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A Century Of Flight

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The Wright brothers did more than conquer the sky.

They unleashed a torrent of engineering genius that created a new world.

By Walter J. Boyne


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When Orville and Wilbur Wright flew their Flyer at Kitty Hawk on Dec. 17, 1903, they did more than achieve the ancient dream of conquering the sky. They ignited the aeronautical equivalent of astronomy's big bang. Although it was not apparent at the time, their awkward-looking flying machine contained in rudimentary form all of the elements--from wings and engine, to propeller and landing gear--that would one day be found on a modern aircraft. Less obvious was the tremendous surge of progress made by those whose names are less familiar than the Wright brothers. As early as 1910, Henri Coanda of Romania demonstrated a jet engine. A retractable landing gear appeared the following year, and two types of adjustable-pitch propellers appeared a year later. By the early 1920s, the shape of modern aviation--including all-metal and composite construction, swept-wings and pressurized cabins--had taken form, in outline if not detail.



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Except for a few experimental designs like the Grumman X-29, the basic plan of the aircraft was established with the Blériot XI.


If the engine is the heart of the aircraft, the wings can be considered its soul, and from the Wrights on, inventors strove to wring more efficiency from an unending variety of designs. The Wright brothers knew instinctively that the great American bridge builder Octave Chanute had hit upon a good formula in his biplane gliders that used the Pratt truss system for bracing. A monoplane may have had less drag, but it was not as strong.

The biplane also lent itself to the Wrights' unique "wing warping" control system, which, with brilliant insight, they linked to a vertical rudder in their 1902 glider. Thus, the rudder automatically coordinated the aircraft's turns and helped solve the problem of control.

Many inventors experimented with wings in an attempt to increase performance. Aviator Louis Blériot was notably successful with his monoplanes until increased power and speed created demands upon his structures that his engineering skills could not meet. Other engineers wanted more wings--the Fokker Triplane had three, the Caproni Ca 60 Triple Hydro-Triplane had nine. However, with too much weight and drag, many multiwinged aircraft proved to be fiascoes.

Still other engineers exploited shapes and arrangements that were carried down through the  years. Thus, the pusher, tail-first design of the unlucky Eugene Lefebvre surfaced again in the 1931 Focke Wulf "Ente," the 1943 Curtiss XP-55 and the Rutan LongEZE.

John Dunne began experimenting with tailless sweptwing aircraft in 1911. Following his lead were such luminaries as Alexander Lippisch, Reimar and Walter Horten, and John Northrop. The now-familiar delta configuration appeared in Lippisch designs, and was used extensively by many manufacturers, including Convair and Dassault. The low-aspect-ratio Kitchen "Doughnut," flown in Chicago in 1911, was followed by the Arup, and Charles H. Zimmerman's Chance Vought V-173 and Chance XF5U-1.

At the opposite end of the spectrum were the extremely high-aspect-ratio aircraft of the French manufacturer Hurel-Dubois and its licensee, Shorts. Wing sweep design underwent an inversion, from the tentative 18.5° sweepback of the Messerschmitt Me 262 to the jutting 35° forward sweep of the Grumman X-29. The Wrights believed thin airfoils would offer less drag, an idea that was pursued for more than a decade--the thin airfoil was incorporated into such aircraft as the SPAD XIII, used during World War I. Tony Fokker's designs took the opposite tack, using thick airfoils that not only generated a great deal of lift, but also provided room for structural members that permitted cantilever construction.

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Photos by Hulton/Getty (Wright Flyer), Boeing (DC-3), Check Six (Boeing 707), Northrop Grumman (B-2)

Airfoils became increasingly sophisticated and eventually high speeds called for thin, swept designs. Modern engineering methods and new materials were able to answer. Many of these advancements owe their due to the Langley Memorial Aeronautical Laboratory of NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). Wing size and shape were dictated by the structural techniques and materials available at the time. In the early years, wood, wire and fabric--not canvas as was often claimed, but good linen--were superior in most applications.

