Creating the Twentieth Century

by Vaclav Smil

  And shortly after WWI diesel engines, helped by their combination of advantageous characteristics, finally began their conquest of heavy automotive market. Besides the engine’s inherently higher conversion efficiency, diesel fuel is also cheaper than gasoline, yet it is not dangerously flammable. The last attribute makes it ideal for applications where fire could be particularly dangerous (on vessels) as well for use in the tropics, where high temperatures will cause little evaporation from truck and bus tanks. Moreover, high engine efficiency and low fuel volatility mean that these diesel-powered vehicles have a much longer range per tankful than do equally powerful gasoline-fueled machines. Additional mechanical advantages include diesel engine’s high torque, its resistance to stalling when the speed drops, and its sturdiness (well-maintained engines can go 500,000 km without an overhaul).

  In 1924 Maschinenfabrik Augsburg-Nurenberg (MAN, the successor of the company where Diesel worked between 1893 and 1897) was the first engine maker to use direct-injection diesel engine, and eight years later the company stopped producing any gasoline-fueled vehicles and concentrated on diesel engines, which remain one its major products (MAN 2003). Both Benz and Daimler produced their first diesel trucks in 1924, and after they merged in 1926 they began developing a diesel engine for passenger cars; it was ready in 1936 when model 260-D, a rather heavy 45-hp saloon that became a favorite taxicab, was displayed at the Berlin car show (Williams 1972; Mercedes-Benz 2003). By the late 1930s, most of the new trucks and buses built in Europe had diesel engines, a dominance that was extended after the WWII to North America and Asia and, with exported vehicles, to every continent. Mass/power ratios of automotive diesels eventually declined to less than 5 g/W, and today’s lightest units in passenger cars are not that different from gasoline-fueled engines.

  The use of steam engines in shipping continued well after WWI, while steam turbines were gaining an increasing share of the market. But by 1939 25% of the world’s merchant marine ships were propelled by diesel engines. Almost a century after the first vessel was equipped with a small diesel engine, that triumph is even more evident. Today some 90% of the world’s largest freight ships, including the crude oil supertankers, are powered by diesel engines. MAN, Mitsui, and Hyundai are their leading producers. Maximum size of these large machines still keeps increasing: in 1996 the world’s largest engine rated about 56 MW, but just five years later Hyundai built a 69.3 MW engine (Hyundai 2003). Dimensions of the largest machines are best illustrated by their cylinder bores and piston strokes: these are, respectively, almost 1 m and more than 2.5 m, dimension an order of magnitude larger than those of automotive diesels (MES 2001).

  FIGURE 3.20. Ayres’s bizarre new aerial machine as illustrated in Scientific American of May 9, 1885.

  Low-rpm diesel engines of different sizes are also deployed in tens of thousands of localities far away from centralized electrical supply—be it in low-income countries of Asia, Africa, and Latin America or in isolated places in North America and Australia—in order to provide light and mechanical energy for refrigeration and crop processing. By 1998 the world’s largest diesel generator, a Hyundai design for India, reached 200 MW. Other market niches where diesel engines are either dominant or claim large shares of installed power include heavy construction (cranes, and earth-moving, excavating, and drilling machines), tractors and self-propelled harvesters, locomotives (both for freight and passenger service, but the fastest ones are electric), and main battle tanks (but the best one, the U.S. Abrams M1/A1, is powered by a gas turbine).

  Engines in Flight

  At the close of the 19th century, the old ambition to fly in a heavier-than-air machine appeared as distant as ever. Utterly impractical designs of bizarre flying contraptions were presented as serious ideas even in technical publications. One of my favorites is a new aerial machine that was pictured and described in all seriousness in May 9, 1885, issue of Scientific American (figure 3.20), but I could have selected other preposterous designs from the last third of the 19th century. The goal was elusive, but some innovators were very determined: Otto Lilienthal (1848–1896), the most prominent German aviation pioneer, completed more than 2,500 short flights with various gliders before he died in 1896 when his glider stalled. So did (fiction anticipating reality) a man obsessively driven to invent a flying machines in Wells’s Argonauts of the Air that was published a year before Lilienthal’s death.

  FIGURE 3.21. Wilbur and Orville Wright seated on the rear porch steps of their house, 7 Hawthorne Street, in Dayton, Ohio, in 1909. Library of Congress portrait (LOT 11512-A).

