|Ki-84 Hayate (Frank) preserved in California in 1970. As of 2014, this aircraft is displayed at a war memorial in Japan.|
|Manufacturer||Nakajima Aircraft Company|
|First flight||March 1943|
|Primary user||Imperial Japanese Army Air Service|
|Number built||3,514 [Notes 1]|
The Nakajima Ki-84 Hayate (キ84 疾風"Gale"?) was a single-seat fighter used by the Imperial Japanese Army Air Service in World War II. The Allied reporting name was "Frank"; the Japanese Army designation was Army Type 4 Fighter (四式戦闘機 yon-shiki-sentō-ki?). 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, inconsistent fuel, and a lack of experienced pilots above all else, Hayates proved to be fearsome opponents; a total of 3,514 were built. The Ki-84 was the fastest fighter in the Imperial Japanese military if good fuel was used and the aircraft was in good shape.
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. Deliveries from Nakajima's Ota factory commenced in April 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 speed. 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 — a potentially difficult challenge to synchronize properly, due to the Hayate's 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 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 35.8 litre 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 the Homare 21 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 captured late-production example was tested in the US and achieved a speed of 680 km/h (422 mph) using 92 octane AvGas, plus methanol injection. 
The complicated direct-injection engine, partly from its already basically compact design (no more than 3 cm/1¼ inches larger in diameter than the A6M Zero's 14-cylinder Nakajima Sakae radial) 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, who sometimes found it difficult to transition to the relatively "hot" Ki-84 from the comparatively docile Ki-43 Hayabusa, which had a significantly lower landing speed.
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.
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.
|Ki-84 Production: Ota & Utsunomiya Aircraft Plant |
|Ki-84 Production: Tachikawa Aircraft Plant |
- Ki-84-a: Prototype.
- Ki-84-b: Evaluation model.
- Ki-84-c: Pre-production model.
- Ki-84-I Ko (Ki-84-Ia): 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-I Otsu (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-I Hei (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-I Tei (Ki-84-Id): Night fighter version of Ki-84 Otsu. Equipped with an additional Ho-5 20mm cannon (300 shells) placed at 45 degree angle behind the cockpit in Schräge Musik configuration. This variant is widely unknown, with only Japanese sources available. 2 Built.
- Ki-84-I Ko (Ki-84-Ia) (Manshu Type): Manufactured in Manchukuo for Manshūkoku Hikōki Seizo KK by Nakajima License.
- Ki-84-II: Similar to models mentioned above (Ki-84 Ko, Otsu, Hei).
- Ki-84-N: High-altitude interceptor version of the Ki-84, with a 2500 hp Nakajima Ha-219 air cooled radial engine and wing area increased to 249.19 square feet. The Ki-84-N production model was assigned the Kitai number 'Ki-117', but both aircraft did not pass the beyond initial design stage before the war ended.
- Ki-84-P: Second high-altitude interceptor version of the Ki-84, with a 2500 hp Nakajima Ha-219 air cooled radial engine, but had wing area increased to 263.4 square feet. Cancelled in favour for further development of Ki-84-R, proving to be a less ambiguous project.
- Ki-84-R: Third high-altitude interceptor version of the Ki-84, with a 2000 hp Nakajima Ha-45-23 with a mechanically-driven two-stage three-speed supercharger. Prototype 80% complete before the war ended.
- Ki-106: Prototype airframes constructed entirely out of wood. 3 Built.
- Ki-113: Based on the Ki-84 Otsu, with certain steel components on different areas of the aircraft. The project was an attempt to sustain light alloys, which were becoming very scarce later in the war. It employed steel sheet skinning and the cockpit section, ribs, and bulkheads were made of carbon steel. It is unconfirmed whether the Ki-113 took flight, with some sources stating it did not take flight due to being overweight, while others say it took successful flight tests.
- Ki-116: Evaluation model, equipped with Mitsubishi Ha-112-II (Ha-33-62), 1,120 kW (1,500 hp). 1 Built.
- Ki-117: Production designation of the Ki-84N.
- People's Liberation Army Air Force operated captured aircraft from 1945 until the 1950s.
- 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.
