The Engineering History of Human Flight
When Orville and Wilbur Wright flew at Kitty Hawk on December 17, 1903, they ignited the aeronautical equivalent of the Big Bang. Although it was not apparent at the time, their awkward-looking Flyer contained all of the elements of modern flight—including the wings, the engine, the controls, and even the landing gear.
While the Wright Flyer might look indistinguishable from planes like the super-advanced F-35, a lot of the same principles the Wrights pioneered survived. But it was a long strange, journey to get from point A to point B, and every single piece of today’s modern aircraft has an incredible story to tell.
When it comes to the Wright Flyer, the wings are everything. The Wright brothers knew that a monoplane may have less drag, but a biplane was stronger. They were also aware that American bridge builder Octave Chanute had hit upon a good formula when he used a Pratt truss system of diagonal and vertical braces. It proved a great fit for the Flyer.
The biplane structure also allowed the Wrights’ unique “wing warping” system, which connected the wings to a vertical rudder. The system allowed that vertical rudder to automatically coordinate the aircraft’s turns.
Other inventors experimented with wing design, attempting to increase performance. Aviator Louis Blériot was successful with his monoplanes, until he hit power and speeds that met the limits of his engineering skills. Other engineers wanted even more wings—the Fokker Triplane had three. The Caproni Ca 60 Triple Hydro-Triplane, one of the strangest-looking airplanes ever built, had a whopping nine. But with too much weight and drag, many multi-winged aircraft ended in disaster.
Other engineers created shapes and arrangements that lasted for years after. The tail-first design of Eugene Lefebvre, an engineer and one of the world’s first stunt pilots, surfaced again in the Focke Wulf “Ente,” the Curtiss XP-55, and the Rutan Long-EZ.
Then came the swept wing, where wings met the fuselage at an angle. This is the wing configuration that would really stick. John Dunne began experimenting with tailless swept wing aircraft in 1911—Alexander Lippisch, Reimar and Walter Horten, and John Northrop followed his lead. The now-familiar delta configuration, in which the wings form a triangle, appeared in Lippisch’s designs, and was used by many manufacturers such as Convair and Dassault.
While the wing’s orientation is important, the airfoil design, or the shape of the wing’s profile viewed from the side-on, might be even more so. The Wrights believed thin airfoils would offer less drag, which appeared in aircraft such as World War I’s SPAD XIII. But Dutch Aviator Tony Fokker went in the opposite direction, instead using thick airfoils which generated a great deal of lift and provided structural support without wires or other bracing.
In those early years, wings were made from wood, wire, and linen (not canvas as was often claimed), but as airfoils and wing design became more complicated, engineers needed a new material. By World War I, improvements in metallurgy solved the initial weight penalty. By then, all-metal designs were the standard for the major components of aircraft, which provided lots of benefits but one big one: easy maintenance.
The Wrights didn’t patent their aircraft, but they did patent the control system. This led aviation inventors all over the world scrambling for other ways to control their flying machines.
In the 1920s, British airplane manufacturer Handley Page stumbled upon something big—the slotted leading edge, a thin bar attached to the forward-facing edge of the wing. Page’s new system were relatively rudimentary, but it would be considered the grandfather of the triple-slotted trailing-edge flaps found on the future Boeing 727.
Another engineering leap came in the 1940s when the Northrop N-9M flying wing used 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.
In the 1950s, the Convair B-58 Hustler employed a rudder, elevons, and a complex automatic trim system. This design eventually led to the stabilators found on many of today’s modern fighters, such as the F-15EX Eagle II and Boeing F/A-18, some of the most complex aircraft in the world.
Although the Wrights knew intuitively that control would be the most difficult challenge, they were also worried about power. When they couldn’t find a suitably light and powerful engine, they solved the problem by building one themselves. The simple but elegant 4-cylinder, 4-stroke engine was designed, like every element of the Wright Flyer, to meet a specific goal: 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, but achieved 16.
It wouldn’t take long for imitators to swoop in. Some of these, such as Glenn Curtiss, were already master engine builders, and 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 it also 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’ executed the idea flawlessly. 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.