  Building the flying machines heavier than air during the last decade of the Age of Synergy was about much more than just mounting a reciprocating engine on a winged fuselage. Airplanes fit perfectly into the class of achievements that distinguish that period from anything that preceded it: they came about only because of the combination of science, experimentation, testing, and the quest for patenting and commercialization. The two men who succeeded where so many other failed—Wilbur (1867–1912) and Orville (1871–1948) Wright (figure 3.21)—traced their interest in flying to a toy, a small helicopter powered by a rubber string they were given by their father as children when they lived in Iowa. This toy was invented by Alphonse Pénaud in 1871, and the two boys built a number of copies that flew well before they tried to construct a much larger toy.

  FIGURE 3.22. Wilbur Wright piloting one of the experimental gliders above the dunes of Kill Devil Hills at Kitty Hawk, North Carolina, in October 1902. Library of Congress images (LC-W861-11 and LC-W861-7).

  Years later, their interest in flying was rekindled by Lilienthal’s gliding experiments and his accidental death. Finally, after reading a book on ornithology in the spring of 1899, Wilbur sent a letter to the Smithsonian Institution inquiring about publications on flight. The letter was answered in a matter of days by a package that contained reprints of works by Lilienthal and Langley. The brothers also ordered Octave Chanute’s (1832–1910) book that described the progress in flying machines (Chanute 1894) and began a correspondence with this theoretical pioneer of manned flight. Soon they augmented the engineering experience from their bicycle business with numerous tests as they embarked on building and flying a series of gliders (figure 3.22). Beginning in the fall of 1901, these experiments also included a lengthy series of airfoils and wing shapes in a wind tunnel (Culick 1979).

  While gliding attempts have a fairly long history, the first successful trial of an unmanned powered plane took place on October 9, 1890, when Clément Ader’s Eole, a bat-winged steam-driven monoplane, was the first full-sized airplane that lifted off under its own power. In 1896 Samuel Pierpoint Langley (1834–1906), astronomer, physicist, and the secretary of the Smithsonian Institution, received a generous U.S. government grant ($50,000) to build the gasoline-powered aircraft (NASM 2000). By 1903 his assistant, Charles M. Manly, designed a powerful (39 kW, 950 rpm) five-cylinder radial engine. This engine was mounted on Aerodrome A, and the plane was launched, with Manly at the controls, near Widewater in Virginia by a catapult from a barge on October 7, 1903. But the plane immediately plunged into the river and did so once more during the December 8 test on the Potomac River in Washington, DC, when it reared and collapsed unto itself. Manly was pulled unhurt from icy water, but the collapse spelled the end of Langley’s project. But the pressure was clearly on the Wrights if they were to claim the primacy of flying a motorized aircraft.

  Nine days after Manly’s mishap, on December 17, 1903, Orville Wright piloted the first successful flight at Kitty Hawk near Kill Devil Hills in North Carolina: just more of a jump of 37 m with the Flyer pitching up and down, staying airborne for just 12 seconds, and damaging a skid on landing (Wright 1953; USCFC 2003; see figure 1.3). Their second flight, after repairing the skid, covered about 53 m, and the third one 61 m. During the fourth flight, the machine began pitching up and down as it did in previous attempts, but Wilbur got it eventually under control, covered nearly 250 m in level flight, and then
the plane began plunging and crash-landed with a broken front rudder frame, but in 59 seconds it traveled 260 m. When it was carried back to its starting point, a sudden wind gust lifted the plane, turned it over, and destroyed it. The first Flyer, a fragile machine with a wingspan of 12 m and weighing just 283 kg, thus made only those four flights totaling less than 2 minutes. The brothers telegraphed their father in Ohio with their news and took their broken Flyer to Dayton.

  Why did the Wrights, bicycle makers from an Ohio town, succeed in less than five years after they ordered information on flight from the Smithsonian? Because they started from the first principles and studied in detail the accomplishments and mistakes of their immediate predecessors. Because they combined good understanding of what was known at that time about the aerodynamics with practical tests and continuous adjustments of this knowledge. Because they aimed to produce a machine that would not only lift off by its own power but that would be also properly balanced and could be flown in a controlled manner. There is no doubt that the matters of aerodynamic design and flight control were a much greater challenge than coming up with an engine to power the flight, although they did that, too (Culick 1979; Wright 1953).

