Essentials of Supersonic Commercial Aircraft Conceptual Design. Egbert Torenbeek

Torenbeek's book, which starts with a chapter on Concorde's development and service. Torenbeek believes that “a new generation of supersonic passenger aircraft could have a commercial future a decade from now”. From this the author takes his motivation. He writes for a potential engineering team producing a conceptual design for a supersonic airliner. For his wider readership Torenbeek digests the best of the available literature and puts it together in a concise form. He draws his own books and papers on aircraft design and quotes authors that were on the forefront of supersonic aerodynamics: L. Prandtl, J. Ackeret, M.M. Munk, T. Von Kármán, A. Busemann, D. Küchemann, R.T. Jones and J.D. Anderson Jr. Moreover, some knowledge from the ESDU Data Sheets is used. Although many books are available about supersonic aerodynamics and supersonic design, Torenbeek puts all this together and writes about supersonic commercial aircraft design. In Chapter 8 about aerodynamic efficiency of supersonic cruise vehicle configurations, the pros and cons of configurations are compared, in particular the aft tail, foreplane and tailles designs. Clearly, the book has an aerodynamic focus as the aircraft cruise speed is supersonic, but the aerodynamic aspects are always discussed from a design perspective. This is especially true for Chapter 3 about weight sensitivity and energy efficiency, where Torenbeek starts this item with the first law of aircraft design, which states that the sum of the payload fraction, the empty weight fraction and the fuel fraction is equal to one. This equation also shows that not every design problem will have a solution if technology parameters for lightweight design and/or fuel weight are suitable. In the case of the Concorde, the maximum payload is only 6%, its empty weight fraction is 44%, and the relative fuel mass fraction is 50%. This is not a favorable comparison with the relative 25% for subsonic short‐range passenger aircraft and 10% for subsonic long‐range aircraft.

In Chapter 4 Torenbeek writes: during the development of the Concorde, devoted proponents suggested that the fuel efficiency at supersonic speed is not very different from the fuel efficiency at subsonic speed, arguing that that the deterioration of the deterioration of L/D at supersonic speed caused by supersonic wave drag is compensated by the high Mach number. Here the proponents used the term ML/D as the factor determining the fuel efficiency. Torenbeek points out that this is not correct since the total effects should be determined by the Breguet range equation, specifying that the range is proportional to ML/D divided by the specific fuel consumption TSFC of the installed engines, which is considerably higher at supersonic speed compared to subsonic speed. The author celebrated this year his 80th birthday and this foreword would be incomplete without looking back at his achievements. Egbert Torenbeek studied at the Delft University and graduated with a degree in aeronautical engineering. In 1961 he took the Guided Missiles Course at the College of Aeronautics in Cranfield (UK) which was followed by his military service in the Dutch Air Force from 1962 to 1963. He supervised a teaching course in the TU Delft to start working under Hans Wittenberg, professor of aircraft design. Torenbeek supervised a teaching course and concluded that there existed no up‐to‐date handbook on aircraft design. So, he collected information that had been published up to 1970, when passenger airplanes such as the DC‐8, the Boeing 707 and the Lockheed Tristar were already operational and Concorde had made its first flight. After about six years of work the book Synthesis of Subsonic Aircraft Design was published by the Delft University Press in 1982 and is presently distributed by Springer. After a sabbatical period of nine months in 1977 at Lockheed Georgia (USA), Torenbeek became full professor in 1980. In 1993 he had the leadership of the EXTRA 400 conceptual design, which was made with the engineering help of tests in the wind tunnel carried out at the TU Delft. The LBA Type Certificate was obtained in 1997. Torenbeek was the co‐founder of the European Workshop on Aircraft Design Education (EWADE), which is held every two years and included one day for informal discussions where new ideas were discussed in a nice setting. The Journal Aircraft Design was started by Elsevier in 1998. Egbert Torenbeek and Jan Roskam acted as editors in chief. Torenbeek served two years as vice‐rector and continued as professor emeritus. His early retirement was closely related to political discussions in the wake of Fokker's bankruptcy. In 2000 he received an honorary doctorate from the Moscow Aviation Institute, which he sent back in 2014 as an act of protest immediately after the MH17 disaster. The book Flight Physics (co‐authored with H. Wittenberg) was published by Springer in in 2009. His book Advanced Aircraft Design was published in 2013 by Wiley and translated into the Chinese language. In 2013 the Aircraft Design Award from the American Institute of Aeronautics and Astronautics (AIAA) was given to Torenbeek and in 2016 he received the Ludwig Prandtl Ring from the German Society for Aeronautics and Astronautics, which is awarded for an outstanding contribution to the field of aerospace engineering. Torenbeek presently acts as Honorary Guest Editor for the Continuous Special Issue Aircraft Design of the journal Aerospace at MDPI.

      What will the future bring for supersonic commercial transport? Several supersonic business jets are in the design stage, whereas several such projects have already been given up. It is difficult to get the economics right. Development costs to cope with technological challenges will be high and numbers produced in the end will be rather limited. Currently, the US law prohibits supersonic flight over land unless authorized by the FAA for purposes stated in the regulations. There are supersonic rule‐making activities, but none of them would rescind the prohibition of supersonic flight over land. Environmental questions remain due to high fuel consumption in the stratosphere and the considerable take‐off noise produced by Concorde will have to be considerably reduced, although the last chapter promises to have a possible solution for the conceptual design problem. First of all, it is important to understand the essential conceptual design concepts. This book by Egbert Torenbeek delivers this knowledge.

      Prof. Dr.‐Ing. Dieter Scholz MSME. Hamburg University of Applied Sciences Hamburg

      1 June 2019

Series Preface

      The field of aerospace is wide ranging and covers a variety of products, disciplines, and domains, not merely in engineering but in many related supporting activities. These combine to enable the aerospace industry to produce exciting and technologically challenging products. A wealth of knowledge is contained by practitioners and professionals in the aerospace fields that will benefit other practitioners in the industry, and to those entering the industry from University.

      The Aerospace Series aims to be a practical and topical series of books aimed at engineering professionals, operators, users, and allied professions such as commercial and legal executives in the aerospace industry. The range of topics is intended to be wide ranging covering design and development, manufacture, operation, and support of aircraft as well as topics such as infrastructure operations, and developments in research and technology. The intention is to provide a source of relevant information that will be of interest and benefit to all those people working in aerospace.

      This book extends the author's previous excellent and informative treatises on concept design to focus on supersonic transport aircraft for commercial use. The heady days of supersonic aircraft designs from the UK, USA, and USSR are long gone with the demise of SST for a number of programme and operational reasons, largely related to operating and support costs. A surge in leisure and business travel together with savage competition to reduce ticket prices led to the emergence of very large aircraft and ETOPS which made long distance travel relatively comfortable and affordable. This, and an increase in e‐commerce and environmental concerns, seemed to indicate that the days of supersonic business travel would never return. However, modern business and diplomacy still requires face to face discussions and rapid responses that can be made easier with supersonic travel, so there is a potential market, if not for mass travel then certainly for business users for whom time is valuable.

The author has taken a practical view of the possible re‐emergence of supersonic transport by examining the history of the previous projects and the lessons to be learned from that era. He has developed this by considering contemporary circumstances that have an impact on concept design, such as modern design methods, modern materials, modern aircraft shapes, and environmental issues. This provides a fund of invaluable experience and material for concept