Fuel economy in aircraft
in aircraft is a measure of how much fuel an aircraft, or a fleet of aircraft of mixed types, needs to operate in relation to a service provided and the distance between points of travel. It can be expressed in several ways, for example by the liters of fuel consumed per passenger per kilometer.
Flight efficiency theory
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.Aerodynamics
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. As parasitic drag increases and induced drag decreases with speed, there is an optimum speed where the sum of both is minimal; this is the best glide ratio. For powered aircraft, the optimum glide ratio has to be balanced with thrust efficiency.
Parasitic drag is constituted by form drag and skin-friction drag, and grows with the square of the speed in the drag equation. The form drag is minimized by having the smallest frontal area and by streamlining the aircraft for a low drag coefficient, while skin friction is proportional to the body's surface area and can be reduced by maximizing laminar flow.
Induced drag can be reduced by decreasing the size of the airframe, fuel and payload weight, and by increasing the wing aspect ratio or by using wingtip devices at the cost of increased structure weight.
Design speed
By increasing efficiency, a lower cruise-speed augments the range and reduces the environmental impact of aviation; however, a higher cruise-speed allows more revenue passenger miles flown per day.Jet engine efficiency increases with velocity because the speed difference between the flight and the exhaust is lower. However, above the drag divergence Mach number, the aerodynamic drag on the airframe overwhelms this effect because supersonic shockwaves begin to form, greatly increasing drag and needing supercritical airfoil designs for transonic flight.
For supersonic flight, drag increases at Mach 1.0 but decreases again after the transition. With a specifically designed aircraft, such as the Aerion AS2, the Mach 1.1 range at 3,700 nmi is % of the maximum range of 5,300 nmi at Mach 0.95, but increases to 4,750 nmi at Mach 1.4 for % before falling again.
Wingtip devices
s increase the effective wing-aspect ratio, lowering lift-induced drag caused by wingtip vortices and improving the lift-to-drag ratio without increasing the wingspan. Airbus installed wingtip fences on its planes since the A310-300 in 1985, and Sharklet blended-winglets for the A320 were launched during the November 2009 Dubai air show. Their installation adds but offers a 3.5% fuel burn reduction on flights over.Weight
As the weight indirectly generates lift-induced drag, its minimization leads to better aircraft efficiency. For a given payload, a lighter airframe generates a lower drag. Minimizing weight can be achieved through the airframe's configuration, materials science and construction methods. To obtain a longer range, a larger fuel fraction of the maximum takeoff weight is needed, adversely affecting efficiency.The deadweight of the airframe and fuel is non-payload that must be lifted to altitude and kept aloft, contributing to fuel consumption. A reduction in airframe weight enables the use of smaller, lighter engines. The weight savings in both allow for a lighter fuel load for a given range and payload. A rule-of-thumb is that a reduction in fuel consumption of about 0.75% results from each 1% reduction in weight.
The payload fraction of modern twin-aisle aircraft is 18.4% to 20.8% of their maximum take-off weight, while single-aisle airliners are between 24.9% and 27.7%. An aircraft weight can be reduced with light-weight materials such as titanium, carbon fiber and other composite plastics if the expense can be recouped over the aircraft's lifetime. Fuel efficiency gains reduce the fuel carried, reducing the take-off weight for a positive feedback. For example, the Airbus A350 design includes a majority of light-weight composite materials. The Boeing 787 Dreamliner was the first airliner with a mostly composite airframe.
Flight distance
For long-haul flights, the airplane needs to carry additional fuel, leading to higher fuel consumption. Above a certain distance it becomes more fuel-efficient to make a halfway stop to refuel, despite the energy losses in descent and climb. For example, a Boeing 777-300 reaches that point at. It is more fuel-efficient to make a non-stop flight at less than this distance and to make a stop when covering a greater total distance.-200 per distance
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. For such flights, the critical fiscal factor is the quantity of fuel burnt per seat-nautical mile. For these reasons, the world's longest commercial flights were cancelled. An example is Singapore Airlines' former New York to Singapore flight, which could carry only 100 passengers on the flight. According to an industry analyst, "It pretty much a fuel tanker in the air." Singapore Airlines Flights 21 and 22 were re-launched in 2018 with more seats in an A350-900ULR.
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. This included the services provided by Singapore Airlines from Singapore to both Newark and Los Angeles that was ended in late 2013. 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.