  What is so remarkable about the Wrights’ accomplishment is that they designed the plane’s every key component—wings, balanced body, propellers, engine—and that in order to do so they prepared themselves by several years of intensive theoretical studies, calculations, and painstaking experiments with gliders that were conducted near Kill Devil Hills between 1901 and 1903. And after getting negative replies from engine manufacturers whom they contacted with specifications required for their machine, the Wrights designed the engine themselves, and it was built by their mechanic, Charles Taylor, in just six weeks. This was by no means an exceptional engine. Indeed, as Taylor noted later, it “had no carburettor, no spark plugs, not much of anything…but it worked” (cited in Gunston 1986:172).

  The four-cylinder 3.29-L engine lied on its side, its body cast of aluminum and its square (10 X 10 cm) steel cylinders were surrounded by water jackets, but the heads were not cooled, so the engine got progressively hotter and began losing its power. The crankshaft was made from a single piece of steel; one of its ends was driving the camshaft sprocket, and the other one the flywheel and two propeller chain sprockets. The Wrights’ initial aim was to get 6 kW, but they did better: the finished engine weighed 91 kg; at first it developed 9.7 kW, and at Kitty Hawk it was rated as high as 12 kW—this unexpected performance gave it a mass/power ratio as low as 7.6 g/W. The brothers applied for a patent on March 23, 1903, nine months before the Flyer took off, and received a standard reply that the U.S. Patent Office was sending to many similar applications: an automatic rejection of any design that had not already flown. Their patent (U.S. Patent 821,393) was granted in May 1906, and, expectedly, it was commonly infringed and ignored. The key patent drawing shows no engine, just the detailed construction of wings, canard, and the tail (figure 3.23).

  Afterward, as with the development of automobiles, there was a pause in development. The Wrights did not do actually any flying in 1906 and 1907 while there were building six or seven new machines. But starting in 1908, the tempo of aeronautic advances speeded up noticeably, with new records set after just short intervals. In September 1908, Wilbur Wright stayed over Le Mans for 91 minutes and 25 seconds, covering nearly 100 km, and during that year’s last day he extended the record to 140 minutes. Louis Blériot (1872–1936)—an engineer whose first unsuccessful flying machine built in 1900 was an engine-powered ornithopter designed to fly by flapping its wings—crossed the English Channel by flying from Le Borques to Dover on July 25, 1909, in 37 minutes. This flight, worth £1,000 from London’s Daily Mail, was done by a monoplane of his own design, the fourth such machine since he built the world’s first single-winged aircraft in 1907 (see figure 7.1).

  FIGURE 3.23. Drawing of the Wrights’ flying machine that accompanied their U.S. Patent 821,393 filed on March 23, 1903. This drawing is available at http://www.uspto.gov.

  Everything of importance was improving at the same time. The Wrights’ first plane was a canard (tail-first) and a pusher (rear engine) with skids, and its engine was stationary with in-line cylinders. But soon there was a variety of propulsion, tail, and landing gear designs as well as the tendency toward a dominant type of these arrangements, and in-line stationary engines were replaced by radial machines (Gunston 1999). The Antoinette—an engine designed by Léon Levavasseur and named after the daughter of his partner—was originally built for a speedboat, but between 1905 and 1910 it became the most popular radial (eight cylinders arranged in 90o V) engine, and its very low mass/power ratio (less than 1.4 g/W) remained unsurpassed for 25 years.

  The first successful rotary engine (with the crankshaft rigidly attached to the fuselage, and cylinders, crankcase, and propeller rotating around it as one unit) was the Gnome, a 38-kW machine designed in France by Séguin brothers in 1908 and whose improved versions powered many fighter planes during WWI (Gunston 1986). Ovington (1912:218) called it “theoretically one of the worst designed motors imaginable, and practically the most reliable aeroplane engine I know of.” Other rotary engines followed soon afterward, including the Liberty, the most popular engine of WWI whose mass/power ratio was just above 1 g/W. Before 1913, there were also planes with shock absorbers and with simple retracting landing gear, as well as the first machines (in 1912) with monococque (single-shell) fuselage that was required for effective streamlining and was made of wood, steel, or aluminum. Hoff (1946:215) captured the speed of these advances, and the driving force behind them, by noting that in the early 1900s “the only purpose of the designer was to build an airplane that would fly, but by 1910 military considerations became paramount.”

