Initially, kamikazes flew only on production aircraft of existing types, which underwent some revision. However, this approach did not justify itself from an economic and tactical point of view. January 20, 1945 army command aviation placed an order to create a new aircraft, originally adapted for a single flight to a target without the possibility of return. At the request of the customer, the aircraft should have been characterized by extreme simplicity of production and the lowest possible cost. In the future, it was planned to assemble it even in small workshops with disabilities.
Serial aircraft "Nakajima" Ki-115 "Tsurugi". Photo San Diego Air & Space Museum / sandiegoairandspace.org
From the aircraft did not require high flight performance, but he had to have a chance to break through the enemy's air defense. For this, the cruising speed had to be at the level of 340-350 km / h, the maximum at the dive in front of the target - more than 500 km / h. The armament was to consist of one medium-caliber aerial bomb carried under the fuselage.
An order to create a kamikaze aircraft was received by the Nakajima company, one of the leaders of the Japanese aviation industry. The development of the project was transferred to the subsidiary Ota Seisakusho. To carry out some work to the project attracted Mitaka Research Institute. The main designer of the project was Aori Kunihara.
In accordance with the Japanese nomenclature of aircraft designations, the new aircraft received the designation Ki-115. In addition, he was given the name "Tsurugi" - in honor of one of the types of the Japanese direct sword.
Scheme of the Ki-115 aircraft after finishing. Photo Airwar.ru
According to the project, the plane Ki-115 was supposed to be a cantilever nizkoplan with a three-point chassis, equipped with a tail crutch. In the nose of the fuselage provided for the installation of engines of several models, which was initially taken into account in the project. To obtain optimal characteristics, it was proposed to use the simplest discharged chassis, to abandon the developed wing mechanization and introduce several other ideas.
The plane was supposed to be simple and cheap, which affected the materials used. The fuselage power set was proposed to be made of steel pipes, the covering - of sheet metal, duralumin and canvas. The whole wing should be made of dural, tail - from wood. The plumage was also supposed to get plywood trim. At the same time, the finished airframe, at least, outwardly resembled the aggregates of many other Japanese and foreign aircraft.
One of the Japanese drawings. Photo by National Air and Space Museum / smithsonian airandspace.si.edu
For most of its length, the aircraft fuselage had a circular cross section. Behind the cockpit, the diameter of the fuselage decreased, forming a tail boom. In the forward part of the fuselage there was a metal motorama, initially compatible with various Japanese engines. Due to this, serial aircraft could be equipped with any available air-cooled motors with sufficient characteristics. The engine was covered with a tin hood.
Directly behind the engine were placed the fuel and oil tank, as well as some other devices. They placed a single cabin. The tail boom was empty, inside it there was only a wiring control rudder.
Design of drop landing gear. "A" and "B" - the design of the locks. Photo by National Air and Space Museum / smithsonian airandspace.si.edu
The aircraft received a duralumin wing with a straight leading edge. The trailing edge of the planes had a negative sweep. Rounded tips were used. The wing planes were installed with a noticeable transverse V. An interesting feature of the wing, associated with the need to simplify the design, was the lack of developed mechanization. On the outer part of the trailing edge, a pair of ailerons with cable wiring was placed. The flaps were initially absent.
The tail fin included a keel with a small sweep of the leading edge and a relatively large rudder. The stabilizer was made straight and also equipped with a large wheel area. It is curious that, despite the desire to simplify the design, the engineers of Nakajima still equipped the rudders with trimmers.
General view of the Ki-115. Photo Airwar.ru
In accordance with the technical specifications, the kamikaze airplane Ki-115 should have been completed with any available engines with a capacity of at least 800 hp. Taking into account the designs of different motors of the time, a universal motor mount was created. However, such opportunities in practice were not useful. All serial "Tsurugi" were completed only with 14-cylinder star-shaped engines Xa-35 Py 23 of Nakajima, which developed the power of 1130 hp. A metal screw of constant pitch with a diameter of 2,9 m was mounted on the motor shaft.
