C.R. Smith, impresario of American Airlines, wanted an even bigger, faster version of the DC-2. A fuselage that was enlarged to accommodate railroad-style sleeper berths morphed into a 21-passenger “dayliner”—the inimitable, indomitable DC-3, which entered service in 1936. With improved engines, twice the passenger capacity of the 247, and an extremely cost-efficient design, the DC-3 flew into aeronautical immortality. Along with its larger, four-engine successors, the DC-3 had wing flaps for added lift during takeoff and landing. By the early 1940s, even larger airliners appeared with pressurized cabins, tricycle landing gear, improved de-icing equipment, autopilot systems, and other technologies that enhanced passenger comfort and safety as well as aircraft reliability and efficiency. By 1943, the Lockheed L-049 Constellation, with its distinctive triple vertical tail, epitomized the era of modern airliners that transformed both wartime air transport and postwar airline transportation.
While enormous strides were being made in fixed-wing design, by the late 1930s Russian émigré Igor Sikorsky had perfected the prototype of the modern helicopter, with a powered rotor overhead to provide both lift and forward thrust and a tail rotor to counteract the main rotor’s torque. The helicopter’s unique ability to hover and its performance in the Pacific theater of World War II won wider acceptance for the rotorcraft, and this was followed by their dramatic success in evacuating casualties during the Korean War in the 1950s.
During the decades of the 1920s and 1930s, as Sikorsky was fleshing out his ideas, a host of suppliers, vendors, and institutional organizations appeared—forming an infrastructure essential to supporting a growing industry. Traditional manufacturers like Westinghouse, AC Spark Plug, Bendix, Standard Oil, and others moved into the flying game. In the late 1920s, Edwin Link scrounged some bellows, push rods, and linkages from his father’s pipe organ company and built a usable flight simulator. At first, only amusement parks showed much interest, but by the late 1930s, the threat of war triggered a surge of military orders. EDO Corporation, named for Earl Dodge Osborn, started to build pontoons for floatplanes in 1925. As a diversified aerospace supplier, EDO continued to flourish in the following years as a fabricator of such military products as under-wing pylons that carry fuel tanks and assorted ordnance. In 1923, Osborn helped launch Aviation magazine, and served as its publisher until he sold it to McGraw-Hill in 1929.The periodical eventually became Aviation Week & Space Technology, the premier source for aerospace news. In 1933, a professional society of engineers organized as the Institute for Aeronautical Sciences and later became the American Institute of Aeronautics and Astronautics. Businesses and organizations like these proved invaluable in meeting crucial challenges of World War II.
Props hit a wall
But aircraft had hit a speed limit. Propellers were limited at high speeds because when their blades moved at supersonic speeds, they lost thrust. A few mavericks began to consider alternative power plants, including gas turbines. In England, Frank Whittle initiated a dogged research program in the face of nearly universal skepticism—until 1937, when he demonstrated a design that compressed air by spinning it centrifugally. The path of technological evolution in one community can often be plotted in other, equally capable research-and-development groups. Working with no knowledge of Whittle’s work, Hans von Ohain, a German, developed a similar engine that powered the first jet airplane, the Heinkel He 178, which flew in 1939. Research in the United States into the new propulsion technology languished despite the fact that a related technology had proved successful: turbosuperchargers.
In April 1941, when U.S. Army Air Forces General Henry “Hap” Arnold paid a visit to England, he was startled to learn of a prototype jet—the Gloster E28/39—then undergoing taxi tests. An irritated Arnold returned home, asking pointed questions about the U.S. aviation community’s obvious lack of progress in jet propulsion. In the end, concerned that the technology would fall into German hands, the British furnished U.S. industry with a Whittle engine, blueprints, and eventually a visit by Whittle himself to explain how everything worked. General Electric won the contract to construct modified versions of the Whittle jet engine. These early turbojets powered the first U.S. combat jets, such as the Lockheed P-80 Shooting Star and the Grumman F9F Panther. Later in the war, Germany developed the more successful axialflow jet engine—its compressor used propellerlike vanes to drive the air in a straight path along the axis of the engine. During the course of Operation Paperclip, which the United States mounted at war’s end to harvest advanced German research and key personnel, much of this technology arrived on U.S. shores, where it provided the foundations for similar American designs and became the configuration used in all modern jet engines.
In addition to jet engines, German legacies included significant verification of the viability of swept-back wings. During World War II, high-performance fighters in 500-mph dives began to encounter severe—and sometimes disastrous—aerodynamic buffeting. Wind tunnel tests revealed that shock waves appeared on aircraft surfaces at about Mach 1—the speed of sound. Some aerodynamic adjustments helped—Lockheed gave the P-38 a set of dive flaps to recover the craft from the Mach effect—but fliers also simply had to avoid excessive speeds. In the postwar era, as jet engines led to designs for even faster aircraft, understanding and coping with what came to be called the “sound barrier” became a paramount challenge. Some aerodynamicists had been thinking about this problem since German researcher Adolph Busemann presented a paper in 1935 at a Rome conference on high-speed flight. Busemann said that when exposed to shock waves trailing from the airplane’s nose at very high speeds, an “arrow” wing would produce less drag than a straight wing. Airplanes of the mid-1930s flew too slowly to encounter sonic buffeting, so his paper received little attention until German aircraft with jet and rocket engines entered service during World War II.
