7The Phantom Propeller
The Pe-33 “phantom propeller”
This was the so-called Pe-33 prototype prop mounted on the Ki-67. This prop was designed at Nippon Gakki’s Tokyo factory under the leadership of Matao Sanuki. Managing Executive Officer Nemoto was also in charge of the design.
The prop featured the same hydraulic motor components for the engine as the Junkers design, and everything below the reduction gearbox assembly to the blade roots were from the Ratier prop. In simple terms, it replaced the electric motor components of the Ratier design with Junkers’ hydraulic motor, giving it the best features of both designs. Use of the Ratier type required major changes to the manufacturing process, giving the production engineers many difficult problems to solve.
Research on gear types was required, including that of worms and worm gears. For the propeller hub, they had to machine the screw and the ball nut to make ball screws using 500 ball bearings, each ball being 5 mm in diameter. Mastering these manufacturing technologies was a huge challenge for the engineers.
Pe-33 propeller structural diagram
To facilitate this process, Nippon Gakki sent a large group of engineers—with some mediation by the military—to the Nippon Kokusai Koku Kogyo factory in Hiratsuka in Kanagawa Prefecture for training. As one of the participants, I was tasked with learning manufacturing process planning and coming up with plans for using jigs and tools. I was in a different company’s factory and making sketches of what I saw, so while it was somewhat embarrassing, we all learned a lot as a team and it was useful when we went back to our own work.
Regarding the manufacturing process for the above-mentioned screw and ball nut, they had to be machined to a very high level of precision. This was challenging for us at the time, but thanks to that experience, the knowledge was immensely beneficial when we later performed precision metalwork for manufacturing motorcycles and the like.
The cylinders were made of nitrided steel. The steel is forged, annealed, rough machined, and then normalized. The almost-complete workpiece is then given a stabilization heat treatment, and then nitrided and ground to give it a thin but very hard surface finish. The surface finish and tolerances had to be absolutely perfect for the screw nut holding the ball bearings to move freely, and that only made things more demanding for us.
To get the nitrided steel forgings, I had to make repeated trips to the Yasugi Factory of Hitachi Metals in Shimane Prefecture while avoiding the frequent air raids. Then, to get the final finishing done on the prototype, I had to go almost every day to the Osaka armory where they had a Lindner thread grinder. It was all very stressful back then to put together a prototype, but I now look back on those days with fondness.
Just before the war ended, Soichiro Honda came up with a lapping machine for finishing the threads on the ball nut. It was a unique idea and garnered expectations, but due to the chaos associated with the war’s end, it unfortunately never saw the light of day. At the time, Honda-san was running a company manufacturing piston rings in Hamamatsu. President Kaichi Kawakami had asked him to help design various specialized machining tools. In addition to the lapping machine, Honda-san also designed a propeller blade modeling machine, but just before these machines were completed, they were destroyed in the bombings.
8Natural Disasters and Air Raids
Hamamatsu after the May 19 air raid
During this time, the engineers at Nippon Gakki were working to prepare the completed Pe-33 propellers that were the crown jewels of all their hard work. The company had been designated a munitions factory under the Munitions Company Law, and as a civilian armory, many expected much more to come from us at Nippon Gakki. Unfortunately, the one-two punch of natural disasters and devastating air raids dashed all our hopes.
First, on December 7, 1944, the area was hit by the Tonankai Earthquake, causing immense destruction. Then a few months later on May 19, 1945, an air raid razed the wooden propeller manufacturing facility at the Tenryu Factory and burned down most of the Hachiman Factory at headquarters. And just a month later on June 10th, seven 250 kg bombs fell on the headquarters factory, burning most of the wooden factory buildings to the ground.
At the time of the air raid, I was accompanying our current auditor Kamiya-san and other company management at a meeting in Yatomi City in Aichi Prefecture put on by the Ministry of Munitions about increasing aircraft production. Halfway through the meeting, we learned of the raid and we tried to rush back to Hamamatsu but the trains weren’t running. When we finally managed to get back, we could only stare in stunned disbelief at the scale of the destruction.
In just a single day, our once-bustling workplace had been turned into ashes. Matsuyama-san, our chief of security, had died in the attack and many others had either been injured or lost their lives. The stark reality of it all was a terrible shock for me. Shortly thereafter, on the night of June 18th, Hamamatsu was subjected to a terrible incendiary raid which burned out much of the city, transforming it into a blackened wasteland. This put an end to all production and operations at our main plant (called the “Kusunoki Factory”) at company headquarters.
9The Sakura Factory
Layout of the Sakura Factory (1945)
From 1944, American air raids against Japan’s main islands increased in intensity. Realizing the danger this posed to our headquarters factory, the government ordered us to evacuate the area and move the factory to the Funagira area of Komyo Village in the district of Iwata.
Today, this area is part of Tenryu City and also where the recently completed Funagira Dam is. The move began in mid-February in 1945; working non-stop with the help of military troops, student workers and the local community, the move was almost done in early May.
The machining department for propeller manufacture was the first to move there from the headquarters factory and it began partial production at the new location in late May. The new factory was located in the cedar forest valley among the mountains surrounding the Funagira basin filled with its rice paddies and crop farming areas. The buildings were about 5.5 meters wide and between 9 and 18 meters long, and they were located in a series of narrow valleys.
As many trees as possible were left standing to try and conceal the buildings and make them invisible from the air. The roofs were camouflaged by covering them with cedar bark and branches, and the windows had no glass and were simply sections of the wooden wall that could be pushed open. Most of the heavy machinery was mounted not on concrete but on piles of wood posts nailed together.
