D8 (Aircraft)
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The Aurora D8, also known as the D8 Airliner, is an
airliner An airliner is a type of airplane for transporting passengers and air cargo. Such aircraft are most often operated by airlines. The modern and most common variant of the airliner is a long, tube shaped, and jet powered aircraft. The largest ...
concept under development The project was initiated in 2008 by
Aurora Flight Sciences Aurora Flight Sciences (AFS) is an American aviation and aeronautics research subsidiary of Boeing that specializes in special-purpose unmanned aerial vehicles. Aurora's headquarters is at Manassas Regional Airport. History In 1989, AFS was ...
, the Massachusetts Institute of Technology (MIT) and
Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of RTX Corporation (formerly Raytheon Technologies). Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially ...
under
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
's sponsorship of $2.9 million (£2.19 million). Aurora is refining the fuel-efficient D8 designed for NASA by MIT, and originally hoped to fly a half-scale demonstrator in 2022. The 180-seat, airliner is designed to fly at within the capabilities of the
Boeing 737 The Boeing 737 is an American narrow-body aircraft, narrow-body aircraft produced by Boeing at its Boeing Renton Factory, Renton factory in Washington (state), Washington. Developed to supplement the Boeing 727 on short and thin routes, the t ...
or
Airbus A320 The Airbus A320 family is a series of narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, Maiden flight, first flew on 22 February 1987, and was introduced in April 1988 by Air France. The first membe ...
and could be in test service by 2027 at the earliest and 2035 at the latest. Aurora Flight Sciences was purchased by
Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...
on November 8, 2017 for their drone developments. The subsidiary is intended to accelerate Boeing's development of autonomous technology.


Design

The side-by-side "double bubble"
fuselage The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...
provides additional lift along the nose section as well as faster turnaround owing to its wider fuselage. As a result, smaller wings can be used to generate lift which reduces drag. The mounting of the engines at the rear end of the D8 instead of below the wings used in conventional aircraft design allows reduction of thrust requirements by minimizing inefficiency from boundary layer ingestion (BLI). This results in the ability to use smaller and lighter high
bypass ratio The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for eve ...
engines An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
. However, the chassis features less radical than competing
blended wing body A blended wing body (BWB), also known as blended body, hybrid wing body (HWB) or a lifting aerofoil fuselage, is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft. The aircraft has distinct wing ...
concepts without modifying existing airport infrastructure, and BLI. The original goal was to reduce fuel burn by 70% and
noise Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrat ...
by 71 dB by flying at Mach 0.74, but a more traditional Mach 0.82 wing and fuselage growth resulted in a more-conservative 49% fuel burn reduction and 40 EPNdB noise reduction against a
Boeing 737-800 The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a twinjet, twin-engine narrow-body aircraft produced by Boeing Commercial Airplanes. Launched in 1993 as the third-generation derivative of the Boeing 737, it ha ...
.


Engines

Clustering the engines together atop the wide tail of a flattened fuselage enables them to reenergize the slow-moving
boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a Boundary (thermodynamic), bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces ...
over the fuselage to increase efficiency, and allow a clean, low drag, high
aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...
wing. Starting with slower flow, the reduction in
exhaust velocity Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the '' impulse'', i.e. change in moment ...
increases the
propulsive efficiency In aerospace engineering, concerning aircraft, rocket and spacecraft design, overall propulsion system efficiency \eta is the efficiency with which the energy contained in a vehicle's fuel is converted into kinetic energy of the vehicle, to acceler ...
with a similar
specific thrust Specific thrust is the thrust per unit air mass flowrate of a jet engine (e.g. turbojet, turbofan, etc.) and can be calculated by the ratio of net thrust/total intake airflow. Low specific thrust engines tend to be more efficient of propellant (a ...
. By ingesting and reenergizing the boundary layer flow, BLI reduces by 40% in the D8 the wasted kinetic energy in the combined high-velocity jet exhaust and slow-speed wake behind the fuselage. Large-scale
wind-tunnel A wind tunnel is "an apparatus for producing a controlled stream of air for conducting aerodynamic experiments". The experiment is conducted in the test section of the wind tunnel and a complete tunnel configuration includes air ducting to and f ...
testing with NASA showed a power-saving from BLI from 8.4% with the same
jet nozzle A propelling nozzle or exhaust ejector is a nozzle that converts the internal energy of a working gas into propulsive force; it is the nozzle, which forms a jet, that separates a gas turbine, or gas generator, from a jet engine. Propelling nozz ...
area to 10.4% with the same mass flow. The BLI benefit is an order of magnitude more than the loss from ingesting distorted boundary-layer flow. A large fan size is needed to exceed a 20:1
bypass ratio The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for eve ...
. Developed by
United Technologies United Technologies Corporation (UTC) was an American multinational corporation, multinational list of conglomerates, conglomerate headquartered in Farmington, Connecticut. It researched, developed, and manufactured products in numerous are ...
Research Center, a distortion-tolerant fan was scale tested at NASA and coped with flow distortion from ingesting the boundary layer close to the upper fuselage surface. As a compact core limits blade
tip clearance Tip clearance is the distance between the tip of a rotating airfoil and a stationary part. * Gas turbine: Rotor blade and casing * Propeller (ship or aircraft): Propeller and structure ** Ground tip clearanc* Wind turbine A wind turbine is ...
s issues due to bending but cannot house the fan to low-pressure turbine driveshaft,
Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of RTX Corporation (formerly Raytheon Technologies). Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially ...
turned the core backwards, similar to
PT6 The Pratt & Whitney Canada PT6 is a turboprop aircraft engine produced by Pratt & Whitney Canada. Its design was started in 1958, it first ran in February 1960, first flew on 30 May 1961, entered service in 1964, and has been continuously upd ...
arrangement, with hot gas discharged forward through a low-pressure power turbine connected to the fan via a short shaft and a gearbox. To avoid the risk of an
uncontained engine failure A turbine engine failure occurs when a Gas turbine, gas turbine engine unexpectedly stops producing Power (physics), power due to a malfunction other than fuel exhaustion. It often applies for aircraft, but other turbine engines can also fail, ...
causing the second engine to fail, the cores are angled by 50° since they are no longer mechanically linked to the fan, with low pressure losses since only the core flow is turned. Not connected to the power section, the core can be disassembled for maintenance.


See also

* Frigate Ecojet *
Middle of the market The middle of the market, often abbreviated MoM, is the airliner market between the narrowbody and the widebody aircraft, a market segmentation used by Boeing Commercial Airplanes since at least 2003. Both Airbus and Boeing produce aircraft that s ...
*
Boeing New Midsize Airplane The New Midsize Airplane (NMA), or New Midsize Aircraft, (culturally referred to as the Boeing 797) is a concept airliner proposed by Boeing to fill the middle of the market segment. In 2015, Boeing determined the market was large enough to la ...


References

{{reflist


External links


Real Engineering: The Future of Airliners? - Aurora D8
Twinjets Twin-boom aircraft NASA aircraft Aurora Flight Sciences aircraft T-tail aircraft Low-wing aircraft Abandoned civil aircraft projects of the United States Aircraft with retractable tricycle landing gear