Cooling of the cylinder block was carried out due to the oncoming flow of air entering under the hood. The oil system of the power plant included a radiator located in the root of the right half wing. Above the center section was a fuel tank with a capacity of 450 l.
Front view. Photo Airwar.ru
Over the rear of the center section placed single cockpit. She had not very developed equipment, but fully complied with the requirements. On the dashboard fit all the necessary devices for monitoring systems and piloting. There was a traditional set of controls based on knobs and pedals.
The cabin was closed with a canopy visor consisting of three glass panels. Behind it was a gargrotta with a pair of side windows. The lantern did not have a central section and did not close.
Ki-115 got the simplest chassis. Under the wing was placed a pair of main racks. These devices were assembled from metal pipes and had a frame structure. The rack was equipped with a relatively large diameter wheel and did not have a shock absorber. On the wing of the rack were fastened with the help of locks: after takeoff, they were asked to drop. In the tail of the fuselage there was a metal crutch, also without a shock absorber.
"Tsurugi" in the assembly shop. The machine has an improved wing and updated mechanization. Photo by National Air and Space Museum / smithsonian airandspace.si.edu
Under the center section in the fuselage there was a recess for the suspension of bombs, in which there were locks. According to the project, the plane "Tsurugi" could fly into the air one bomb in caliber from 250 to 800 kg. It was assumed that this would be enough to defeat various ships or enemy ground targets. In connection with the alleged specificity of combat use, the pilot should not have dropped the bomb: he was asked to crash into the target along with it. For an exact exit on the appointed purpose it was offered to use the elementary telescopic sight fixed on a peak of a lamp.
Ki-115 was not supposed to fight with the enemy's aircraft, and therefore did not receive cannon or machine-gun weapons. It was assumed that on the way to the target the kamikaze aircraft would cover their fighters. In addition, the presence of barreled weapons could significantly increase the cost of the machine.
Dashboard aircraft. Photo Airwar.ru
The finished aircraft "Tsurugi" was supposed to have a length of 8,55 m with a wingspan of 8,57 m. The wing area is 12,2 sq.m. Parking height - 3,3 m. Own weight of the structure was only 1640 kg. Normal take-off weight was determined at the level of 2630 kg, the maximum - at 300 kg more. According to calculations, the plane was supposed to develop cruising speed in 300 km / h, maximum - 500 km / h. Flight range - to 1200 km.
The first prototype of the Nakajima Ki-115 Tsurugi aircraft was built in March of the 1945 of the year, and was immediately put to the test. Checking the car on the ground ended in failure and showed the need for many improvements. The chassis without springs and brakes significantly hampered taxiing on the ground and run. An attempt to lift the plane into the air was also unsuccessful. He was too heavy for his wing, and therefore the run was different in unacceptable length.
Handle control aircraft. Photo by National Air and Space Museum / smithsonian airandspace.si.edu
The next few weeks, the designers headed by A. Kukhinara spent on refining the various elements of the design. First of all, improved wing. The rear edge had to be strengthened and equipped with new flaps of a small area. Also it was necessary to develop a new control system for the release of these planes. Despite the noticeable complication of the design of the aircraft, this made it possible to lift it into the air and carry out comprehensive tests.
Also in the course of refining engineers redesigned the chassis several times. At first, only brakes appeared on the racks of a simplified design. This had some effect, but the lack of depreciation did not eliminate all the problems. Soon a new version of the main rack with rubber shock absorbers appeared. A simple crutch received a simplest spring.
Engine control knob. Photo by National Air and Space Museum / smithsonian airandspace.si.edu
During the tests and refinement, new original ideas were worked out. So, for additional acceleration at the time of the attack it was proposed to use solid fuel boosters. This idea was tested during the tests, but the results of these tests, unfortunately, are unknown.
