Fuel economy in aircraft

The fuel economy in aircraft is the measure of the transport energy efficiency of aircraft. Efficiency is increased with better aerodynamics and by reducing weight, and with improved engine BSFC and propulsive efficiency or TSFC. Endurance and range can be maximized with the optimum airspeed, and economy is better at optimum altitudes, usually higher. An airline efficiency depends on its fleet fuel burn, seating density, air cargo and passenger load factor, while operational procedures like maintenance and routing can save fuel. Average fuel burn of new aircraft fell 45% from 1968 to 2014, a compounded annual reduction 1.3% with a variable reduction rate. In 2018, CO2 emissions totalled 747 million tonnes for passenger transport, for 8.5 trillion revenue passenger kilometres (RPK), giving an average of 88 grams CO2 per RPK (this represents g of fuel per kilometre, or a fuel consumption per passenger, on average. The worst-performing flights are short trips of from 500 to 1500 kilometres because the fuel used for takeoff is relatively large compared to the amount expended in the cruise segment, and because less fuel-efficient regional jets are typically used on shorter flights. New technology can reduce engine fuel consumption, like higher pressure and bypass ratios, geared turbofans, open rotors, hybrid electric or fully electric propulsion; and airframe efficiency with retrofits, better materials and systems and advanced aerodynamics. A powered aircraft counters its weight through aerodynamic lift and counters its aerodynamic drag with thrust. The aircraft's maximum range is determined by the level of efficiency with which thrust can be applied to overcome the aerodynamic drag. A subfield of fluid dynamics, aerodynamics studies the physics of a body moving through the air. As lift and drag are functions of air speed, their relationships are major determinants of an aircraft's design efficiency. Aircraft efficiency is augmented by maximizing lift-to-drag ratio, which is attained by minimizing parasitic drag and lift-generated induced drag, the two components of aerodynamic drag.