In 2009, a combined team of Aurora Flight Sciences, Massachusetts Institute of Technology (MIT), and Pratt & Whitney was awarded a contract to study technologies and designs for the plane of the future. The target date for entry into service was to be around 2030, and was targeted to have lower fuel burn and noise pollution than other models. The concept the team developed was really quite extraordinary.
The double bubble
The ‘double bubble’ concept would be based on the Boeing 737-800, but would essentially be a double width fuselage. It would fly 180 passengers to a range of 3,000 nautical miles; not bad for a short-haul aircraft. With its widebody configuration, turnaround at airports could be faster than current single-aisle aircraft too.
As with many concept aircraft, the D8 was designed to tackle the problem of carbon emissions and noise. By flying at Mach 0.74, developers believed fuel burn would be reduced by as much as 70% and noise by 71 dB compared to a standard Boeing 737-800. However, changes to the design and a desire to fly just as fast as a standard jet, at around Mach 0.82, has driven this down to a 49% fuel burn 40 dB reduction.
The beauty of the Aurora D8 is in its unusual shape. The natural laminar flow on the bottom of the wing and lifting body shape would reduce Boundary Layer Ingestion (BLI), meaning it could successfully fly with smaller and lighter engines. Positioning the engines at the top of a wide tail and above a flattened fuselage means they are better able to re-energize the wake to reduce drag.
But that’s where Aurora Flight Sciences has a challenge to overcome. Wake-filling propulsion requires distortion tolerant fans if they are to cope with the turbulent air entering the engines. United Technologies tested a scale model of a distortion tolerant fan at NASA, which produced some encouraging results.
Will we ever see the D8 fly?
The likelihood of the Aurora D8 actually making it to production is higher than some of the concepts that have floated through aviation in the past. For a start, in November 2017, Boeing completed the purchase of Aurora Flight Sciences. While it remains an independent operating model, the company is now able to benefit from Boeing’s resources and market position.
At around the same time, NASA confirmed funding would continue into the project, and the development of the X-plane experimental model. The XD8 would serve to demonstrate the positive technologies and attributes of the D8 through wind tunnel testing, propulsion technologies and a large-scale structural test model.
Everything has gone a bit quiet since then, but the concept retains some impressive characteristics. It might be that the idea has been shelved for a little while, or perhaps testing is quietly ongoing behind closed doors. Either way, the notion of redesigning what we think of as a typical passenger plane is long overdue, and the D8 could hold some clues to the future of air travel.