Jet Propulsion A Simple Guide to the Aerodynamics and Thermodynamic Design and Performance of Jet Engines

Introduction

This chapter returns to some general issues related to both civil and military engines. These are topics which can be more satisfactorily addressed with the background of earlier chapters.

Civil aviation and the environment

The choice of aircraft here, the New Efficient Aircraft, was predicated on the need to reduce fuel burn. The cruise Mach number was lower than current new large aircraft and the full payload maximum range, R1, was distinctly smaller than recent designs of aircraft offered for sale. The small reduction in speed would have little effect on the passenger and the vast majority of flights currently offered would be accommodated with the reduced range. The industry as a whole does not seem willing to embrace this approach to reducing fuel burn, even though fuel is now a major cost, perhaps 40% of the direct costs. No aircraft flying in 2015 has been designed with fuel cost approaching the values currently prevailing and expected in the future. Despite the relatively high cruise Mach numbers and long R1 ranges being offered, most people nevertheless agree that global warming mitigation demands a reduction in CO2 emissions.

ICAO have come forward with a metric for fuel burn but, as described in Chapter 1, this is not well conceived if the object is to display the relative efficiency of different aircraft and aircraft types in moving people or freight. Now ICAO has to decide how to turn this metric into regulations for fuel burn. The earliest these regulations could begin to affect new aircraft types is probably 2020 with existing types several years later. It seems unlikely, however, that this will matter very much, for there is already major economic pressure to reduce mission fuel burn. The situation with fuel and CO2 is quite unlike other areas in which ICAO is involved as setter of regulations, such as noise (discussed in the Appendix) and pollutants (like NOx, discussed in Chapter 11). Without regulations of some sort there would be no incentive for an airline to reduce these noise and NOx because there is no direct cost.