The most successful attempts at all-metal aircraft, such as the Junkers J-1 and J-9, were hampered by the weight and expense of their construction. Metal structures were introduced gradually, and became important during World War I in the steel tube fuselage of the Fokkers and the metal airframes of the Breguets. Improvements in metallurgy and better design techniques soon led to a widespread application of metal construction. One of the benefits of all-metal aircraft is that they are easier to maintain under adverse weather conditions.



Older techniques lingered on for many reasons--for one, the workforce was more familiar with wood construction. In fact, some remarkable aircraft made entirely of wood or a combination of metal and wood were produced during World War II. But aluminum alloys became the primary structural material. Metal construction also permitted sophisticated variations, including an adjustable wing area and variable-position sweptwings, all of which aimed at increasing speed. Inventors soon sought to improve wing design with high-lift devices, and among the earliest of these were the automatic trailing-edge flaps found on the 1916 Breguet 14. As landing speeds increased in the postwar years, simple split flaps were replaced by the more sophisticated Fowler flaps.

Leading edges were not immune to improvement. Airplane manufacturer Handley Page patented the slotted leading edge in the early 1920s. This technology eventually led to the triple-slotted trailing-edge flaps and leading-edge devices of the Boeing 727. Because the Wrights had patented their control system but not their aircraft, inventors all over the world sought alternate means to achieve control. Glenn Hammond Curtiss set off a long and bitter legal fight when he professed that his midwing ailerons did not infringe upon the Wright patent. Other competitors, relying upon distance and long court fights to protect them, simply adopted the wing warping or the use of inset ailerons without so much as a "by your leave." World War I forced the settlement of the patent issue, and in subsequent years many variations of control surfaces appeared. The Northrop N-9M flying wing employed a pitch trimmer with a split-drag rudder and an elevon (for both roll and pitch) so that all surfaces could be operated together or independently. The magnificent Convair B-58 Hustler employed a rudder, elevons and a complex automatic trim system. The requirement for high speed led to the "stabilators" found on today's North America F-100 and McDonnell Douglas F-4. Many of today's modern fighters, such as the Northrop Grumman F-14 and Boeing F/A-18, use individually controlled stabilators for roll and pitch control.


Creating Thrust

While the Wrights had developed a surprisingly powerful engine for their Flyer, making use of that power was another challenge. To their amazement, they could find no useful data on propeller performance. Their investigation revealed that naval propeller design was an apparently ad hoc discipline for which intuition and past experience were the guides.

As engines developed more power, propellers evolved to deliver and meter that power in the most effective manner possible. The goal, of course, was to create propellers that would optimize takeoff, climb and cruise. Eventually, feathering--allowing the propeller to freewheel--was introduced to reduce drag on engines that lost power. Reversing thrust entirely reduced landing rolls and improved braking. With the Jet Age, sophisticated gearing was required to match high-speed engine output to turboprop efficiency.

Rotorcraft posed challenging problems of thrust and lift. The designs ranged in complexity from the simple blades of early autogiros to the tremendously complicated rotor system of the Bell/Boeing V-22 Osprey.



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Massive passenger seaplanes, like the Martin M-130 China Clipper, introduced the public to transoceanic flight.


Although the Wrights knew intuitively that control would be their most difficult challenge, they also were concerned with power. When they couldn't find a suitably light and powerful engine, they solved the problem by designing and building one. The simple but elegant 4-cylinder, 4-stroke engine was designed, like every element of the Wright Flyer, to meet a specific goal--that is, to generate a relatively high horsepower for a relatively short time. Needing to obtain 8 hp, just enough to get the Flyer into the air, they hoped for 12 and were delighted to achieve 16

The Wrights soon had scores of imitators. Some of these, such as Curtiss, were already master engine builders. A number of manufacturers began to offer light, powerful engines for aircraft use. Most of these arranged 4, 6 or 8 cylinders in a row or a V shape, and were either air- or liquid-cooled. Horsepower depended for the most part on displacement: More and bigger cylinders produced greater power, but of course this added weight.

