The Kawasaki Ki-61 Hien and the Naka­jima Ki-84 Hayate are arguably two of the most recognisable Japanese fighters of World War 2 after the immortal Zero.

The Ki-61 was initially designed in and flown in 1941 where as the Ki-84 was designed in 1942 and flown in mid 1944. The span of time that elapsed between the designs of these two aircraft and the lesson learnt during a long and bitter war resulted in two very distinctly different aircraft.

Airframe:

The Ki-61 and Ki-84 can both be described a slow wing monoplanes of stress light alloy construction, but the similarity basically stops there. The Ki-61 featured a reasonably high aspect ratio wing with traditional flaps were the Ki-84 featured a lower aspect wing that

featured Fowler style flaps that added to the wings overall surface area for landing and increased manoeuvrability. The KI-61 featured a raised spine where as the Ki-84 feature a cut down rear fuselage with a tear drop canopy (though still heavily framed that gave increased visibility to the rear. This was an important feature that was learnt through the experience of war.

The most noticeable airframe differences however came about because of the difference in the power plants. The Ki-61 utilised an inverted liquid cooled V-12 engine that gave a slender profile and cross section that also necessitated the need for ventral radiator housing. To accommodate this engine the-Ki-61 displayed a unique engine mounting bearing design that was integral to the fuselage structure. This was in direct contrast to bolt on engine mountings in almost every aircraft design at this period of time.

The Ki-84 featured a large 18 cylinder air-cooled radial engine that featured only a small under cowl fairing to house the oil cooler. The Frank was a stressed skinned monoplane utilising the standard construction methods employed in the early 1940s. The exceptions to this were to come late in the war as Japan faced a shortage of raw materials. The attempts to conserve light alloys other materials were tested on the Franks construction. The first attempts of introducing wood into the construction of the Frank saw wooden wing tips and rear fuselage sections made of this material. An all wooden version of the Frank was re-designated KI 106 and was represented by the single prototype as was the sole Ki 113 version of the Frank that used a high percentage of steel in its construction.

Power Plants:

The Ki-61 most notable feature amongst all Japanese fighters produced in WW 2 was the Ha-40 engine. This was a licence built version of the Daimler Benz DB 601A. The Ki 60 which is similar to the Ki61 was the first aircraft to be powered by this engine but this aircraft proved disappointing and development was ceased and efforts then concentrated on the Ki-61. The Ha 40 produced 1,175 Hp (876 KW) and propelled the Hien to a top speed of 348 mph (560 kph). The 40 however would display major problems with main bearing failures. This problem coupled with the Japanese unfamiliarity with maintaining liquid cooled engines would lead to diminishing production of Ha 40 and eventually see the last versions of Ki-61s being adapted accept radial engines and receiving the new designation of Ki-100.

The Ki-84 Hayate was powered by a Nakajima Ha-45 radial engine that had an output of 1900Hp (1416 KW) giving the Ki-84 a top speed of 392 mph (631 Kph). The Ha-45 proved to be an excellent engine whose reputation was only tarnished by most Ki-84 being extremely overworked in their struggle against allied superiority.

Weapons:

A weapon fit out on both aircraft was not dissimilar and was in line with the Japanese designs of the times. The Ki-61 was typically armed with a pair of 7.7 Mm machine guns, mounted in the fuselage above the engine and a pair of 12.7 mm guns in the wings. The 12.7 mm guns were soon replaced with imported 20mm Mauser MG 151 cannons in the Ki-61 Ia. The Ki-61 Ib was armed with four 12.7 mm guns. The Ki-84 was originally fitted with two fuselage mounted 12.7 mm guns and two wing mounted 20 mm cannon. Later variants would be armed with four 20 mm cannon and the Ki-84 Ic would be armed with two 20 mm cannon and two 30 mm cannon.

Both aircraft had provision to mount under wing drop tanks and later versions of both had the capability to carry a pair of 250 Kg bombs.

