The fuel economy in aircraft is the measure of the transport energy efficiency of aircraft.
Fuel efficiency is increased with better aerodynamics and by reducing weight, and with improved engine brake-specific fuel consumption and propulsive efficiency or thrust-specific fuel consumption.
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.
Refuelling an Airbus A320 with biofuel
A Boeing 787-8 of Norwegian Long Haul
An Airbus A330-300 of Thai Airways at Tokyo Narita
The earliest jet airliner, the de Havilland Comet
A propfan, also called an open rotor engine, open fan engine or unducted fan, is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed and performance of a turbofan, with the fuel economy of a turboprop. A propfan is typically designed with a large number of short, highly twisted blades, similar to the (ducted) fan in a turbofan engine. For this reason, the propfan has been variously described as an "unducted fan" (UDF) or an "ultra-high-bypass (UHB) turbofan".
A mockup of the GE36 at the Musée aéronautique et spatial Safran
The GE36 on a McDonnell Douglas MD-80 demonstrator at the 1988 Farnborough Air Show. The gearless unducted fan engine had an overall diameter of 11.67 ft (3.56 m), with either eight or ten blades in front (depending on the particular configuration) and eight blades in back.
The Progress D-236 propfan engine on the Yak-42E-LL testbed aircraft at the Paris Air Show in 1991
Progress D27 Propfans fitted to an Antonov An-70