Aviation of World War II
In 1937, almost immediately after the release of the mission for the high-speed single-engine reconnaissance aircraft Ki-15, the Army Air Headquarters, represented by Major Fujita and engineers Tanaka and Ando, began to prepare specifications for the next generation aircraft in this class. On December 12, 1937, these specifications were transferred to Mitsubishi. The aircraft required a long range and the ability to avoid interception by fighters. The plane had to go for six hours at a speed of 400 km / h at an altitude of 4000-6000 m. The maximum speed was set at 600 km / h. The armament was to consist of one 7.7-mm type 89 machine gun in the rear of the cockpit. Mitsubishi could choose the configuration of the aircraft itself: single or twin engine. The engine could be chosen among the Nakajima Ha-20b with a capacity of 790 hp, the Nakajima Ha-25 with a capacity of 950 hp. and Mitsubishi Ha-26 with 850 hp. To achieve such high flight data, the company was exempted from any other requirements usual in such cases.
By the time the preliminary study of the Ki-46 began, the chief engineer of the Tomno Kubo company had experience working on the Ki-39 project, a two-seat twin-engine long-range fighter that competed with the Kawasaki Ki-38, and on the reconnaissance project based on it. In addition, Tomio Kubo worked closely with the Aviation Research Institute of the University of Tokyo, where aerodynamically very clean hoods were developed for the Mitsubishi Ha-26 engines - 14-cylinder "stars". The hoods not only improved the pilot's view to the sides and reduced air resistance, they also made it possible to completely remove the landing gear legs into the nacelles. To achieve high performance, Kubo chose a very thin wing profile and a fuselage with a minimum diameter. The fuel was located in a large tank near the center of mass of the aircraft, so that the pilot and radio operator were housed in separate cabins, separated by the tank. The design of the aircraft progressed slowly, as it required blowing in the wind tunnel of the Aviation Institute. The aircraft was produced by the Nagoya plant only in early November 1939.
On the first flight, the plane was lifted by Major Fujita - the one who developed the specifications for the car. The aircraft was equipped with two Mitsubishi Xa-26-I engines with a combat power of 900 hp. at an altitude of 3600 m. The propellers were three-bladed, variable pitch. The prototype aircraft proved to be quite satisfactory, and although the maximum speed was only 540 km / h at an altitude of 4000 m - 60 km / h below the target, the aircraft was well received by the army, since it still exceeded the speed of the Ki-15-I and was not inferior even to the A6M2 fighter, which had just been adopted by the fleet. The reconnaissance aircraft was put into production under the designation "Army reconnaissance aircraft, type 100, model 1" Ki-46-I.
While the Ki-46 was being tested, Mitsubishi developed an improved version of the Na-26-I engine with a two-speed supercharger - the Ha-102, which produced 1080 hp at takeoff. and 1055 hp. in combat mode at an altitude of 2800 m. It was expected that with the new engines the Ki-46 would be able to fulfill the speed requirements, and Mitsubishi received an order to urgently prepare the Ki-46-II for them. Before the new version was ready, the pre-production Ki-46-I entered service with the army flight school in Shimositsu. They were used for pilot training and military trials. During military tests, a number of minor problems were solved, but in general, the pilots and maintenance personnel decided that the new aircraft turned out to be much more complex than its predecessor Ki-15, and it is rather difficult to operate it in the field. Fuel vapors have often blocked the operation of fuel lines, especially in hot and humid climates. In Taiwan, in June 1940, special tests of the Ki-46-I were carried out, and in June 1941, with the Ki-46-II. As a result, they switched from 87-octane gasoline to 92-octane gasoline, and the wiring of the fuel lines in the area of the engines was changed. The pilots noted that on long flights at operating altitude, the oil overheated, which required a slow climb, the response to the ailerons was slow, and the elevator was ineffective. In addition, the crew's oxygen system was unreliable. However, the main problem turned out to be the landing gear - because of the sharp failures of the aircraft on alignment, it often came to the breaking of the struts. Despite the introduction of a rear reinforcing brace, landing gear struts were literally the weak point of the aircraft throughout its entire career. However, all these problems did not prevent the aircraft from flying - it quickly went into series, and the shortcomings, in the main, were solved by successive improvements.
The first Ki-46-II with the Ha-102 engine flew in March 1941 and at the very beginning of the tests showed a speed of 604 km / h at an altitude of 5800 m, which even exceeded the task figure. Since the design of the Ki-46-II airframe practically did not differ from the Ki-46-I, the tests took place very quickly. As the serial production expanded, starting in July 1941, the aircraft began to enter service with the 18th, 50th, 51st, 70th, 74th, 76th and 81st "dokuritsa dai sidjugo chutais" (separate squadrons) in Manchuria and China. The Ki-46's high speed allowed it to get away from the few fighters available to the Chinese Air Force. With the beginning of preparations for the war in the Pacific, the Ki-46-IIs were moved to French Indochina. On October 20 and 22, 1941, headquarters officer Captain Ikedo carried out additional reconnaissance of the landing area in Malaya, which was chosen by the Japanese high command. With the outbreak of hostilities, small Ki-46 units were deployed throughout Southeast Asia. The "Army Type 100" carried out its missions practically without fear of interception by allied fighters.
Without locator guidance, obsolete American and British fighters simply did not have time to gain the desired altitude in time. Such advantages of the aircraft attracted the attention of the fleet to it, which obtained several aircraft. These naval vehicles were used from North Timor for reconnaissance in Northern Australia, while the army Ki-46s operated as far as the Bay of Bengal.
