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Distributed propulsion cuts C[O.sub.2].

Researchers have shown that distributing propulsor fans around an aircraft and integrating them inside the fuselage may be key to reaching future efficiency C[O.sub.2] targets for aircraft.

The research, which is soon to be published by the Royal Aeronautical Society, was conducted by German aviation think-tank Bauhaus Luftfahrt with the support of Airbus, MTU Aero Engines and French aerospace research agency Onera.

"Distributed propulsion" distributes the power of a single core engine to two or more fans in an aircraft. This increases propulsive efficiency because of a larger total fan area while maintaining a moderate increase in fan diameter and weight. Unlike in aircraft today, where aerodynamic drag is mainly compensated for by excess thrust, strategic placement of fans can also affect aerodynamic wake so power is not wasted and fuel saved.

Using advanced computer simulations, the researchers modelled an aircraft featuring technologies expected to be in use by 2035, such as ultra-high bypass ratio geared turbofan engines, to use as a benchmark. This aircraft saved 30% of fuel compared to current aircraft.

They then looked at a number of different propulsor configurations and assessed how much more fuel could be saved during cruise flight compared to the benchmark aircraft. Design iterations arrived at two configurations, a single--or counter-rotating fan in the aft of the fuselage, a "propulsive fuselage" and fans distributed on the airframe.

Dr Arne Seitz, engineer for visionary aircraft concepts at Bauhaus Luftfahrt, said: "For the distributed multiple fans we achieved an 8-9% fuel reduction against the advanced reference aircraft. For C[O.sub.2] reduction we come down to 11% for the multiple fans and 8% for the propulsive fuselage. The advanced reference had a gap of 20% against future EU C[O.sub.2] requirements. This technology halves that gap to 10%. It's very promising.

"One of our next steps will be to experimentally validate the findings. We also believe hybrid electric powertrains should be particularly focused on for this future research. "

Electric motors will offer scaleability and can be controlled using wiring instead of driveshafts, enabling flexibility for their placement on the aircraft structure.

A roadmap developed as part of the study aims for a technology freeze by 2030 and a prototype aircraft by 2035.


Fuel reduction achieved with the distributed multiple fans against the advanced reference aircraft

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Title Annotation:News & Analysis: All the latest technology stories from the world of engineering
Publication:Professional Engineering Magazine
Date:Nov 1, 2015
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