Gliders, hang-gliders, and ultralights

MODERN GLIDERS ARE AMONG the most graceful and aerodynamically efficient of all aircraft. Unpowered but with a large wingspan (up to about 82 ft, or 25 m), gliders use currents of hot, rising air (thermals) to stay aloft, and a rudder, elevators, and ailerons for control. Modern gliders have achieved flights of more than 900 miles (1,450 km) and altitudes above 49,000 ft (15,000 m). Hang-gliders consist of a simple frame across which rigid or flexible material is stretched to form the wings. The pilot is suspended below the wings in a harness or body bag and, gripping a triangular
A-frame, steers by shifting weight from side to side. Like gliders, hang-gliders rely on thermals for lift. Ultralights are basically powered hang-gliders. A small engine and an open fiberglass car (trike),
which can hold a crew of two, are suspended beneath a stronger version of a hang-glider frame; the frame may have rigid or flexible wings. Ultralight pilots, like hang-glider pilots, steer by shifting their weight against an A-frame. Ultralights can reach speeds of up to 100 mph (160 kph).

Light aircraft

LIGHT AIRCRAFT, SUCH AS THE ARV SUPER 2 shown here, are small, lightweight, and of simple construction. More than a million have been built since World War I, mainly for recreational use by private owners. Virtually all light aircraft have piston engines, most of which are air-cooled, although some are liquid-cooled. Open cockpits, almost universal in the 1920s, have today been replaced by enclosed cabins. The cabins of high-wing aircraft have one or two doors, whereas those of low-wing aircraft usually have a sliding or hinged canopy. Most modern light aircraft are made of aluminum alloy, although some are made of wood or of fiberreinforced materials. Light aircraft today also usually have navigational instruments, an electrical system, cabin heating, wheel brakes, and a two-way radio.

Helicopters

HELICOPTERS USE ROTATING BLADES for lift, propulsion, and steering. The first machine to achieve sustained, controlled flight using rotating blades was the autogiro built in the 1920s by the Spaniard Juan de la Cierva. His machine had unpowered blades above the fuselage that relied on the flow of air to rotate them and provide lift as the autogiro was driven forward by a conventional propeller. Then, in 1939, the Russian-born American Igor Sikorsky produced his VS-300, the forerunner of modern helicopters. Its engine-driven blades provided lift, propulsion, and steering. It could take off vertically, hover, and fly in any direction, and had a tail rotor to prevent the helicopter
body from spinning. The introduction of gas turbine jet engines to helicopters in 1955 produced quieter, safer, and more powerful machines. Because of their versatility in flight, helicopters are today used for many purposes, including crop spraying, traffic surveillance, and transporting crews to deep-sea oil rigs, as well as acting as gunships, air ambulances, and air taxis.

Modern military aircraft

MODERN MILITARY AIRCRAFT ARE AMONG THE MOST SOPHISTICATED and expensive
products of the 21st century. Fighters need computer-operated controls for maneuverability, powerful engines, and effective air-to-air weapons. Most modern fighters also have guided missiles, radar, and passive, infrared sensors. These developments enable today’s fighters to engage in combat with adversaries that are outside visual range. Bombers carry a large weapon load and enough fuel for long-range flights. A few military aircraft, such as the Tornado and the F-14 Tomcat, have variable-sweep (“swing”) wings. During takeoff and landing their wings are fully extended, but for high-speed
flight and low-level attacks the wings are pivoted fully back. A recent development is the “stealth” bomber, which is designed to absorb or deflect enemy radar in order to remain undetected. Earlier
bombers, such as the Tornado, use terrain-following radars to fly so close to the ground that they avoid enemy radar detection.

Jet engines

JET ENGINES ARE USED BY MOST MILITARY and heavy aircraft, and by many helicopters. The simplest type of jet engine, or gas turbine, is the turbojet. It works by continuously burning a mixture of fuel and air in a combustion chamber to produce a jet of hot exhaust gas that is expelled through a nozzle to produce thrust. The hot gas also spins turbine blades, which, in turn, spin the blades of an air compressor; the compressor forces air into the combustion chamber. Many of the fastest aircraft use turbojets, with additional booster units called afterburners, but their use is restricted by their high noise emission. Most jetliners use turbofan jet engines, which are quieter. An enormous fan, driven by a lowpressure turbine, feeds some air into the compressor but feeds most of it through bypass ducts to join the exhaust jetstream in the tail cone. The bypass stream produces
most of the thrust. Many smaller, propellerdriven aircraft use turboprop jet engines, in which the engine powers a propeller.

