Hiro H3H1 Navy Type 90-1 Flying-boat.

Hiro H3H1 Navy Type 90-1 Flying-boat

With the knowledge gained in manufacturing and developing the F.5, R-3, Type 15 and Type 89 Flying-boats, Hiro was the most experienced producer of large flying-boats in Japan. Because of this, plans were developed by the Hiro Arsenal in 1930 to build a large three-engined flying-boat, the first large all-metal aircraft entirely of Japanese design. General Manager for the project was Cdr Misao Wada, with as his chief designer, Lieut-Cdr (Ordnance) Jun Okamura.

The new flying-boat was a cantilever monoplane embodying the proven Wagner box-spar acquired from Rohrbach, and hull features used in the Supermarine Southampton and the previously built Hiro Type 89 Flying-boats. To aid in determining the hull contours, water-tank tests were made at the Naval Technical Research Institute under the supervision of Naval Architect Rear Admiral Yuzuru Hiraga. The main requirements were that it was to be capable of flying on two engines and that it must have good water-borne characteristics. This would be the first Japanese Navy aircraft capable of carrying a one metric-tonne (one-ton) bomb load.

The test aircraft was completed at the Hiro Naval Arsenal in 1931 and given the designation Type 90-1 Flying-boat, short designation (H3H1). (Another aircraft that year, the Type 90-2 Flying-boat, was built by Kawanishi). The H3H1, was then flown to Yokosuka where exhaustive flight testing was undertaken by Lieut-Cdr Daizo Nakajima. Many problems were encountered which brought about modifications, including moving the radiators further aft under the engine nacelles, and experimenting with different propellers. To improve flying control, auxiliary vertical fins were added to the tailplane, and struts to the horizontal surfaces were relocated so that the angle of incidence could be adjusted. With each modification, a new dash number was assigned so the final configuration became the Type 90-1-4 Flying-boat.

By 1933, without proving satisfactory, the aircraft was relegated to use as a flying testbed for the 950 hp Mitsubishi Shinten fourteen-cylinder double-row air-cooled engine before it was retired from service. It was regarded as being inferior in stability to the Kawanishi Type 90-2 Flying-boat (H3K1) of the same period regardless of the revolutionary monoplane design features for a large flying-boat. As a result, only the one aircraft was built, but the design and fabricating experience gained proved very useful in developing later all-metal aircraft.

Technical Data
Manufacturer: Hiro Kaigun Kosho (Hiro Naval Arsenal).
Type: Three-engined experimental Flying-boat
Crew (9).
Powerplant: Three 650-790 hp Misubishi-Type Hi (Hispano-Suiza) twelve-cylinder vee water-cooled engines, driving four-blade wooden propellers.
Armament: twin flexible 7.7 mm (0.303 in) machine-guns in open bow position, twin flexible 7.7 mm (0.303 in) machine-guns amidships either side, twin flexible 7.7 mm (0.303 in) machine-guns in open tail poisition. Bomb load: two 500 kg (1,102 lb) or four 250 kg (551 lb) bombs.
Dimensions: Span 31.047 m (101 ft 10 1/2 in); length 22.705 m (74 ft 6 in); height 7.518 m (24 ft 8 in); wing area 137 sq m (1,474.703 sq ft).
Weights: Empty 7,900 kg (17,416 lb); loaded 11,900 kg (26,245 lb); wing loading 86.7 kg/sq m (17.7 lb/sq ft); power loading 6.1 kg/hp (13.4 lb/hp).
Performance: Maximum speed 123 kt (142 mph) at sea level; cruising speed 85 kt (98 mph); alighting speed 60.4 kt (69.5 mph); clinb to 3,000 m (9,843 ft) in 17 min; service ceiling 4,500 m (14,763 ft); range 1,105 nm (1,273 miles); endurance 13 hr.
Production: One prototype was built by Hiro kaigun Kosho in 1931.