Kawanishi E15K Shiun “Norm”

IJN Observation floatplane (1942) – 15 built (incl. prototypes) 1944

Development

In 1939 the Imperial Japanese Navy instructed Kawanishi (a well known lead manufacturer and designer of floatplanes and flying boats) to develop a two-seat high-speed reconnaissance floatplane. The main specifications were on one hand, having sufficient performance to escape interception from land based fighters (1939 standard, 450 kph) and capable of a 800-nautical mile range (1,480 km). It was planned for new class of cruisers (the Ibuki class, lead vessel reconverted as a light carrier, but never completed) and the light cruisers intended to lead (as flagships) submarines squadrons. Each was to carry six of these new Kawanishi models to screen for the submarines, in search of targets. But unlike the Ibuki, only the first was ever completed, IJN Ōyodo, ordered at the same time in 1939. Each Ibuki (larger ships) would carry two of the new floatplane as well.

The first prototype was called E15K1 (Navy short designation system), presented with a countra-rotative propeller, something quite new in Japan and in the world in 1940. It did its maiden flight on 5 December 1941. This was successful enough that the admiralty ordered Five more prototypes, built during 1941 and 1942 with gradual improvements. Here it shows already how long this project dragged on. Development was protracted indeed due to the numerous E15K1 innovative features, and new issues surged at each flight, that in turn led to modifications, so much so that the whole program fell behind schedule. Among other the retractable stabilizing floats proved troublesome, broke and provoked several accidents when they could not be lowered for landing. In the end, the whole retractable system was dropped and stabilizing floats were made fixed. In 1942 also Mitsubishi’s aero engine department progressed, and presented the more powerful MK4S Kasei 24. It was fitted to compensate for increased drag, but needed to redesign the cowling, fuselage structure, and fuel line.

Design

Kawanishi designed a single-engine monoplane, low-wing and centred around a 1,460 hp (1,090 kW) Mitsubishi MK4D Kasei 14. This 14-cylinder radial was unusual as it drove two contra-rotating, two-bladed propellers (which oddly seemed like a step back). This was a first. The concept was being tried also in Europe, but was never implemented until late in the war. It presented multiple advantages, notably torque balancing and extra propulsion.

The new floatplane had also a single central float, plus two retractable stabilizing floats under wings, initially to reduce drag. More so, the main central float was designed to be jettisoned in emergency as it boosted top speed to 50 knots (90 km/h) more, judged enough to escape 1941 generation fighters (like the Wildcat). Wings had a refined laminar flow airfoil section, to further reduce drag. Like the Kawasaki Ki-100, the fuselage was refined to make a clean transition between the bulk of the radial engine and the rest of the fuselage. The canopy and engine cowling were also long refined in wind tunnel.

Detailed specs

Service

All these problems were eventually revolved, as the E15K1 was ordered into limited production (pre-production batch) as the “Navy Type 2 High-speed Reconnaissance Seaplane Shiun Model 11”. Six were delivered and trialled as E15Ks, evaluated in 1942. Production was greenlight in early 1943, but the first operational E15K1 only arrived by April 30, 1944, and six first models were assigned to the 12th Reconnaissance Squadron, 61st Air Flotilla. In between, the Oyodo class were cancelled (apart the lead ship, also completed in 1943). So the need for more was not that urgent.

On June 1, the first early Shiuns arrived at Palau, South Pacific. But by that stage, the Grumman Hellcat had long replaced the Wildcat, seconded by the excellent Vought F4U Corsair. Both were about 150 kp faster than the Shiun. Compounded with the inexperienced of the crews this was already an issue. But more son was the immense frustation if pilots that realized the vaunted “float trick” did not worked in practice.

The main float jettison mechanism was wind-tunnel tested, but in actual trials, and just time and again refuse to work. With this, the new E15K1 had unusually high maintenance and proved still troublesome in operations in many areas. Given the reports, the Navy brass decided to cut down production in February 1944. This left only 15 Shiuns completed, six prototypes and eight production models. Two were planned to serve on IJN Oyodo and the Mogami class, but due to their poor performances the Aichi E13A1 “Jake” was used instead.

Gallery

E15K on the cruiser IJN Oyodo, 1944

Read More/Src

Books

Francillon, René J. (1979). Japanese Aircraft of the Pacific War (2nd ed.). Putnam & Company.
Green, William (1962). War Planes of the Second World War: Volume Six, Floatplanes. London: Macdonald & Co.
Jackson, Robert (2002). The Encyclopedia of Military Aircraft. Bath: Parragon.
Layman, R. D.; McLaughlin, Stephen (1991). The Hybrid Warship. London: Conway Maritime Press.
Millot, Bernard (May 1978). “Kawanishi E15K1 “Shiun” (Norm) Fana de l’Aviation (in French) (102) 42–45.
“61st Air Flotilla, 12th Recon Sqn wartime report No.1-3.”, Japan Center for Asian Historical Record (in Japanese)

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