Supersonic jetliners

SUPERSONIC AIRCRAFT FLY FASTER than the speed of sound (Mach 1). There are many supersonic military aircraft, but only two supersonic passenger-carrying aircraft (also called SSTs, or
supersonic transports) have been produced: the Russian Tu-144, and the Concorde, produced jointly by Britain and France. The Tu-144 was withdrawn in 1978, after only seven months in service. The
Concorde remained in service from 1976 until 2003, with a break for modifications from July 2000 until October 2001. Its features included a droop nose, which lowered during takeoff and landing to aid visibility from the cockpit; the pumping of fuel between forward and aft trim tanks helped stabilize the aircraft. The Concorde had a narrow fuselage and short span wings to reduce drag during supersonic flight. Its noisy turbojet engines with afterburners enabled it to carry 100 passengers at a cruising speed of Mach 2 at 50,000-60,000 ft (15,000-18,000 m). Once an aircraft is flying faster than Mach 1, it produces a continuous air-pressure wave, which is heard as a “sonic boom.”

Modern jetliners 1

MODERN JETLINERS HAVE ENABLED ordinary people to travel to places where once only the wealthy could afford to go. Compared with the first jetliners (which were introduced in the 1940s), modern ones are much quieter, burn fuel more efficiently, and produce less air pollution. These advances are largely due to the replacement of turbojet engines with turbofan engines . The greater power of turbofan engines at low speeds enables modern jetliners to carry more fuel and passengers than turbojet aircraft; a modern Boeing 747-400 (popularly known as a “jumbo jet”) can fly 400 people for 8,500 miles (13,700 km) without needing to refuel. Jetliners fly at high altitudes, typically cruising at 26,000-36,000 ft (8000-11,000 m), where they can use fuel efficiently and usually avoid bad weather. The pilot always controls the aircraft during takeoff and landing, but at other
times the aircraft is usually controlled by an autopilot. Autopilots are complex on-board mechanisms that detect deviations from an aircraft’s route and make appropriate adjustments to the flight controls.
Flight decks are also equipped with radars that warn pilots of approaching hazards, such as mountain ranges, bad weather, and other aircraft.

Modern piston aero-engines

PISTON ENGINES today are used mainly to power the vast numbers of light aircraft and microlights, as well as crop-sprayers and crop-dusters, small helicopters, and firebombers (which dump water on large fires). Virtually all heavier aircraft are now powered by jet engines. Modern piston aero-engines work on the same basic principles as the engine used by the Wright brothers in the first powered flight in 1903. However, today’s engines are more sophisticated than earlier engines. For example, modern aero-engines may use a two-stroke or a four-stroke combustion cycle; they may have from one to nine air- or water-cooled cylinders, which may be arranged horizontally,
in-line, in V formation, or radially; and they may drive the aircraft’s propeller either directly or through a reduction gearbox. One of the more unconventional types of modern aero-engine is the rotary engine shown here, which has a trilobate (three-sided) rotor spinning in a chamber shaped like a fat figure-eight.

World War II aircraft

WHEN WORLD WAR II began in 1939, air forces had already replaced most of their fabric-skinned biplanes with all-metal, stressed-skin monoplanes. Aircraft played a far greater role in military operations during World War II than ever before. The wide range of aircraft duties, and the introduction of radar tracking and guidance systems, put pressure on designers to improve aircraft performance. The main areas of improvement were speed, range, and engine power. Bombers became larger and more powerful—converting from two to four engines—in order to carry a heavier bomb load; the US B-17 Flying Fortress could carry up to 6.8 tons (6.2 metric tons) of bombs over a distance of about 2,000 miles (3,200 km). Some aircraft increased their range by using drop tanks (fuel tanks that were jettisoned when empty to reduce drag). Fighters needed speed and manoeuvrability: the Hawker Tempest shown here had a maximum speed of 435 mph (700 km/h), and was one of the few Allied aircraft capable of catching the German jet-powered V1 “flying bomb.” By 1944, Britain had introduced its first turbojetpowered aircraft, the Gloster Meteor fighter, and Germany had introduced the fastest fighter in the world, the turbojet-powered Me 262, which had a maximum speed of 540 mph (868 km/h).