Propulsive efficiency
The efficiency can be defined as the amount of energy imparted to the plane per unit of energy in the fuel. The rate at which energy is imparted equals thrust multiplied by airspeed.To get thrust, an aircraft engine is either a shaft engine – piston engine or turboprop, with its efficiency inversely proportional to its brake-specific fuel consumption – coupled with a propeller having its own propulsive efficiency; or a jet engine with its efficiency given by its airspeed divided by the thrust-specific fuel consumption and the specific energy of the fuel.
Turboprops have an optimum speed below. This is less than jets used by major airlines today, however propeller planes are much more efficient. The Bombardier Dash 8 Q400 turboprop is used for this reason as a regional airliner.
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. For instance, Airbus has patented aircraft designs with twin rear-mounted counter-rotating propfans. Propfans are a more fuel-efficient technology than jet engines or turboprops. NASA has conducted an Advanced Turboprop Project, where they researched a variable-pitch propfan that produced less noise and achieved high speeds.
Operations
Speed
At constant propulsive efficiency, the maximum range speed is when the ratio between velocity and drag is minimal, while maximum endurance is attained at the best lift-to-drag ratio.Altitude
Air density decreases with altitude, thus lowering drag, assuming the aircraft maintains a constant equivalent airspeed. This means an aircraft may be more efficient at higher altitude. With increasing altitude, air pressure and temperature both decrease, causing the maximum power or thrust of aircraft engines to reduce. In a piston engine, this trend towards a decline in maximum power can be mitigated by the installation of a turbocharger. Decreasing air temperature with altitude increases thermal efficiency.Airlines
From 2010 to 2012, the most fuel-efficient US domestic airline was Alaska Airlines, due partly to its regional affiliate Horizon Air flying turboprops.In 2014, MSCI ranked Ryanair as the lowest-emissions-intensity airline in its ACWI index with 75 g -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. In 2015 Ryanair emitted 8.64 Bn t of for 545,034 sectors flown: t per average sector representing kg per 90.6 million passengers.
In 2016, over the transpacific routes, the average fuel consumption was 31 pax-km per L. The most fuel-efficient were Hainan Airlines and ANA with 36 pax-km/L while Qantas was the least efficient at 22 pax-km/L.
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%.
That same year, Cathay Pacific and Cathay Dragon consumed 4,571,000 tonnes of fuel to transport 123,478 million revenue passenger kilometers, or 37 g/RPK, 25% better than in 1998:.
Again in 2016, the Aeroflot Group fuel consumption is 22.9g/ASK, or per seat, per passenger at its 81.5% load factor.
Fuel economy in air transport comes from the fuel efficiency of the aircraft + engine model, combined with airline efficiency: seating configuration, passenger load factor and air cargo. Over the transatlantic route, the most-active intercontinental market, the average fuel consumption in 2017 was 34 pax-km per L. The most fuel-efficient airline was Norwegian Air Shuttle with 44 pax-km/L, thanks to its fuel-efficient Boeing 787-8, a high 85% passenger load factor and a high density of 1.36 seat/m2 due to a low 9% premium seating. On the other side, the least efficient was British Airways at 27 pax-km/L, using fuel-inefficient Boeing 747-400s with a low density of 0.75 seat/m2 due to a high 25% premium seating, in spite of a high 82% load factor.
In 2018, CO₂ emissions totalled 918 Mt with passenger transport accounting for 81% or Mt, for 8.2 trillion revenue passenger kilometres: an average fuel economy of g/RPK CO₂ - g/km of fuel
In 2019, Wizz Air stated a 57 g/RPK CO₂ emissions, 40% lower than IAG or Lufthansa, due to their business classes, lower-density seating, and flight connections.
Procedures
Airbus presented the following measures to save fuel, in its example of an A330 flying on a route like Bangkok–Tokyo: direct routing saves fuel by flying less; more fuel is consumed if flying below optimum altitude without vertical flight profile optimization; cruising 0.01 mach above optimum consumes more fuel; more fuel on board consumes more fuel while of unused potable water consumes more fuel.Operational procedures can save fuel for every 10-minute reduction in use of the Auxiliary power unit, with a reduced flap approach and with reduced thrust reversal on landing. Maintenance can also save fuel: more fuel is consumed without an engine wash schedule; with a slat rigging gap, with a spoiler rigging gap, and with a damaged door seal.
