Answer The emerging effects of research and technology programs on airframes and engines will influence future fleets of subsonic aircraft. A group of aerospace industry experts has developed some technology projections relating to fuel efficiency and NO x emissions of aircraft by the years 2015 and 2050. The corresponding scenarios for improvement between 1997 and 2050 involved two different technology scenarios to take account of tradeoffs between fuel efficiency and low NO x in aircraft designs. New commercial supersonic transport aircraft, operating at speeds of Mach 2 to 2.4, have been proposed for introduction into service, though not before 2015. It now seems unlikely that any commercial supersonic transports will exceed flight speeds of Mach 2.5 within the next 50 years as a result of engineering problems, materials limits, fuel efficiency, and other economic considerations.
Supersonic aircraft are intrinsically less fuel efficient than subsonic aircraft.
They consume about twice as much fuel, on a passenger-kilometer basis, as subsonic aircraft of the same size and range. To minimize stratospheric ozone depletion, the major design criteria for supersonic aircraft focus on flight altitude and low NO x output. Water vapor emissions may become more important than NO x emissions. If so, control of H 2 O emissions will depend solely on the achievement of greater fuel efficiency. Sulfur aerosols originating in the fuel are an emerging concern in the altitude bands used by supersonic aircraft.