Early passenger aircraft

UNTIL THE 1930s, most passenger aircraft were biplanes, with two pairs of wings and a wooden or
metal framework covered with fabric or, sometimes, plywood. Such aircraft were restricted to low speeds and low altitudes because of the drag on their wings. Many had an open cockpit, situated behind or in front of an enclosed—but unpressurized—cabin that carried a maximum of 10 people. The passengers usually sat in wicker chairs that were not bolted to the floor, and the journey could be bumpy when flying through turbulence. Warm clothing, and ear plugs to reduce the effects of prolonged noise, were often required. During the 1930s, powerful, streamlined, all-metal monoplanes, such as the Lockheed Electra shown here, became widespread. By 1939, the advent of pressurized cabins allowed fast flights at high altitudes, where there is less turbulence. Flying boats were still necessary on many routes until 1945 because of inadequate runways and the frequency of emergency sea landings. World War II, however, resulted in enough good runways being built for landplanes to become standard on all major airline routes.

World War I aircraft

WHEN WORLD WAR I STARTED in 1914, the main purpose of military aircraft was reconnaissance. The British-built BE 2, of which the BE 2B was a variant, was wellsuited to this duty; it was very stable in flight, allowing the occupants to study the terrain, take photographs, and make notes. The BE 2 was also one of the first aircraft to drop bombs. One of the biggest problems for aircraft designers during the war was mounting machine-guns. On aircraft that had front-mounted propellers, the field of fire was restricted by the propeller and other parts of the aircraft. The problem was solved in 1915 by the Dutchman Anthony Fokker, who designed an interrupter gear that prevented a machine-gun from firing when a propeller blade passed in front of the barrel. The German LVG CVI had a forward-firing gun to the right of the engine, as well as a rear-cockpit gun, and a bombing capability. It was one of the most versatile aircraft of the war.

Biplanes and triplanes

BIPLANES DOMINATED AIRCRAFT DESIGN until the 1930s, largely because some early monoplanes were too fragile to withstand the stresses of flight. The struts between biplanes’ wings made the wings strong compared with those of early monoplanes, although the greater surface area of biplanes’ wings increased drag and reduced speed. Many aircraft designers also developed triplanes, which had a particular advantage over biplanes: more wings meant a shorter wingspan to achieve the same lifting power, and a shorter wingspan gave greater manoeuvrability. Triplanes were most successful as fighters during World War I, the German Fokker triplane being a notable example. However, the greater maneuverability of triplanes was no advantage for normal flying and so most manufacturers continued to make biplanes. Many other aircraft designs were attempted. Some were quadruplanes, with four pairs of wings. Some had tandem wings (two pairs of monoplane wings, one behind the other). One of the most bizarre designs was by the Englishman Horatio Phillips: it had 20 sets of narrow wings and looked rather like a Venetian blind.

Early monoplanes

MONOPLANES HAVE ONE WING on each side of the fuselage. The principal disadvantage of this arrangement in early, wooden-framed aircraft was that single wings were weak and required strong wires to brace them to king posts above and below the fuselage. However, single wings also had advantages: they experienced less drag than multiple wings, allowing greater speed; they also made aircraft more manoeuvrable because single wings were easier to warp (twist) than double wings, and warping the wings was how pilots controlled the roll of early aircraft. By 1912, the French pilot Louis Blériot had used a monoplane to make the first flight across the English Channel, and the Briton Robert Blackburn and the Frenchman Armand Deperdussin had proved the greater speed of monoplanes. However, a spate of crashes caused by broken wings discouraged monoplane production, except in Germany, where all-metal monoplanes were developed in 1917. The wings of all-metal monoplanes did not need strengthening by struts or bracing wires, but despite this, such planes were not widely adopted until the 1930s.

Pioneers of flight

FLIGHT HAS FASCINATED MANKIND for centuries, and countless unsuccessful flying machines have been designed. The first successful flight was made by the French Montgolfier brothers in 1783, when they flew a balloon over Paris. The next major advance was the development of gliders, notably
by the Englishman Sir George Cayley, who in 1845 designed the first glider to make a sustained flight, and by the German Otto Lil ienthal, who became known as the world’s first pilot because he managed to achieve controlled flights. However, powered flight did not become a practical possibility until the invention of lightweight, gas-driven internal combustion engines at the end of the 19th century. Then, in 1903, the American brothers Orville and Wilbur Wright made the first powered flight in their Wright Flyer biplane, which used a four-cylinder, gas-driven engine. Aircraft design
advanced rapidly, and in 1909 the Frenchman Louis Blériot made his pioneering flight across the English Channel . The American Glenn Curtiss also achieved several “firsts” in his Model-D Pusher
and its variants, most notably winning the world’s first competition for airspeed at Reims in 1909.