Ironically, the rocket-propelled Bell XS-1, which in 1947 became the first airplane to break the sound barrier, had straight wings. Because its configuration evolved before theories of swept wings had become well known, designers carefully gave the wings a thin cross-section, using thicker wing skins to provide needed load-bearing qualities at supersonic speed. The overall shape of the XS-1, including its rather blunt nose, reflected what was known about the aerodynamic qualities of a .50-caliber bullet; the airplane’s job was to fill in massive gaps of information about the dynamics of aircraft cleaving the air beyond the speed of a gunshot. America’s nimble shift to swept wings relied in part on key contributions from a Russian immigrant and a maverick aerodynamicist at the NACA’s Langley center. A man named Jones At work for Republic Aviation (founded by fellow Russian immigrant Alexander de Seversky), Michael Gluhareff concluded that a triangular, or delta, wing had great potential at sonic speed. World War II diverted his attention, but a wind tunnel model wound up on the desk of the NACA’s Richard Jones. A college dropout, Jones had flown with a barnstorming troupe and eventually wound up in a New Deal-era work program at Langley, where he blossomed into a highly regarded engineer. Examining the Gluhareff model and test documents, Jones realized that recent mathematical formulas and tunnel data sustained the postulates that swept wings are better performers at sonic speeds. When the German work on swept wings came to light during Operation Paperclip, the NACA and the Air Force adroitly exploited the convergence of these lines of investigation. The Boeing B-47 bomber and the North American F-86 fighter, both flown in 1947, acquired swept wings and a configuration that set the pattern for a host of postwar bomber, transport, and fighter designs. The swept-wing North American F-100 Super Sabre, which first flew in 1953, became the first U.S. fighter to crack the sound barrier in level flight. During the 1960s, swept wings and speeds around Mach 2 became the norm.
Military programs like the Convair F-102 interceptor and B-58 supersonic bomber also relied heavily on newfangled management approaches. Exceedingly complex, such aircraft were designed from scratch with aerodynamic framework, avionics, engines, armament, payload, and maintenance all considered as part of an organic whole—in other words, a weapon system. Systems management required new levels of documentation and bureaucratic expertise. In the cold war era, such aerial weapons usually evolved in the context of what was considered a national emergency—catching up to or gaining an advantage over the Soviets. It took years for the protracted design-build-test-accept sequence to produce an airplane. “Concurrency” became the watchword, with construction of production facilities, tooling, and other fabrication requirements running in parallel with design and test of the airplane itself.
As high-speed aerodynamics evolved, designers wrestled with problems involving the performance of Mach 2 fighters; aerodynamic forces on ailerons, rudders, and elevators were too great for the pilot. Mechanical and hydraulic systems solved some problems, but they added weight and complexity to airframes and were vulnerable to hostile fire. Moreover, modern aircraft, like sensitive racehorses, had a certain degree of inherent instability; this enhanced their agility in combat and reduced the size and weight of their control surfaces. To manage control dilemmas, designers sought a solution using computers and electronic systems: “Fly-by-wire” technology replaced mechanical cables and linkages to control surfaces with slim electrical cables carrying signals to actuators that moved ailerons, rudders, and elevators. The pilot's joystick was no longer directly connected to the surfaces it controlled—except by electrical impulses. During the 1970s, a series of NASA test programs involving a converted Vought F-8 Crusader supersonic fighter led the way to the first successful fly-by-wire control systems. In the case of the Lockheed F-117A Nighthawk fighter and Northrop’s B-2 Spirit bomber, stealth technology dictated designs for completely unstable aircraft. Without the computerized flyby-wire systems, these aircraft would have been unflyable.
A new class of aircraft, unmanned aerial vehicles, or UAVs, completed the evolutionby ushering in a total reliance on computers and fly-by-wire technology. The genre began as drones during World War I—like torpedoes with a biplane’s wings and tail—and by the time of the Vietnam War, remotely piloted vehicles, or RPVs, had jet engines and carried electronic surveillance gear. The subsequent generation of UAVs included quiet, propeller-driven designs like the General Atomics Predator and jet-powered, long-endurance types like the Northrop Grumman Global Hawk, which operates at high altitudes and carries an impressive array of video cameras and ultrasensitive electronics. Some UAVs toted missiles, while others took on such challenges as trans-Pacific journeys from the U.S. West Coast to Australia.