As part of its New Aviation Horizons initiative, NASA is developing a series of new X-planes that include one concept that uses the air flowing along the fuselage to reduce fuel consumption. The Single-aisle Turboelectric AiRCraft with an Aft Boundary-Layer (STARC-ABL) propulsor harvests a jet airliner's boundary layer to provide more thrust with a 10 percent increase in efficiency.
The Aviation Horizons initiative is intended to study a number of ideas for the next generation of commercial aircraft, including a quieter supersonic passenger plane, blended wing designs, and new, more efficient, greener propulsion systems. Among these is the STARC-ABL concept being developed by Jim Felder and Jason Welstead at NASA's Glenn Research Center in Cleveland, which is an advanced turboelectric configuration that combines turbofan jets with a boundary-layer ingesting (BLI) engine that encircles the stern of the aircraft fuselage.
In a conventional aircraft, the boundary layer is a cocoon of slow-moving air that clings to and flows along the fuselage. Though this does help to reduce friction, as it flows off the rear of the aircraft, the boundary layer breaks up into turbulence. In the STARC-ABL concept, the BLI engine is a giant ducted fan that encircles the stern of the fuselage while the aft control surfaces are moved to a top of the T-shaped empennage. As the boundary layer flows backward, the fan collects it, accelerates the air, and turns it into thrust.
To power the fan, the 737-like aircraft has two slightly smaller underwing engines that not only provide thrust, but also about 3 megawatts of electricity for the BLI engine as well as the other flight subsystems. The BLI provides 20 percent of takeoff power and 45 percent of cruising power. Despite its weight and the need for the other two engines to power it, NASA says the BLI may improve fuel efficiency by 10 percent.
Currently, NASA engineers are working on the STARC-ABL's aerodynamic efficiency, engine optimization, weight compensation, and safety and operational requirements. If the project goes as scheduled, a subscale STARC-ABL concept will undergo initial ground tests at the space agency's Electric Aircraft Testbed (NEAT) at Plum Brook Station in Sandusky, Ohio.
Meanwhile, other X-plane configurations will be explored as part of a year-long study to create a next-generation, hybrid or turboelectric aircraft concept that could fly within 20 years that uses less fuel while generating less noise and fewer emissions.
"During the 12-month cycle, we'll work with the teams to take a deep dive into their hybrid and turboelectric aircraft concepts," says Amy Jankovsky, NASA's AATT subproject manager. "These concepts will provide in-depth, detailed analyses of the propulsion and electrical systems, and we will recommend technology development paths for their concepts."
The video below shows how the BLI works.