Frigates and submarines

FROM THE MID-19TH CENTURY, ARMORED SHIPS provided a new challenge to enemy craft. In response, huge revolving gun turrets were developed. These could fire in any direction, could be loaded from the breech very rapidly, and, instead of cannonballs, they discharged exploding shells. Modern fighting ships, like the frigate, combine heavy ship-borne armament with light helicopter weaponry. Submarines function below the surface of the sea. Their speed and ability to fire missiles from under water are their major assets. The nuclear submarine can stay under water for several years without refueling.

The battleship

IN THE EARLY YEARS OF THE 20TH CENTURY, sea warfare— attacking enemy vessels or defending a ship—was revolutionized by the introduction of Dreadnought-type battleships like the Brazilian vessel below. These new ships combined the latest advances in steam propulsion, gunnery, and armor plating. The gun turret was designed to fire shells over huge distances. It was protected by armor 12 in (30 cm) thick. The measurements given for the guns of this ship refer to the bore diameter. Where “weight” is quoted, this is the weight of the shell that the gun fires. Torpedoes— as portrayed on the upper cigarette card (right)—were self-propelled underwater missiles, often steered by gyrocontrol. Depth charges were designed in the First World War for use against submerged U-boats. They are canisters filled with explosives that are detonated by depth-sensitive pistols. The lower cigarette card shows depth charges being fired by a “thrower,” fired from a torpedo tube, and rolled from the stern. Ship’s shields were fitted to warships from the late 19th century onward. The shield shown opposite depicts a traditional ship’s cannon.

Anatomy of an iron ship

IRON PARTS WERE USED IN THE HULLS OF WOODEN SHIPS AS EARLY AS 1675, often in the same form as the wooden parts that they replaced. Eventually, as on the tea clipper Cutty Sark (below), iron rigging was found to be stronger than the traditional rope. The first “ironclads” were warships whose wooden hulls were protected by iron armor plates. Later ironclads actually had iron hulls. The model opposite is based on the British warship HMS Warrior, launched in 1860, the first battleship built entirely of iron. The plan of the iron paddlesteamer (bottom), built somewhat later, shows that this vessel was a sailing ship; but it also boasted a steam propulsion plant amidships that turned two side paddlewheels. Early iron hulls were made from plates that were painstakingly riveted together (as below), but by the 20th century vessels began to be welded together, whole sections at a time. The Second World War “liberty ship” was one of the first of these “production-line vessels.”

Paddle wheels and propellers

THE INVENTION OF THE STEAM ENGINE IN THE 18TH CENTURY made mechanically driven ships fitted with paddle wheels or propellers a viable alternative to sails. Paddle wheels have fixed or feathered floats, and the model shown below features both types. Feathered floats give more propulsive power than fixed floats because they are almost upright at all times in the water. Paddle wheels were superseded by the propeller on oceangoing vessels in the mid-19th century. Propellers are more efficient, work better in rough water, and are less vulnerable in collisions. The first propellers were two-bladed but later threeand four-bladed versions are more powerful; the shape and pitch of blades have also been refined over the years. At the beginning of the 18th century, tillers were superseded on many larger ships by the ship’s wheel as a means of steering.

Ropes and knots

ALL KINDS OF ROPES ARE USED AT SEA, from thin twines and yarns to thick hawsers. Synthetic fibers have been developed specifically for use at sea. Nylon ropes stretch, and so are ideal
for anchoring; polyester (frequently called by the trade name Dacron) has little stretch, so is ideal for halyards and sheets. Different knots have different uses. Knots that join two ropes are called bends; hitches join a rope to another object; and bowlines produce an eye (loop) in the end of a rope. Ropes can be joined by splicing (unraveling the ends and weaving them together) or seizing (lashing the ropes together side by side).

Mooring and anchoring

FOR LARGE VESSELS IN OPEN WATER, ANCHORAGE IS ESSENTIAL. By holding a ship securely to the seabed, an anchor prevents the vessel from being at the mercy of wave, tide, and current. The earliest anchors were nothing more than stones. In later years, many anchors had a standard design, much like the Admiralty pattern anchor shown on this page. The Danforth anchor is somewhat different. It has particularly deep flukes to give it great holding power. On large sailing ships, anchors were worked by teams of sailors. They turned the drum of a capstan by pushing on bars slotted into the revolving cylinder. This, in turn, lifted or lowered the anchor chain. In calm harbors and estuaries, ships can moor (make fast) without using anchors. Berthing ropes can be attached to bollards both inboard and on the quayside. Berthing ropes are joined to each other by bends, like those opposite.