Kawanishi H6K5

Specifications (Navy Type 97 Flying Boat Model 23 – Kawanishi H6K5)

Allied Codename: Mavis (Transport versions were given the Allied codename “Tillie”)

Type: (H6K1, H6K2, H6K4 & H6K5) Nine Seat Long Range Reconnaissance Bomber. (H6K2-L, H6K3 & H6K4-L) Eight Seat Long Range Troop & VIP Transport with room for up to 18 passengers.

Accommodation/Crew: (H6K5) Pilot, Co-pilot, Bombardier, Navigator, Radio Operator, Flight Engineer and three gunners.

Design: Kawanishi Kokuki Kabushiki Kaisha Design Team led by Yoshio Hashiguchi and Shizuo Kikahura.

Manufacturer: Kawanishi Kokuki Kabushiki Kaisha (The Kawanishi Aircraft Company Limited) at Naruo Mukogun Hyogoken, near Kobe.

Powerplant: (H6K1) Four Nakajima Hikari 2 nine-cylinder air-cooled radials, rated at 840 hp for take-off and 700 hp at 1,200 m. (H6K1 Model 1, H6K2, H6K2-L, H6K3 and H6K4 Model 2-2) Four Mitsubishi Kinsei 43 fourteen-cylinder air-cooled radials, rated at 1,000 hp for take-off and 990 hp at 2,800 m. (H6K4 Model 2-3 and H6K4-L) Four Mitsubishi Kinsei 46 fourteen-cylinder air-cooled radials, rated at 930 hp for take-off and 1,070 hp at 4,200 m. (H6K5) Four Mitsubishi Kinsei 51 or Kinsei 53 fourteen-cylinder radials, rated at 1,300 hp for take-off, 1,200 hp at 3,000 m and 1,100 hp at 6,200 m. All versions of the aircraft used three-bladed metal propellers.

Performance: Maximum speed 190 mph (304 km/h) at 8,000 ft (2440 m) and 239 mph (385 km/h) at 19,685 ft (6000 m); cruising speed 161 mph (260 km/h) at 13,125 ft (4000 m); service ceiling 31,365 ft (9560 m); climb to service ceiling in 13 minutes 23 seconds.

Fuel Capacity: 1,950 Imperial gallons (8864 litres).

Range: Normal range 3,067 miles (4939 km) on internal fuel with a maximum range of 4,204 miles (6770 km).

Weight: Empty 27,117 lbs (12380 kg) with a maximum take-off weight of 50,706 lbs (23,000 kg). Loaded weight was typically 38,581 lbs (17,500 kg).

Dimensions: Span 131 ft 2 3/4 in (40.0 m); length 84 ft 1 in (25.63 m); height 20 ft 6 3/4 in (6.27 m); wing area 1,829.92 sq ft (170.0 sq m); wing loading 21.1 lbs/sq ft (102.9 kg/sq m); power loading 7.4 lbs/hp (3.4 kg/hp).

Defensive Armament: One 7.7 mm (0.303 in) Type 92 machine-gun in forward turret, one 7.7 mm (0.303 in) Type 92 machine-gun in an open dorsal position, one 7.7 mm (0.303 in) Type 92 machine-gun in each beam blister and one flexible mounted 20 mm Type 99 Model 1 cannon in tail turret.

Disposable Ordnance: Two 17.7″ (44.9 cm) 1,841 lbs (835 kg) Type 91 Mod 2 or 1,872 lbs (849 kg) Type 91 Mod 3 torpedoes or up to a maximum of 4,409 lbs (2000 kg) of bombs attached to the wing support struts. The normal operational bombload would have only been 2,205 lbs (1000 kg).

Variants: H6K1 (4 prototypes), H6K1 Model 1 (3 modified from the prototypes), H6K2 Model 11 (10 aircraft 1938-39), H6K3 (2 aircraft in 1939 completed as VIP transports), H6K4 Model 22 (major production version – 127 aircraft completed between 1939-42), H6K5 Model 23 (36 aircraft completed in 1942), H6K2-L (unarmed transport – 16 completed between 1940-42), H6K4-L (unarmed transport – 20 completed between 1942-43 with another two aircraft being modified from H6K4 airframes in 1942).

Avionics: None.

History: First flight (prototype) 14 July 1936 by test pilot Katsuji Kondo.

Operators: Japan (Imperial Japanese Navy)

Units: 8th, 801st, Toko and Yokohama (later 802nd) Kokutais.