History
Past
Modern jet aircraft have twice the fuel efficiency of the earliest jet airliners. Late 1950s piston airliners like the Lockheed L-1049 Super Constellation and DC-7 were 1% to 28% more energy-intensive than 1990s jet airliners which cruise 40 to 80% faster. The early jet airliners were designed at a time when air crew labor costs were higher relative to fuel costs. Despite the high fuel consumption, because fuel was inexpensive in that era the higher speed resulted in favorable economical returns since crew costs and amortization of capital investment in the aircraft could be spread over more seat-miles flown per day.Productivity including speed went from around 150 ASK/MJ*km/h for the 1930s DC-3 to 550 for the L-1049 in the 1950s, and from 200 for the DH-106 Comet 3 to 900 for the 1990s B737-800.
Introduced in 1961, the Tupolev Tu-114 with up to 200 persons and a cruise burned 6.5 kg/km, at 11 L/km and per seat.
Today's turboprop airliners have better fuel-efficiency than current jet airliners, in part because of their propellers and turbines that are more efficient than those of the 1950s-era piston-powered airliners.
-300 is the most fuel-efficient, compared with the A319neo and Boeing 737 MAX 7
Jet aircraft efficiency is improving: between 1960 and 2000 there was a 55% overall fuel-efficiency gain. Most of the improvements in efficiency were gained in the first decade when jet craft first came into widespread commercial use. Between 1971 and 1998 the fleet-average annual improvement per available seat-kilometre was estimated at 2.4%. Nonetheless, from the 1960s to the present, total fleet emissions of the greenhouse gas have outpaced efficiency gains, due to growth in the air-travel market.
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. Airbus states a fuel rate consumption of their A380 at less than 3 L/100 km per passenger ; however this is for an unspecified number and configuration of seats. The maximum configuration is 850 economy passengers, but with a typical 525-seat multi-class configuration the fuel consumption is "comparable to that of a B747-400ER and even about 15% worse than a B777-300ER on a passenger-mile basis."
Lufthansa, when it ordered both, stated the Airbus A350-900 and the Boeing 777X-9 will consume an average of per passenger.
The Airbus A321 featuring Sharklet wingtip devices consume per person with a 200-seat layout for WOW Air.
Example values
The aviation fuel density used is 6.7 lb/USgal or 0.8 kg/l.Commuter flights
For flights of :| Model | First flight | Seats | Fuel burn | Fuel per seat |
| Antonov An-148 | 2004 | 89 | ||
| Antonov An-158 | 2010 | 99 | ||
| ATR 42-500 | 1995 | 48 | ||
| ATR 72-500 | 1997 | 70 | ||
| Beechcraft 1900D | 1982 | 19 | ||
| Bombardier CRJ100 | 1991 | 50 | ||
| Bombardier CRJ200 | 1995 | 50 | ||
| Bombardier CRJ700 | 1999 | 70 | ||
| Bombardier CRJ900 | 2001 | 88 | ||
| Bombardier Dash 8 Q400 | 1998 | 78 | ||
| Dornier 228 | 1981 | 19 | ||
| Dornier 328 | 1991 | 32 | ||
| Embraer Brasilia | 1983 | 30 | ||
| Embraer ERJ-135ER | 1998 | 37 | ||
| Embraer ERJ-145ER | 1995 | 50 | ||
| Saab 340 | 1983 | 32 | ||
| Saab 2000 | 1992 | 50 | ||
| Xian MA700 | 2019 | 78 |
Regional flights
For flights of| Model | First flight | Seats | Sector | Fuel burn | Fuel efficiency per seat |
| Airbus A319neo | 2015 | 144 | |||
