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A propulsive fuselage for the planes of the future

27 June 2016

More energy efficient, less polluting, an innovative aircraft concept developed by an EU-funded project could help reduce the environmental impact of aviation.

Credit: DisPURSAL Consortium

The main aim of the research was to study the practical implementation of distributed propulsion and the implications of using hybrid power architectures, i.e. architectures that combine different power sources such as gas turbines, advanced batteries or fuel cells. The proposed concept involves a propulsor built into the tail of the plane. This component adds thrust by re-accelerating air slowed down by contact with the fuselage.

The DisPURSAL project focused on distributed propulsion — the use of a combination of engines at various locations on the airframe — as a possible enabler for cleaner and quieter planes. It considered a number of possible improvements to the currently predominant design for large passenger planes, which relies exclusively on podded engines attached to the wings.

“DisPURSAL looked into various configurations and aircraft morphologies,” says Mirko Hornung, executive director of research and technology of Bauhaus Luftfahrt, the organisation that coordinated the project. Based on this analysis, the consortium selected two particularly compelling concepts to take forward.

“One of these is the propulsive fuselage, which features a fan installed in the rear fuselage. This turned out to be the most feasible and promising one,” Hornung explains. This propulsor would complement the under-wing engines, which could therefore be smaller. “One advantage of this approach is that the general layout of the proposed vehicle is similar to that of existing planes,” adds his Bauhaus colleague Julian Bijewitz, who performed key parts of the research.

The second concept advanced by DisPURSAL involves a radically different type of airframe: a so-called hybrid-wing body, where the wing and fuselage are blended in a continuous shape. In this alternative concept, multiple propulsors are installed on the body of the craft.

Fast forward with far less fuel

Both concepts are based on the same underlying principle: they re-energise air decelerated by drag effects to produce thrust, by means of principles known as ‘boundary layer ingestion’ and ‘wake filling’. “The boundary layer that is being ingested is the air immediately surrounding the aircraft. As it flows around the flying plane, this air is slowed down relative to the vehicle by its contact with the structure, causing aerodynamic drag,” says Arne Seitz, also of Bauhaus Luftfahrt, who led the work on the propulsive fuselage concept.

Conventional podded engines have to work hard to compensate for this phenomenon. “So the idea is to add energy locally at the back of the fuselage, where the air is moving slowly,” he notes. “This way, you can maintain the required thrust while reducing engine jet speeds, which helps to minimise the losses in aircraft wake.”

This is the role of DisPURSAL’s propulsors. They take in the boundary layer and accelerate it to fill the velocity gap in the wake of the fuselage.

Of course, accelerating the air in the boundary layer also requires energy. “However,” says Seitz, “it takes less energy to produce thrust from slower-moving air in the fuselage wake flow than from the air at freestream velocity.”

Powering ahead

Overall, the DisPURSAL partners expect their propulsive fuselage system to reduce fuel consumption in flight by some 10 percent for the type of aircraft that is likely to be in use by 2035. Compared to typical aeroplanes in the year 2000, the savings could amount to nearly 40 percent.

These energy savings would automatically translate into reduced carbon dioxide emissions, the researchers note. “It is a very promising advance,” according to Seitz. “Very often, when you add new propulsor technology to an aircraft, there are drawbacks for other components,” he notes. “Many innovations therefore involve trade-offs, but this one has the potential to be complementary.”

The DisPURSAL partners are hoping to see their propulsive fuselage take to the skies by 2035 and have produced a roadmap that outlines the steps required to reach this milestone. The project ended in January 2015, and the consortium is now looking into ways to take this innovation forward.

“It is one of very few concepts that hold genuine potential to reduce the environmental impact of planes significantly within the coming years,” says Bijewitz. “A potential follow-on project could make the concept even more attractive,” he adds: the under-wing engines could be designed to additionally generate electricity, which would enable them to power the fuselage propulsor. This advance could permit further improvements in the design and integration of the rear fuselage section.

For more information visit the European Commission website.

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