The first radical advance in piston engine performance came with Louis and Laurent Seguin's Gnome Rotary in 1909. The idea of fixing the propeller to cylinders rotating around a fixed crankshaft was not new, but the Seguins' superb execution was. Weighing about 120 pounds, the original 5-cylinder Gnome delivered 34 hp at 1300 rpm. A 7-cylinder 50-hp Gnome, installed in

Louis Paulhan's Voisin biplane, was the first to fly, on June 16, 1909. Development of rotary engines progressed swiftly, for their high power-to-weight ratio more than offset the fact that they burned a lot of fuel (a mixture of gasoline and castor oil) and emitted unbearable fumes.

Conventional liquid-cooled engines became dominant, either with cylinders in line or in V's. But the engines--the heart of the aircraft--would never be as famous as the aircraft themselves. While we read of World War I's Fokker D VII, SPAD XIII and Bristol F.2B fighter, we rarely hear of the 185-hp BMW, 235-hp Hispano-Suiza and 275-hp Rolls-Royce Falcon engines that, respectively, powered them. Yet it has always been the power plant that led the way, whether it was the magnificent Rolls-Royce racing engines that evolved ultimately into the Merlin or, beginning in the mid-1920s, the rise of the radial configuration  that would dominate commercial aviation until the Jet Age. Liquid-cooled engines, which grew in popularity with the advent of coolants that permitted higher temperatures and smaller radiators, were favored for fighter aircraft because their inline shape allowed better stream-lining. Yet, beginning in 1921, engineer Charles Lawrance's innovative experiments led to a marvelous competition between Pratt & Whitney and Wright Aeronautical that resulted in the most powerful and reliable radial engines in the world. These power plants were aided by streamlined cowlings that improved cooling and increased speed.


Rotary WingsA wing is not the only way to fly. The rotor of the gyroplane (left) creates lift while the conventionally positioned propeller provides thrust. In a helicopter (right), the rotor produces both lift and thrust. The latest variation, demonstrated in the V-22 Osprey, is the tiltrotor. The wind assembly rotates upward for vertical takeoffs and landings. Once airborne, it moves to the horizontal position, thus delivering the speed, range and economy of a fixed-wing aircraft.





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The supersonic transport represented the perfect marriage of engine and airframe design. Alas, high operating costs would limit its commercial viability.


By 1942, piston engines were reaching their upper limits. Increases in power would have to come from more cylinders, increasingly complex superchargers, or systems to inject water, alcohol or chemicals into the fuel. Propellers, also at their upper levels of efficiency, were producing supersonic speeds.

Fortunately, the replacement for the piston engine was at hand, thanks to the pioneering work of Flying Officer Frank Whittle, a Royal Air Force aerobatic pilot, and Hans Joachim Pabst von Ohain, a newly minted Ph.D. from Germany's University of Goettingen. Working independently, each developed successful jet engines. While Whittle had to suffer initial rejection from the British government, Ohain received the backing of industrialist Ernst Heinkel. Thus, the Heinkel He 178, powered by Ohain's HeS 3B engine, became the first jet aircraft. It made its maiden flight on Aug. 27, 1939. Whittle's Power Jets W.1 engine flew in the Gloster E.28/39 on May 15, 1941. These jet engines generated about the same power as the more complex piston engines they would replace. Although fuel consumption was high and reliability low, the smooth-

running jet engine developed quickly. Fuel consumption improved and reliability soared, so much so that corrosion, rather than wear and tear, is the greatest enemy of the modern jet engine. Jet engines gained power in increments far beyond anything experienced with piston engines.

Piston Limits

Every possible piston configuration was experimented with in the first half-century of flight. Ultimately, adding power required adding pistons, but this complicated the task of cooling the engine. By World War II, the piston engine had reached perfection with large radial engines, including the Pratt & Whitney R4350.

