Nakajima Ki-84



The Nakajima Ki-84 "Hayate" (キ84 疾風"Gale") was a single-seat fighter used by the Imperial Japanese Army Air Force in World War II. The Allied reporting name was "Frank"; the Japanese Army designation was Army Type 4 Fighter (四式戦闘機). Featuring excellent performance and high maneuverability, the Ki-84 was considered to be the best Japanese fighter to see large scale operations during World War II. It was able to match any Allied fighter, and to intercept the high-flying B-29 Superfortresses. Its powerful armament (that could include two 30 mm and two 20 mm cannon) increased its lethality. Though hampered by poor production quality in later models, a high-maintenance engine, a landing gear prone to buckle, and lack of experienced pilots above all else, Hayates proved to be fearsome opponents; a total of 3,514 were built.

Design and development
Design of the Ki-84 commenced in early 1942 to meet an Imperial Japanese Army Air Service requirement for a replacement to Nakajima's own, earlier Ki-43 Oscar fighter, then just entering service. The specification recognized the need to combine the maneuverability of the Ki-43 with performance to match the best western fighters and heavy firepower. The Ki-84 first flew in March 1943. Although the design itself was solid, the shortage of fuel and construction materials, poor production quality, and lack of skilled pilots prevented the fighter from reaching its potential.

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 power. The Ki-84 was a cantilever low-wing monoplane of all-metal construction, except for the fabric-covered control surfaces. It had retractable tailwheel landing gear. Armament comprised two fuselage-mounted, synchronized 12.7 mm (.50 in) machine guns and two wing-mounted 20 mm cannon, a considerable improvement over the two 12.7 mm (.50 in) machine guns used in the 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 Ha-45 radial powerplant that gave the Hayate its high speed and prowess in combat. Derived from the Homare engine common to many Japanese aircraft, the Hayate used a direct-injection version of the engine, using 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. After the war, a late-production, captured example was tested in the US with high octane fuel, and achieved a speed of 687 km/h (426 mph).

The complicated direct-injection engine required a great deal of care in construction and maintenance and, as the Allies advanced toward the Japanese homeland, it became increasingly difficult to support the type's designed performance. Compounding reliability problems were the Allied submarine blockade which prevented delivery of crucial components, such as the landing gear. Many further landing gear units were compromised by the poor-quality heat treatment of late-war Japanese steel. Many Hayates consequently suffered strut collapses on landing. Further damage was caused by inadequately trained late war pilots.

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. The 22nd Sentai re-equipped with production Hayates. Though it lacked sufficient high-altitude performance, it performed well at medium and low levels. Seeing action against the USAAF 14th Air Force, it quickly gained a reputation as a fighter to be reckoned with. Fighter-bomber models also entered service. On April 15, 1945, 11 Hayates attacked US airfields on Okinawa, destroying many aircraft on the ground.

The IJAAF's Ki-84, Kawasaki Heavy Industries' Ki-100, and the Kawanishi Aircraft Company's N1K2-J IJNAF naval fighter were the three Japanese fighters best suited to combat the newer Allied fighters.

Camouflage and markings
The Ki-84 is known to have appeared in three Japanese Ministry of Munitions sanctioned camouflage schemes;

Type N: The entire airframe was left in its original natural metal. Because of the different grades of alloy used for various panels, the overall finish soon weathered or oxidized to a pale metallic grey, with variations in shade and texture, depending on the grade of duralumin used for each area of skin. A black "anti-glare" panel was painted on the top forward fuselage and engine cowling (see photo of 73 Hiko-Sentai aircraft).

Type B: Irregular blotches or stripes of dark green on the basic natural metal scheme. This was applied once the aircraft reached its operational base. On occasion the edges of national (hinomaru) and Sentai markings were accidentally covered.

Type S: Three variations were seen on Ki-84s; S1 – Dark green upper surfaces, with light gray/green lower surfaces. S2 – The light gray/green on the lower surfaces was replaced by a pale blue/gray. These colors were often applied on an unprimed airframe; because of this and the poor adhesion of Japanese paints in the later years of the war this scheme often weathered quickly, with large patches of natural metal being visible (see photo of 85 Hiko-Sentai Ki-84 on a Korean base). S10 – The upper surfaces were left in a red/brown primer with the under surfaces in natural metal. The black anti-glare panel was optional.

Other schemes were applied, particularly by the Shinbu-Tai "Special Attack" units. For example, a Ki-84 of 57 Shinbu-Tai, flown by Corporal Takano, had very dark brown-green upper surfaces (some sources state black), with a large red "arrow" outlined in white painted along the entire length of the fuselage and engine cowling. White Kana characters "hitt-chin" (be sure to sink) were painted above the arrow on the rear fuselage. The under surfaces were light gray.

Factory applied markings included six hinomaru (national insignia), outlined with a 75 mm (2.95 in) white border on camouflaged aircraft, on either side of the rear fuselage and on the upper and lower outer wings. Yellow/orange identification strips were applied to the leading edges of wings, extending from the roots to ⅓ of the wingspan.

It was a general rule that Japanese planes in overseas territories had a narrow white line called the "border break through line" or "field identification mark" surrounding their hinomaru; planes belonging to interception forces in Japan proper placed the insignia inside a white square (colloquially known as the "Homeland Defense bandage"), so that anti-aircraft defense units could more easily distinguish them from enemy planes.

The inside of the fuselage and the wheel cover wells were painted in a dark opaque bluish gray, and the propeller spinner was painted with a variety of colors based on the unit it belonged to.

Versions

 * Ki-84-a
 * Prototype.


 * Ki-84-b
 * Evaluation model.


 * Ki-84-c
 * Pre-production model.


 * Ki-84-Ia Hayate
 * Fighter Type 4 of Army. Armed with 2 × 12.7 mm Ho-103 machine guns and 2 × 20mm Ho-5 cannon in wings (most widely produced version).


 * Ki-84-Ib
 * Version armed with 4 × 20 mm Ho-5 cannon. (very limited production run. May never have equipped a full Sentai)


 * Ki-84-Ic
 * Version against Bombers, with 2 × 20 mm Ho-5 cannon and 2 × 30 mm (1.18 in) Ho-155 cannon in wings.


 * Ki-84-Ia (Manshu Type)
 * Manufactured in Manchukuo for Mansyu by Nakajima License.


 * Ki-84-II
 * Similar to models mentioned above (Ki-84-Ia, -Ib, -Ic).


 * Ki-84 N/P/R
 * High altitude versions.


 * Ki-106
 * Prototype airframes constructed entirely out of wood. 10 examples were produced of this type.


 * Ki-113
 * Prototype similar at Ki-84-Ib in steel.


 * Ki-116
 * Evaluation model, equipped with Mitsubishi 62 (Ha-33), 1,120 kW (1,500 hp).


 * Ki-117
 * Redesigning of Ki-84 N.

Operators
Wartime
 * Imperial Japanese Army Air Service
 * Imperial Japanese Army Air Service

Post-war
 * People's Liberation Army Air Force operated captured aircraft from 1945 until the 1950s.
 * Chinese Nationalist Air Force held some Ki-84 in reserve in case American aid was cut.
 * 🇮🇩 Indonesia
 * 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.
 * 🇮🇩 Indonesia
 * 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.

Survivors
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 aircraft was operated and flown by the Planes of Fame Museum in Chino, California, before being returned to Japan for display at the Arashiyama Museum in Kyoto. This aircraft is now exhibited at the Tokko Heiwa Kinen-kan Museum at Chiran, Japan. It is the only surviving Ki-84.

Japanese aircraft of the Pacific war