The early aircraft were limited in speed, range, and payload and were unable to fly in bad weather. Their reliability and safety were such that early aviators, like today's astronauts, were regarded as daredevils and heroes; early passengers were regarded as somewhat foolhardy for risking their lives. But the dream of fast transportation of mail and passengers by aircraft persisted. Private persons, newspapers, and aviation clubs sponsored well-publicized competitions with substantial monetary rewards to spur aircraft engineers and pilots to achieve such goals as building an aircraft capable of flying nonstop from New York to Paris. Governments, through their military agencies, set challenging performance specifications for new types of aircraft for manufacturers to produce.
In the mid-1930s several important technological advances occurred: the development of reliable, high-power, lightweight, radial, air-cooled piston engines, such as the Wright Whirlwind and Pratt & Whitney Wasp; the introduction of the variable-pitch metal propeller, which offered efficiencies at both takeoff and cruise; the development of the retractable undercarriage, which reduced cruise drag; the use of duralumin alloys to construct stiff, all-metal, lightweight shell structures for fuselages and wings; the invention of the electronic autopilot for cruise flight; and the use of wind tunnels for fuselage, wing, and engine design.
These technologies were all used on the Douglas DC-3, the first profitable passenger aircraft in U.S. domestic air transportation without airmail subsidies from the federal government. It rapidly became the predominant U.S. domestic transport aircraft, and in 1938 it carried 95% of all U.S. passengers. During World War II it became the ubiquitous military transport aircraft for the Allies when over 10,000 were constructed for all theaters of war. About half of these were converted to civil transports by the end of 1946, to become the initial transport aircraft for many airlines all around the world. Some 50 years later they are still in commercial service.
The DC-3 was powered by two 1,200-horsepower Pratt & Whitney engines and cruised at 180 miles (290 km) per hour at altitudes of up to 10,000 feet (3,000 meters). It had an unpressurized cabin, carrying 21 passengers over a nonstop distance of 700 miles (1,125 km). Its productivity was 3,780 seat-miles per hour, triple the productivity values of prior aircraft. Profitable domestic airfares dropped in 1938 to 52 cents per passenger mile (all dollar amounts are in terms of 1990 dollars). The remarkable increase in aircraft productivity owing to continuing technological advances over the next 40 years is the key factor in the corresponding reductions in airfares.
The pioneering aircraft for intercontinental air service, the S-42, also appeared in 1935. It was the first of the "Clipper" flying boats built for Pan American World Airways by the Sikorsky division of United Aircraft. In the years 1935–1938 it opened new long-distance routes to Bermuda, South America, and Europe and across the Pacific to China and New Zealand.
The Sikorsky S-42B had four 750-horsepower Pratt & Whitney Hornet engines and cruised at 155 miles (250 km) per hour over a range of 1,200 miles (1,930 km). It could carry 32 passengers in eight separate compartments that could be converted to provide 14 berths, since some of the flight stages were over 20 hours in length. The advantage of the flying boat was that by using existing harbors and lagoons it made unnecessary the building of new airports.
In 1939 Pan American initiated service on both the Pacific and Atlantic routes, using the largest aircraft built up to that time, the Boeing 314 flying boat. It had four 1,500-horsepower Wright Cyclone engines capable of carrying 74 passengers on two decks. It had 40 berths, a separate dining room capable of seating 15, and a honeymoon suite with private bath, and it cruised at 165 miles (265 km) per hour over a range of 3,100 miles (4,490 km). During World War II these aircraft provided long-distance transport for military and political leaders.
But the flying boat disappeared after the war, supplanted by pressurized long-range transports with four turbocharged piston engines. These aircraft operated from the many new airports with long, paved runways constructed all over the world during the war. They cruised at 15,000 to 25,000 feet (4,600 to 7,600 meters) at 270 to 300 miles (435 to 485 km) per hour. They could seat 60 to 90 and had a range of over 4,000 miles (6,500 km), allowing nonstop flights across the Unites States and the North Atlantic and one-stop flights across the Pacific.
Typical of these aircraft was the Lockheed Constellation (the "Connie"), which introduced nonstop transcontinental service in 1947. It cruised at 270 miles per hour at 22,000 feet (6,700 meters), using on-board weather radar to fly above and around bad weather. It carried 64 passengers over 3,000 miles (4,800 km), and its productivity was more than four times that of the DC-3. Average domestic yields were almost halved, dropping to 28 cents per passenger mile. In the 1950s a new class of service was introduced, called coach or economy class, which offered spartan cabin service and substantially reduced fares in order to attract the "nonbusiness" traveler.
In 1952 British Overseas Airline Corporation introduced the first jet transport aircraft, the de Havilland Comet, on the old "Imperial" routes to Egypt, South Africa, and India. This aircraft was a radical innovation, increasing speeds to 490 miles (790 km) per hour, cruising at 30,000 to 35,000 feet (9,100 to 10,700 meters), and carrying 36 passengers some 2,100 miles (3,375 km). Planned during the war, the Comet was the British answer to the U.S. aircraft manufacturers, but it suffered a series of tragic accidents traced later to catastrophic metal-fatigue failures of the thin skins of the pressurized cabin at cruising altitudes. The aircraft was grounded for over two years, and the hiatus in its program allowed Douglas and Boeing to offer the DC-8 and B-707 aircraft, respectively. These were to become the spearhead aircraft of the worldwide transition of air transportation into the jet age.
