On the evening of May 15, 1938, the Koken Long Range Monoplane, known as the Kokenki in Japan, landed on a runway in Kisarazu, Chiba Prefecture, to great public acclaim.
The Japanese-made aircraft had just set a new world record for a long-distance nonstop flight, as acknowledged by the Federation Aeronautique Internationale, a Switzerland-based body governing aeronautical world records.
The Kokenki traveled 11,651.011 km in a flight lasting more than 62 hours, breaking the previous record of 10,601.48 km set by a French plane in 1932.
Marking the 70th anniversary of the historic flight, Yuichi Yamamoto, the oldest son of one of the Kokenki’s designers, is now working to increase the recognition of the aircraft by opening a Web site.
“This is the only world record (certified by the FAI) that Japan has ever had,” said Yamamoto, 72, who lives in Yokohama. “I want more people to learn about the Kokenki.”
The Kokenki project was started in 1934 by researchers at the aviation research institute at Tokyo Imperial University, now the University of Tokyo.
At the time, when Japan was advancing along the road to war, the nation, which was lagging Western countries in developing aviation technology, imported aircraft from the West or made knockoffs of them.
The research institute got funding from the government to develop a diesel engine and airplane with the goal of setting a world record in two years, according to a book on the Kokenki written in 1983 by Kiyoshi Tomizuka, one of the project members.
However, it was hard going for the university researchers, who had never made an aircraft before, said Shigezo Oyanagi, director of Misawa Aviation & Science Museum in Aomori Prefecture.
To proceed, they sought the help of private companies, including Tokyo Gas Electric Engineering Co., now Hino Motors Ltd. They had also to give up on developing a diesel engine, turning instead to modifying a BMW gasoline engine to increase fuel efficiency and boost power at takeoff. Members of the team didn’t always see eye to eye, according to Oyanagi.
Yamamoto’s father, Mineo, an assistant professor at the university, was in charge of designing its fabric-covered wings, fuel tanks and landing gear. He sometimes clashed with Tomiji Kudo, a factory manager from Tokyo Gas Electric who had worked at a French company for 17 years, over the design of the wings, according to Oyanagi.
“My father was the kind of man who didn’t compromise. He was stubborn and always pursued the best things,” Yamamoto recalled about his father, who died in 1979.
By 1938, the Kokenki was completed and underwent test flights. After solving some problems, including a malfunctioning retractable landing gear, it was ready to shoot for the record.
At 4:55 a.m. on May 13, 1938, the 15-meter-long aircraft with a 27.9-meter wingspan took off from the Kisarazu runway, carrying two Imperial army pilots and an engineer.
The aircraft flew a 402-km circuit that took it from Kisarazu to Choshi in Chiba Prefecture, then to Ota, Gunma Prefecture, and finally through Hiratsuka, Kanagawa Prefecture. After flying the course 29 times, the Kokenki landed on the Kisarazu runway at 7:20 p.m. on May 15.
The record-setting flight, which was broadcast live on the radio, made newspaper headlines and delighted the nation, according to Oyanagi of the Misawa museum.
Although the plane’s technology was not particularly outstanding, “the flight demonstrated to Japanese people that a Japanese-made aircraft could reach a world-class level, which greatly encouraged people in those days,” Oyanagi said.
With the success, the project team was disbanded, and the Kokenki’s role ended.
Aviation technology was progressing fast, and the Japanese aircraft’s achievement was eclipsed the following year by an Italian plane.
Seventy years later, however, few remember the Kokenki.
Oyanagi figures people probably don’t want to remember the prewar aircraft due to the connection to Japan’s militaristic past.
When Japan lost the war, warplanes were dismantled by order of the Allied Occupation and documents were discarded, according to Kazuyoshi Suzuki, a senior curator at the National Museum of Nature and Science, Tokyo.
Although it was not made for the military, the Kokenki, which had been kept in a hangar at Haneda airport in Tokyo during the war, was buried at the airport, he said.
Fortunately, roughly 80 percent of its documents, including blueprints and a film, have survived at the national museum, donated from the University of Tokyo and some project participants, including Yamamoto’s father, Suzuki said.
To increase the recognition of the aircraft, Oyanagi’s museum made a replica to commemorate three Aomori Prefecture natives who took part in the project — pilot Yuzo Fujita, designer Hidemasa Kimura and factory manager Kudo. The replica has been on display since 2003.
Last year, Yamamoto opened a Web site, Mineo Yamamoto Cyber Museum, to tell about his father’s life and the Kokenki. The site carries photos and footage of making the plane and its historic flight.
“This is one of the things I’m doing to tell people about the aircraft,” Yamamoto said. “It’s our task to preserve the intellectual legacy that my father and his colleagues left.”