Technological Development of Transport Aircraft-Past and Future

I is common to study the history of a technology with a growth curve showing the annual production vs time. Growth usually starts slowly, as only the bold and/or the rich can afford, psychologically and financially, to explore the new invention. Then if the product is useful, acceptance grows exponentially. Increased production lowers costs, further accelerating the demand. Eventually, the market is saturated and demand slows to the replacement market. The technology is said to have matured. A major improvement, such as the development of color capability in television, may start the cycle over again. In addition to charting production and popular acceptance in this manner, technical progress can be similarly displayed. Figure 1 shows the speed history of transport aircraft. From 1928 to 1958, speed increased fivefold; the beginning of the jet age in 1958, however, established speed levels that have shown little change in the past 20 years. We have known how to increase speed above the typical airline cruise Mach numbers of 0.80-0.84 for decades, but we have not known how to substantially increase these speeds while simultaneously complying with the other major aircraft trend characteristic, namely, ever decreasing cost. Figure 2 shows the relative direct operating cost per seat mile from the DC-3 in 1936 to the Boeing 747 and DC-10 of the present. The standard 707/DC-8 aircraft have a relative cost value of 1.0. This chart has been constructed on an approximate constant dollar basis by using the cost ratios between one aircraft and the one proceeding it, as determined at the time of the aircraft's development. The smaller aircraft, such as the DC-9-30, show costs for their own shorter ranges which are similar to the larger aircraft with the same technology at the same short range, but only because they are designed for these much shorter ranges. Normally, increasing size decreases seat-mile cost up to 350-400 passenger capacities, after which this trend flattens out. The trend toward improved operating cost is strong and steady with only the Boeing Stratocruiser, the DC-7, and the Comet rising above the curve. The message to be learned from 50 years of aircraft history is clear. Successful aircraft have almost always had equal or lower operating cost compared to their predecessor, while offering service improvement in either speed, range, comfort, or combinations of them. In some cases, they have offered a significantly different size suitable to certain markets. The exceptions have offered a unique service at a moderately higher (10-15%) direct operating cost—and their success was generally limited. The rapid improvement in speed, the main commodity offered by aircraft, together with comparable gains in range and comfort, and the cost decrease led to the huge growth in air travel shown in Fig. 3 from Ref. 2 and in aircraft capacity shown in Fig. 4 from Ref. 1. As an industry, we became accustomed to rapid technical progress, imposing technological functional obsolescence on each succeeding type within two to seven years. Table 1 shows the chief technological developments that enabled each generation to reign supreme—although usually only for a brief period. Not listed specifically but continuing throughout the entire period have been significant improvements in airfoil design, flap systems, structural materials, and increasingly sophisticated methods of detail design and manufacture. The enormous contributions of avionics to aerial navigation, both en route and in the terminal area, were essential to the growth and safety of the air transport system. Great strides have been made in the electrical, hydraulic, pneumatic, and mechanical systems, which have permitted greater capability with reduced weight and exceedingly high reliability. But from the overall airplane design point of view, the items listed in Table 1 were most significant in making each succeeding design possible. Except for the World War II period, a first-line aircraft held that position for no more than six to seven years. Technological functional obsolescence was the way of life