An MIT aeronautics team revealed this design for a new generation of airplanes that would be quieter and up to 70% more fuel-efficient than the ones we fly in now. The research was funded by a $2.1 million NASA program — called N+3 — aimed at developing more eco-friendly, high-performance planes over the next 25 years.
The engineers conceived of the D series by reconfiguring the tube-and-wing structure. Instead of using a single fuselage cylinder, they used two partial cylinders placed side by side to create a wider structure whose cross-section resembles two soap bubbles joined together. They also moved the engines from the usual wing-mounted locations to the rear of the fuselage. Unlike the engines on most transport aircraft that take in the high-speed, undisturbed air flow, the D-series engines take in slower moving air that is present in the wake of the fuselage. Known as the Boundary Layer Ingestion (BLI), this technique allows the engines to use less fuel for the same amount of thrust, although the design has several practical drawbacks, such as creating more engine stress.
Air travel is becoming more frequent and is expected to double by 2035; without going through major overhaul, the current system won’t scale. As Ed Greitzer, the lead investigator in this project, points out, airplanes have looked pretty much the same for the last half century, and are way too inefficient when it comes to fuel, noise, and runway usage. So he changed it by coming up with two designs: the 180-passenger D series to replace the Boeing 737 and the 350 passenger H series to replace the 777.