Shinkansen: The bullet train inspired by Kingfishers
In the late ’90s, Japanese engineers modeled the Shinkansen bullet train after Kingfisher birds to solve one of their biggest problems… tunnel sonic booms.
Tokaido Shinkansen is one of the world’s busiest high-speed rail lines. Having moved almost 5 billion passengers from its opening in 1964 for the 2010 Tokyo Olympiad, it was fast, well-known, and ready to expand. Unfortunately, at the time when it was first designed, it was also well-known for disturbing thousands of nearby residents as it emerges from tunnels.
Boom, Boom, Boom!
The bullet train travels throughout Japan at speeds of 150–200mph to support millions of passengers yearly. However, its first design didn’t consider how the train’s high speed would cause atmospheric pressure waves to build up in front of the train as it passes through tunnels. This compression wave propagates through the tunnel at the speed of sound, forming a micro-pressure wave, or a tunnel sonic boom at the exit. Additionally, every unit increase in speed produced an increase in pressure to the power of three!
Shinkansen trains ran through many tunnels in dense neighborhoods, and the sonic booms were so forceful that residents could hear them 400 meters away. Pantographs, the connections to overhead wires, made the loudest noise as trains emerged from tunnels. Thousands of residents were disturbed, concerned, and annoyed. I mean, don’t you hate when construction is happening in your neighbor’s house while you’re trying to nap?
Eiji Nakatsu and the Kingfisher
An engineering team was tasked to design an even faster and more efficient train, but to do that, they had to make them quieter first without decreasing speed or use more energy. One of the team’s young engineers looked at the situation and shared his thoughts with Eiji Nakatsu, the general manager of the technical development department for the bullet trains in 1997. He said that he feels the train has shrunk when the train rushes into the tunnel. Immediately, Nakatsu thought, “This must be due to a sudden change in air resistance.”
The question then occurred to Nakatsu: “Is there some living thing that manages sudden changes in air resistance as a part of daily life? Yes, there is, the kingfisher.” You see, Nakatsu wasn’t only an engineer, he was also an avid bird watcher and an active member of the Wild Bird Society of Japan.
Kingfishers are birds that can dive from the air (low resistance) to water (high resistance) at speeds of up to 25mph without making a splash. Knowing this, Nakatsu believed Kingfishers could dive like that because of the streamlined shape of its long, pointed, wedge-shaped beak. With an idea in mind, the team of engineers conducted tests to measure pressure waves from bullets of various shapes and designs shot into a pipe. The resulting data showed the ideal shape for the Shinkansen’s head is practically identical to a kingfisher’s beak! Using this information, they designed the new train series after the Kingfisher’s beak.
This design reduced the noise of the tunnel sonic booms and the train was running at higher speeds even when maintaining a standard of a 70 A-weighted decibels noise level! Immediate benefits emerged alongside. The new Shinkansen 500 series reduced their energy consumption proportionally when there was 30% less air resistance in the new predecessor of the model. In an actual train run of a max 270 km/hr speed, the design showed a 13% decrease in power that was needed in the predecessor 300 series.
On March 22, 1997, the 500-Series Shinkansen train was put to commercial service. At a world speed record, the train can run up to 300 km/h and shortened the travel time between Shin-Osaka and Hakata by 15 minutes (a significant difference based on the business of the train). Here we have a train that needs less power, consumes less fuel, is cheaper, faster, cleaner, and quieter.
Speeding into Nature’s Inspiration
Nakatsu’s design is a flawless example of biomimicry, the case where we use observations of the structures and systems of organisms from nature to mimic strategies and solve design challenges faced. Nature created the Kingfisher, Nakatsu had to design a train that can adapt to sudden changes in air resistance, and Nakatsu mimicked the Kingfisher’s beak to launch a design that not only solved a big problem the Shinkansen trains were against but changed the ways Japan’s Tokaido Shinkansen trains are designed forever.
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