Nakajima Ki-49 Donryū

The Nakajima Ki-49 Donryū (呑龍, "Storm Dragon") was a twin-engine heavy bomber designed and produced by the Japanese aviation manufacturer Nakajima Aircraft Company. Operated by the Imperial Japanese Army Air Service (IJAAS) as the Army Type 100 Heavy Bomber Model 1, it was known to the Allied by the reporting name "Helen".

The design of the Ki-49 was greatly shaped by a forerunning bomber operated by the IJAAS, the Mitsubishi Ki-21. Specifically, officials came to recognise that, no matter how advanced the Ki-21 may have been at the time of its introduction, it would not be long before the bomber would be unable to operate without support from friendly fighters. Accordingly, in 1938, a specification for a replacement bomber was issued, which stipulated that such an aircraft should have the speed and defensive weaponry to enable it to operate independently, even during daylight bombing missions, without the protection of escort fighters. Consequently, the Ki-49 was furnished with formidable defensive armament and armor, although these features restricted the Ki-49 to payloads comparable to those of lighter medium bombers – the initial production variant could carry only of bombs. A mid-wing, cantilever monoplane of all-metal construction, the Ki-49 was one of the first Japanese aircraft fitted with a retractable tailwheel and a tail turret.

Performing its maiden flight in August 1939, the type was introduced to service two years later and made it combat debut during the Second Sino-Japanese War. Upon Japan's entry into World War II, the Ki-49 became a staple of the Pacific War, being active in the New Guinea and conducting numerous air raids against Australia. Improved versions of the aircraft were introduced during the conflict, such as the up-engined Army Type 100 Heavy Bomber Model 2. It was active during Battle of the Philippines up to December 1944, at which point most surviving Ki-49s were used to conduct kamikaze attacks the advancing Allied forces. Production of the Ki-49 was terminated in December 1944.

Development The origins of the Ki-49 can be traced back to the issuing of a specification in 1938 for a replacement to the Mitsubishi Ki-21 ("Sally"), which was introduced to service with the Imperial Japanese Army Air Service (IJAAS) that same year. This specification called for a bomber that had sufficient speed and armament to not be reliant upon escorting fighter for its defence. Specific performance criteria included a maximum speed of at least 500 kmph (311 mph), a range of 3,000 km (1,864 miles), a bombload of (2,205 lb), and multiple flexibly-mounted machine guns for self-defence, including at least one in the tail. Furthermore, the envisioned aircraft was also to have sufficient protection from enemy fire; this included the incorporation of self-sealing fuel tanks.

In Summer 1938, Nakajima Aircraft Company assembled a design team that included multiple of its senior engineers to produce its response. During the procurement of the Ki-21, the company had received valuable information on the Mitsubishi aircraft, and made use of this data in their design process. The defensive armament consisted of one 20 mm Ho-1 cannon installed within a dorsal turret, and several 7.7 mm Type 89 machine guns located in the aircraft's nose, ventral, port, and starboard positions as well as in a tail turret; the latter was a novel feature for the IJAAS at the time of its introduction. A single bomb bay was contained within the fuselage, which was almost as long as the centre-section of the wing.

One key area of focus during the design process was the aircraft's handling characteristics; this contributed to the selection of a mid-wing configuration that had an atypically low aspect ratio that was both relatively stable and provided for favourable manoeuvrability when flown at medium or low altitudes. This wing's centre-section had a wider chord than the outer sections, the internal volume of which was used to accomidate a total of six self-sealing fuel tanks. Other attributes of the wing included its relatively low drag properties and the positioning of the Fowler flaps well aft of the engine nacelles. An additional pair of fuel tanks, as well as a single oil tank, were located within each of the outer wing sections.

In August 1939, the first prototype performed its maiden flight; this aircraft would be largely used for handling trials, during which positive feedback was received from service pilots. An additional two prototypes and seven pre-production aircraft would be procured. While the first prototype was powered by a pair of Nakajima Ha-5 KA-I radial engines, the next two prototypes were outfitted with the Nakajima Ha-41 engines that were intended for the production version. The pre-production aircraft, which were almost identical to the latter pair of prototypes aside from the fitting of constant-speed three-bladed propellers, were completed during 1940 and underwent an extensive flight testing process, which involved only minor changes in armament, protection, and seating arrangements being evaluated.