Background

The air arm of the Imperial Japanese Navy had gained its first experience of large flying boats from the Kawanishi H3K2, or Navy Type 90-11 Flying Boat. This had its beginnings in the British Short Brothers K.F.1 prototype designed for the Japanese navy which, after a first flight on 10 October 1930, was soon sent to Japan where it served as a pattern for four H3K2s, built by Kawanishi under the supervision of a British technical team. This emphasises how, in its early involvement in aviation, the Japanese industry was dependent upon copying the designs of foreign manufacturers. From their study of these designs and the constructional techniques adopted, Japan ‘s young engineers gained valuable experience in a comparatively short time. By the early and mid-1930s they had acquired sufficient knowledge to start the design and development of a number of first-class aircraft.

When, in 1933, the navy considered the moment had come to acquire a larger and more efficient flying boat, Kawanishi was given a specification against which it was required to submit proposals for two alternative designs with three and four engines, identified as the Type Q and R respectively. Unfortunately the proposals were not satisfactory, and in early 1934 the navy issued a revised and more demanding specification, which called for a cruising speed of 137 mph (220 km/h) combined with a range of approximately 2,795 miles (4500 km). This performance (if achieved) would better that of the Sikorsky S-42 flying boat, which had made some important pioneering flights. Kawanishi’s reappraisal of the requirement resulted in a new design, identified initially as the Type S and the work of a team headed by Yoshio Hashiguchi and Shizuo Kikahura, who had both had an opportunity of studying flying boat design at Short Brothers in the UK.

Required to fulfill the roles of bombing, reconnaissance and transport, the prototype had a slender and graceful two-step hull above which was mounted a parasol wing, the wing having a stabilizing float strutted and braced beneath its undersurface just outboard of midspan, and mounting at its leading edge four 840 hp (626 kW) Nakajima Hikari (Splendour) 2 nine-cylinder air-cooled radial engines. The tail unit, strut-mounted high on the rear fuselage, comprised a monoplane tailplane and twin fins and rudders, and for normal operations use the hull provided accommodation for a crew of nine.

First flown on 14 July 1936, the H6K1 prototype in early tests showed a need of hull modification to improve water handling, and the more extended manufacturer’s tests and service trials that followed this work revealed the type to be satisfactory but underpowered. Three more prototypes were ordered, all with Hikari 2 engines originally, but the first, third and fourth of the prototypes were each given four 1,000 hp (746 kW) Mitsubishi Kinsei (Golden Star) 43 fourteen-cylinder air-cooled radial engines before they entered service in January 1938 under the designation Navy Type 97 Flying Boat Model 1. Simultaneously, the type was ordered into production and eventually a total of 215 of all versions were built, the initial H6K2 production model being generally similar to the re-engined prototypes except for minor equipment changes. Armament comprised three 7.7 mm (0.303 in) machine-guns on trainable mounts in bow, power-operated dorsal turret and non-powered tail turret, and up to 2,205 lbs (1000 kg) of bombs could be carried. Two generally similar aircraft, which were equipped to serve specifically as VIP transports had the designation H6K3.

The major production version was the H6K4 which had greater fuel capacity and improved defensive armament comprising four 7.7 mm (0.303 in) machine-guns in bow, two side blisters and open dorsal position, plus one 20 mm cannon in a tail turret. Its powerplant was unchanged initially, but from August 1941 the Kinsei 43 engines were replaced by 930 hp (694 kW) Kinsei 46 fourteen-cylinder air-cooled radial engines which gave better performance at altitude. Final armed military production version was the H6K5 which, generally similar to the H6K4, deleted the open bow gun position and introduced a turret with a single 7.7 mm (0.303 in) machine-gun immediately to the rear of the flight deck, and performance was improved by the installation of uprated 1,300 hp (970 kW) Kinsei 51 or 53 radial engines. In 1939 two H6K2s had been modified to serve as prototypes for an unarmed version for use as a military staff transport and for operation on the long over-water routes of Dai Nippon Koku K.K. (Greater Japan Air Lines).

Following successful testing the company began production of the H6K2-L, based on the early H6K4 with 1,000 hp (746 kW) Mitsubishi Kinsei (Golden Star) 43 engines, and equipped to accommodate 18 passengers. Sixteen of this version, plus two similar aircraft converted from H6K4s, were supplied to Dai Nippon Koku K.K. (Greater Japan Air Lines), being followed by 20 H6K4-L unarmed transports for the Japanese navy; these later aircraft differed by being based on the H6K4, with Kinsei 46 engines, and were provided with additional cabin windows.

