Design Engineering

NASA studies rear aircraft engine design for performance enhancements


General Aerospace NASA X-Planes

Researchers are exploring how engine placement can take advantage of boundary layer ingestion (BLI).

When it comes to designing next-gen aircraft, aerospace engineers are required to factor in more and more criteria to ensure the best performance.

Researchers at NASA are studying Boundary Layer Ingestion (BLI) as a promising concept that will help reduce fuel burn in jet engines, reducing emissions and overall operating costs.


This NASA graphic describes how Boundary Layer Ingestion happens and some of its potential benefits. Courtesy of Double Bubble Concept: Don Foley. BLI Illustration: NASA/Lillian Gipson.

With BLI, engineers design the aircraft with the engines located near the rear. This allows air flowing over the plane’s body to become part of the mix of air entering the engine, which then gets accelerated out the back.

This concept will help deal with the drag an airplane experiences in flight. Drag occurs when a layer of slow moving air builds up along the skin of the fuselage and wings, called the boundary layer. With conventional design, where the engines are fixed beneath the wings, the slow airflow builds up over the aircraft and continues off the rear of the plane, mixing with undisturbed air.


However, NASA researchers are exploring different design options in order to capitalize on this airflow. When an aircraft’s engines are put in the path of this boundary layer, say at the rear of the aircraft, the boundary layer air is able to enter the engine, and is thus ingested (BLI). It is then accelerated with the rest of the air passing through the engine and exhausted out the back.

This BLI doesn’t make the engines and more powerful. However, what it does do is limit the amount of drag as some of the slow air is sped up and removed from the boundary layer. Thus, engines need less thrust to push the aircraft forward, using less fuel.

NASA researchers, though, are still exploring some challenges this design configuration. With rear-mounted engines, the engine’s fan blades are exposed to additional stresses every time they pass through the distorted airflow due to the boundary layer.


Inside the 8’ x 6’ wind tunnel at NASA Glenn, engineers recently tested a fan and inlet design, commonly called a propulsor. Photo courtesy of NASA, Rami Daud (Alcyon Technical Services).

To better understand how to design and build an engine inlet and fan blades that effectively deal with these stresses, a NASA-led research team has tested a BLI engine configuration in the 8’ by 6’ wind tunnel at Glenn.

The results are promising, and NASA’s aeronautical innovators and industry partners are studying several airplane concepts that could take advantage of BLI.

These designs could potentially be incorporated into a series of X-planes NASA hopes to build and fly within the next decade to demonstrate advanced technologies and accelerate their adoption by industry.


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