Why did a 787 fly above 1,000 microphones 88 times?

Over an eight-day period, Boeing flew a Dreamliner with more than 200 acoustic sensors attached to it over a set of ground-based microphones 88 times. Here’s why… 

American aircraft manufacturer Boeing is known for its innovation especially when it comes to the 787 Dreamliner.  

The company’s ecoDemonstrator programme takes promising innovations out of the lab and tests them in the air – allowing revolutionary technologies to be used in future aircraft developments. 

Earlier this week, the airframer concluded its programme for this year, which was conducted in partnership with Etihad Airways.  

One of the main focuses of the 2020 agenda was aeroacoustics research. The most comprehensive NASA aircraft system noise flight tests ever were conducted in collaboration with the agency.  

The Boeing ecoDemonstrator programme has been running since 2011. Boeing

More than 1,000 microphones were placed on the ground and 214 acoustic sensors were attached to the outside of the 787. These devices recorded sound levels that included over 50 unique test configurations and flight manoeuvres during 88 separate passes. 

The 1,200 microphones were attached at various locations on the fuselage. Boeing

The testing generated 1.6 terabytes of noise data – that’s equivalent to around 25 average high-definition movies. Boeing says the objectives, which were fully accomplished, are expected to improve NASA’s aeroplane noise prediction capabilities, advance ways for pilots to reduce noise and inform future quiet aircraft designs. 

The noise testing also gave Boeing the opportunity to evaluate the effectiveness of quiet landing gear. Up to 30% of noise from aeroplanes approaching an airport is caused by air flowing around the landing gear.

In partnership with Safran Landing Systems, Boeing also tested gear leg fairings designed to reduce noise levels. Boeing

Testing was performed using landing gear designed to be quieter by Safran Landing Systems. Modifications included perforated fairings covering part of the nose landing gear and aerofoil-shaped fairings wrapped around struts on the main gear. 

Eight separate sensors were mounted to the landing gear, in addition to the 1,200 microphones for the NASA project, to record sound. Although data from the test has not yet been analysed, Boeing says the preliminary results were positive: “Observers on the ground heard a noticeable reduction in noise,” a statement said. 

The microphones were positioned in carefully planned locations on the ground. Boeing

The noise tests were conducted very early in the morning at the manufacturer’s facility in Glasgow, Montana – which benefits from isolated location and quiet surroundings. 

Meanwhile, a new system was tested that connects pilots, air traffic controllers and airline operation centres simultaneously to optimise aircraft flight routing and arrival times. Tools included a text messaging system, flight path application and NASA’s Tailored Arrival Manager.  

During a series of transcontinental flights between the company's facilities in South Carolina and Seattle, Boeing simulated 17 rerouting scenarios using the technology. Boeing 

The system simplifies the process for course changes due to weather and traffic and minimises holding time before landing. Boeing says this enhances safety by reducing radio frequency congestion and improves communications efficiency for pilots and controllers while also saving time and fuel and lowering CO2 emissions. The testing included 17 rerouting scenarios during two transcontinental flights across the US.

This year, Boeing used a 50/50 blend of sustainable and traditional aviation fuels for several of its flights during the programme. Boeing

The effectiveness of a handheld ultraviolet light wand was also tested. Using 222 nanometre far UV light, the wand disinfected the flight deck in less than 15 minutes. An antimicrobial surface coating was also analysed on the flight deck during 16 flights. These projects are part of efforts by Boeing, Etihad, and the industry to identify the safest, most effective methods to disinfect the interior of an airplane. 

All of Boeing’s ecoDemonstrator flights are conducted using a blend of sustainable and traditional aviation fuels. Several flights this year flew on a 50/50 blend – the maximum allowed for commercial airlines.