Fuel economy in aircraft
[citation needed] By increasing efficiency, a lower cruise-speed augments the range and reduces the environmental impact of aviation.
Another analysis from 2014 compared the Airbus 320 from 2009 with a hypothetical turboprop successor flying at a 33% lower Mach number, concluding that the slower aircraft would have 36% less fuel consumption.
In other words, subsonic turboprop aircraft would be more profitable than transonic turbofan aircraft even at current energy prices without additional costs related to climate action like emission fees, aviation fuel taxation or higher prices for sustainable aviation fuels compared to fossile kerosene.
To obtain a longer range, a larger fuel fraction of the maximum takeoff weight is needed, adversely affecting efficiency.
[11] Very long non-stop passenger flights suffer from the weight penalty of the extra fuel required, which means limiting the number of available seats to compensate.
In the late 2000s/early 2010s, rising fuel prices coupled with the Great Recession caused the cancellation of many ultra-long haul, non-stop flights.
[14][15] But as fuel prices have since decreased and more fuel-efficient aircraft have come into service, many ultra-long-haul routes have been reinstated or newly scheduled[16] (see Longest flights).
[20][21][verification needed] Jet fuel cost and emissions reduction have renewed interest in the propfan concept for jetliners with an emphasis on engine/airframe efficiency that might come into service beyond the Boeing 787 and Airbus A350XWB.
NASA has conducted an Advanced Turboprop Project (ATP), where they researched a variable-pitch propfan that produced less noise and achieved high speeds.
Air density decreases with altitude, thus lowering drag, assuming the aircraft maintains a constant equivalent airspeed.
However, air pressure and temperature both decrease with altitude, causing the maximum power or thrust of aircraft engines to reduce.
[citation needed] Since early 2006 until 2008, Scandinavian Airlines was flying slower, from 860 to 780 km/h, to save on fuel costs and curb emissions of carbon dioxide.
[20] In 2014, MSCI ranked Ryanair as the lowest-emissions-intensity airline in its ACWI index with 75 g CO2-e/revenue passenger kilometre – below Easyjet at 82 g, the average at 123 g and Lufthansa at 132 g – by using high-density 189-seat Boeing 737-800s.
[30] Key drivers for efficiency were the air freight share for 48%, seating density for 24%, aircraft fuel burn for 16% and passenger load factor for 12%.
[41] By taking advantage of wake updraft like migrating birds (biomimicry), Airbus believes an aircraft can save 5-10% of fuel by flying in formation, 1.5–2 nmi (2.8–3.7 km) behind the preceding one.
[42] Certification for shorter separation is enabled by ADS-B in oceanic airspace, and the only modification required would be flight control systems software.
[51] Concorde, a supersonic transport, managed about 17 passenger-miles to the Imperial gallon, which is 16.7 L/100 km per passenger; similar to a business jet, but much worse than a subsonic turbofan aircraft.
For the 787, this is achieved through more fuel-efficient engines and lighter composite material airframes, and also through more aerodynamic shapes, winglets, more advanced computer systems for optimising routes and aircraft loading.
[53][verification needed] A life-cycle assessment based on the Boeing 787 shows a 20% emission savings compared to conventional aluminium airliners, 14-15% fleet-wide when encompassing a fleet penetration below 100%, while the air travel demand would increase due to lower operating costs.
[118] While this shows the capabilities of the vehicles, the load factors (percentage of seats occupied) may differ between personal use (commonly just the driver in the car) and societal averages for long-distance auto use, and among those of particular airlines.
NASA and Boeing flight-tested a 500 lb (230 kg) blended wing body (BWB) X-48B demonstrator from August 2012 to April 2013.
[122] The BWB concept offers advantages in structural, aerodynamic and operating efficiencies over today's more-conventional fuselage-and-wing designs.
These features translate into greater range, fuel economy, reliability and life-cycle savings, as well as lower manufacturing costs.
The International Air Transport Association (IATA) technology roadmap envisions improvements in aircraft configuration and aerodynamics.
It projects the following reductions in engine fuel consumption, compared to baseline aircraft in service in 2015:[126] Moreover, it projects the following gains for aircraft design technologies:[126] Today's tube-and-wing configuration could remain in use until the 2030s due to drag reductions from active flutter suppression for slender flexible-wings and natural and hybrid laminar flow.
[127] Large, ultra high bypass engines will need upswept gull wings or overwing nacelles as Pratt & Whitney continue to develop their geared turbofan to save a projected 10–15% of fuel costs by the mid-2020s.
[127] NASA indicates this configuration could gain up to 45% with advanced aerodynamics, structures and geared turbofans, but longer term suggests savings of up to 50% by 2025 and 60% by 2030 with new ultra-efficient configurations and propulsion architectures: hybrid wing body, truss-braced wing, lifting body designs, embedded engines, and boundary-layer ingestion.
[127] By 2030 hybrid-electric architectures may be ready for 100 seaters and distributed propulsion with tighter integration of airframe may enable further efficiency and emissions improvements.
[127] Research projects such as Boeing's ecoDemonstrator program have sought to identify ways of improving the fuel economy of commercial aircraft operations.
[citation needed] Multiple concepts are projected to reduce fuel consumption:[128] The growth of air travel outpaces its fuel-economy improvements and corresponding CO2 emissions, compromising climate sustainability.
