Millionaire aviator Howard R. Hughes and four crew members took off from Floyd Bennett Field, New York, in a Lockheed 14 Super Electra twin-engine transport on July 10, 1938. Three days, nineteen hours, and fourteen minutes later, the silver monoplane, named the New York World's Fair 1939, had covered 14,824 miles in a round-the-world flight that symbolized the imminent arrival of the futuristic “World of Tomorrow” that the exposition celebrated. The NAA awarded Hughes and his crew the 1938 Collier Trophy for their well-executed long-range flight that highlighted innovations in navigation, communications, and engineering and illustrated overall the superiority of American aeronautical technology. Hughes “praised highly” the two Hamilton Standard Hydromatic constant-speed propellers, which had only become available just a few months before the flight. Hughes's flight marked the arrival of a modern and refined airplane, propeller and all, in its most complete form.

Spectacular intercontinental flights such as Lindbergh's solo Atlantic crossing in 1927, the Uiver in the MacRobertson Race in 1934, and Hughes's around-the-world flight were indications that the aeronautical community expanded its conception of the synergistic system of the commercial and military airplane. Such spectacular uses of the airplane led many in the United States to believe that a new era in history, an Air Age of peace, unlimited progress, and opportunity for humankind, was just around the corner. The world's other aeronautical nations demonstrated the promise of aviation in different ways during the late 1930s. For Nazi Germany, the airplane was a potent technological symbol of fascism. Great Britain used commercial and military airplanes to connect its far-flung global empire.

The constant-speed propeller was a central technology in these modern airplanes. It was the ultimate form of a variable-pitch mechanism because it changed blade pitch automatically according to varying flight conditions while the engine speed remained the same, which maximized propeller, engine, and fuel economy and offered hands-off operation. Proposed first by Hele-Shaw and Beacham in 1924, not a single one had flown on an operational airplane in Europe or North America in the decade that followed. National aeronautical communities in the United States, Nazi Germany, and Great Britain approached this next step in different ways in the 1930s.

When I was a small boy, my parents gave me a little wood airplane with a big red plastic propeller. Holding the fuselage in one hand, I turned the propeller to wind up the rubber band “engine.” The power of the rubber band spun the propeller and I could feel a breeze flow over my airplane until I let it go. If I did not wind enough, the airplane would jump and skid along the ground, unable to take off. If I wound too much, the propeller would “race” and the airplane would vibrate and careen out of control. I spent hours in our backyard learning how to wind the propeller so my airplane would fly straight and level.

During one of our many family visits to museums and air shows during my childhood, I got close to some of my favorite airplanes. One of those was the Curtiss Jenny, a fabric-covered biplane that the wandering barnstormers flew from town to town across America in the 1920s selling rides to brave and curious folks. As I looked at the Jenny's wood propeller, I could see a long, flat curve that moved all the way along its length, from the tip at one end, through the hub in the center, and on to the tip at the other end. This aerodynamic twist, called pitch, gave the propeller its shape and allowed it to turn the engine's power into thrust – the “breeze” created by my toy airplane – to propel the Jenny forward.

Another favorite was the Douglas DC-3 airliner from the 1930s. The DC-3 was a very different airplane than the Jenny. It was a sleek twin-engine monoplane capable of carrying twenty-one passengers. Unlike my toy airplane and the Jenny, each of its two propellers had three shiny metal blades that could change pitch in flight. When needed, the propellers generated a lot of thrust for takeoff and prevented “racing” as the DC-3 cruised through the sky. The technical transformation, or reinvention, of the airplane propeller – from the one found on the Jenny to the advanced design installed on the DC-3 – by a community of specialists and what it had to do with increasing the performance of aircraft over the course of the twentieth century is the focus of this book.

During the early winter of 1955, well-known travel writer William W. Yates of the Chicago Daily Tribune paused to reflect on the state of commercial aviation in the ten years since the end of World War II. Every five seconds saw the takeoff of a propeller-driven airliner on a long-distance flight that would take passengers and cargo across continents and oceans. Flying through all types of weather to one of the 3,500 international airports around the world was as routine as driving a car along Lake Shore Drive in Chicago. More than 324 million passengers had taken flight since 1945. Propeller-driven airliners had turned the “ocean of the air” into a “highway for the traffic of all nations.” Yates acknowledged that aircraft capable of flying “higher, faster, and farther” made that worldwide travel revolution possible. The technology at that crucial intersection of altitude, speed, and range found in modern high performance aircraft since the 1930s was the propeller.

As one of the most important innovations of the Aeronautical Revolution, the variable-pitch propeller was a transformative technology that made the modern airplane a weapon of war and instrument of global travel through the rapid onset of the Air Age during the 1940s and 1950s. That triumph was the result of the perseverance of propeller specialists over the preceding two decades. Ironically, within twenty years after World War II, a significant portion of the aeronautical community and society in general came to consider the propeller an obsolete relic of aviation's past. The variable-pitch propeller was no longer a technology capable of making commercial and military airplanes fly even higher, faster, and farther. With the introduction of the jet, a new cultural resistance against the continued use and further refinement of the propeller emerged.

Modern Propellers at War

During the 1940s, nations in Asia, Europe, and North America fought each other around the world with airplanes that were, at their technical foundations, the product of the interwar period. The Aeronautical Revolution of the 1920s and 1930s created the modern airplane and World War II solidified its position as a global technology. It was clear that the revolution in propeller design and construction was well over by the spring of 1941.