Soon conventional liquid-cooled engines became dominant, either with cylinders in line or in V’s, and were favored for fighter aircraft because their inline shape allowed better streamlining.
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 powerplants were aided by streamlined cowlings that improved cooling and increased speed, and they would take aircraft aviation ever higher—until World War II would change aircraft forever.
In 1942, piston engines were about as powerful as they’d ever be. To get more power, engineers would have to add more cylinders, increasingly complex superchargers, or systems to inject water, alcohol, or chemicals into the fuel. It just wasn’t feasible.
Luckily, two engineers—working independently from each other—would usher in an entire new era of aviation. Royal Air Force aerobatic pilot Frank Whittle and Hans Joachim Pabst von Ohain, a newly minted Ph.D. from Germany’s University of Goettingen, each developed successful jet engines. While Whittle suffered initial rejection from the British government, Ohain received enthusiastic backing from industrialist Ernst Heinkel.
So on August 27, 1939, the Heinkel He 178—powered by Ohain’s HeS 3B engine—became the first jet aircraft. Two years later, Whittle’s Power Jets W.1 engine flew in the Gloster E.28/39. These jet engines generated about the same power as the more complex piston engines they replaced. 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. It wouldn’t belong before jet engines surpassed the power found in even the most advanced piston engines.
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 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.
Although the jet engine was initially thought to have limited application to high-altitude fighters, its use spread quickly to bombers and transports. 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.
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 wings had to be swept even more radically at higher speeds. 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 commercial aircraft—the Boeing 747 and the Airbus A380—have four engines, but most large airliners rely on only two.
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, but when effective brakes became widely available, designers returned to the tricycle undercarriage. On larger aircraft, other styles, including bicycle and multi-bogie types, were adapted to the task.
Although it seems the most advanced, the retractable landing gear is one of aviation’s oldest components, stretching back to 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 Hawk, Supermarine Spitfire, and others soon followed. Over the course of time, landing gears became more sophisticated, especially on heavyweight transport aircraft.
But before airports dotted the world, engineers relied on the planet’s biggest runways—water. Henri Fabre paved the way with his first aquatic 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.
Today, Curtiss is rightly known as the father of naval aviation.
While aircraft manufacturers the world over continue to fine tune every element of modern aircraft design, the late 20th and 21st centuries have seen an explosion in the electronics housed inside the airplane’s fuselage. From the introduction of satellite-based global positioning for aviation navigation in the mid-1990s to linking stealth fighters with networked drones in the 2020s, new technology being hardwired into modern aircraft continues to shape the future of aviation.
With the advent of drones, efforts are underway to pair advanced drone wingmen equipped with artificial intelligence with crewed aircraft in programs like Skyborg, Loyal Wingman, and Russia’s Sukhoi S-70 Okhotnik-B.
The 1960s and early 1970s saw the introduction of “glass cockpits” in both commercial and military applications, or cockpits that featured electronic displays rather traditional analog gauges. But it wasn’t until the data fusion revolution at the turn of the century that the real power of these displays could be leveraged in advanced tactical aircraft like the F-35 Joint Strike Fighter.
Now, older fourth-generation jets like the F-15 and F/A-18 are both receiving cockpit facelifts—and it’s all about data management. These jets are replacing a slew of gauges and readouts with a streamlined combination of touchscreens and heads-up-displays. Modern cockpit electronics can combine data gathered from within and well beyond the aircraft itself, fuse it all into an easy-to-digest interface, and project it right into the pilot’s line of sight through helmet displays and multi-use touchscreens.
Open system digital architecture in both military and commercial applications, or the separation of an aircraft’s software from the hardware it runs on, is just beginning to allow for pulling new capabilities out of existing aircraft. The F-35, as one example, can receive wireless updates that improve capabilities just like the iPhone in your pocket.
While these electronic advancements would be unthinkable in the Wright Brothers’ time, the basic principles of that first flight in Kitty Hawk are still on display today. After more than a century of innovation, many of the Wrights’ original ideas still endure.
Published at Sun, 23 May 2021 13:00:00 +0000