Gentlemen (Ladies too),
Ok, this is another attempt to promote better understanding of Japanese planes. Kindly bear with me as this is one of the ways I can contribute to this community.
This is a translation (by me), so it is crude. Original is from ISBN4-89319-014-8 Army Type 3 Fighter Hien, page 15-16. I have no idea why the author presents the fuel tanks in this way but diagrams on other sources show that there is two No1 tanks, one No2 tank, and one No3 tank for a total of four. (in this translation it seems like five but Mitsu tells me that it is actually four as well). I am not a physicist, so there is a leakness in that area of the translation. Click on the attachment for the scanned images of the pages for this translation.
BTW, the term "Model 1" refers to the Ki-61-I and "fire prevention device" refers to the self-sealing fuel tanks in this translation
Mitsu, I need your quality assurance check
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Continued ModificationsStrengthening of Armament on the Model 1 The first plane from production of the Model 1 was completed in August 1942 and until the summer of 1944, a total of 1,381 planes were produced. By armament, there were four types, the Ko, the Otsu, the Hei, and the Tei. (This designations was made in December 1943)
The Model 1 Ko had one Type 89 7.7mm fixed mount machine guns in each wing, and had one Ho-103 (Type1 12.7mm fixed mount machine gun) on each side of the fuselage. (Total of 7.7mm machine guns X 2A12.7mm machine guns X 2). There was a shortage of the Ho-103 12.7mm which resulted in the usage of the type 89 7.7mm. Production numbers were from 113 to 500.
From number 113 to 420, as a fire prevention device on the fuel tanks, 3mm of rubber and 10mm of cotton felt was used. Fuel tanks consisted of the No1 Tanks, one in each wing (190 liters, total 380 liters), the No2 Tank (100 liters, total 200 liters) and No3 Tank in the fuselage (200 liters) for a total of 750 liters.
From 421 to 500, the fire prevention device on the fuel tanks consisted of 9mm of rubber on the top side, 6mm on the sides and none on the bottom. Sizes of the fuel tanks were the same.
The Model 1 Otsu had wing mounted guns replaced with the Ho-103, for a total of four 12.7mm machine guns. Production numbers were from 501. From 514, there was a detachable 8mm armour plating on the rear top side of the cooling system, which weighed 22kg.
From 514 to 649, the No3 Tank (200 liters) was removed. (Decision to remove No3 Tanks from 513 and earlier productions for both the Ko and the Otsu types was made on September 11, 1943)
From 650, the Fuel tanks were covered with 12mm of rubber on all sides. To accommodate this, the sizes of the fuel tanks decreased by about 50 liters for each tanks, making the No1 tanks to a total of 340 liters and No2 tanks to 160 liters.
It became apparent after the experience of Model 1 Otsu in actual combat that even with four 12.7mm machine guns, there was not enough firepower. In September 1943, it was decided to replace the wing mounted guns with the Mauser 151/20 20mm cannons imported from Germany.
This was the Model 1 Hei and to modify the existing Ko and Otsu planes to Hei type, a mission of engineers was sent to the southern front. At the same time, planes in production was also modified to the Hei type. Amount of production of the Model 1 Hei, including those modified and produced as the Hei type from the beginning, reached to a total of 388 planes by July 1944. Production numbers were from 3001 to 3401.
One of the Model 1 planes was used experimentally for the surface evaporation cooling system. It flew its maiden flight in October 1942 and by the end of 1943, it flew 35 times. The result of the experiment showed that it increased the top speed by about 40km/h but maintenance took time and handling was difficult.
This surface evaporation cooling system was used in the then experimental Ki-64 High Speed Fighter.
The Model 1 Tei ( Model 1 Kai)Not long after the Model 1 Hei with the Mauser cannons became active, in November 1943, the then Chief of the General Staff of the Army, General Sugiyama, visited the Gifu Factory of Kawasaki Aviation to officially request for the Ho-5 (20mm cannon) to be placed on the Ki-61.
The Technical Team was afraid of losing performance and was rather reluctant to this request. However, research was begun and in January 1944, the first plane with the modification was completed.
The Ho-5, like the Ho-103 (Type 1 12.7mm fixed mount machine guns), was a 20mm cannon derived from the American Browning design. Prototype was designed at the Army Research Institute of Aviation Technology in the 2nd half of 1942, and the prototype was produced at the Chou Industrial Technology Research Institute. It was the first 20mm cannon originally made by the Army.
It was light with a high muzzle velocity and it was on par with the German Mauser and the British Hispano in term of firepower.
The modified Ki-61 carried two Ho-5 on the fuselage and two Ho-103 12.7mm in the wings. Because from the number 650 Model 1 Otsu, the fuel tanks were decreased in size by about 50 liters due to the fire prevention rubber, the No3 tank (95 liters) was reinstated. The total fuel capacity was 595 liters.
Due to this, the nose was lengthened by 200mm to compensate (?) the center of gravity by 28.5%. The total length of the plane increased from 8.740m to 8.940m. In addition, the engine oil (?) tank which in the Ko, Otsu, Hei types had 28 liters main tank and 17 liters additional tank (for a total of 45 liters), was changed to 40 liter main tank without the additional tank.
Because this was considered as a major modification, the Ki-61-I-Kai or the Type 3 Fighter Model 1 Kai was officially designated as the Type 3 Fighter Model 1 Tei.
With this modification, the weight of the plane increased by 250kg to 2,630kg, full armament increased by 330kg to 3,460kg (according to documents in Kawasaki). Air resistance increased, and the top speed became to 580km/h (5,000m) and climb time to 5,000m to 7minutes.
1,368 Model 1 Tei were produced from January 1944 to January 1945. A few of them were modified with two wing mounted Ho-105 30mm cannons and two fuselage mounted Ho-103 12.7mm machine guns as experiments. Model 1 Tei had production numbers from 4001.
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