Variants:

The Ki-61 was to retain its profile for most of its variants. The later type featured a slightly extended nose (21.6 cm) on the Ki-61- II. The key change was the last version being the Ki-61-III that featured the extended nose and a cut down rear fuselage spine coupled with a tear drop canopy. It is believed that only one of these aircraft was produced before hostilities ceased. This canopy was a major feature of later radial powered Ki 100s.

The Ki-84 on the other hand was to retain its profile through to the end of the war. The fast approaching end of the war denied the Frank further development apart from alternative building materials being tested. As can be seen in the photograph above, once the radial engine was mated with the Tony‘s fuselage, the Ki-100 would have been easy to confuse with the Frank by Allied pilots with the similarly bulbous nose and teardrop canopy profiles. Only a keen eye would pick the difference, particularly in the heat of battle.

Operational Use:

Early tests of the Ki-61 against a captured P40E and a purchased Bf 109E soon showed that the Ki-61 was superior to both aircraft in all aspects. The Ki-61 was to prove to be a very capable aircraft in all aspects. The aircraft however was hampered by engine problems and engine supply problems. The bombing by the USAF of the Akashi engine plant resulted in the total cease of production of the Ha-40 engine. Despite these many problems Ki-61s were proven in action against B29s raiding Japan and against allied fighters of the time. Many Ki-61s were to be used successfully in special attacks (ramming) against high flying B29s some of which were stripped of all armament to allow them the ability to reach the fast and high flying B29s. The Ki-84 made its first operational appearance at the battle of Leyte in 1944 and served in the most intense battle areas as the Allied forces steadily pushed towards the Japanese homelands. Ki-84s were employed as fighters, fighter bombers, dive bombers and air interceptors over Tokyo.

The Ki-84 proved in combat to possess a higher manoeuvrability and climb rate than the much vaunted P51 Mustang and P47N. The aircraft’s only vice was un-serviceability due to being extremely over worked and the simple fact that there were too few Ki-84s to stem the
overwhelming allied forces. Had the Ki-84 been able to be produced in numbers, and with sufficiently trained pilots, it would have proven to be of a major concern for all Allied flyers.
Despite its late introduction into the conflict the Ki-84 was to be the mount of several Imperial Japanese Army Air Force aces. Aces clearly demonstrated the lethality of the Frank in combat. Isamu Sasaki, an aces with 38+ victories, flew Franks from Fussa airfield in Tokyo in 1945. Whilst operating from this field, Isamu Sasaki managed the incredible feat of destroying 3 B-29s on the night of 25 May 1945.

Capt Tomojiko Ogawa was another ace who demonstrated the Frank was able to engage Allied single engine fighters on at least an equal basis and succeeded in destroying 5 of the much vaunted P-51 Mus-tangs and a further 2 P-47 Thunderbolts. Both of these aces were awarded the Bukusho in recognition of the courage in combat. In the later days of the conflict Ki-84s were used in ground attacks, as escorts to other ‗special attack‘aircraft and then engaged in ship strafing when released from their escort duties. Ki-84s were also utilised as special attack aircraft themselves.

Related aircraft to the Ki-61:

The Ki-61 had a large influence from the BF 109E. It featured the same engine and similar armament but the BF 109 could only be termed a cousin to the Ki-61. The aircraft that could be closer termed as a step brother was Italy‘s MC 202 Folgore.

Both aircraft feature utilisation of the DB 601 engine heavy machine guns mounted above the engine with 20 mm Mauser cannon in the wings, ventral radiator mounting and a high fuselage decking behind the cockpit and were produced by Germany‘s axis partners using German designed engines and weapons.

The Ki-61 and the MC 202 were excellent aircraft for their time but both were plagued by insufficient numbers being available to make a serious contribution to their country ‘s war efforts. Italy had more success than Japan with the in line Daimler Benz engines that would see further development of the MC 202 into the MC 205 and other designs using inline V-12 engines.
Japan on the other hand was to rely far heavily on radial engines for most of its designs.