The first jet engines were either centrifugal or axial-flow types. In time, jet engines became more intricate, but never reached the degree of complexity of the last generation of piston engines. The genius of Pratt & Whitney's designs came to the fore in the early 1950s with the twin-spool JT-3, which provided 10,000 pounds of thrust with good fuel economy and, for then, fantastic time-between-overhaul (TBO) periods of almost 15,000 hours. By comparison, the Junkers Jumo 004, an early German jet which powered the Messerschmitt Me 262, was a 25-hour TBO engine. In 1958, P&W took the next great step with the development of its TF33 turbofan, a civil version of the JT8D engine. The engine seemed to do the impossible--get thrust for nothing by simply bypassing cold air through an attached fan. In the years that followed, improvements in power and fuel economy set the stage for the development of similar engines from General Electric, Rolls-Royce and others.

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America's ability to project power rests heavily on the technology that makes it possible to base the F-18 Super Hornet on aircraft carriers thousands of miles from land.

ILLUSTRATION BY Keith Ferris     

Until recently, it was customary for designers not to combine a new aircraft and a new engine in one package, but today, future jet aircraft, particularly airliners, are designed for future jet engines. For example, the twin-deck, 555-passenger Airbus Industries A380 is being designed simultaneously with its 70,000-pound-thrust engines. It will use either the Rolls-Royce Trent 900 or the General Electric/Pratt & Whitney Engine Alliance GP7000.

Although the jet engine was initially thought to have limited application to high-altitude fighters, its use spread quickly to bombers and transports, and the future of propellers seemed dim. However, from the very start, engineers planned to use jet engines to drive propellers, providing a more efficient powerplant combination at subsonic speeds. The first turboprop was flown experimentally on a Gloster Meteor, but the first commercial application was on the highly successful Vickers Viscount airliner of 1948. Turboprops quickly became a staple for designs requiring high lift capacity and medium airspeeds.

Jet technology breathed new life into aircraft propulsion. For their size they produced more power and ran for thousands, rather than hundreds, of hours between overhauls.

The advent of jet power, with its higher speeds and altitudes, presented aircraft designers with entirely new challenges. Aircraft had to be pressurized to provide comfort at high altitudes, and where higher speeds were sought, wings had to be swept. New materials were introduced to withstand the great stress of multiple pressurization cycles.

As jet engine power increased, larger aircraft could be built with fewer engines. Today the largest aircraft--the Boeing 747 and the Airbus Industrie A380--have four engines, but most large airliners are beginning to rely on two. Supersonic aircraft, such as the recently retired Concorde, Tupolev Tu-144 and the Rockwell XB-70, have been built and flown successfully, if not with great economy. Oddly enough, the future of jet engines may reside in a variation of an engine that has no moving parts--the ramjet. In the newest engines, the scramjets--or supersonic-combustion ramjets--the airflow through the whole engine remains supersonic. Once perfected, the scramjet will make it possible to compress intercontinental air travel times to only a few hours.


Landing Gears

Some of the early pioneers of aviation gave little thought to the problem of landing. Not so the Wright brothers, who elected to use skids for takeoff and landing. They were built into the structure of their Flyer as the simplest, strongest, lightest solution. Wright contemporary Glenn Curtiss took an entirely different approach, equipping his early designs with a tricycle landing gear that stemmed, at least in part, from his experience with building motorcycles. The rear-wheeled "Taildragger" landing gear soon grew in popularity, for it put the aircraft in an attitude well suited for both takeoff and landing. When effective brakes became widely available, designers returned to the tricycle undercarriage. On larger aircraft, other styles, including bicycle and multibogie types, were adapted to the task.

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Without heavy-duty landing gear, like that on the Airbus A380 (above), the widebody jets that are the workhorses of the international travel industry could not exist.

Retractable landing gear had been part of Alphonse Pénaud's 1876 patent for a monoplane amphibian. It appeared on an aircraft for the first time in the 1908 Matthew Sellers aircraft. The first practical retractable undercarriage was used by the Dayton Wright R.B. 1 racer, a Pulitzer Trophy racing contestant in 1920. There followed several experimental types including one used on the Verville Sperry racer.