The first variable-pitch propeller developed in the United States took to the air over southern California as America entered World War I in April 1917. Pioneer aviator Earl S. Daugherty flew his Daugherty-Stupar Tractor biplane with a variable-pitch propeller designed by Los Angeles inventors Seth Hart and Robert I. Eustis (Figure 7). Starting off with a low pitch setting for high thrust, he gradually increased the pitch of the propeller to generate more speed as the plane leveled off over the airfield. Daugherty was “very much impressed” with the propeller's effect on his airplane's performance. The new propeller was controlled manually by the pilot, meaning that it relied on a series of mechanical linkages and the strength of the pilot to change the pitch. Daugherty's flights were the American propeller community's first steps toward developing a practical variable-pitch mechanism. That work, combined with the efforts of other experimenters in North America and Europe, met varying degrees of success between 1917 and 1927.

World War I served as a catalyst for the reinvention of the airplane in Europe and the United States, but the path and direction that new technology would take, as well as the nature of the organizations that used it, were not clear. In the United States, the newly created Army Air Service was at a crossroads regarding the primary role of military aviation in the postwar period. A tension existed between the old Army leadership, who favored using airplanes in a supplementary tactical role, and the youthful Air Service officers who sought to create an entirely new military doctrine based on strategic bombing. As this internal battle played out, the Army Air Service's strategy was to focus on wide-ranging improvements that enhanced the speed, range, load, and maneuverability of observation airplanes, bombers, fighters, transports, trainers, even airships. One of the key technologies for the service's future airplane – no matter what its role – would be the propeller.

The aeronautical community was aware of the potential value of controllable and reversible variable-pitch propellers. Controllable-pitch mechanisms offered enhanced operating performance and fuel economy at the different operating regimes of takeoff and cruise for both single- and multiengine aircraft.

Just as the American aviation industry started to grow in the wake of ground-breaking government legislation and Lindbergh's transatlantic flight, the stock market crash of October 1929 and the Great Depression threatened its continued existence. The newly formed Hamilton Standard Propeller Corporation, suffering from dwindling military and commercial contracts, scrambled for a new product to sustain itself. Chief engineer, Frank Caldwell, designed a hydraulic two-position, controllable-pitch, or hydro-controllable, propeller that promised to increase Hamilton Standard's place in the aviation marketplace. His new propeller used the engine's oil supply and centrifugal force exerted by counterweights to keep the blades at the desired pitch during flight. Eugene E. Wilson, the president of Hamilton Standard, knew instantly the propeller was an innovation the corporation desired and was looking for, which in his words, was “the answer to a maiden's prayer.” He enthusiastically supported the development of the two-position, controllable-counterweight design, which was an extreme financial undertaking during the Great Depression. The innovation was both an investment in the further improvement of the airplane and the financial fortunes of the company.

The creation of an industrial propeller community within the context of the emergence of the modern aviation corporation in the late 1920s made the variable-pitch propeller possible. Overall, from the end of World War I to the mid-1920s, the foundation of the American aviation industry changed from one that traced back to individual pioneers such as Wilbur and Orville Wright and Glenn Curtiss to one based on a mainstream American corporate model characterized by heavy Wall Street involvement. The modern variable-pitch propeller required the necessary managerial, financial, technical, and personnel infrastructure that only a corporate environment could provide, but that in turn meant the innovation had to have the potential for financial success. An understanding of that vital interrelationship is crucial to a broader understanding of the development of aeronautical technology in the 1920s and 1930s.

The momentum begun by government aviation legislation and the technical and symbolic success of Lindbergh's transatlantic flight contributed to the creation of modern aviation corporations in the United States in 1929. The struggling aviation industry, a collection of small businesses catering to a limited specialty market, underwent a period of rapid growth marked by consolidation into corporations with impressive financial, technical, and managerial resources.

Aviation journalist Carl Dienstbach traveled to Dayton in July 1905 to interview the world's leading aeronautical technologists. Beginning in 1896, Wilbur and Orville worked to invent the first airplane through a synergy of the technical systems of lift, control, structures, and propulsion, which culminated in the December 17, 1903 flight of their Flyer at Kitty Hawk, North Carolina. In the process, Wilbur and Orville created the first practical, efficient, and purpose-built aerial propellers and a design theory to support them. Acknowledging their ability to design an efficient propeller according to their aerodynamic principles, Wilbur still recognized the limitations of their invention. He informed Dienstbach that “the best propeller for starting is not the best for flying.” The elder Wright's statement highlighted the fact that the technology that turned the engine's power into thrust and enabled aircraft to take to the air was far from meeting the needs of aviation.

The Wrights were the leading members of a distinct community of American and European technologists that created the airplane in the late nineteenth century. Their efforts provided the basis from which modern flight evolved. They chose the wood, fixed-pitch propeller as its standard through their adherence to the already established design paradigms of light weight and simplicity. At the same time, this early flight community took the Wrights’ original creation and attempted to change its composition as well as its ability to alter pitch.

The Early History of the Propeller

The idea of how an airplane propeller might work existed for centuries in human history. The Greek mathematician and engineer Archimedes described a method of transporting water uphill through the helical motion of his “water screw” during the third century BCE. The emergence of propeller-like windmills in Western Europe in the twelfth century CE indicated a reverse understanding of the principles and capabilities of thrust. Their builders used wind-driven wood-framed and fabric-covered blades, called sails, to create power for agricultural purposes. The inventor-philosopher-artist Leonardo da Vinci sketched an “aerial screw” in the late fifteenth century that was a precursor of the helicopter. Though mainly conceptual, these ideas influenced the development of both marine and aerial propellers. Seagoing ships, lighter-than-air balloons and airships, and the fanciful flying machines from the late eighteenth and nineteenth centuries all featured various forms of propellers.