Japan for Sustainability
JFS Bio-mimicry Interview Series: No.6
Technologies Learned from Living Things: Concepts and Examples - Front Line Reports
"Shinkansen Technology Learned from an Owl?" - The story of Eiji Nakatsu
The train that runs between Tokyo and Hakata is, like the TGV in France, one
of the fastest trains in the world. This train is the 500-Series Shinkansen,
operated by JR West and known for futuristic design and characteristic long
"nose" on the front of the train. The Shinkansen enables us to move
comfortably and quietly at 300 km/h, but you will no doubt be surprised to
learn that a bird inspired Shinkansen technology. We interviewed Mr. Eiji
Nakatsu, an engineer and the director responsible for the test runs of this
Shinkansen series. He is also an active member of the Wild Bird Society of
Q. How did you end up learning from a bird?
You might assume that the challenge for the Shinkansen is how to make it run
faster, but thanks to current technology it is now not so hard to make it
run faster. In fact, the greater challenge for us is how to make it run
The faster the train runs, the more noise it makes. And, a large aerodynamic
noise is generated when air hits pantographs, the current collectors that
receive electricity from the overhead wires.
Noise standards for the Shinkansen are one of the worlds strictest for
railway operation, so we cannot run the train without solving this noise
issue. We, as the engineers responsible for developing the technology, were
searching for solutions to this challenge.
One day, I happened to see a notice for a lecture in a newspaper; attending
the lecture, I had the honor of meeting Mr. Seiichi Yajima, then an aircraft
design engineer and also a member of the Wild Bird Society of Japan. From
him I learned how much of current aircraft technology has been based on
studies of the functions and structures of birds.
I learned that the owl family has the most silent fliers of all birds. Some
hawk species even make large noises on purpose when hunting - the sound
functions to freeze their prey with fear. But somehow, an owl's feathers
emit virtually no noise. It seems that the owl family has acquired the
function of "quiet flying" so that prey such as mice, will receive no
warning that the owl is about to strike.
Inspired by this fact, we conducted wind tunnel tests* to analyze the noise
level coming from a flying owl, using a stuffed owl courtesy of the Osaka
Municipal Tennoji Zoo. We learned that one of the secrets of the owl
family's low-noise flying lies in their wing plumage, which has many small
saw-toothed feathers protruding from the outer rim of their primary
feathers. Other birds do not have these feathers.
These saw-toothed wave feathers are called "serration feathers," and
generate small vortexes in the air flow that break up the larger vortexes
which produce noise. It took 4 years of strenuous effort by our younger
engineers to practically apply this principle. Finally, "serrations" were
inscribed on main part of the pantograph, and this succeeded in reducing
noise enough to meet the world's strictest standards. This technology is
called a "vortex generator;" it has already been applied to aircraft and is
now being applied to the caps and boots of professional skaters.
From this experience, I was struck by the amazing functions that have been
developed by living things. I learned first hand that truth can be found in
the way life exerts itself in order to persist and carry on in this world.
From then on, "learning from nature" became a recurrent theme for me.
Q. I had no idea that "technology" developed by an owl had been applied to
the Shinkansen. Are there other examples in which learning from Nature has
been applied to the Shinkansen?
In fact, we had another challenge that we pursued to the test run phase.
Half of the entire Sanyo Shinkansen Line (from Osaka to Hakata) is made up
of tunnel sections. When a train rushes into a narrow tunnel at high speed,
this generates atmospheric pressure waves that gradually grow into waves
like tidal waves. These reach the tunnel exit at the speed of sound,
generating low-frequency waves that produce a large boom and aerodynamic
vibration so intense that residents 400 meters away have registered
complaints. For this reason, we gave up doing test runs at over 350 km/h.
Then, one of our young engineers told me that when the train rushes into a
tunnel, he felt as if the train had shrunk. This must be due to a sudden
change in air resistance, I thought. The question the occurred to me - is
there some living thing that manages sudden changes in air resistance as a
part of daily life?
Yes, there is, the kingfisher. To catch its prey, a kingfisher dives from
the air, which has low resistance, into high-resistance water, and moreover
does this without splashing. I wondered if this is possible because of the
keen edge and streamlined shape of its beak.
So we conducted tests to measure pressure waves arising from shooting
bullets of various shapes into a pipe and a thorough series of simulation
tests of running the trains in tunnels, using a space research
super-computer system. Data analysis showed that the ideal shape for this
Shinkansen is almost identical to a kingfisher's beak.
