In September 1922, a patriotic organisation known as the Teikoku Kaibo Gikai (Imperial Maritime Defence Volunteer Association) recognised that an all-metal aircraft of the quality being demonstrated by other countries, had not been manufactured in Japan, and therefore undertook such a project. For the design they organised the All Metal Aeroplane Committee which consisted of leading authorities of the Aeronautical Research Institute of Tokyo Imperial University, the Army, and the Navy. Although this was a joint effort, the design was identified with the PMBRA since the main component the hull, was built by the Army Arsenal.
The committee was led by Dr. Sc. Aikichi Tanakadate, the other members being Narihisa Yokota who became the chief designer, Yuzo Hishida, Matsutaro Honda, Shuhei Iwamoto, Yoshitake Ueda, Haruhiko Uemura, Hisakichi Akaishi, Masayuki Hori, Fumio Murase and Kyohei Arisaki. Joining the committee at a later date were two engineers, Keikichi Satake and Jun Okamura. The basic design for what was at first called the All Metal Seaplane was undertaken at the Aeronautical Research Institute, Tokyo Imperial University. Detail design, tooling and manufacturing of components and airframe were provided by the Army Artillery Arsenal, Army Ordnance Arsenal, Tokyo. Wind-tunnel model testing, powerplant and control system installations became the responsibility of the Aeroplane Factory, Department of Ordnance, Yokosuka Naval Arsenal.
The planned performance was a operational altitude of 3,000 m (9,843 ft) with a maximum speed of 108 kt (125 mph) provided by two 200 hp engines, giving a range of more than 1,080 nm (1,250 sm). A unique feature of this parasol-wing design was that the wing was supported by two massive wide-chord outward sloping structures in place of the more normal pylon connecting the hull to the wing. This feature was later patented, along with the type of metal propellers developed as well as the all-metal metal hull. A spare hull was built for additional tests purposes.
Although the work was suspended temporarily by the severe Kanto earthquake in September 1923, the airframe was nearly completed by March 1924, with the exception of the engine installation and other systems. In July of that year, the airframe was transported to the Department of Ordnance, Yokosuka Naval Arsenal, where the engines and other systems were installed. Because of development delays with the Japanese engines which were to deliver 200 hp at 3,000 m (9,843 ft), it was decided to use two 185 hp BMW IIIa engines instead. With these installed, the KB Flying-boat (KB for Kai Bo) as it was now called, was completed in December 1924.
The Kaibo Gikai KB was a twin-engined parasol-wing monoplane flying boat with a two-step hull and sponsons. It was of all-metal construction with metal stressed skin covering apart from some fabric covering on the wings and control surfaces.
After the aircraft was donated to the Navy by the Kaibo Gikai, flying trials began at Taura Beach, Yokosuka, with Navy test pilot Lieut-Cdr Hisakichi Akaishi, at the controls. As a result of minor modifications, the aircraft showed excellent take-off and alighting performance under light load conditions. The preliminary performance in speed and range gave strong indications that the desired performance would be met at the intended operational altitude. However, on 22 March, 1926, during its seventh test flight, the aircraft was seen in a glide with both engines stopped, its gliding angle continued to steepen and it crashed into the water nearly vertical, killing all four crew members on board. The cause of the crash was attributed to a malfunction of the flight control system.
With this loss, further development of the design was ended; however tests did continue with the second hull that was built for structural analysis. Considerable experience was gained thorough the design of this aircraft and it greatly influenced the 1928 Giyu No.3 flying-boat sponsored by the Kaibo Gikai and built by Kawasaki.
Technical Data
Manufacturer:
Type: Twin-engined flying-boat.
Crew(4):
Powerplant: Two 185-230 hp BMW IIIa six-cylinder water-cooled inline engines, driving two-blade metal (Later wooden) propellers.
Dimensions: Span 21.78 m (71 ft 5 1/2 in); length 13.95 m (45 ft 9 in); height 4 m (13 ft 1 1/2 in).
Weights: Empty 2,012 kg (4,435 lb); loaded 3,086 kg (6,803 lb); power loading 6.7 kg/hp (14.7 lb/hp).
Performance: maximum speed 109 kt (125 mph); minimum speed 50 kt (58 mph); climb to 3,000 m (9,843 ft) in 15 min; service ceiling 6,500 m (21,325 ft).
Production: Only a single prototype was built in 1924.
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