Whats in a name?:

To identify Japanese fighter due to their sometimes unknown and complex naming system, Allied intelligence began assigning code names to various aircraft. This department was lead by Major Frank McCoy and most of this work was performed while based in Brisbane Australia in 1942. To categorise various aircraft types it was decided that Fighters would be assigned boys names, bombers would be assigned girls names, transports with names starting with T. Training aircraft would receive names of trees while gliders would receive the names of birds. Names selected were generally selected based on the known people that members of the unit had contact with or knew of. As Major Frank McCoy was the head of this intelligence unit he decided to use his name as well of those of his staff and family. After originally using his name on what was later discovered to be a fictitious aircraft, McCoy reassigned the code name Frank to the Ki-84 . At the time the Ki-61was viewed as being very similar to the MC 202 and to potentially have had a great deal of Italian influence in its design. As such McCoy‘s team assigned it what they believed to be a significant Italian name of Tony as the shortened version of Antonio.

 

 

Modelling the Ki-61 and Ki-84:

32nd scale:

The recent appearance of the Hasegawa KI-61 and Ki-84 has offered modellers a fine example of both subjects. Both kits build easily and have the excellent surface and cockpit detail that is expected from this manufacturer.

The only criticism with these kits is that that are relatively simple and do not have some of the features that other manufacturers are doing in this scale such as highly detailed engines that can be displayed in the exposed set up or a wider option of weapons stores. Revell Japan produced a 32 scale Ki-61 many years ago. While it has some faults in the canopy area and inaccurate engine mounts requiring the engine bay to be closed up, it however has recessed panel lines and indented rivets. The cockpit area is a bit sparse. Never the less it is sought as a collectable as the injection moulds no longer exist. The most sought after boxing is the‘made in Japan‘boxing that featured a small information booklet and an alternative decal sheet produced by Super Scale. It appears that the Revell 32 scale Tony will build into a passable Ki-61 with surface detail that is similar to that currently offered by Hobby Boss and Trumpeter large scale aircraft.

48 scale:

The late Hasegawa 48 scale Ki-84 is considered as one of Hasegawa‘s best kits and is a delight to build with excellent detail in the surface area detail and cockpits. The same can be said of the Hasegawa Ki-61which has been around for some while now. The simplicity of the 48 scale KI-61 can be boosted with details sets such as Aires produces for this kit. The detail set gives weapons and engine bay detail as well as some cockpit enhancements.

Right Staff and Toycraft Berg produced limited run kits of the Ki-61. Both these companies no longer exist and both are sought after as collectables. The novel feature of these kits was the injected resin manufacturing process utilised to produce the main airframe components. There is a single small injected plastic sprue, mainly for the props and spinner. The remainder of the kit is supplied in white metal castings, brass tubing, and photo etched metal.

The instruction sheet is very basic and requires a bit of modeling assembly knowledge as step by step assembly is not covered. The result will be a finely detailed model but is slightly marred by the scribed panel lines being slightly heavy. This kit can only be recommended to an experienced builder due to its cost, lack of detailed instructions and the heavy use of multi media.

The ARII kit of the Ki-61 is passable but suffers from a lack of accurate detail in the cockpits and wheel well details. They however build up into reasonable rendition of the Ki-61 and are recommended if you want to build a fleet of Ki-61s as decal and colour scheme carriers.

72 scale:

Hasegawa produces an excellent kit of the Ki-61 in 72 scale with good cockpit detail in this scale. Scribed panel lines are a feature of this kit which builds with no vices at all.

The only criticism that extends to the majority of the Ki-61 kits is the inability of the cockpit canopy to be displayed in the open position though this can be rectified by the aftermarket vac form canopies that are available.

The 1/72 range of Tony‘s can‘t be let go without mentioning the range of Fine Molds kits ranging a great span of the Ki-61 and radial engine Ki-100 variants. Great builds and suitable for excellent out-of-box or detailed projects.

Just Scratching The Surface:

This article has only been a small insight into these two outstanding Japanese flying machines, their history and modelling options. A big thank you goes to Richard Caruana and Claes Sundin for their profiles which hopefully will inspire some ―Frank ‘n‘ Hiens to hit modelers benches sooner rather than later.