There was a tunnel originally built for a railway line but it went unused, so we took advantage of it. We called factory buildings “Valley 1” through “Valley 13,” based on where the buildings were located.
These buildings were the first stage of constructing the provisional factory. The second stage was to be the facilities for propeller blade finishing and forging. As it happened, I was part of the group that stayed behind at headquarters during the first stage of construction, but on June 12th, shortly after the June 10 air raid, I joined the group for the second stage of construction and headed to the area.
The office for the second construction stage was located in the nearby town of Futamata. We rented a building for drying silkworm cocoons and the office was up and running by July 13th. We set out to find suitable sites for the next part of construction somewhere other than Funagira in order to move the rest of the facilities. We planned to build the blade finishing factory in Otani, a cedar forested area near a small mountain stream, and the forges in Kamida. The work pace was unrelenting; once we had decided on the locations, we would be on site the next day already pounding in stakes for the foundation while the military convinced the property owner that it would be in his best interests to let us use the site.
Throughout this period, the region was subjected to repeated bombings from carrier aircraft and the trains and other transportation services were often not running. This made it very difficult to find and move the necessary labor to the site and it caused me more than a few headaches. In spite of this, one young man helping us would walk to and from the town of Kasai over 10 km to the south. It was a show of dedication for which I will always be grateful.
For food, we had little more than rice gruel with diced sweet potatoes or flour dumplings boiled in soup. When you arrived at the factory for work, you got some “rations” to serve as a replacement for snacks, but instead of the original filling, they were stuffed with ground up straw instead—nothing in the world could make you say it tasted good. But it filled our stomachs and for that we were grateful.
Construction materials were in extremely short supply, yet in spite of these difficulties we never thought Japan would lose the war. It was awe-inspiring to see the construction workers wearing their helmets, air-raid protection hoods and leg gaiters working tirelessly to get the Sakura Factory up and running to start producing propellers.
On the night of July 29th, the Kusunoki Factory at Nippon Gakki headquarters was hit by a naval bombardment, but fortunately by this time, most of the machinery had been moved to the Sakura Factory. I was on duty that night at the Futamata office. Carrier aircraft dropped flares over the central area of Hamamatsu City to confirm the target and the shelling from the battleships began shortly thereafter. Although we were 20 km away, I could see the pillars of flames and hear and feel the tremendous explosions. It was a terrible scene I will never forget.
Nippon Express mobilized a vehicle fleet to move around 800 of our manufacturing machines to the Sakura Factory. Their trucks were shuttling back and forth like a piston all day and night on the roads to and from Futamata. The heavy machinery went by train to Nishikajima Station or Futamata Station and was then transported the rest of the way by truck.
10The War Ends
The day after the naval bombardment, President Kaichi Kawakami sent a long letter to Aisa-san, the chief of the second construction project, stating that the damage to the headquarters factory was so great that it was impossible to continue operations. He urged us to complete the second stage of construction as quickly as possible. I remember that things were becoming desperate and we were asked to come up with emergency countermeasures a lot more often.
On August 13th, the headquarters was officially moved from Kusunoki to the Sakura Factory. There was a radio set up facing the street in front of the office we had in Futamata that would broadcast news about the war, air raid warnings and other matters. Just before noon on August 15th, we were all gathered together at the radio. A rumor had been circulating that a very important announcement would be made and we were all very uneasy.
It began at noon and we heard the voice of the Emperor for the first time in our lives. There was so much static that we could barely understand what he said. With just this broadcast, I don’t think many of the people who were there actually understood that he was announcing the termination of the war.
As the hours passed, we all came to understand that Japan had officially surrendered and the war had ended. Even today, I have trouble describing my feelings when I realized that the war was really over.
After all the stress, hard work and personal sacrifices we made to produce propellers, I suppose my emotions were a mix of frustration and sadness at losing the war, but also relief at no longer having to fear the terrible air raids and a deep sense of uncertainty about the future. I was despondent about anything and everything.
When the war ended, Japan descended into chaos and many unpleasant aspects of human behavior bubbled to the surface. The area around the Sakura Factory was no exception and all sorts of wild rumors were thrown around. However, at our office at Jorozuka in Funagira a few days after the war’s end, President Kaichi Kawakami announced his strong intentions to rebuild and return the company to peaceful pursuits.
When I and the rest of the employees heard this, it was like a bright light illuminating a dark night and it made us immensely happy. His words echoed the joy we felt in no longer having to spend every night in the semi-darkness of the blackouts. The dark shades came off the bulbs and we were once again able to enjoy the night.
There was also some confusion among the workers about what they should do at the Sakura Factory for a while after the war ended. But after the GHQ of the Allied Occupation Forces ordered that the factory be closed and properly guarded, quite a number of workers were entrusted with this task.
The special machinery for producing propellers, in other words, the modeling machine for shaping the blades, the Natoko drill presses and other machines, the propellers themselves and aircraft drop tanks were all destroyed. However, the large Lapointe broaching machines and other general purpose machinery not dedicated to the production of wartime equipment were spared destruction and spent the next few years sleeping silently in the Sakura Factory buildings among the cedar forests.
These machines would later be what led to the birth of Yamaha Motor and they would be recalled to duty, making a significant contribution to the beginnings of the new company.
Nippon Gakki Seizo Kabushiki Kaisha Shashi, Nippon Gakki Co., Ltd.
The development, production and supply of army aviation weaponry, Asagumo Shinbunsha Inc.
Propeller drawings supplied by Toshio Takeuchi
Pe-33 propeller photo supplied by Managing Executive Officer Nemoto (in 1978)