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 which was captured at Clark Field during 1945, was transported aboard the USS Long Island (CVE-1) to the United States. In 1952 it was sold off as surplus to Edward Maloney owner of the Ontario Air Museum (Planes of Fame Museum) and restored to flying condition before being returned to Japan for display at the Arashiyama Museum in Kyoto. The aircraft is now displayed at Tokko Heiwa Kinen-kan Museum, Kagoshima Prefecture. It is the only surviving Ki-84.
Data from Report on Frank 1 
- Crew: One
- Length: 9.92 m (32 ft 7 in)
- Wingspan: 11.238 m (36 ft 11 in)
- Height: 3.385 m (11 ft 1 in)
- Wing area: 21 m² (226.041 ft²)
- Empty weight: 2,660 kg (5,864 lb)
- Loaded weight: 3,601.5 kg (7,940 lb)
- Max. takeoff weight: 4,170 kg (9,194 lb)
- Powerplant: 1 × Nakajima Ha-45-21 Homare 18-cylinder radial engine, 1,522 kW at SL, 1360 kW at 17,900 ft (1,970 hp at SL, 1850 hp at 17,900 ft)
- Never exceed speed: 800 km/h (496 mph)
- Maximum speed: 686 km/h (426 mph) at 7,020 m (23,000 ft)
- Range: 2,168 km (1,347 mi)
- Service ceiling: 11,826.24 m (38,800 ft)
- Rate of climb: 21.84 m/s at SL, 18.29 m/s at 3050 meters (4300 ft/min at SL, 3600 ft/min at 10,000 ft)
- Wing loading: 171.47 kg/m² (35.1 lb/ft²)
- Power/mass: 1.8 kg/hp (4 lb/hp)
- 2× 12.7 mm Ho-103 machine guns in nose, 350 rounds/gun
- 2× 20 mm Ho-5 cannon in wings, 150 shells/cannon
- 2× 100 kg (220 lb) bombs
- 2× 250 kg (551 lb) bombs
- 2× 200 L (53 US gal) drop tanks
- Related development
- Aircraft of comparable role, configuration and era
- Focke-Wulf Fw 190
- Kawanishi N1K
- Kawasaki Ki-100
- Lavochkin La-7
- Mitsubishi J2M
- North American P-51 Mustang
- Republic P-47 Thunderbolt
- Related lists
- Figure includes: 1 Ki-106, 1 Ki-113, 3 Ki-106 and 3415 Ki 84 I and Ki-84 II builds 
- Francillon, 1979, p. 238
- Glancey 2006, p. 174.
- Ethell 1995, p. 102.
- Ethell 1995, p. 103.
- Air International Volume 10 No. 1, pp. 22–29, 43–46.
- Green 1961, p. 79.
- USSBS 1947, p. 72.
- USSBS 1947, p. 78.
- Mondey 1996, p. 230.
- Chiran Peace Museum, Hayate Exhibition Room
- Archives of M. Williams, TAIC 156A-1, Report on Frank 1
- Fearis 1996, p. 44.
- Caruana 2004, pp. 950–951.
- USSBS, Appendix M., p. 40–42
- Bueschel 1971, p. 52.
- Pacific Wrecks, JAAF Unknwon Sentai, Ki-84-I Ko
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- Fearis, P. "The Emperor's Wings; The Nakajima Ki-84 Hayate." Article and scale drawings. Scale Aviation Modeller. Volume 2 Issue 1 January 1996. Bedford, UK.
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- United States Strategic Bombing Survey Aircraft Division. Nakajima Aircraft Company, Ltd. Corporation Report II, Washington, D.C. 1947.
- Wieliczko, Leszek A. Nakajima Ki-84 Hayate. Lublin, Poland: Kagero, 2005. ISBN 83-89088-76-2. (Bilingual Polish/English)
- Unknown Author Review in "AIRVIEW".
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- Various Authors. Yon-Shiki Sentoki Hayate (Pacific War No.46). Tokyo, Japan: Gakken, 2004. ISBN 4-05-603574-1.
- User: 'machta'. Ki 84 Hayate ‘Frank’ Redux, Weapons and Warfare, September 19, 2014.
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