Some observations about the Ki-78

As a follow-on to discussion of the Friendship Scale Models Ki-78 kit some further observations about that interesting aircraft. The experimental (Ken-3) high speed research plane (試作 [研三] 高速研究機- shisaku [ken san] kousoku kensan kyuu ki) was the outcome of an initially civil research initiative into high altitude and high speed distance flight subsequently taken over by the Army as the Ki-78. The abbreviation 'Ken' was for kensan (研鑽 - research or study). The background and basic details of its origin, development and testing are readily accessible through Francillon* and even Wiki so won't be laboured here beyond some interesting details which are seldom explored.

* Francillon, René J., Japanese Aircraft of the Pacific War (Putnams)

Ki-78 - note dark prop blades, absence of Hinomaru and lack of wheel covers

The project began in 1938 under the auspices of the Aeronautical Research Institute at the University of Tokyo but was taken over by the Army in May 1940, whereupon the projected design was designated Ki-78 and Kawasaki were requested to create two prototypes based on a completed wooden mock-up.

Note also absence  of counter balances on elevators

The aeroplane was diminutive, with length and span just over 26 feet. The wing had a laminar flow, low-drag profile (with a very fine leading edge) of low area designed by Echiro Tani with three different types of wing section applied - LB-510-3A16, LB-510-3B14.5 and LB-5103B12. This resulted in a high wing loading and tricky low speed flight during take-off and landing exacerbated by limited vision from the tiny streamlined cockpit canopy. The take off speed was 128.13 mph and landing speed was 106.25 mph. Combination Fowler and split flaps were augmented by drooping ailerons to improve low speed lift. As the main flap deployed the split flap opened to correspond and when the flaps were fully down a synchronised system dropped both ailerons to 10 degrees down. 

The selected power plant was an imported Daimler-Benz DB 601A of 1,175 hp enhanced with water-methanol injection to 1,550 hp. Wing fuel tanks held a total of 250 litres and 60 litres of methanol were carried. Various cooling systems were considered including surface evaporation but ultimately conventional radiators in closely faired housings either side of the rear fuselage were decided on. 

An initial test flight was made from Gifu at dusk on 26 December 1942 with Kawasaki test pilot Saizaburo Kataoka at the controls. All went well and he reported that the acceleration of the aircraft was phenomenal. Following further test flights an issue with elevator flutter was encountered at a speed of 393.75 mph at 3,608 feet as a result of which modifications were made which may have incorporated the counter balances seen in some photographs. Speed tests continued satisfactorily through September to December 1943 culminating in the highest speed recorded of 435 mph at 11,539 ft during the 31st test flight on 27 December 1943. Ultimately the Ki-78 suffered the ignominious fate (below) of many historic Japanese aircraft which if preserved would now be considered priceless.

AZ Models What if?

A 244th Sentai Ki-78 approaches USN Helldivers - is it going to ram them?

The 2010 AZ Models 1/72 injection moulded kit was issued in two versions, each containing parts for two models. It appears to be exactly similar to the Planet Models resin kit which is reviewed here. The rear fuselage looks a wee bit suspect compared to the photographs, a little stunted and hump backed, slightly too deep from the rear of the cockpit back. Checking the dimensions suggests that the kit is short in length by almost a scale foot, just over 4 mm, and this takes away slightly from the sleek look of the original. For those who are bothered by this it is feasible to separate the fuselage at the panel line just in front of the tail and insert a plastic card plug to increase the length, sanding down the depth of the fuselage at top and bottom to achieve a sleeker appearance. The radiators are also too deep but correcting them is more difficult; removing and replacing them with plastic card not being an easy proposition. The relatively thick leading edge of the wing also needs work to represent the razor sharp edge of  the original.

The prototype schemes as presented in AZ 7302 - the second looks very orange!

The first kit AZ 7302 features the actual prototype in two schemes, the painted scheme being shown as orange with the photographic reference panels in red and white. The second kit AZ 7303 presented the Ki-78 in various permutations of what-if warlike garb providing three spurious markings options for the 244th Sentai, the IJN Yokosuka Kokutai and possibly the 1st Sentai, but without identifying them as such. However, the high wing loading and closely cowled power plant made it extremely unlikely that any weapons could be fitted without extensive modification to the airframe, probably resulting in something heading towards Ki-61 territory anyway. The top speed of 435 mph achieved by the Ki-78 was without armament, armour or fuel protection, whereas the armed and armoured Ki-61-II Kai achieved 379 mph at 19,685 ft.  There appears to be no provision in the kit for representing any armament. If the Ki-78 was going to be deployed belligerently it was probably suitable only for use as a fast air-to-air rammer against the B-29!