  France—where Alberto Santos Dumont (1873–1932), an avid and famously flamboyant Brazilian airship pioneer, made his first flight in a biplane of his own design in 1906—led this military development. By 1914 the country had about 1,500 military and 500 private planes, ahead of Germany (1,000 military and 450 private). Much like with cars, early development of American military airpower was slow. The U.S. Army bought a Wright biplane in 1908, but little progress was achieved even by April of 1917 when the United States declared war on Germany: at that time the country had only two small airfields, 56 pilots (and 51 students), and fewer than 300 second-rate planes, none of which could carry machine guns or bombs on a combat mission (USAF Museum 2003). Only in July 1917 did the Congress approved the largest ever appropriation sum ($640 million, or about $8 billion in 2000 US$) to build 22,500 Liberty engines; by October 1918 more than 13,000 of them were built.

  But it was an American pilot who demonstrated for the first time a capability that eventually became one of the most important tools in projecting military power. On November 14, 1910, Eugene Ely (1886–1911) took off with a Curtiss biplane from the USS Birmingham to complete the first ship-to-shore flight, and less than 10 weeks later, on January 18, 1911, he took off from the Tanforan racetrack and landed on an improvised deck of cruiser Pennsylvania anchored in the San Francisco Bay (see figure 6.8). Thirteen years later the Japanese built the world’s first aircraft carrier, and it was the destruction of their carrier task force by three American carrier air groups during the battle of Midway between June 4 and 7, 1942, that is generally considered the beginning of the end of Japan’s Pacific empire (Smith 1966).

  Of course, both the pre-WWI and the dominant WWI (wood-steel-fabric) airplane designs were constrained by many limitations. Most obviously, in order to minimize the drag (an essential consideration given the limited power of early aeroengines), structural weight had to be kept to minimum and thin wings (maximum thickness to length ratio of 1:30), be they on mono- or biplanes, had to be braced. This requirement disappeared only with the adoption of light alloys (Hoff 1946), and today’s largest passenger planes have unbraced cantilevered wings, some as long as 50 m. These structures are designed to withstand considerable vertical movements:
even seasoned air travelers may get uncomfortable as they watch a wingtip rising and dipping during the spells of high turbulence.

  American airpower lagged in WWI, but an unprecedented mobilization of the country’s resources made it globally dominant during WWII. Some P-51 Mustangs, perhaps the best combat aircraft of WWII with engines that rated as high as 1.1 MW, had maximum level speed just over 700 km/h (Taylor 1989). That was the pinnacle of reciprocating engines. Jet propulsion eliminated them first from combat and long-distance passenger routes and soon afterward from all longer (generally more than two hours) flights. But reciprocating engines still power not only those nimble, short-winged machines that perform amazing feats of aerial acrobatics at air shows but also airplanes that provide indispensable commercial and public safety services (Gunston 2002). These range from suppressing forest fires (Canadian water bombers are the best) and searching for missing vessels to seeding Californian or Spanish rice fields, from carrying passengers from thousands of small airports (Canadian Bombardier Industries and Brazilian Embraer are now the main contenders in this growing market) to applying pesticides to food and feed crops.

  And before leaving the world of engines for the world of new materials and new syntheses that follows in chapter 4, I should mention that even Diesel’s inherently heavier machine did eventually get light enough to power airplanes. The first success came in 1928 with Packard DR-980, a 168-kW radial engine that weighed only 1.4 g/W, that set a new world record of keeping a plane aloft (circling above Jacksonville) without refueling for 84 hours (Meyer 1964). Diesel engines were eventually installed on German WWII bombers, and recently lightweight diesels have become finally available to the general aviation market. In 2002 the Socieétée de Motorisations Aeéronautiques (SMA) received the FAA certification for its SR305 diesel engine, which weighs only 1.29 g/W (i.e., no more than typical modern gasoline-fueled aeroengines) and is suitable for installation in such small single-engine airplanes as Cessna, Piper, or Socata (SMA 2003). In the U.S. Delta Hawk and Continental Motors are working on similar engines.