Nakajima Ki-84

The is a single-seat fighter flown by the Imperial Japanese Army Air Service in the last two years of World War II. The Allied reporting name was "Frank"; the Japanese Army designation was . The Ki-84 is generally considered the best Japanese fighter to operate in large numbers during the conflict. The aircraft boasted high speed and excellent maneuverability with an armament (up to two 30 mm and two 20 mm cannon) that gave it formidable firepower.

The Ki-84's performance matched that of any single-engine Allied fighter it faced, and its operational ceiling enabled it to intercept high-flying B-29 Superfortress bombers. Pilots and crews in the field learned to take care with the plane's high-maintenance Nakajima Homare engine and landing gear prone to buckling. The Ki-84 first flew in March 1943 and deliveries from Nakajima's Ota factory commenced the following month. Although the design was itself solid, growing difficulties in securing skilled pilots, proper fuel and construction materials, and adequate manufacture often prevented the aircraft from reaching its full potential in the field.

The design of the Ki-84 addressed the most common complaints about the popular and highly maneuverable Ki-43: insufficient firepower, poor defensive armor, and lack of climbing speed. The Ki-84 was a cantilever low-wing monoplane of all-metal construction, except for the fabric-covered control surfaces, with conventional landing gear.

Armament comprised two fuselage-mounted, synchronized 12.7 mm (.50 in) machine guns — these proved challenging to synchronize properly with the Hayates four-blade propeller — and two wing-mounted 20 mm cannon, a considerable improvement over the two 12.7 mm (.50 in) machine guns used in the Ki-43 Hayabusa. Defensive armor offered Hayate pilots better protection than the unsealed wing tanks and light-alloy airframe of the Ki-43. In addition, the Ki-84 used a 65 mm (2.56 in) armor-glass canopy, 13 mm (.51 in) of head and back armor, and multiple bulkheads in the fuselage, which protected both the methanol-water tank (used to increase the effectiveness of the supercharger) and the centrally located fuel tank.

It was the Nakajima firm's own-designed displacement, Ha-45 Homare ("Praise" or "Honor") air-cooled eighteen-cylinder radial engine, first accepted for military use in 1941, that gave the Hayate its high speed and prowess in combat. Derived from the Nakajima Homare engines common to many Japanese aircraft, the Hayate used several versions of the Homare engine, including the carbureted model 21 and the fuel-injected model 23 versions of the engine. Most Homare engines used water injection to aid the supercharger in giving the Ki-84 a rated 1,491 kW (2,000 hp) at takeoff. This combination theoretically gave it a climb rate and top speed roughly competitive with the top Allied fighters. Initial Hayate testing at Tachikawa in early summer 1943 saw test pilot Lieutenant Funabashi reach a maximum level airspeed of 624 km/h (387 mph) in the second prototype. In 1946, US Technical Intelligence bench-tested a Homare 45, Model 21 engine and verified the engine's maximum horsepower output using 96 octane AvGas, plus methanol injection.

The complicated Ha-45-21 carbureted engine was a compact design (only larger in diameter than the Ki-43's 14-cylinder Nakajima Sakae radial) that required a great deal of care in construction and maintenance and it became increasingly difficult to maintain the type's designed performance as the Allies advanced toward the Japanese homeland. To compound reliability problems, the Allied submarine blockade prevented delivery of crucial components, such as the landing gear. Many landing gear units were compromised by the poor-quality heat treatment of late-war Japanese steel. As a result, many Hayates suffered strut collapses on landing. Further damage was caused by inadequately trained late war pilots, who sometimes found it difficult to transition to the relatively "hot" Ki-84 from the comparatively docile Ki-43, which had a significantly lower landing speed.

Operational service

The first major operational involvement was during the Battle of Leyte at the end of 1944, and, from that moment until the end of the Pacific War, the Ki-84 was deployed wherever the action was intense.

! rowspan=2| Year

! Jan. || Feb. || Mar. || Apr. || May || June || July || Aug. || Sept. || Oct. || Nov. || Dec. || Annual

|style="text-align:center"| 1943

| || || || || || || || 1 || 1 || 3 || 11 || 8 || style="background: #eee;" | 24

|style="text-align:center"| 1944

| 9 || 25 || 25 || 97 || 86 || 138 || 145 || 121 || 261 || 301 || 323 || 373 || style="background: #eee;" | 1,904

|style="text-align:center"| 1945

| 357 || 129 || 216 || 185 || 198 || 168 || 194 || 48 || || || || || style="background: #eee;" | 1,485

|- style="background: #eee;"

| style="text-align:center" | Total

| || || || || || || || || || || || || style="border-top: black solid"| 3,413

Not included:

Pre-production started with two prototypes completed in March and April 1943.

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Indonesian Air Force - In 1945, Indonesian People's Security Force (IPSF) (Indonesian pro-independence guerrillas) captured a small number of aircraft at numerous Japanese air bases, including Bugis Air Base in Malang (repatriated 18 September 1945). Most aircraft were destroyed in military conflicts between the Netherlands and the newly proclaimed Republic of Indonesia during the Indonesian National Revolution of 1945–1949.

Surviving aircraft

After the war a number of aircraft were tested by the allied forces, two at the Allied Technical Air Intelligence Unit - South-West Pacific Area (ATAIU-SWPA) as S10 and S17 and a further two in the United States as FE-301 and FE-302 (Later T2-301 and T2-302).

One example captured at Clark Field during 1945, serial number 1446, was transported aboard the aircraft carrier USS Long Island to the United States. In 1952 it was sold off as surplus to Edward Maloney, owner of the Ontario Air Museum (Planes of Fame Air Museum) and restored to flying condition before being returned to Japan for display at the Arashiyama Museum in Kyoto in 1973. With unsupervised access allowed to the aircraft, parts were stolen from the Ki-84, and coupled with the years of neglect it could no longer fly. Following the museum's closure in 1991, the aircraft was transferred to the Tokko Heiwa Kinen-kan Museum, Kagoshima Prefecture, where it still is displayed to this day. It is the only surviving Ki-84.

Gallery

File:Ki-84-Right_front_view.jpg|

File:Ki-84-Right_fuselage_and_wing_root.jpg|

File:Ki-84-Front_view.jpg|

File:Ki-84-Left_front_view.jpg|

File:Ki-84-Left_rear_view.jpg|

File:Ki-84-Left_tail.jpg|

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Specifications (Ki-84-Ia)

thumb|3-view drawing of Nakajima ki-84