The Japan Aerospace Exploration Agency (JAXA) has teamed with Boeing on a joint research project to make quieter mid-sized passenger planes – by figuring out how to cut the noise generated by their airframes.
Aircraft noise is an issue around the world, and the aviation industry is keenly aware that its social licence depends on operating as quietly as possible – especially at urban airports that travellers prefer because they're closer to big city centres.
One such airport is Tokyo's Haneda, which in 2020 opened new routes. Although the numbers of flights arriving were suppressed by unexpected subsequent travel bans, pre-COVID the new routes would have increased Haneda's annual international arrivals and departures from 60,000 to 99,000. The result would be many aircraft flying at low altitudes over Tokyo, as seen in the following tweet.
Any city dweller, city planner or unfortunate person living along a flight path can see this plan's inherent noise pollution problem.
Japan's Transport Ministry has tried different methods to combat the acoustic by-product of international travel. It has even ordered planes to descend at steeper angles – a tactic which can lead to an increase in hard landings and has caused some planes to divert to Narita, 70km outside Tokyo.
Aircraft and engine manufacturers have worked on the problem for a while, too. Turbojet and turbofan engine designs have helped by increasing bypass ratios, thereby improving efficiency and dramatically reducing sound.
But ballooning volumes of air travel has made such progress insufficient.
All this puts the aviation industry in a bit of a tricky spot as it strives to meet future passenger traffic demands and, in the case of Haneda airport, maintain an internationally competitive facility.
JAXA worked with Japanese aircraft industries, universities, and NASA to further quiet aircraft by tackling airframe noise for six years starting in 2013 through the Flight Demonstration of Quiet Technology to Reduce Noise from High-lift Configurations (FQUROH) project.
FQUROH researchers have largely considered noise coming from flaps, slats and landing gear – all indispensable equipment that slow the aircraft while descending without thwarting lift. Aerodynamic noise caused by turbulent airflow from these sources at times exceeds engine noise as the pilot closes the engine throttle during approach procedures.
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Probable solutions determined by FQUROH to reduce the noise-causing turbulent flow are practical flap-edge configuration devices, serrated lower parts of the slat to break down large-scale vortices, and perforated fairings on the landing gear.
Testing such designs with wind tunnels and computer simulations only gets you so far, hence JAXA's partnership with Boeing to build on the FQUROH research and their development of a plan for validating designs in flight tests.
JAXA said it will continue working with Japanese manufacturers on the noise-reduction design concepts in the meantime.
The agency also said it will finalise design concepts by March 2022 and that these would be ready for flight test in 2023 "or later." ®