Mitsubishi B4M
{{Short description|Japanese torpedo bomber}}
| {{Infobox aircraft begin
|name=B4M |image=File:Mitsubishi B4M1.jpg |caption= }}{{Infobox aircraft type |type=Torpedo bomber |manufacturer=Mitsubishi |designer=Hajime Matsuhara |first flight=August 1934 |introduced= |retired= |status= |primary user=Imperial Japanese Navy |more users= |produced= |number built=2 |unit cost= |developed from=Mitsubishi 3MT10 |variants with their own articles= }} |
The Mitsubishi Ka-12 or B4M was a Japanese carrier-based torpedo bomber of 1934. Two prototypes were built by Mitsubishi for the Imperial Japanese Navy. A development of the company's 3MT10 of 1932, the design differed primarily in the use of a radial engine and metal wing, which made the whole aircraft significantly lighter and faster. However, the design could not realise its potential as the wing was inefficiently stiff and the B4M was not selected for production. The competing Yokosuka B4Y was chosen to serve on the Navy's aircraft carriers instead.
Design and development
In 1933, the Japanese Navy still relied on the Mitsubishi B1M as the backbone of its carrier-borne attack force. The Yokosuka B3Y was starting to enter service, developed in response to the 7-shi, competition.{{sfn|Mikesh|Abe|1990|page=280}} However, already, the new aircraft was suffering engine reliability and other problems, and an early replacement was deemed expedient.{{sfn|Mikesh|Abe|1990|page=281}} The B3Y had seen off competition from Mitsubishi and Nakajima, and both were invited, along with Yokosuka, to enter a design to the ensuing 9-shi competition in February 1934.{{sfn|Mikesh|Abe|1990|page=236}}
In response, Mitsubishi submitted a design based on their unsuccessful 7-shi entry, the 3MT10. However, instead of the bulky Rolls-Royce Buzzard V-12, a less powerful but lighter experimental Mitsubishi 8-Shi radial engine was fitted. Despite having an expected power rating of {{convert|650|hp|abbr=on}}, substantially less than the {{convert|835|hp|abbr=on}} of the Buzzard, the much reduced weight enabled the designer Hajime Matsuhara to substantially reduce the total weight of the aircraft by {{convert|590|kg|abbr=on}}. Weight-saving measures included introducing aluminium wings and removing the wheel fairings. Overall, the effect of these changes were to increase the theoretical speed to {{convert|270|km/h}}.{{sfn|Mikesh|Abe|1990|page=172}}
Matsuhara's final Ka-12 design was a single bay biplane of composite construction, with a fabric covered wooden frame fuselage and metal upper wings. The lower wings were of a new inverse gull shape, with fixed undercarriage attached to the wing and fuselage. The undercarriage had a wide track to allow for the carriage of a single {{convert|800|kg|lb|abbr=on}} torpedo or the equivalent weight in free-fall bombs. The three crew were seated in open cockpits and shared a total of three {{convert|7.7|mm|in|abbr=on}} machine guns, two mounted on flexible mounts firing aft and a single fixed mounting firing forward.{{sfn|Nohara|1999|page=180}}
Operational history
The first prototype was completed and first flew in August 1934.{{sfn|Mikesh|Abe|1990|page=172}} The aircraft was designated B4M1 by the Navy and flown against designs from both Nakajima and Yokosuka. Performance was considered superior to the aircraft in service, but the aircraft was unstable and difficult to fly. The lack of stiffness in the aluminium wing caused problems and the aircraft could not safely fly at its theoretical maximum speed. A second prototype designated was built with design changes, including a new nose fairing for the engine and a tailwheel instead of a skid, but these did not solve all the problems.{{sfn|Nohara|1999|page=180}} The Navy rejected the design and the competing Yokosuka B4Y was chosen for production instead. However, Mitsubishi did gain some consolation from the outcome as they eventually produced 135 of the Yokosuka type.{{sfn|Mikesh|Abe|1990|page=236}}
Operators
;{{JPN}}
Specifications (B4M1)
{{Aircraft specs
|ref=Japanese Aircraft 1910-1941{{sfn|Mikesh|Abe|1990|page=172}}
|prime units?=met
|crew=3
|length m=9.96
|length note=
|span m=14.80
|span note=
|height m=3.94
|height note=
|wing area sqm=54.00
|wing area note=
|aspect ratio=
|airfoil=
|empty weight kg=2000
|empty weight note=
|gross weight kg=3824
|gross weight note=
|max takeoff weight kg=
|max takeoff weight note=
|fuel capacity=
|more general=
|eng1 number=1
|eng1 name=Mitsubishi 8-Shi
|eng1 type=14-cylinder air-cooled radial piston engine
|eng1 hp=650
|eng1 note=
|prop blade number=
|prop name=
|prop dia m=
|prop dia note=
|max speed kmh=241
|max speed note=
|cruise speed kmh=185
|cruise speed note=
|stall speed kmh=
|stall speed note=
|never exceed speed kmh=
|never exceed speed note=
|range km=
|range note=
|combat range km=
|combat range note=
|ferry range km=
|ferry range note=
|endurance=6 hours 10 minutes
|ceiling m=
|ceiling note=
|g limits=
|roll rate=
|climb rate ms=
|climb rate note=
|time to altitude=14 minutes 33 seconds to {{convert|3000|m|ft|abbr=on}}
|wing loading kg/m2=
|wing loading note=
|fuel consumption kg/km=
|power/mass=
|thrust/weight=
|more performance=
|guns= 1 × forward firing 2 × flexible {{convert|7.7|mm|in|abbr=on}} machine guns in rear cockpit
|bombs= 1 × {{convert|800|kg|lb|abbr=on}} torpedo or equivalent weight of bombs
}}
See also
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|related=
|similar aircraft=
|lists=
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References
=Citations=
{{commons category|Mitsubishi B4M}}
{{Reflist}}
=Bibliography=
- {{cite book|last1=Mikesh|first1=Robert C.|first2=Shorzoe|last2=Abe|title=Japanese Aircraft 1910-1941|location=London|publisher=Putnam|year=1990|isbn=978-0-851-77840-2}}
- {{cite book|last=Nohara|first=Shigeru|title=日本陸海軍試作/計画機 : 1924-45図解世界の軍用機史|trans-title=The X-Planes of Imperial Japanese Army & Navy 1924-45|year=1999|location=Tokyo|publisher=Gurīn Arōshuppansha|language=Japanese|isbn=978-4-76633-292-6}}
{{Mitsubishi aircraft}}
{{Japanese Navy short aircraft designations}}
Category:1930s Japanese bomber aircraft
Category:Aircraft first flown in 1934