| Airbus A319neo | 2015 | 124 | |||
| Airbus A320neo | 2015 | 154 | |||
| Airbus A321neo | 2015 | 192 | |||
| Antonov An-148 | 2004 | 89 | |||
| Antonov An-158 | 2010 | 99 | |||
| Boeing 737-300 | 1984 | 126 | |||
| Boeing 737-600 | 1998 | 110 | |||
| Boeing 737-700 | 1997 | 126 | |||
| Boeing 737 MAX 7 | 2017 | 128 | |||
| Boeing 737 MAX 7 | 2017 | 144 | |||
| Boeing 737-800 | 1997 | 162 | |||
| Boeing 737 MAX 8 | 2017 | 166 | |||
| Boeing 737-900ER | 2006 | 180 | |||
| Boeing 737 MAX 9 | 2017 | 180 | |||
| Boeing 757-200 | 1982 | 200 | |||
| Boeing 757-300 | 1998 | 243 | |||
| Bombardier CRJ100 | 1991 | 50 | |||
| Bombardier CRJ200 | 1995 | 50 | |||
| Bombardier CRJ700 | 1999 | 70 | |||
| Bombardier CRJ900 | 2001 | 88 | |||
| Bombardier CRJ1000 | 2009 | 100 | |||
| Airbus A220 100 | 2013 | 115 | |||
| Airbus A220 300 | 2015 | 140 | |||
| Airbus A220-100 | 2013 | 125 | |||
| Airbus A220-300 | 2015 | 160 | |||
| Bombardier Dash 8 Q400 | 1998 | 82 | |||
| Dornier 328 | 1991 | 31 | |||
| Embraer E-Jet E2-175 | 2020 | 88 | |||
| Embraer E-Jet E2-190 | 2018 | 106 | |||
| Embraer E-Jet E2-195 | 2019 | 132 | |||
| Embraer E-Jet-170 | 2002 | 80 | |||
| Embraer E-Jet-175 | 2005 | 88 | |||
| Embraer E-Jet-190 | 2004 | 114 | |||
| Embraer E-Jet-195 | 2004 | 122 | |||
| Embraer ERJ-135ER | 1998 | 37 | |||
| Embraer ERJ-145ER | 1996 | 50 | |||
| Pilatus PC-12 | 1991 | 9 | |||
| Saab 340 | 1983 | 31 | |||
| Saab 2000 | 1992 | 50 | |||
| Sukhoi SSJ100 | 2008 | 98 | |||
| Xian MA700 | 2019 | 78 |
Short-haul flights
For flights of :| Model | First flight | Seats | Fuel Burn | Fuel efficiency per seat |
| Airbus A319 | 1995 | 124 | ||
| Airbus A319Neo | 2015 | 136 | ||
| Airbus A320 | 1987 | 150 | ||
| Airbus A321-200 | 1996 | 180 | ||
| Airbus A330-200 | 1997 | 293 | ||
| Antonov An-148 | 2004 | 89 | ||
| Antonov An-158 | 2010 | 99 | ||
| Boeing 737-600 | 1998 | 110 | ||
| Boeing 737-700 | 1997 | 126 | ||
| Boeing 737-700 | 1997 | 128 | ||
| Boeing 737 MAX-7 | 2017 | 140 | ||
| Boeing 737-800 | 1997 | 162 | ||
| Boeing 737-800 | 1997 | 160 | ||
| Boeing 737-800W | 1997 | 162 | ||
| Boeing 737 MAX-8 | 2017 | 162 | ||
| Boeing 737-900ER | 2006 | 180 | ||
| Boeing 737-900ERW | 2006 | 180 | ||
| Boeing 737 MAX-9 | 2017 | 180 | ||
| Boeing 757-200 | 1982 | 190 | ||
| Boeing 757-200 | 1982 | 200 | ||
| Boeing 757-300 | 1998 | 243 | ||
| Airbus A220-100 | 2013 | 125 | ||
| Airbus A220-300 | 2015 | 160 | ||
| Airbus A220-300 | 2015 | 135 | ||
| Quest Kodiak | 2004 | 9 |
Medium-haul flights
For flights of. The larger end of this range includes transatlantic flights.| Model | First flight | Seats | Sector | Fuel burn | Fuel per seat |
| Airbus A320 | 1987 | 150 | |||
| Airbus A321NeoLR | 2016 | 154 | |||
| Airbus A330-200 | 1997 | 241 | |||
| Airbus A330-300 | 1992 | 262 | |||
| Airbus A330neo-900 | 2016 | 310 | |||
| Airbus A340-300 | 1992 | 262 | |||
| Boeing 737 MAX-8 | 2017 | 168 | |||
| Boeing 737 MAX-9 | 2017 | 144 | |||
| Boeing 747-400 | 1988 | 416 | |||
| Boeing 747-8 | 2011 | 467 | |||
| Boeing 757-200W | 1981 | 158 | |||
| Boeing 767-200ER | 1984 | 181 | |||
| Boeing 767-200ER | 1984 | 193 | |||
| Boeing 767-200ER | 1984 | 224 | |||
| Boeing 767-300ER | 1988 | 218 | |||
| Boeing 767-300ER | 1988 | 218 | |||
| Boeing 767-300ER | 1988 | 269 | |||
| Boeing 767-400ER | 1999 | 245 | |||
