Nakatsu’s Kingfisher; or how biomimicry beat the boom
The incredible story of how nature helped to solve the prestigious Japanese Bullet Train’s sonic boom headache.
Japan’s so-called “Bullet train” is more aptly named than you might imagine. When the locomotive was first was first unveiled in 1964 it was heralded as a design masterpiece.
However, by 1990, the applause had turned to anger as the project engineers and people of Tokyo discovered a deafeningly obvious issue with the train’s design.
Reaching speeds of over 320km per hour, every time the Shinkansen train carriages entered a tunnel they would essentially become a shotgun round. And just like a rifle, every time the train would blast out of a tunnel, it did so with an explosive bang.
The phenomenon, which is called ‘Tunnel Boom’, is created by the train forcing air along the enclosed tunnel, and building up the air pressure in waves until it reaches the end of the tunnel when it is released in the form of a sonic boom (similar to the noise once made by Concorde jets). Disgruntled, local residents reported hearing bangs up to 400m away from the railway.
Consequently, Japan enforced an acceptable limit of 70 decibels to prevent further noise-pollution levels. The problem for the Bullet Train’s engineers was how to reduce the noise, without compromising on the speed?
It wasn’t until 1994 that an engineer, called Eiji Nakatsu stumbled across the solution thanks to his unusual hobby: bird-watching.
Following a chance encounter with a fellow avian enthusiast, Nakatsu realised that there might already be a solution to the train’s problem in the natural world. Taking inspiration from the kingfisher, which dives nose first into water to catch fish and barely makes a splash, Nakatsu gave his train a 50-foot steel ‘beak’ which solved the noise-pollution problem, but also unexpectedly made the Shinkansen train between 10–15 percent more efficient.
In design this is referred to as biomimicry. In simple terms the practice involves looking to the natural world for solutions to problems. Beth Rattner, Executive Director of The Biomimicry Institute, explains the process as “innovation inspired by nature.”
She adds, “the idea is that we can emulate how living organisms function in order to create materials, products, and systems that support a healthy planet.”
“There are some great examples of how innovators have looked to nature to solve issues related to sound or noise. Engineers at Ziehl-Abegg created the Owlet, an energy-efficient, quieter fan, by developing fan blades that mimic the shape and serration of owl feathers. Another example is the Sycamore ceiling fan, which mimics the sycamore seed tree pod to create a design that provides lots of airflow with minimal noise.”
As well as its new ‘beak’, Nakatsu applied his bird-watching knowledge to add more animalistic characteristics to the train.
Like the engineers at Ziehl-Abegg he became obsessed with the way that owls silently swooped down on their prey. Nakatsu redesigned the train’s pantograph (the link to power source cables running above the carriages) which was the part that made the most noise, to reflect the shape of an owl’s wings. He additionally recreated the noise-dampening qualities of an owl’s feather, with an array of serrations on the pantograph’s ‘wing’ which broke up the rushing air turbulence.
Perhaps the next time you’re sipping coffee on the morning commuter train you’ll consider the unusual ways it’s design might have been inspired by a swooping bird of prey.
GOODDESIGN/BADDESIGN is a series aimed at showing how creative thinking can simultaneously create and solve design and engineering problems.
Read more about the design process of biomimicry here…
