03/31/2013. The last floatplane to be produced by the Kawanishi Kokuki K.K., the radical Shiun (Violet Cloud) was designed to undertake reconnaissance missions in areas where aerial supremacy was held by the enemy, the primary requirement thus being speed. This 14-Shi specification was only issued to Kawanishi whose design team began work on the project in July 1939.
From the outset of design work the aim was to produce a floatplane faster than land-based aircraft that it was likely to encounter, and which could, therefore, rely on its speed for protection. Of all-metal construction, the three-seat Shiun employed an LB laminar flow aerofoil which had been evolved by Professor Ichiro Tani of the Tokyo Imperial University.
The outboard stabilizing floats were unique in having metal planing bottoms and rubberized-fabric tops which were inflated when the floats were extended. For retraction the floats were deflated by vacuum pumps so that only the planing bottoms projected beneath the wing undersurfaces. The cantilever pylon-mounted central float could be jettisoned in an emergency, more speed thus being gained in order to elude pursuing enemy fighters. The float pylon was attached to the fuselage by means of two pins. The fore pin could be removed by means of a lever in the pilot's cockpit, the aft pin thereupon being forced free by the air pressure. The jettisonable float scheme was adopted after extensive wind tunnel tests had proved that the float would not hit the fuselage or wing after being jettisoned, although, in the event, no full-scale tests had been undertaken when the Shiun entered service.
The Mitsubishi MK4D Kasei 14 fourteen-cylinder radial engine rated at 1,620 hp for takeoff was fitted with two-blade contra-rotating airscrews, the first of their type to be tested in Japan, the front blades rotating in a clockwise direction and the aft blades rotating counter-clockwise.
The first prototype Shiun, which bore the manufacturer's designation K-10, was completed in October 1942, but was heavily damaged at the beginning of its flight trials when, during a landing, malfunctioning of the flaps resulted in the stabilizing floats being torn off. The aircraft was then completely dismantled, a new engine installed and a ventral fin added beneath the rear fuselage.
Prior to being dubbed Shiun, the E15K1 had entered production as the Type 2 High-speed Reconnaissance Seaplane Model 11, and five additional aircraft had been completed by the end of 1942, these being fitted with the 1,850 hp Mitsubishi MK4S Kasei 24 fourteen-cylinder radial air-cooled engine.
A series of accidents were experienced with the stabilizing floats during subsequent trials, the inflation and deflation system proving extremely unreliable, and on occasions the floats were retracted inadvertently during a landing. The float shape was therefore modified and the inflation system eliminated, but the retraction system was also troublesome and, finally, was also eliminated, the stabilizing floats being fixed and attached to the wings by slim cantilever struts.
Four Shiun float-planes had been passed to the JNAF for evaluation by the end of 1942, a further eight were delivered during 1943, and the last three aircraft of this type were handed over in January-February 1944, quantity production having been cancelled. The reason for this cancellation was the disappointing result of service testing. Six Shiun reconnaissance aircraft had been sent to Palau in the South Pacific, but it had been found that the central float could not be jettisoned as easily as had been supposed, and with the float attached the maximum speed of 292 mph (470 kmh) was insufficient to enable the Shiun to elude enemy lighters. The single 0.303 in (7.7 mm) machinegun installed for defensive purposes was totally inadequate, and all six machines had been quickly lost to Allied lighters. The type was given the reporting name 'Norm' by the Allies.