Page 37 - Spring 2015

Figure 2. Nature of the sonic boom ground footprint for a transat- lantic flight by the Concorde. See text for description. ∆p, Difference between the sonic boom pressure and the ambient pressure. From Maglieri et al. (2014).
The French aircraft flew supersonic on October 1, 1969. In the interim, development costs had increased significantly. This, along with the cancellation of the US SST in 1971 and the oil crisis in 1973 (Concorde’s fuel consumption was about 16 passenger miles per gallon compared with about 54 passenger miles per gallon of fuel for the Douglas DC-10), resulted in only 20 aircraft being built; 6 were prototypes and the other 14 Anglo-French-built Concordes were placed in commercial service with 7 each being assigned to British Airways and Air France.
Since the first commercial passenger carrying flight in 1976, these 14 aircraft flew a combined total of some 240,000 hours. The highest number of hours flown by any one Con- corde per year was 926, which is low in comparison to some 2,000-3,000 hours flown by subsonic long-haul transports. It is estimated that one-third of all Concorde flight hours were flown at Mach 2. Thus, the Concorde fleet would have accu- mulated some 80,000 supersonic flight hours, more than the combined total of all of the world’s military aircraft.
Much has been written about the Concorde highlighting high-ticket, operational, and maintenance costs; low utiliza- tion; high development and subsidy costs; its sonic boom; and its excessive airport community noise. However, as stated by McLean (1985, p. 58), “In spite of being cast as a transportation ‘heavy’ by critics around the world, the Brit- ish/French Concorde ranks as one of the foremost technical achievements that has ever been made. The two nations that developed this aircraft not only spoke different languages, but also used different measurement systems. Yet, out of this unusual alliance came the first and, so far, only commercial
supersonic transport in regular passenger service. Like it or not, the Concorde is a remarkable airplane. It reduced the trip times between continents to one-half of those of the best subsonic jet transports, an accomplishment that would have been cheered in bygone years. The Concorde is perhaps the world’s most tested transport airplane and, in its operations to date, has experienced no major accidents and has had no passenger fatalities.”
Concorde’s exemplary safety record ended tragically with the crash of Air France flight 053 on July 25, 2000 (Riding, 2000). The accident marked the beginning of the end for the Concorde and commercial supersonic travel.
sonic boom footprint
Considerable criticism about the Concorde derived from the sonic boom trail it imposed along the ground during its supersonic flight. The nature of the sonic boom ground foot- print for a flight such as that of the Concorde, during which the aircraft cruises supersonically for a large portion of the distance, is shown in Figure 2. Two ground exposure pat- terns in which booms are observed are shown.
The primary sonic boom “carpet” is the region on the ground ensonified by the part of the sonic boom that propagates di- rectly downward from the aircraft to the ground. It begins with the transition focus boom region resulting from accel- eration of the aircraft from subsonic to supersonic speeds. This focus is a one-time occurrence; it does not move with the aircraft and is unavoidable. It is followed by the N-wave boom signatures produced during the climb-and-cruise phase of flight. (The pressure waveform of the carpet boom has the shape of the letter “N” as seen in Figures 2 and 3.) The primary carpet booms are observed shortly after the passage of the aircraft and result from wave propagation through only that part of the atmosphere below the aircraft. The secondary boom “carpet” is the region on the ground ensonified by the boom that initially goes upward from the aircraft but is refracted back to the ground by winds in the stratosphere above the plane. Between the primary and sec- ondary carpets exists a region in which no booms are ob- served. The secondary booms arrive some 10-15 minutes af- ter the passage of the aircraft, and these disturbances tend to be very weak in intensity (on the order of 1-10 pascals versus around 100 pascals for the primary booms) but persist over longer periods of time (on the order of 5-10 seconds).
The manner in which the atmosphere above and below the aircraft is involved in developing the primary and secondary boom carpets is shown in the ray diagram in Figure 4. On
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