The H6K saw early operational service during the Sino-Japanese War, but was used extensively with the outbreak of the Pacific war, the armed versions receiving the Allied codename ‘Mavis’ in 1942, by which time the increasing capability of fighter aircraft ranged against the type was such that it could no longer be deployed in a bomber role. Instead the type found increasing reconnaissance/transport use in areas where comparatively little fighter opposition could be expected, many remaining in service until the end of the war .The unarmed transport versions were given the Allied codename ‘Tillie.’   

Variants

Kawanishi H6K1 ‘Type S’ Prototypes – The first prototype had a slender and graceful two-step hull above which was mounted a parasol wing, the wing having a stabilizing float strutted and braced beneath its undersurface just outboard of midspan, and mounting at its leading edge four 840 hp (626 kW) Nakajima Hikari (Splendour) 2 radial engines. The tail unit, strut-mounted high on the rear fuselage, comprised a monoplane tailplane and twin fins and rudders, and for normal operations use the hull provided accommodation for a crew of nine. First flown on 14 July 1936, the H6K1 prototype in early tests showed a need to improve water handling, so the forward step was moved back 1 ft 7 11/16 inches (50 cm). The more extended manufacturer’s tests and service trials that followed this work revealed the type to be satisfactory but underpowered. The second and third prototypes were delivered in 1937, with a fourth being completed in early 1938. The last three prototypes differed from first by having increased span ailerons, enlarged fins and a redesigned dorsal turret installation.

Kawanishi H6K1 Model 1 – Following the completion of Service Trials, the first, third and fourth prototypes were re-engined with 1,000 hp (746 kW) Mitsubishi Kinsei (Golden Star) 43 radial engines and entered service in January 1938 under the designation Navy Type 97 Flying Boat Model 1.

Kawanishi H6K2 Model 2 – First production model being generally similar to the re-engined prototypes except for minor equipment changes. Armament comprised three 7.7 mm (0.303 in) machine-guns on trainable mounts in bow, power-operated dorsal turret and non-powered tail turret, and up to 2,205 lbs (1000 kg) of bombs could be carried. In April 1940 this version was redesignated Model 11. Ten aircraft were built but the seventh and eighth aircraft were modified as experimental transports.

Kawanishi H6K3 – Two more aircraft virtually identical to the H6K2 were completed for use as VIP Transports and designated H6K3.

Kawanishi H6K4 Model 22 (Model 2-2 & 2-3) – The major production version was the H6K4 which had the fuel capacity increased from 1,708 Imp. gallons (7765 litres) to 1,950 Imp. gallons (8864 litres) and improved defensive armament comprising of two beam blisters, each holding a single 7.7 mm (0.303 in) machine-gun (this replaced the dorsal turret), two open bow positions, each holding a single 7.7 mm (0.303 in) machine-gun and an open dorsal position with a 7.7 mm (0.303 in) machine-gun plus one 20 mm Type 99 Model 1 cannon in a tail turret. Its powerplant was unchanged initially, but from August 1941 the Kinsei 43 engines (Model 2-2) were replaced by the 930 hp (694 kW) Kinsei 46 (Model 2-3). A total of 127 aircraft were completed (with both engines) and were jointly redesignated Model 22.

Kawanishi H6K2-L – Following successful testing of the H6K3, the company began production of the H6K2-L, based on the early H6K4 with Kinsei 43 engines, and equipped to accommodate 18 passengers. Sixteen of this version, were completed and delivered to the Kaiyo (Ocean) Division of Dai Nippon Koku K.K. (Greater Japan Air Lines) which assigned the type to the Yokohama-Saipan-Palau-Timor, Saigon-Bangkok and Saipan-Truk-Ponape-Jaluit routes. Modifications included the removal of all armament, and the interior fuselage arrangement was revised to provide for the installation of a mail and cargo compartment in the hull forward of the cockpit, galleys behind the cockpit, a midship cabin with seats for eight or sleeping accommodations for four followed by an aft cabin with 10 seats and aft of this were toilets and another cargo compartment.

Kawanishi H6K4-L – Unarmed transports based on the H6K4 using Kinsei 46 engines and supplied with additional cabin windows. Production totaled 20 aircraft but a further two H6K4 aircraft were converted to the transport standard. For some unknown reason the tail turret was retained, but without armament. 20 aircraft used by the Japanese Navy with the two converted aircraft being supplied to Dai Nippon Koku K.K. (Greater Japan Air Lines).

Kawanishi H6K5 Model 23 – Generally similar to the H6K4, deleted the open bow gun position and introduced a turret with a single 7.7 mm (0.303 in) machine-gun immediately to the rear of the flight deck, and performance was improved by the installation of uprated Kinsei 51 or 53 engines. 36 aircraft.

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