Boeing has completed a new series of flight tests under its ecoDemonstrator program, using a Rolls-Royce Trent 1000-powered Boeing 787 fitted with a modified shorter engine inlet. The aim of the campaign was to determine whether the design could reduce fuel consumption without increasing noise levels.

According to Aviation Week, the tests were conducted in cooperation with Rolls-Royce at Boeing’s facility in Glasgow, Montana, under the FAA’s Continuous Low Energy, Emissions and Noise (CLEEN) program. The aircraft used for the campaign was a Boeing 787 provided by Lufthansa.

Shorter engine inlets are of interest to aircraft and engine manufacturers because they can reduce nacelle weight and aerodynamic drag, particularly on high-bypass turbofan engines. The drawback is that a shorter inlet provides less surface area ahead of the fan for sound-absorbing acoustic treatment, potentially making the engine noisier.

To address this issue, Boeing fitted the modified inlet with a new acoustic treatment. The objective of the current configuration was to maintain noise levels comparable with those of the existing 787 design while improving fuel efficiency by up to approximately 0.5%.

Boeing said the campaign was completed ahead of schedule and that all data required for further evaluation and development of the tested technologies had been collected. Engineering teams are now analyzing the results.

According to flight-tracking data cited by Aviation Week, the test aircraft completed around 12 flights and accumulated approximately 52 flight hours during the campaign, including its July 16 ferry flight from Columbia, South Carolina, to Montana. The aircraft returned to Columbia on August 2.

Boeing sees significantly greater potential in future versions of the concept. A further optimized short inlet combined with a more compact nacelle could, according to the manufacturer, improve fuel efficiency by as much as 2%, while also reducing noise by up to around 1.5 dB.

The campaign also included tests of optimized approach and departure procedures that Boeing refers to as intelligent operations. By adjusting how certain phases of flight are conducted, the company believes the concept could provide an additional 3 to 5 dB reduction in noise.

The latest tests build on several years of joint development work by Boeing and Rolls-Royce. Development of the short inlet for the Trent 1000, featuring a 112-inch-diameter fan, began in 2016. Ground testing followed in 2018 at Rolls-Royce’s facility at NASA’s John C. Stennis Space Center, where the standard and shortened nacelle designs were compared under various crosswind conditions.

The next phase took place in late 2022, when Rolls-Royce evaluated the aerodynamic characteristics of the short inlet in flight using its Boeing 747-200 flying testbed.

This year’s campaign was the 13th test campaign conducted under Boeing’s ecoDemonstrator program, which has been running since 2012 and is used to evaluate new technologies aimed at reducing fuel burn, emissions and noise while improving the operational efficiency of future aircraft.