In 2008, NASA asked industry aviation leaders to develop advanced concepts for aircraft that could satisfy the future commercial needs for air transportation (specifically, for the year 2030 and beyond). The goals would involve not only improving upon energy efficiency, but also addressing environmental and operational goals such noise pollution and reducing carbon emissions. The benchmarks set by NASA that industry leaders were required to meet for 2030-era aircraft, in comparison with today’s aircraft were:
- 71-dB reduction below current FAA noise standards, aimed at containing objectionable noise within airport boundaries
- Greater than a 75% reduction on the International Civil Aviation Organization’s Committee on Aviation Environmental Protection Sixth Meeting’s (CAEP/6) standard for nitrogen oxide emissions, which aims to improve air quality around airports
- Greater than 70% reduction in fuel burn performance, so as to help reduce greenhouse gas emissions and the cost of air travel
- Exploit metroplex concepts that offer optimal use of runways at multiple airports within metropolitan areas, with the goal of reducing air traffic congestion and delays
These goals comprised the N-level goals, which are comprised of three different levels. The N+3 levels are the next stage of airplane designed being targeted by Aurora Flight Sciences, a recent acquisition of Boeing.
Originally proposed by the Massachusetts Institute of Technology and Pratt & Whitney in 2008, Aurora Flight Sciences took the lead in refining the 180-passenger D8 “double bubble” configuration. Its design is based on a modified tube and wing with a very wide fuselage, which provides extra lift; the low sweep wing reduces drag and weight. The design is rather unconventional, as it fuses two aircraft bodies together lengthwise and mounts two turbofan jet engines on the tail.
Important components of the design are the use of composite materials for lower weight and turbofan engines with an ultra-high bypass ratio. This means that the amount of {Is this correct?} air flowing through the core of the engine is even smaller, while airflow through the duct surrounding the core is substantially larger, than in a conventional engine for more efficient thrust. The concept used to create the high bypass ratio is the opposite of current design trends. It achieves a higher bypass ratio by minimizing expansion of the overall diameter of the engine and shrinking the diameter of the jet exhaust instead.
The D8 is designed to achieve the same amount work as a Boeing 737-800, while its unusual shape gives it a roomier coach cabin than the 737. D8 series aircraft are intended for domestic flights and are designed to fly at Mach 0.74 carrying 180 passengers 3,000 nautical miles. The configuration has the potential to achieve a 71% reduction in fuel burn, 60 decibel reductions in noise pollution, and 87% reduction in LTO NOx.
The D8 is well on its way to being the next wave of aircraft, as it was just awarded another research grant from NASA. The 12-month grant will help reduce the risk and cost of future X-planes procurements by utilizing block testing before its first flight. The testing will be completed in three phases:
- D8 aerodynamics will be further developed via the design of a transonic wind tunnel test
- The readiness of the boundary layer ingesting (BLI) propulsion system will be advanced through the design of a transonic BLI fan test
- The complex propulsion-airframe structural integration will be perfected through the design of a large-scale structural test article
The D8 design has already gone through two wind tunnel test campaigns and has completed its System Requirements Review and Concept Design Review. In the face of competition from China and other countries, Aurora Chairman and CEO John Langford hopes that the D8 will lead the world market in huge commercial airliners. “The D8 is part of a sustained innovation initiative aimed at keeping [aviation] world leadership here in the U.S.,” he said.
