Essentials of Supersonic Commercial Aircraft Conceptual Design. Egbert Torenbeek

Figure 1.3 Configuration of the Boeing 2707‐300. Courtesy: Boeing.

Others held the opinion that economic disadvantages and reordering of US national priorities were the major causes for the cancellation of the SST program. Meanwhile, a new generation of very large transonic airliners was under development in the USA and in fact many considered the Boeing 747 as a direct (in‐house) competitor of the 2707.

1.3 Transonic Transport Configuration Studies

The history of near‐sonic cruise airliner designs dates back to the late 1950s. One of the concepts discussed by the British STAC was the M‐wing layout depicted in Figure 1.4, which was considered as an alternative to the slender wing. This novel configuration was primarily aimed at allowing cruise speeds near Mach 1.2 over land without producing a sonic boom. The M‐wing incorporated highly swept thin wing segments with

forward sweep inboard and

aft sweep outboard in combination with an area‐ruled fuselage1. Other design aspects were aimed at avoiding the poor aerodynamic efficiency and flying qualities at low speeds of a highly sweptback wing. The unusual inboard forward sweep was intended to compensate for the outboard sweep and the relatively high aspect ratio should contribute to avoiding the high vortex‐induced drag of a slender wing. The STAC rejected the M‐wing concept since the arguments in favor of a more ambitious Mach 2.0 cruise speed that dominated in the decision‐making process. Renewed interest in the development of transonic transport began in the mid 1960s when Boeing and Lockheed generated a series of study layouts based on highly swept wings and area‐ruled fuselages. These concepts complied with the principles of transonic flight successfully applied to fighters designed in the 1950s and the technology of supercritical wing sections developed at NASA‐Langley. It was also realized that a transport aircraft flying at Mach 1.12 in the standard atmosphere could fly without producing a sonic boom at ground level. Since wind and non‐standard temperatures change the boomless cruise speeds between Mach 1.05 and 1.25, a typical cruise speed for transonic flight is Mach 1.20. However, the irregular floor plan due to the mid‐cabin body waist made it difficult to configure the cabin according to the manner that individual customers would like, and thus formed an enduring drawback of this airplane concept.

Figure 1.4 The M‐wing layout for cruising at Mach 1.20, generated by the STAC in 1956.

By the early 1970s it was recognized that the higher fuel prices and risk of a transonic airplane development outweighed its potential benefits, an opinion that was widely held throughout the mid‐1990s. Around the year 2000 Boeing marketed a concept that was designed for extended ranges greater than 17,000 km, flying at cruise speeds of Mach 0.95 or above. It was derived from “slowing down” supersonic configurations rather than “speeding up” conventional subsonic configurations and became known as the “Sonic Cruiser”. This project came to an end after the events of September 2001, when airlines that were enthusiastic about the Sonic Cruiser initially were struggling for their survival.

1.4 US High Speed Research and Development Programs

During the 1970s and 1980s several projects of the American industry were aimed at investigating applications of NASA research of advanced supersonic configurations. Study projects were part of the supersonic cruise aircraft research (SCAR) program, focusing on a second generation of supersonic airliners transporting some 300 passengers over trans‐Pacific routes at speeds up to Mach 2.70. The SCAR Program was brought to an end by the marginal performance and economic potentials that appeared possible with the then available technology base. A resurgence of interest in a second‐generation high‐speed commercial transport (HSCT) occurred during the 1990s in Europe, the USA and Asia. Projections in 1989 for the 1995–2015 period indicated that the market in terms of passenger miles would increase by a factor of six (relative to 1971–1989) in the North‐Mid Pacific and by a factor of seven in the Far East. Based on these projections, a potential market for approximately a thousand HSCT aircraft was foreseen in 1989, well over the minimum needed for a a profitable development program launch. NASA studies concluded that a supersonic transport launched in the early 21st century could be compatible with current airports, use jet fuel, and be within ten to fifteen years' technology reach.

      In 1989 NASA and the US industry began investigating the potential of HSCT specifications and required technologies. The original SST of the 1960s was planned for Mach 2.70 but the required titanium structure was too heavy, and the HSCT program of Boeing and McDonnell Douglas converged on a more modest Mach 2.40, 300 seat, 9,270 km range jet A fueled aircraft as a focus for technology development. The challenges facing the HSR program were the extremely restrictive constraints placed on emissions, airfield noise, and operation costs. After approximately five years of research it was concluded that insufficient advancement in technology was available to achieve economic viability and to comply with environmental requirements. In particular an acceptable level of the sonic boom could not be achieved and the program was terminated in 1998.

Figure 1.5 Design study of the European Supersonic Commercial Transport.

      

1.5 European Supersonic Research Program

Similar to the US studies during the 1990s, the European industry indicated a market potential for an aircraft substantially larger and with longer longer range than the Concorde, linking the world's major cities. In 1990 the companies Aerospatiale, British Aerospace, and Deutsche Airbus launched a three‐year study into the technical feasibility of a second‐generation supersonic transport successor of the Concorde. In 1994 the Supersonic Research Program (ESRP) was established to undertake the research and technology development required to produce the enabling technologies for second generation supersonic commercial transport. The ESRP was supported by a common reference configuration known as the European Supersonic Commercial Transport (ESCT). Its main characteristics are compared with those of the Concorde and the Tu 144 in Table 1.1.

Table 1.1 Characteristics of the first generation supersonic transport and the ESCT

		Concorde	Tu‐144	ESCT
Maximum take‐off mass	tonnes	185	200	320
Range	km	6,200	3,500	10,000
Span	m	25.6