The 3 markings options in the What if? kit AZ 7303

The Platz Kit

The Platz kit consists of a solid fuselage, single piece wing and separate tailplanes very finely moulded in grey resin. The radiators are moulded integrally to the fuselage with neatly recessed intakes. There is no interior and the canopy is solid clear resin. All other parts, spinner, prop, undercarriage components and tailwheel are cast in good quality white metal. A decal sheet provides the Hinomaru, red prop blade warning stripes and black and white photo reference markings. The comprehensive instructions are in Japanese but all the colours are called out in English. In comparison to the AZ Models kit the Platz kit better captures the svelte look of the original aircraft.

Platz (Unlimited Air Models) Ki-78 'Kensan' Box Art

This kit is now shown as discontinued at HLJ (despite what it says there the Platz instructions do include details for the dark grey option). But if you really want one it can still be ordered direct from Platz and in confidence as they have an excellent mail order service via Hobby Collective. Use the contact form at their site and they will send a confirmation in English and a PayPal invoice on receipt of an email order.

AZ Models vs Platz ~ note position of vertical panel line forward of tail

Colour Schemes

There were two main schemes, documented and evidenced by photographs. The overall metal finish as seen in the photographs above, varied by the addition of an anti-glare panel and Hinomaru in six positions, as shown below. The sequence of at least three different schemes is debatable but the different propeller blade finishes provide clues. The polished blades with red warning stripes usually represent an earlier IJAAF standard whilst the dark brown painted blades with yellow warning stripes came later.

Note prop blade finish and apparent black and white wing tip markings

Whether the metal finish was anodised or treated in any way is unknown. The overall painted finish has been depicted in Japanese sources as a glossy medium blue grey with a matted anti-glare panel (in the same colour) and six photographic reference panels in black and white, three on each side of the fuselage. In addition the upper wing tips had black and white chord wise stripes. The Platz kit depicts the Hinomaru in six positions but the aircraft has also been depicted without upper wing Hinomaru.

The blue-grey painted finish

The Platz 1/72nd scale resin kit showing the two main finishes

Why this painted finish has so often been depicted as orange is puzzling. IJAAF experimentals and prototypes do not appear to have followed IJN requirements or Army-Navy conventions and were generally unpainted. Despite the Naval General Staff Order No.162 ‘Army-Navy Agreement With Regard To Distinguishing Markings For Friendly Military Airplanes’ of 21 August 1942 which called for experimental aircraft to be painted yellow (黄色 - ou-shoku) where possible, Kawasaki Army experimental prototypes before and after Ken-3 remained unpainted - e.g. Ki-60, Ki-61, Ki-64. In any case the Army colour was more an orange-yellow than the deep orange suggested by the AZ Models kit and other depictions. The reason for painting Ken-3 in the unusual blue grey scheme is obscure; whether that was connected to the secrecy of the first test flight or whether it just represented an attempt to improve aerodynamics by filling, painting and smoothing the airframe is unknown. 

United Air Models (Platz) prototype model in flight

The Platz kit suggests that the grey finish was used for the 31st test flight on 27 December 1943 and that it has often been described as dark grey but that Takeo Doi (the Kawasaki designer responsible for the Ki-61 Hien) maintained that it was a light grey. With medium greys the degree of darkness or lightness perceived in the colour is often subjective. But however dark or light it was it wasn't remembered as orange!

In models of the Ki-78 some variation in the metal finish scheme could be achieved by differencing the fabric covered flying control surfaces which were finished in aluminium dope and by representing an anodised or coated finish on the metal panels to give a slightly golden or amber effect. The anti-glare panel on the metal finish was possibly painted in the standard Army # 32 Koku ran shoku (黒藍色 - black indigo colour) which was a blueish-purple black similar to the colour of aubergines (eggplant). For the blue-grey finish a paint like the French gris bleu foncé is suggested, a little darker than FS 35164 and just a little more blue than RAL 7031 Blaugrau. Humbrol 79 Matt Blue Grey and Revell 79 Greyish blue (which is supposed to match RAL 7031) are in the ball park but bear in mind that the finish was glossy and that will slightly darken the appearance of the paint. The prop blades on the grey scheme appear to be polished metal with red tip stripes and the rear faces painted dark brown or possibly black.

Interior colours are anyone's guess but the Army standard at the time was the dark blue-grey of # 3 Hai Ran Shoku (灰藍色 - ash [grey] indigo colour). Was that same colour also used on the exterior?

Whichever kit is selected the diminutive Kansen makes an interesting display companion to Kawasaki's Ki-60 and  Ki-61 or in any collection of experimental prototypes.

Image credits: Artwork unknown; Photographs: SanDiego Air and Space Museum and web; Post-war photo courtesy James F Lansdale; Box art © AZ Models; Platz model images © Platz ; with special thanks to Tetsuya Inoue