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University professor proposes Aerotrain as more efficient alternative to maglev
By Yamada Kumi
Maximum speed is 500 kph. Research and development is underway on the Aerotrain, a new type of transportation that goes head-to-head in speed with JR Central’s magnetic levitation (maglev) linear motor car—which boasts the world speed record of 581 kph—while consuming about one-ninth the energy.
1,500 km—albatrosses can travel this distance airborne on a single meal. If humans were to travel that distance on foot, even assuming a speed of 5 kph, the journey would take 300 hours—in other words, close to two weeks straight walking without rest. But why do albatrosses have such good “fuel efficiency”? One of the reasons is a natural phenomenon known as the “ground effect.”
The ground effect refers to a phenomenon observed when traveling with wings at a height just above ground level in which air squeezed between the ground surface and wings generate a powerful aerodynamic lift.
Squeezing air between the ground surface and wings
Research and development is underway on the Aerotrain, a new type of transportation that permits high-speed travel at 500 kph by putting this ground effect to practical application. The motive power for the Aerotrain comes only from natural energy sources such as solar and wind power. The R&D effort is being undertaken by Professor Kohama Yasuaki of Tōhoku University’s Future Science and Technology Joint Research Center, the New Industry Creation Hatchery Center (NICHE).
The third-generation prototype of the Aerotrain under development at Tōhoku University.
Airplanes use aerodynamic lift to rise. When the front of the wings cuts into the wind, air pressure is higher underneath the wings than above the wings. As a result, the wings are pushed upwards by the air underneath, causing the plane to rise. This upward force is aerodynamic lift.
But what if we don’t increase the plane’s elevation? As air will accumulate between the ground surface and the wings, the air pressure underneath the wings will increase, in turn increasing the upward force. This is the ground effect.
As the ground effect weakens as we increase our separation from the ground surface, airplanes rise to a certain elevation, only beginning to descend when the ground effect disappears. As long as we continue moving forward, however, the air trapped between the ground surface and wings will serve as a cushion, and we will never fall to the surface. The elevation from the surface will reach a certain equilibrium depending on the travel speed. In other words, it’s possible to continue in flight at a height just above ground level.
The Aerotrain is equipped with four wings on its body, and is designed to run levitated inside a trench-shaped exclusive guideway that surrounds the vehicle with walls on three sides.
The wings are L-shaped, with the tail of the “L” called the safety wing. The ground effect occurs at a total of eight locations, between the wings and the ground surface and between the safety wings and the guideway walls. The ground effect generated between the safety wings and the guideway walls serves to prevent the train from colliding with the walls.
The force to propel the train is gained by the rotation of two propellers affixed to either side of the train body. The motive power for the propellers uses solar cells installed on the sides of the guideway. Currently, the energy is stored in batteries and loaded onto the train, but in the future, the plan is to convert to a pantograph-based system allowing for a constant supply of electrical power.
Vehicles operating on the ground surface such as automobiles and railways, on the other hand, witness increased air resistance when attempting to increase speed. Normally, air resistance increases with the square of speed. Traveling at twice the speed generates four times as much air resistance, while three times the speed generates nine times as much air resistance.
The reason the Aerotrain can travel at high speeds while consuming very little energy is because the ground effect also has the effect of reducing air resistance.
In reality, there has been past development of vehicles that use the ground effect. However, the focus of these efforts has been on military-purpose “wing-in-ground-effect (WIG) vehicles” that stay elevated through ground effect interactions with water surfaces; there were no examples of the technology for general use, running on the ground. In the past, there have been several incidents of the craft being struck by waves on the surface of the water and sinking, so the vehicles are no longer being produced.
In fact, it was the WIG vehicles the first alerted Professor Kohama, who had been researching air resistance on airplanes and other vehicles, to the ground effect. When he studied overseas in Germany for two years starting in 1986, he became interested in the field when a colleague of his was working on a model test of WIG vehicles.
Professor Kohama recounts the events: “I thought, ‘Wow, this is amazing!’ Even after returning to Japan, I couldn’t get the ground effect out of my head.”
After returning home to Japan, Professor Kohama would immediately have a hand in a project that would provide the impetus to begin research and development of the Aerotrain: development of the Shinkansen’s first-generation Nozomi.
The Shinkansen opened in 1964. Looking back and comparing the end cars of past Shinkansen trains from the first-generation 0 series Hikari trains to the latest N700 series, one can observe the shape becoming more and more streamlined. This transition is the result of efforts to reduce air resistance. In particular, the first-generation Nozomi, which in one fell swoop boosted the 220 kph maximum speed that had persisted since the opening of the line to 270 kph, has an undeniable presence. And the mastermind who developed the shape of the nose on those trains was none other than Professor Kohama.
“Unfortunately, however, the resulting reduction in air resistance through improvements to the shape of the train’s nose were like drops in the bucket. As long as the train runs close to the ground, substantial reductions in air resistance wouldn’t be possible, no matter how much you try and redesign the train’s nose,” confides Professor Kohama.
Air resistance beneath the Shinkansen floor becomes an obstacle
In the past, discussion of air resistance on railways was focused solely on the train’s nose. In reality, however, there was an even larger source of air resistance—the air resistance generated between the Shinkansen floor and the trackbed.
