Kawasaki Ki-100

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A Ki-100 at the RAF Museum at Hendon, London

The Kawasaki Ki-100 was a fighter aircraft used by the Imperial Japanese Army in World War II. The Japanese Army designation was "Type 5 Fighter" (五式戦闘機).

The emergency measure of adapting a Ki-61-II-KAI fighter to carry a Mitsubishi radial engine resulted in an excellent interceptor fighter, one of the best used by the Army during the entire war. Missions began in March 1945; from the first engagements the Ki-100 showed its good qualities against the USAAF B-29 heavy bombers at high altitudes, and showed itself equally effective against U.S. Navy carrier fighters. A new variant, the Ki-100-Ib, was constructed during the last weeks of conflict to equip five sentais for home defense.

1 Origins
2 Deployment
3 Service
4 Variants
5 Specifications (Ki-100-1a/b Goshikisen)
6 External links
7 Related content

[edit] Origins

By mid-1944, one of the best fighters of the IJAAF was the Kawasaki Ki-61 Hien (飛燕、" Flying Swallow", named "Tony" by the Allies). It was the only production Japanese fighter to have an in-line powerplant (The Kawasaki Ha-40, a Japanese adaptation of the German Daimler-Benz DB 601 engine) during World War II, as well as the first one with factory-installed armor and self-sealing fuel tanks. It had also a respectable performance, more in line with current American and European designs of the time, with focus on speed and rate of climb instead of maneuverability and range. It was an effective design, but suffered from engine shortages and reliability problems.

The problems mentioned above (as well as the growing performance of enemy fighters, especially the F6F Hellcat) lead to the development of an improved model, the Ki-61-II (later Ki-61-II kai), powered by the new 1,120 kW (1500 hp) Kawasaki Ha-140 engine. Maximum speed grew from 590 km/h to 610 km/h (368 mph to 379 mph) and general performance (except climbing rate) improved as well. However, it was never able to perform as planned due to the continued degradation of the engine's assembly line quality. The production of this model ended at the beginning of 1945, when a B-29 raid destroyed the engine's production plant, leaving some 280+ finished Ki-61s without a powerplant. At this point of the war, the IJAAF was in desperate need of effective interceptors to stop the enemy bomber raids over the Japanese mainland, so it was ordered that a Mitsubishi Ha-112-H engine should be installed on those frames.

The Mitsubishi Ha-112-H was a powerful powerplant, in fact equivalent to the Ha-140, but was a radial engine. After the study of an imported Fw 190A, an example of an aircraft in which a wide radial engine had been successfully installed in an airframe with a narrow width, three Ki-61II airframes were modified to carry this engine and to serve as prototypes. As a result, on February 1, 1945, the new model was flown for the first time. The army general staff was amazed by the flight characteristics of the plane, which surpassed the Hien's in all but maximum speed (this was degraded in a small degree by the larger drag zone), and the model was order to be put in production as Army Fighter Type 5 Model 1a. The company's name was Ki-100-1a and soon another 272+ frames were modified as well.

[edit] Deployment

Army units to be equipped with this model included the 5th, 59th, 200th and 244th sentais and the 81st Independent Fighter Company. At the same time, the army ordered the development of a new, slightly modified, type, which was called Ki-100 Ib or Type-5. This model had a shorter fuselage with a bubble type canopy for improved visibility and was purposely built as a radial-engined machine. When the supply of engineless Ki-61-IIs ended, the new model came into production. Along with the previously named Army air units, the 17th, 18th, 25th, 111th, and 125th sentais were provided with training on this type.

The same Ki-100 viewed from the front. Photograph at the RAF Museum at Hendon, London

[edit] Service

The Ki-100 was soon encountered in combat by Allied forces, and it was rated by them as a first-class combat machine. A well-handled Ki-100 was able to out-maneuver any American fighter, and was (more or less) equally fast to them, specially at medium altitudes. In one encounter over Okinawa, one Ki-100-equipped unit destroyed 14 Hellcats without losses to themselves. The Ki-100 was also able to match the P-51D Mustangs and the P-47N Thunderbolts which were escorting the B-29 raids over Japan by that time, and in the hands of an experienced pilot, it could defeat them (the Army's Ki-84 and the Navy's Kawanishi N1K-J being the only other types able to achieve this). Against the B-29s themselves, however, things began to get difficult for the Japanese fighters, as the engine's performance decreased at high altitudes. The most effective way to attack the Superfortress, then, was by making very dangerous head-on attacks, changing their approach path as they neared the bombers. Of course, a failure while attempting this was deadly, because of the defensive fire concentration of the bombers. In this type of combat, the navy's Mitsubishi J2M Raiden interceptor was superior. After the bombing of the Kagamigahara plant and the slow deliveries of components by the satellite plants, production rates of the Ki-100 began to fall more and more, and in the period between May and July, only 12 units were delivered. Finally, production ended due to the bombing, with only 99 examples of the type-5 delivered, which was, in fact, very fortunate for the Allies.

Improvement of the basic model lead to the Ki-100-II, with a supercharged engine for high altitude interception of the B-29s, but only four examples were built, and it never saw combat.

The engine was reliable in contrast to the higher-powered mechanical nightmares of the Nakajima Ki-84, Kawasaki Ki-61, and Kawanishi N1K-J that kept many aircraft grounded. Although slow in level flight for 1945, Ki-100 could dive with P-51 Mustangs unlike most Japanese fighters and hold the speed on pullout. The cannons had 250 20x94 mm rounds/gun, each projectile weighing 112 g (armor-piercing) or 79 g 12% high explosive. Muzzle velocity was 700 (730 HE) m/s (2,300 ft/s; 2,400 ft/s) giving an effective range of 900 m (2,950 ft). The 850 rounds/min firing rate decreased by roughly 27% when synchronized through the propeller. Still, it remained fast enough (620.5 rounds/min) even by Western standards. The wings carried 250 12.7x81 mm rounds/gun. Each machine gun bullet weighed 35.4 g AP (33-38 g 2.2%HE) and had a muzzle velocity of 760 m/s (770-796 HE) (2,450 ft/s; 2,500-2,600 ft/s) giving an effective range of 750 m (2,460 m). Rate of fire was 900 rounds/min.

Unlike nearly all other Japanese military aircraft, the Ki-100 was not given an allied codename, a very glaring omission considering that the aircraft was frequently encountered in combat during the last months of the war.

[edit] Variants

Ki-100 (prototypes): one batch of Kawasaki Ki-61 II KAI with radial engine.
Ki-100 Ia: Fighter Type 5 of Army (mark Ia) initial model of series, KI-61 II KAI modified
Ki-100 Ib: (Mark Ib) total vision cabin
Ki-100 II (prototypes): engine Mitsubishi Ha-112-II Ru with turbocompressor, 1,500 hp (1,100 kW).
Total production: 121 examples.

[edit] Specifications (Ki-100-1a/b Goshikisen)

General characteristics

Crew: 1
Length: 8.82 m (28 ft 11 in)
Wingspan: 10.48 m (34 ft 4 in)
Height: 3.75 m (12 ft 4 in)
Wing area: 20 m² (215 ft²)
Empty weight: 2,525 kg (5,567 lb)
Loaded weight: 3,495 kg (7,705 lb)
Powerplant: 1× Mitsubishi Ha 112-II radial engine, 1,119 kW (1,500 hp) at 6,000 m (19,685 ft)