According to the results of the first tests of the Ki-115 in the base configuration, it was proposed to develop an improved version of the project. Airplane Ki-115 Otsu first of all had to be different from the existing “Tsurugi” wooden wing of increased size. Metal remained only aileron framework and flaps. It was proposed to move the cockpit slightly forward to improve visibility on takeoff
From a certain point, the command of the Japanese became interested in the Ki-115 project fleet. They proposed the development of a special deck modification of this aircraft, which had characteristic differences. This project started in the spring of 1945, but did not manage to give real results. Design work continued until the very end of the war, because of which the decked version of the Tsuruga did not reach the test stage.
Serial Ki-115 after removing some units. Probably a post-war snapshot. Photo Airwar.ru
By the beginning of the summer of 1945, Nakajima had completed the tests and received permission to start mass production. The main site for production was to be the company's plant number XXUMX in the city of Ota. A little later, the plant in Ivata was attracted to the project. According to the original plans of the customer, the new kamikaze planes could be made even in various small workshops, but this proposal was never implemented, and all the serial "Tsurugi" were assembled by a pair of full-fledged plants.
Before the end of the war and the surrender, Japan managed to build X-NUMX planes such as the Ts-105 Tsurugi. The bulk of this technology - the 115 prototype and the 1 serial machines - was assembled in Ote. Another 82 aircraft built a factory in Iwate. According to various sources, at least a part of this equipment was transferred to the customer and entered service.
Trophy "Tsurugi" at the entrance to the air base in Yokot, 1948 year. Photo of US Air Force
Apparently, the end of spring and the summer of 1945, the year went to the development of a new aircraft and the preparation of future suicide pilots. Despite all the efforts of the designers, the simplified and cheap aircraft was not very easy to fly, and therefore the kamikaze pilots had to spend time and effort on their studies. Apparently, this fact led to the fact that the serial Ki-115 could not take part in the battles.
Until the very end of the war in the Pacific, Tsurugi aircraft remained far from the front. They have never been used for its intended purpose. As a result, the opponents in the person of the United States, and then the Soviet Union, did not even realize what a severe surprise for them Japan is preparing in an atmosphere of strict secrecy. Moreover, the foreign military learned about the existence of a new kamikaze aircraft only after victory. The commission of the victorious countries inspected the Japanese military factories, and during such trips found several previously unknown samples of aircraft.
The Ki-115 aircraft at the Pima Air & Space Museum (USA, Tucson). Photo Wikimedia Commons
Planes found were carefully studied on the ground and tested in the air. According to the results of such tests, experts made one or other conclusions. In particular, a search was conducted for ideas and solutions suitable for use in their own projects. The project of a simplified aircraft intended for a single flight to a target, as expected, did not arouse much interest. However, information about the Ki-115 allowed to supplement the existing picture and expand the available data on the Japanese aircraft industry.
After the defeat of the Japanese Empire, special aircraft had no prospects. Constructed serial "Tsurugi" turned out to be useless, which determined their further fate. Unusual aircraft sent for recycling. In the shortest possible time, almost all of the built machines were dismantled at Japanese enterprises. Only a few of these aircraft survived. In particular, one of them is part of the exposition of the National Museum of Aeronautics and Aeronautics of the USA (Washington, DC), the other is stored in one of the Japanese museums. The “Japanese” model from the late forties stood at the gate of one of the air bases. Later it was restored and became a museum exhibit. Also known other instances in varying degrees of preservation.
The main goal of the Nakajima Ki-115 Tsurugi project was to create a promising aircraft of the simplest design possible to perform a single sortie and at the cost of its own life to destroy the designated target. The task of simplifying and reducing the cost of construction, with certain reservations, was solved. However, this led to several significant technical and operational problems that could hinder combat use. As a result, the finished equipment did not hit the front and had no influence on the course of the war.
On the materials of the sites:
https://airandspace.si.edu/
http://airwar.ru/
http://alternathistory.com/
http://aviadejavu.ru/
https://militaryfactory.com/