When the Americans began to use the Lightning P-38F in the Pacific, and the British in the Darwin area - the Spitfire-V, the losses of the Ki-46-II increased dramatically. Fortunately for the Japanese, the army's air headquarters had already foreseen such a situation, and already in May 1942, Mitsubishi issued an order to install the 1500 hp Ha-112-II engines on a new version of the Ki-46-III aircraft. The maximum speed was required at 650 km / h for one hour. In addition, the flight duration should be increased, which, together with the greater "gluttony" of the new engines, forced the redesign of the fuel system. Another tank was installed in front of the pilot, which increased the fuel supply from 1675 to 1895 liters. The suspension of the ventral discharged fuel tank of 460 liters was provided. The nacelles were also slightly enlarged due to the larger diameter of the Xa-112-II engines - modifications of the Xa-102 for direct fuel injection. The landing gear has been reinforced. The defensive machine gun was no longer installed in the rear of the cockpit - although it was provided for on previous models, it was usually removed in the field units. Externally, the new model was distinguished by a new cockpit canopy - already without a ledge in the nose, as in the first modifications.
Ki-46. Combat Use.
The first two Ki-46-IIIs were ready in December 1942. After accelerated testing, the aircraft was put into production under the designation "Army reconnaissance aircraft, Type 100, Model 3". Ki-46-III was produced at the plant in Nagoya along with the previous model - production of the Ki-46-II was discontinued only at the end of 1944, amounting to 1,093 aircraft. However, in December 1944, the plant was damaged by an earthquake, and subsequent raids by American B-29s forced the transfer of work to a new plant in Toyama, where another hundred aircraft were built. The last serial Ki-46-III produced by the factories in Nagoya and Toyama received jet pipes, which somewhat improved the aircraft's speed data. A total of 609 Ki-46-IIIs were produced.
Ki-46-III arrived primarily in areas where the Allies established air superiority, and they were often used in conjunction with the previous model - Ki-46-II, which was never completely replaced. After solving minor problems with the fuel injection system on the Na-112-II, the Ki-46-III showed excellent flight data, primarily at altitudes of 8000-10000 m.The aircraft turned out to be difficult to intercept - only fighters with maximum climb rate, guided by radar data, had a chance ... All this allowed the Japanese reconnaissance aircraft to carry out their tasks even over such well-defended bases as the B-29 airfields on the Mariana Islands. However, by the end of the war, the losses of the Ki-46 still began to grow sharply.
With the expansion of the production of "Model 3", a small number of the previous "Model 2" were redesigned for three-seater aircraft for training radio navigators. A ledge was installed behind the cockpit for the third crew member. This aircraft was designated Army Type 100 Trainer (Ki-46-II KA1) and was used by the Army Flight School in Shimositsu.
The high speed of the aircraft also made it possible to hope for the creation of an effective interceptor fighter on its basis. Work on converting the reconnaissance aircraft into a fighter began in June 1943 by the Army Aviation Research Institute (in Japanese "Rikugun kokugitsu kenkuyo"). The reason for them was the excellent altitude characteristics of the Ki-46 - at an altitude of 6000 m, it developed 637 km / h and had a long flight duration. The last modification of the Ki-46-III with engines of the Mitsubishi Xa-112-II company with 1500 hp each was taken as a basis. The front gas tank and photographic equipment were removed from the bow and two Ho-5 cannons were placed there. The cockpit canopy was redesigned to resemble the earlier Ki-46-II (with a "stepped" nose). A Ho-203 cannon was placed between the pilot's and the gunner's seats with an inclination of 30 "to the 37th horizon, so that it could shoot forward - upward. The 7.69-mm machine gun was removed from the gunner to save weight.
The first sample, designated Ki-46-III-KAI, was manufactured in October 1944. It was successfully tested and was adopted as a "Type 100 fighter-interceptor". Serial production of new heavy fighters was established by the 1st Aviation Arsenal, located there, in Tachikawa. Since the end of November, Ki-46-III-KAI began to arrive in air defense units, mainly in the metropolis. The 106th regiment and the 81st separate squadron (the last in Manchuria) were the first to master these machines. In total, two regiments, five separate squadrons and one separate link received them.
The disadvantages of the Ki-46 as a fighter were, first of all, a low rate of climb and insufficient combat survivability. The first led to the fact that it was required to raise planes in the air in advance, gain altitude and wait for a suitable enemy formation. But for this it was necessary to have a deployed air defense radar network, which the Japanese did not have. Low combat survivability greatly reduced the value of the Ki-46 when attacking formations of enemy bombers. While he was a scout, he was saved by speed and height, making it possible to evade collisions with the enemy. Now it was necessary to "shake on the rampage" and the lack of body armor and protected fuel tanks cost dearly to the crew of improvised fighters. The Ho-203 cannon, which had a low rate of fire, was also criticized.
In January 1945, Mitsubishi completed a modification of the Ki-46-IIIOtsu. It actually differed from the Ki-46-IIIKAI only in the absence of the Ho-203 cannon, and was intended primarily for the destruction of ground targets. It was adopted as a "Type 100 attack aircraft", but only a few copies were produced. The Ki-46-III Hey variant with two obliquely mounted Ho-5 cannons remained in the blueprints.
On the basis of the excellent Ki-46-IV reconnaissance aircraft with Ha-112-II-Ru engines equipped with turbochargers, the Ki-46-IV-Otsu high-altitude fighter with cannon armament was designed according to the model of the Ki-46-IIIOtsu. This plane was never built.