Thursday, August 05, 2021
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Nakajima (JAAF Ki-84, type 4) Hayate (Hurricane): ‘Frank’ (Richard M. Bueschel)  First ordered by the JAAF in May 1942, ten months later the prototype (8401) was completed and five weeks after completion (April 1943) took to the air.  Second model (8402) which incorporated numerous changes was completed in June and flew in August.  A third experimental machine (8403) quickly followed.  The new fighter had a top speed of 388 mph, which was faster than previous JAAF fighters but did not have the performance hoped for.  There were, however, considerably production advantages.  

By August a number of pre-production models were complete, these aircraft having thrust-augmented exhaust stacks instead of the single large exhaust which was fitted to the three experimental machines. 


When flown against the Ki-44 Shoki and a FW190 A/5, the pre-production Ki-84 was found to be competitive in maneuverability but the FW190 had the advantage in speed and dive tests.  Between August 1943 and March 1944 eighty three evaluation models were produced.  In April 1944 the JAAF ordered mass production, by October over 300 machines a month were being manufactured. 


The first unit to operate the Ki-84 was the 22nd Air Regiment.  The skilled ground crew of the 22nd gave a lot of ‘tender loving care’ to the sophisticated Ha.45/11 2000hp radial engines that powered the Hayate, with the result that these power plants were incorrectly felt to be almost ‘bug’ free.  This mistake was later to cost the JAAF dearly.


The Ki-84 went into combat against P-51 and P-38s in late August 1944 where the crack pilots of the 22nd, flying machines that had been maintained to a high order, had considerable success.  By October other units were operating the Ki-84 and as the fighting continued the efficiency of these Hayate units fell rapidly.  The Ha 45/11 and 45/12 power units proved to be unreliable under field maintenance conditions. 


Many pilots were not able to cope with the new fighter, in particular, during landing the propeller wake had a habit of hitting the dropped landing flaps which snapped the nose of the aircraft up which often resulting in an accident.  There were many other landing accidents as the metallurgy of the landing gear legs depreciated as production rates increased.  Poor heat-treating made the main members very brittle.  In October 1944 eighty Ki-84 were flown in one delivery flight.  Of these only fourteen reached their destination, the other sixty six machines experiencing engine trouble, landing gear failure or fuel and hydraulic problems. 


Throughout the end of 1944 JAAF losses mounted.  Most of these losses were non-combative, with the majority of the aircraft lost on the ground. 


By the beginning of the new year an air worthy ‘Frank’ was in the hands of the American Technical Air Intelligence Unit and evaluation revealed its attributes and pinpointed its failings.  Allied pilots now had first hand knowledge of the Ki-83.


Back in Japan the Hi-84A which was armed with two wing mounted 20mm cannons was superseded by the Hi-84B which was fitted with two additional 20mm cannons in the fuselage.  A model C also went into production armed with two 20mm and two 30mm cannons. 


The major problem facing the Hayate was the total unreliability of its power plant.  Low oil pressure and high operating temperatures continually caused problems.  Once the engine temperature began to rise within fifteen minutes the engine froze.  Many Japanese pilots were too far from their base when the first indication of a problem arose to make it back to base, it was just like getting shot down. 


When a Ki-84 was inverted (flown upside down) the oil pressure dropped to zero with the result that the engine seized up.  The problems associated with the Ha.45  radials was still under investigation at the laboratories at Tachikawa when the war ended.  From the spring of 1945 there were also material problems due to low stocks of Dural.  Experimental work was carried using wood and steel in the manufacture of some of the airframe components.


As the bombing raids of the B-29s over Japan began to take effect production was displaced throughout the mainland.  The Manshu design group undertook conversion of the Ki-84 to be powered by a Mitsubishi Ha.112, a lower rated (1350hp) power plant that was lighter than the Ha.45. 


This resulted in the overall weight of the Hayate being reduced by a thousand pounds which created a good performance and gave a top speed of 500mph.  The Ha.112 powered Ki-84 would have been in production by 1946.


The 50th Fighter Regiment was a ‘crack’ overseas unit operating Ki.27s, Ki.43, Ki-44s in Burma and Thailand.  In the spring of 1945 the unit was moved north to Formosa where they were converted to Ki.83s.  The 64th Fighter Group were converted to Ki.84s in Thailand as the war ended having briefly flown Ki-44s prior to conversion.  The 64th was the only two Fighter Regiment to operate the ‘Frank’ in the area flown by SEAC aircraft.