I was once again experiencing what it is to learn from Nature, seeing first
hand that a solution obtained through large-scale tests and analysis by a
state-of-the-art super-computer turned out to be very similar to a shape
developed by a living creature in the natural world. The nose of our new
500-Series Shinkansens has a streamline shape that is 15m in length and
almost round in cross section.
This shape has enabled the new 500-series to reduce air pressure by 30% and
electricity use by 15%, even though speeds have increased by 10% over the
former series. Another benefit has been confirmed through a favorable
reputation among customers that these trains give a comfortable ride. This
is due to the fact that changes in pressure when the trains enter tunnels
Q. You have learned from Nature and succeeded in reducing significant
environmental impacts. This is a wonderful achievement.
Through these experiences, I came to a clear realization that answers or
clues can be found in nature. It is possible to imagine other lines of
inquiry using this approach. For example, there are spaces between the cars
of rolling stock. It must be possible to reduce air resistance and
aerodynamic noise further by virtually "connecting" these rolling stock
However, connecting the trains with conventional materials won't work,
because of stresses that occur when the train goes through a tight curve.
Would it then be possible to develop a "train skin" that learns from the
skin of seals, which stretches without wrinkling? I asked our partner
manufacturers to look into the potential for developing this kind of
technology, but it did not happen because the market would be too limited
even if it were technologically feasible.
Yet, technology development using this approach is entirely possible, and
there are more and more cases emerging. I know that there are other products
already on the market, such as swimming suits developed through studies of
shark skin and kingfisher feathers.
Q. How can we see nature in such a way that we can learn from it, as you do?
The most important thing, I think, is to observe. I myself have observed a
lot about birds. Inspiration comes from building up a stock of observations
over the years. So, one important factor is whether you were taught to
observe nature during childhood. It is said that students nowadays tend to
feel less attracted to science. I think that students have too little time
to actually touch and feel nature. I would like to see more time set aside
for children to observe nature and nurture such abilities, both in school
and at home.
I studied engineering at school and worked as an engineer, but when I look
back at my school days I wish I had studied biology more. One of the reasons
why I did not take an interest in biology was that my teacher concentrated
too much on memorizing details. I would like to urge schools and
universities to teach students, especially engineering students, more about
the survival strategies of living things as expressed in their shapes and
For example, how did birds become birds, and fish become fish? For birds,
why do some migrate? Why did whales return back to the ocean after living on
land? Engineering Professor Nobuaki Kumagai, a former chairman of University
of Osaka, echoes this thinking by saying "all college students should study
My recommendation to young engineers is not to get stuck in their own
fields, but to have reliable advisors in completely different fields. A
railroad engineer tends to think only about trains. I was lucky enough to
have a mentor in the field of aircraft, and I applied what I learned from
My mentor, Seiichi Yajima, had me read a book, "Aircraft Designing Theory"
by Dr. Masao Yamana and Dr. Hiroshi Nakaguchi. This book says, "A tree, a
blade of grass, a bird or a fish, all can be brilliant and everlasting
teachers." This philosophy continues to inspire my work as an engineer.
I would also like to add that learning from nature ultimately leads to the
knowledge that nature is a society with sound material cycles. Global
environmental issues are now my major concern and I am currently helping
start a citizen's movement "Be Modest to the Earth."
http://www5f.biglobe.ne.jp/~kenkyoni/index.html (Japanese only)
After the Interview--What JFS Learned
Mr. Nakatsu's experience teaches us the following.
To practice "learning from nature," it is important to start with our own
needs and have a wide-angle view in looking for answers in the natural
Here are concrete steps you can take.
1. Understand the needs and problems occurring in the human world (e.g..
2. Have a wide-angle view that takes in other fields (e.g.. Air pressure is
an issue for aircraft)
3. Look for answers in the natural world (e.g.. Owls fly silently)
4. Repeatedly analyze data and conduct experiments and simulations (e.g..
Why and how do an owl's feathers erase noise?)
5. Consult experts in other fields (ex. Aircraft aerodynamic engineering,
material sciences, physics, ecology of wild birds)
6. Apply the principles learned (ex. Putting triangular vortex-generator on
7. Refer to and create application in other fields (boots and hats for
In the future, not only engineers, but also product designers, urban
planners, and architects may go through these steps to learn from nature and
actually put the principles they learn into practice.
(Staff Writer: Kazunori Kobayashi)
*This interview series is supported by the Hitachi Environmental Foundation.