There is limited separation between the trackbed and the floor of the train, and both the train’s underbelly and the trackbed are uneven. As a result, turbulence is generated that becomes a substantial source of air resistance. However, improving these sections of the train is difficult, not to mention that that Shinkansen trains are 16 cars and 400 meters in total length.
“In other words, there is naturally a limit to reducing air resistance on trains, and we came to the conclusion that the N700 series’ 270 kph was the end of the line when considering the balance of speeding up service and limiting energy consumption,” recounts Professor Kohama.
But if that’s the case, then what about the maglev, which has been in research and development and is targeted for an opening in 2027? Professor Kohama also has a less than optimistic view of the maglev.
“From the perspective of energy consumption, the maglev has very poor energy efficiency, consuming three times as much energy as the Shinkansen. And I can’t say it’s a very environmentally-friendly mode of transport,” says Professor Kohama.
One of the reasons is that use of a superconducting maglev means that only about one percent of the electrical power used can be converted into propulsive power. In addition, even though the maglev travels at over 500 kph, there is limited space between the train and the walls on all three sides, resulting in substantial air resistance.
So when faced with the question of whether or not there were any options left for ground-based transportation systems that maintain and ensure both high speed and energy efficiency, what crossed Professor Kohama’s mind was the ground effect.
“Let’s a make a vehicle like the Shinkansen, with wings like a plane, that makes use of the ground effect and can operate levitated at high speed just above the surface of the ground.” In 1986, Professor Kohama took his first steps to realize this dream in parallel with the project to develop the Nozomi.
The first 10 years or so were focused on theoretical calculations. But between 1997 and 1998, significant progress was made.
First, an investigative committee regarding the Aerotrain was established with support from the former Ministry of Transport. The government gave its certification that the technology could operate consuming one-third the energy of the Shinkansen and one-ninth the energy of the maglev when running at 500 kph. With this, Professor Kohama gained confidence in his work.
Next, with the relocation of the maglev test track formerly in Hyūga City, Miyazaki Prefecture to Yamanashi Prefecture, the Railway Technical Research Institute (RTRI) began searching for candidates to reuse the former site of the experimental track in Hyūga City. As it was the perfect facility for test runs of the Aerotrain, the timing couldn’t have been better. Professor Kohama immediately filed an application and was able to lease the facilities for free.
Professor Kohama quickly built the prototype Aerotrain unit to test the theoretical research he had amassed over the years, and in 1999, he became the first in the world to prove that the ground effect could be used for stable, levitated running above the ground surface.
Running in an underground tunnel between Haneda and Narita!?
The second prototype unit proved the possibility of propulsion using electrical power generated through solar panels, showing the technology’s ability to run with limited energy consumption.
And now, with the support of the New Energy and Industrial Technology Development Organization (NEDO), Professor Kohama is performing multiple experiments using a 3.3 m wide, 8.5 m long third-generation prototype with capacity for two passengers. According to a proposal by the National Institute for Advanced Industrial Science and Technology (AIST), the body of the vehicle was changed to a composition using magnesium alloy, which has fire resistance qualities. This is a new material that allows an approx. 60 percent reduction in weight compared to aluminium alloys with equivalent strength.
In tests using the third-generation prototype, NEDO has given Professor Kohama some “homework”: “When transporting one person at 200 kph, reduce the needed energy to move one kilometer to 35,000 kcal or less.” Professor Kohama is confident: “I expect we’ll meet the target.”
If this goes well, Professor Kohama could enter into research to put the technology to practical use starting next fiscal year. The ultimate plan is to develop a three-car train for 360 passengers, completing a roundtrip at 500 kph and 12-minute headways over a 500 km distance using 45 MW of generated electricity. Professor Kohama believes he can develop the technology for practical use by 2025.
Rendering of final three-car Aerotrain, with capacity for 360 passengers. The plan calls for operating the train at 500 kph over a 500 km distance at 12-minute headways, using 45 MW of generated electricity.
“To that effect, we will now need more support and cooperation, as well as understanding, from the industry,” says Professor Kohama.
But in order to introduce the Aerotrain, a guideway must be constructed. A high-speed railway in the Shinkansen has already been constructed in Japan, and it isn’t very realistic to convert the Shinkansen to Aerotrain technology. As a result, Professor Kohama instead has his eyes on an underground tunnel connecting Haneda Airport and Narita Airport. If realized, it will be possible to move between Haneda and Narita in about 10 minutes. Of course, he also has future plans to actively market the technology to emerging nations, where there is a demand for new transportation technologies.
Japan’s strategy of “sparkling new”
Japan is faced with several key issues, including the need to reduce carbon dioxide emissions, an aging population, and declining ridership demand. As a result, a feeling of despair has struck all across Japan, making it difficult to craft a vision for a future society filled with hope. But these are also issues that all countries across the globe are facing, and in this respect, we could call Japan a “nation at the forefront” in dealing with these issues.
“This is a once-in-a-lifetime chance for Japan,” says Komiyama Hiroshi, Mitsubishi Research Institute chairman and University of Tōkyō president emeritus. Japan will now purse the cutting edge and the “emerging new” of technologies that will lead the world. Green, smart, silver… Japan has many outstanding technologies at its disposal to realize a sustainable society. We should take full advantage of them, and build a bright and brilliant future.
As the article says, this has been under development for many years now. There have been occasional stories about this here and there over that time, but I figured I would put this latest article up, which has some news about the third-generation prototype.