By the mid-1930s, higher airspeeds had made retractable landing gear essential. Some designers opted to leave the retracted wheels exposed, as was done on the Boeing Model 247 and the Douglas DC-1, 2 and 3, to ease the stress of an emergency wheels-up landing.

In fighters, the Soviet Union had led the way in 1932 with the first operational aircraft to feature a retractable gear, the Polikarpov I-16. The tubby Grumman biplanes, Messerschmitt Bf 109, Hawker Hurricane, Seversky P-35, Curtiss P-36, Supermarine Spitfire and others soon followed. Over the course of time, landing gears became more sophisticated, especially on heavyweight transport aircraft in which intricate suspension systems using multiple wheels became necessary.

For landing on water, Henri Fabre paved the way with his first flight on March 28, 1910. However, it was Curtiss who made the seaplane practical, beginning with his Flying Boat No. 1, which flew on Jan. 10, 1912. Curtiss never looked back, fielding one superb flying boat design after another. His NC-4 was the first aircraft to fly across the Atlantic, on May 31, 1919. Anything but a quick flight, it took 24 days, with multiple landings to take on fuel. Today, Curtiss is rightly known as the father of naval aviation.

Gen. Chuck Yeager was first to crack the sound barrier in the rocket-powered "Glamorous Glennis" Bell X-1.


Only the X-15 and the space shuttle have successfully flown both in space and in the Earth's atmosphere. Here, the shuttle orbiter is shown being ferried on a 747.

Not all of the progress in seaplanes was driven by military needs. The Schneider Trophy races fostered the growth of seaplane speed. In fact, the current world's piston engine seaplane record of 440.683 mph is still held by the Macchi Castoldi M.C. 72 twin-float, twin-engine (tandem inline) seaplane of 1934. The desirability of amphibious landing gear was quickly realized, the first expression being the already mentioned Pénaud patent, and the first realization being a 1910 Voisin. Among the first truly practical amphibians, one must list the series of Loening biplanes that served both military and civil uses for many years. The first aircraft to use skis may have been a Farman flown at St. Petersburg, Russia, in 1910. Skis, a natural alternative in colder climates, have been used extensively wherever weather has dictated. They are invaluable for work in the Arctic and Antarctic.


Into Space

Since that first morning at Kitty Hawk, achieving faster speeds and reaching higher altitudes have been the driving goals of aircraft designers. Today, the SR-71 Blackbird is recognized as the fastest air-breathing bird in the sky. Designed as a Cold War spyplane at Kelly Johnson's remarkable Skunk Works, the SR-71 applied America's most advanced knowledge of metallurgy and engine design. The result is an aircraft that can consistently and reliably fly at speeds over Mach 3.

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The SR-71, used by NASA as a high-altitude environmental monitoring platform, pushed airframe materials and supersonic engine technology to the limits.

The unquestioned holder of the records for speed and altitude is a vehicle that some might argue is not truly an aircraft at all, the space shuttle.

Conceived as a truck for flying satellites and space station parts into orbit, the shuttle is powered by a rocket rather than a jet. Any doubt that it is an aircraft was put to rest on Nov. 14, 1981, by Capt. Joe Engle. During the second flight of the Columbia, the former X-15 test pilot manually flew the re-entry from orbit, at Mach 25, through landing.

As breathtaking as progress has been, it is satisfying to note how many of the Wrights' original ideas, including the biplane configuration, counter-rotating propellers and canard surfaces, have endured.

And given all the variations on the Wright brothers' theme, it is perhaps most fitting of all that in 2003, NASA is experimenting with wing warping on its Active Aeroelastic Wing (AAW), which now equips the Dryden Boeing F/A 18. The AAW promises total aircraft roll control, permitting the elimination of tail surfaces and reducing weight, drag and radar signature. Orville and Wilbur would be proud.



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