Aviation of World War II
Heavy Fighter Interceptor
Chief Designer Kyunosuke Ozawa. The first flight of the prototype took place in February 1944.
At the end of 1943, Japanese intelligence was able to obtain very detailed information about the new US heavy bomber B-29 "Superfortress", which was supposed to be used for massive strategic attacks on Japan. In response, it was necessary to create a heavy interceptor fighter capable of destroying high-altitude, well-armed American vehicles. Build a car from scratch? But there was no time left for that.
Specialists of the 1st Aviation Arsenal of the Japanese Army in the city of Tachikawa came to the conclusion that the well-proven Ki-67 heavy bomber would be suitable for these purposes, which by that time had demonstrated excellent speed and maneuverability. The project received the designation Ki-109 and provided for two options: Ki-109a - "killer" with a pair of 37-mm No-203 cannons, mounted tilted under the fuselage, and Ki-109b - "hunter" with a locator and a 40-cm anti-aircraft searchlight ... However, the project was soon revised - at the suggestion of Major Sakamoto, it was decided to install the usual 75-mm Type 88 anti-aircraft gun on the Ki-67. It was assumed that the firing range of this gun, more than 1 km, would allow the fighters to operate without entering the defensive fire zone. Since the army's air headquarters assumed that the B-29s would operate without fighter cover, the project was considered successful. The work was approved in January 1944, and the aircraft retained the designation Ki-109.
The Mitsubishi design team, led by the chief engineer of the project, Kyunosuke Ozawa, developed a new nose and strengthened the Ki-109 fuselage, keeping all the firing points. The first prototype was ready in August 1944, and two months later the B-29s made their first raid on Japan. Ground and air fire tests were conducted by Major Makiura from the Aviation Institute in Tachikawa. The tests were successful, and an order for 44 aircraft followed. The first 22 were powered by two 1900hp air-cooled Mitsubishi Ha-104 engines. Subsequent aircraft were planned to be equipped with Ha-104 Ru with Ru-3 turbochargers, which would improve the fighter's altitude performance, so important for intercepting the B-29. These engines were tested on the second prototype Ki-109, but in reality production vehicles did not receive them.
The only problem with the Ki-109 was its too heavy weight, which drastically reduced the aircraft's climb rate. This was unacceptable for the interceptor. To raise the rate of climb on the first prototype aircraft, solid fuel boosters were placed in the bomb bay, but this scheme was not adopted. Starting with the third Ki-109, the turrets were removed and the bomb bay repaired. Reduced the fuel supply (from 5116 liters to 2152 liters). The gun's ammunition consisted of 15 rounds. The gun was manually reloaded by the co-pilot. The defensive armament consisted of a 12.7 mm Type 1 Ho-103 machine gun in the tail mount.
Despite the insufficient altitude characteristics, the Ki-109s were adopted by the 107th Sentai, but by the time a sufficient number of such fighters arrived, the B-29 had already switched to night raids from low altitudes and the Ki-109 was out of work. The 107th Sentai was disbanded on July 30, 1945, and there are no air victories for it.