| Boeing 767-400ER | 1999 | 304 | |||
| Boeing 767-400ER | 1999 | 304 | |||
| Boeing 777-200 | 1994 | 305 | |||
| Boeing 777-200ER | 1996 | 301 | |||
| Boeing 777-300 | 1997 | 368 | |||
| Boeing 787-8 | 2009 | 291 | |||
| Boeing 787-8 | 2009 | 238 | |||
| Boeing 787-9 | 2013 | 304 | |||
| Irkut MC-21 | 2017 | 163 |
Long-haul flights
For flights of. This includes transpacific flights.| Model | First flight | Seats | Sector | Fuel burn | Fuel per seat |
| Airbus A330-200 | 1997 | 241 | |||
| Airbus A330neo-800 | 2017 | 248 | |||
| Airbus A330neo-900 | 2017 | 300 | |||
| Airbus A340-300 | 1992 | 262 | |||
| Airbus A350-900 | 2013 | 315 | |||
| Airbus A350-900 | 2013 | 315 | |||
| Airbus A380 | 2005 | 525 | |||
| Airbus A380 | 2005 | 544 | |||
| Boeing 747-400 | 1988 | 416 | |||
| Boeing 747-8 | 2011 | 467 | |||
| Boeing 747-8 | 2011 | 405 | |||
| Boeing 777-200ER | 1996 | 301 | |||
| Boeing 777-200ER | 1996 | 301 | |||
| Boeing 777-200LR | 2005 | 291 | |||
| Boeing 777-300ER | 2003 | 365 | |||
| Boeing 777-300ER | 2003 | 344 | |||
| Boeing 777-9X | 2020 | 395 | |||
| Boeing 787-8 | 2011 | 243 | |||
| Boeing 787-9 | 2013 | 294 | |||
| Boeing 787-9 | 2013 | 304 | |||
| Boeing 787-9 | 2013 | 291 |
For a comparison with ground transportation - much slower and with shorter range than air travel - a Volvo bus 9700 averages per seat for 63 seats. In highway travel an average auto has the potential for per seat and for a 5-seat 2014 Toyota Prius, . While this shows the capabilities of the vehicles, the load factors may differ between personal use and societal averages for long-distance auto use, and among those of particular airlines.
General aviation
For private aircraft in general aviation, the current FAI Aircraft Efficiency record is 37.22 km/kg fuel or L/100 km in a Monnett Sonerai single-seat racer for 500-1,000 kg MTOW airplanes, and 9.19 km/kg or L/100 km in a four-seat diesel-powered Cessna 182 for 1,000-1,750 kg MTOW airplanes.Business aircraft
| Type | Aircraft | US gal | L | lb | kg |
| Turboprops | Pilatus PC12 | - | - | ||
| Turboprops | Cessna Grand Caravan EX | - | - | ||
| Turboprops | King Air 350 | - | - | ||
| Light Jets | Cessna Citation M2 | - | - | ||
| Light Jets | Embraer Phenom 100 | - | - | ||
| Light Jets | Cessna Citation CJ3+ | - | - | ||
| Light Jets | Embraer Phenom 300 | - | - | ||
| Light Jets | Learjet 70/75 | - | - | ||
| Mid-Size Jets | Bombardier Challenger 300 | - | - | ||
| Mid-Size Jets | Gulfstream G200 | - | - | ||
| Mid-Size Jets | Hawker 900XP | - | - | ||
| Mid-Size Jets | Cessna Citation X+ | - | - | ||
| Mid-Size Jets | Dassault Falcon 7X | - | - | ||
| Long-Range Jets | Gulfstream G550 | - | - | ||
| Long-Range Jets | Bombardier Global 6000 | - | - | ||
| Long-Range Jets | Airbus ACJ319 | - | - |
Future
NASA and Boeing flight-tested a blended wing body X-48B demonstrator from August 2012 to April 2013. This design provides greater fuel efficiency, since the whole craft produces lift, not just the wings. 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. NASA has created a cruise efficient STOL concept.Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research have researched a sharkskin-imitating paint that would reduce drag through a riblet effect. Aviation is a major potential application for new technologies such as aluminium metal foam and nanotechnology.
