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Ki-84 Hayate

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Warenwolf #1 Posted 23 January 2012 - 07:28 PM

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Nakajima Ki-84 Hayate


The best known Japanese fighter World War Two is undeniably the Imperial Japanese Navy's Mitsubishi A6M Rei-sen (code named "Zero" by allied intelligence), however as the allies introduced new aircraft models the A6M hardly remained competitive.

It would be the Imperial Japanese Army Air Service's search for an aircraft that was a combination of their own agile Ki-43 Hayabusa and their fast Ki-44 Shoki that would result in an aircraft that could compete with newest allied designs.
That aircraft was the Ki-84 Hayate ("Gale") or the Army Type 4 Fighter which was it's official IJA designation. Hayate was capable of matching the best allied aircraft in the Pacific theater and with its powerful armament to bring down any allied bomber.

Specifications (Ki-84-Ia)

Maximum speed  : 630 km/h @ 6,100 m 
Armament	   : 2x 12.7 mm Ho-103 machine guns in fuselage + 2x 20 mm Ho-5 cannon in the wings
Service ceiling: 10,500 m (34,450 ft)
Rate of climb  : 19.25 m/s
Range		  : 2,155 km 


29th December 1941 a requirement for the new plane was formulated, calling for an aircraft as maneuverable as the Ki-43 but also able to act as interceptor for use against high flying enemy bombers, a role initially given to Ki-44.

Its designation was to be Ki-84 (Ki is standing for Kitai, meaning airframe).

The development of the new aircraft was assigned to the designer of the Ki-44, Toro Koyama that incorporated much of the lessons learned from his earlier work on designs competing with Kawasaki's Ki-61 Hien.

The first prototype was completed in March 1943 and made its first flight one month later. The second prototype followed in June same year.

The airframe was cantilever low-wing monoplane of all-metal construction but before the production was commenced to save aluminum Nakajima made some components of the wood.

Nakajima Ha-45 "Homare" engine was modified into a direct injection engine where also water injection was used to cool down the combustion chambers of the engine, allowing for greater compression ratios and effectively increasing the power of the engine. The new engine was called Ha-45-21 and gave the Ki-84 1,990 horsepowers (1,484 kW).

It was armed with pair of fuselage-mounted 12.7mm Type 1 machine guns (Ho-103) with 350 rounds each and a pair of two wing-mounted 20 mm Army Type 2 (Ho-5) cannons with 150 shells per cannon.

Armor, almost totally absent in the Ki-43 and Ki-44, was installed in fuselage (so that the fuel tanks were protected) and the pilot seat. In addition the cockpit glass was 65 mm thick armor glass.

Ki-84 was also fitted with external racks giving it ability to preform in fighter-bomber operations with 2x 250 or 2x 100 Kg bombs or have range extended with drop tanks (200 liters fuel each) installed.

The test pilots at Akeno Fighter Army Flying School were impressed with the new aircraft and the Army ordered Nakajima to start producing a so-called pre-production series (which is a series of the aircraft that is meant to test the aircraft during operational duty or combat trials where experiences can gathered and finally incorporated in final version of an aircraft). Eighty three trial aircraft were built between August 1943 and March 1944, with modifications being introduced all the time.  

During this time the aircraft was tested against Ki-44 and Luftwaffe's Fw-190A-5. The Ki-84 outperformed the Ki-44 in all areas and was more maneuverable than the Fw 190A-5, but the later was faster in level flight and could outdive the Ki-84.

In June 1944, the Army ordered the aircraft into the production as Ki-84-Ia or Army Type 4 Fighter Model A.


Operational duty

The first unit to use Ki-84s was the 22nd Sentai in Summer 1944, stationed in China and facing the USAAF Fourteenth Air Force. The excellent quality of this particular unit coupled with the excellent new aircraft achieved great success against P-51 Mustangs and P-47 Thunderbolts.  

However on the Philippines in October 1944, Ki-84 revealed the unreliability of the Homare engine. It's landing gear was also a weak point (according to some not because of structural design but because of poor workmanship) - leading to great many accidents. Also the allied bombing of the Japanese industry and the increasing lack of war resources meant that the build quality of the Ki-84 suffered.
All this contributed to drop the readiness rates of the Ki-84 units dangerously low.

In air battles over Japan the Ki-84 proved effective against both bombers and escorting fighters. It also proved effective in hit-and-run attacks against US forces in Okinawa where Mustangs found it hard to intercept the fast low flying Ki-84 or "Franks" (Allied codename for Ki-84 Hayate).


In addition to below outlined variants, in the spring of 1945 Nakajima introduced Ki-84-II which was produced in variants of a,b and c outlined below but where, in an attempt to save duralumin (which was in short supply in Japan at the time) wing tips, control rods and large parts of rear fuselage were made of wood.

  • Ki-84-Ia : Armed with two 12.7 mm Ho-103 machine guns and two 20 mm Ho-5 cannon in wings
  • Ki-84-Ib : Same as Ki-84-Ia but Ho-103 replaced with Ho-5 cannons (4x Ho-5 cannons in totall). Produced at same time as Ia.
  • Ki-84-Ic : 20 mm cannons in wings replaced with 30 mm cannons. Meant to fight bombers. Few produced.


The Ki-84 was the most effective Japanese single-seat fighter that was hampered by the fact that Japanese war industry was not able to build it in sufficient numbers with sufficient quality. The quality of pilots in later stages of war and the sheer number of enemies would also ensure that Ki-84 never lived up to its potential.
As testament to the above, when after the war the Ki-84 was tested in the USA with high octane fuel,the achieved speed was 687 km/h, much higher than that of the war time performance of Ki-84 - 630 km/h...

By purely technical aspects this plane could match any allied airplane in the Pacific theater. It's weakpoint was the engine that demanding on maintenance and unreliable in less than perfect conditions prevailing in the pacific theater.
Official BETA RELEASE DATE (according to ESLAF announcement (disinformation manager) ): 30.02.2012

So no need to ask further.

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