the early 1930s, such as the British Hawker Fury, had a top speed of only 210 miles per hour (338 kilometers per hour). By the mid-1930s, however, a new era was dawning. Streamlined mono­planes were flying at over 300 miles per hour (480 kilometers per hour). Biplanes could not be stream­lined, and even with bigger engines they were unable to com­pete in terms of speed.

О An early airliner, the Handley Page 42 (HP-42) of the 1930s was a biplane with a luxurious lounge.

THE SESQUIPLANE

A variation of the biplane is the sesquiplane (literally, "one-and-a – half wings"). It has one wing (the lower) much smaller than the normal-sized upper wing. One of the largest of the sesquiplanes was the Antonov 2, originally a Soviet design of 1947, but later built in Poland and China. This sesquiplane carried up to twelve passengers, and it could land on snow (with skis) or on water (with floats) as well as operate from small wilderness airfields.

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