The technologies that allowed the radical jump from piston to jet aircraft were the subsonic aerodynamics of swept wings and the development of fuel-efficient jet engines that thrived on operating in the cold, thin air of the stratosphere. At a true airspeed of 550 miles (885 km) per hour at 40,000 feet (12,290 meters), the modern jet transport is indicating an airspeed of only 275 miles (443 km) per hour because of the reduced air density. This is the secret of high-speed subsonic air travel: the reward for climbing to reach the cold (−58° F, or −50° C), thin air (one-quarter sea level density) is that both drag and fuel consumption are reduced by one-quarter.
The Boeing 707 was the first of a long series of successful aircraft that have made the Boeing Commercial Aircraft Company of Seattle, Wash., the dominant manufacturer of jet transports since 1960. The company has consistently captured a 60% share of world production measured in sales volume. The initial versions of the B-707, introduced in the early 1960s, cruised at 35,000 feet at a speed of 550 miles per hour, carrying up to 180 passengers over 3,600 miles (5,800 km). Its productivity was 99,000 seat-miles per hour, quadrupling the values of the earlier piston transports. Average yield in the 1960s was reduced by 30% to roughly 20 cents per passenger mile, and the airlines began marketing air services to leisure travelers at a variety of discount fares.
Because of its cruising efficiencies, the jet transport was initially considered appropriate only for long-haul services, but in 1964 Boeing introduced a short- to medium-haul trijet, the B-727, which carried up to 150 passengers over ranges of 2,500 miles (4,000 km). The B-727-200 became the standard transport for all domestic airlines in the 1970s, allowing a complete transition to jet service on most routes. It introduced new aerodynamic technology in the form of leading and trailing edge wing flaps that produced very high lift for takeoff and landing and reduced the required length of runways, allowing it to operate from most of the smaller cities and airports around the United States. Another technological improvement that became increasingly apparent in the 1960s was the unusual reliability of the jet engine. There were significant decreases in the cost of maintaining jet engines by eliminating unnecessary preventive maintenance.
The next step in the evolution of jet transport aircraft came with the introduction of "wide-body" or "jumbo-jet" aircraft during the 1970s. Boeing built the four-engine B-747 aircraft for long-haul international service for Pan American. Douglas and Lockheed introduced the DC-10 and Lockheed L-1011, respectively, in response to a competition initiated by American Airlines. While the wide bodies were no faster, capacities and productivity were doubled. These craft, with their twin aisles and modern (if not luxurious) high-technology atmosphere (even in coach), did much to build public confidence and interest in flying.
The technology that made the wide bodies possible was the result of intense government research directed at producing the high-thrust, turbofan engine necessary for a very large military cargo aircraft, the C-5, that would allow the rapid deployment of troops and equipment from the United States to any point in the world. These "high-bypass ratio" fan engines are now the standard type of engine for all new subsonic jet transports, since they simultaneously provide much more thrust at takeoff with much less noise and significantly improve cruise fuel consumption. Improved materials technology was able to provide the high-temperature alloys required for the core of these engines.
The DC-10-10 is a typical wide-body jet transport in domestic service. It carries up to 350 passengers over 2,760 miles (4,440 km) at 550 miles per hour, doubling productivity and (by 1978) reducing the average domestic yield to 17 cents per passenger mile.
Having failed to achieve success in the subsonic jet transport market, the British and French governments joined forces in the 1960s to produce the world's first supersonic transport (SST), the Concorde. Although the U.S. Congress refused in 1974 to fund a similar SST project, the Concorde development continued, and the world's first SST service was introduced by the national airlines of Britain and France in 1976. The Concorde cruises at 60,000 feet (18,300 meters) at a speed of 1,300 miles (2,100 km) per hour (twice the speed of sound), carrying 100 passengers over the North Atlantic with a range of up to 3,800 miles (6,100 km). While it is deemed a technical and operational success, it has been (as predicted) an economic failure, carrying less than 1% of North Atlantic traffic even though its high fares are set to recover only its marginal operating costs.
In the 1990s the Boeing B-747-400 is the premier transport aircraft for all long-haul international routes. It has only two pilots, seats up to 450 passengers, and flies nonstop over 8,200 miles (13,200 km). Its productivity is 250,000 seat-miles per hour, and it has proved a very profitable aircraft. A single nonstop round-trip on the Los Angeles–Sydney route produces more than $1 million of revenue (in less than 36 hours) at an operating cost of less than $300,000.
While the advancement of aeronautical technologies created expanded air transportation around the world, the increase of jet operations also created severe noise and environmental problems for the communities near major airports. Airport noise became an important political issue in the 1970s, resulting in the closing of many airports to night operations. Strong opposition arose to the expansion of existing airports or the construction of new commercial airports anywhere near the cities they were intended to serve. As a result, many cities experienced shortages of airport capacity as well as congestion and delays during busy periods of the year.
A three-stage international program was instituted by the ICAO to limit the takeoff and landing noise of new jet aircraft and to phase out the older, noisier aircraft. Fortunately, the high-bypass turbofan engine was amenable to various noise suppression techniques, which allowed the noise "footprint" of newer and larger transport aircraft to be reduced significantly. Designing new airports that are environmentally sound is still a worldwide problem.