The International Air Transport Association technology roadmap envisions improvements in aircraft configuration and aerodynamics. It projects the following reductions in fuel consumption:
- 10–15% from advanced and geared turbofans in 2016
- 15–20% from open rotor/unducted fans in 2019
- 5–10% by natural laminar flow and 10–15% by hybrid laminar flow in 2022
- 15–20% from Counter-rotating propellers in 2023
- 25–30% from second-generation core concepts in 2026
- 10–25% from Hybrid Wing Body in 2026
- 5–10% from airframe morphing in 2027
- 10–15% from truss or strut-braced wing design in 2028
- 10–20% by flying without landing gear in 2032
Large, ultra high bypass engines will need upswept gull wings or overwing nacelles as Pratt & Whitney continue to develop its geared turbofan to save a projected 10–15% of fuel costs by the mid-2020s.
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.
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.
Research projects such as Boeing's ecoDemonstrator program have sought to identify ways of improving the fuel economy of commercial aircraft operations. The U.S. government has encouraged such research through grant programs, including the FAA's Continuous Lower Energy, Emissions and Noise program, and NASA's Environmentally Responsible Aviation Project.
Multiple concepts are projected to reduce fuel consumption:
- the Airbus/Rolls-Royce E-Thrust is a hybrid electric with a gas turbine engine and electric ducted fans with energy storage allowing peak power for takeoff and climb while for the descent the engine is shut down and the fans recover energy to recharge the batteries;
- Empirical Systems Aerospace is developing the 150-seat ECO-150 concept for turboelectric distributed propulsion with two turboshaft engines mounted on the wing and driving generators powering ducted fans embedded in the inboard wing sections, effectively increasing the bypass ratio and propulsive efficiency for 20–30% fuel savings over the Boeing 737 NG, while providing some powered lift;
- NASA's single-aisle turbo-electric aircraft with an aft boundary layer propulsor is a conventional tube-and-wing 737-sized airliner with an aft-mounted electric fan ingesting the fuselage boundary layer hybrid-electric propulsion, with 5.4 MW of power distributed to three electric motors: the design will be evaluated by Aurora Flight Sciences;
- The Boeing blended wing body with a wide fuselage mated to high-aspect-ratio wings is more aerodynamically efficient because the entire aircraft contributes to the lift and it has less surface area, producing less drag and offering weight savings due to lower wing loading, while noise is shielded by locating the engines on the aft upper surface;
- Developed with the U.S. Air Force Research Laboratory and refined with NASA, the Lockheed Martin Hybrid Wing Body combines a blended forward fuselage and wing with a conventional aft fuselage and T-tail for compatibility with existing infrastructure and airdrop; the engines in overwing nacelles on struts over the trailing edge enable higher-bypass-ratio engines with 5% less drag, provide acoustic shielding and increases lift without a thrust or drag penalty at low speed;
- Airbus-backed German Bauhaus-Luftfahrt designed the Propulsive Fuselage concept, reducing drag with a fan in the tail ingesting air flowing over the fuselage via an annular inlet and re-energizes the wake, driven with a gearbox or as a turbo-electric configuration;
- Conceived by the Massachusetts Institute of Technology for NASA, Aurora Flight Sciences developed the "double-bubble" D8, a 180-seat aircraft with a wide lifting fuselage, twin-aisle cabin to replace A320 and B737 narrowbodies, and boundary-layer ingestion with engines in the tail driving distortion-tolerant fans for a 49% fuel-burn reduction over the B737NG;
- The Boeing truss-braced wing concept was developed for the NASA-funded Subsonic Ultra Green Aircraft Research program with an aspect ratio of 19.5 compared to 11 for the Boeing 787: the strut relieves some bending moment and a braced wing can be lighter than a cantilevered wing or longer for the same weight, having better lift-to-drag ratio by lowering the induced drag and thinner, facilitating natural laminar flow and reducing wave drag at transonic speeds;
- Dzyne Technologies reduces the thickness of the blended wing body for a 110–130-seat super-regional, a configuration usually too thick for a narrowbody replacement and better suited for large aircraft, by placing the landing gear outward and storing baggage in the wing roots, enabling 20% fuel savings;
- the French research agency ONERA designed two concepts for a 180-seat airliner Versitalie Aircraft including turbofans with higher bypass ratios and fan diameter: a gull wing with increased dihedral inboard to accommodate larger geared turbofans under without lengthening the gear and the other with engines embedded in the tail to ingest the low-energy fuselage boundary layer flow and re-energize the wake to reduce drag;
- with Cranfield University, Rolls-Royce developed the Distributed Open Rotor with high-aspect-ratio wing and V-tail to minimize drag, and turbogenerators on the wing driving electric propellers along the inboard leading edge with open rotor high-propulsive efficiency and increasing the effective bypass ratio.
Climate change