In March 1941, Nakajima was informed that the Ki-49 had been accepted into production as the Army Type 100 Heavy Bomber Model 1. Akin to the prototype, early production aircraft were armed with five machine guns and one cannon. Combat experience in China and New Guinea showed the aircraft to be somewhat underpowered, restricting both bomb capacity and airspeed as a result. This was addressed during the spring of 1942 by the arrival of an up-engined model of the Ki-49, fitted with more powerful Ha-109 engines and this became the production Army Type 100 Heavy Bomber Model 2 or Ki-49-IIa. The Model 2 also introduced improved armor and self-sealing fuel tanks; it was followed by the Ki-49-IIb in which Ho-103 machine guns replaced three of the Type 89 machine guns. In early 1943, further power increases were delayed on account of development difficulties with the Nakajima Ha-117 engines, leading to the Ki-49-III never entering production and only six prototypes being built.

After 819 aircraft had been completed, production of the Ki-49 was terminated in December 1944. In addition to Nakajima's own production activities, fifty Ki-49s were completed by the Tachikawa Aircraft Company, although their efforts were hindered by poor quality jigs. Plans for the type to be produced by Manshukoku Hikoki Seizo KK never came to fruition.

Operational history

The first Ki-49s became operational in autumn 1941 and flew its first combat missions in the Chinese theatre. Following the outbreak of the Pacific War, the Ki-49 was also active in the New Guinea area. Furthermore, it was one of the primary aircraft used to conduct air raids against Australia between 1942 and 1943.

Combat experiences contributed to IJAAS officials not being fully satisfied with the Ki-49; feedback from operational units was fed back to Nakajima and led to various design improvements during the production run of the type. While the Ki-49 did supplement the older Ki-21, it was unable to entirely supplant the older bomber as had been intended. In spite of these improvements, losses continued to mount, as the quantity and quality of fighter opposition rose. In the face of its increasing vulnerability to opposing fighter aircraft while performing its intended role, the Ki-49 was used in other roles towards the end of the Pacific War, including anti-submarine warfare patrol, troop transport, and even night fighter missions.

When the Allies launched the Battle of the Philippines in 1944, the Ki-49 was used extensively in the IJAAS's efforts to resist the advance. During December 1944, most of the surviving aircraft were expended in kamikaze attacks upon Allied naval vessels supporting the landing at Mindoro. Typically, those Ki-49s intended for suicide attacks were stripped of all armaments, the crew reduced to only the two pilots, and an increase payload of (or 3,527lb) of bombs carried.

Variants

Ki-49 Prototypes and pre-series models with a Nakajima Ha-5 KAI or the Ha-4. The pre-series with little modifications from the prototype. Ki-49-I Army Type 100 Heavy Bomber Model 1, initial production version. Ki-49-II Two prototypes fitted with two Nakajima Ha-109 radial piston engines. Ki-49-IIa Army Type 100 Heavy Bomber Model 2A - Production version with Ha-109 engines and armament as Model 1. Ki-49-IIb Version of Model 2 with Ho-103 machine guns replacing rifle caliber weapons. Ki-49-III Six prototypes fitted with two Nakajima Ha-117 engines. Ki-58 Escort fighter with Ha-109 engines, 5 x cannon, 3 x machine guns. Three prototypes built. Ki-80 Specialized pathfinder aircraft - two prototypes; employed as engine test-beds.

Operators Wartime

Imperial Japanese Army Air Service No. 61 Hikō Sentai IJAAS No. 62 Hikō Sentai IJAAS No. 74 Hikō Sentai IJAAS No. 95 Hikō Sentai IJAAS No. 110 Hikō Sentai IJAAS No. 11 Hikōshidan IJAAS Hamamatsu Army Heavy Bomber School

Post-war

Three captured aircraft were used between 1946 and 1949 in Indochina

Indonesian Air Force - Ex-Japanese Aircraft were operated by Indonesian guerilla forces after the conflict.Japanese Aircraft in Foreign Service WWII and Post WWII retrieved 24 August 2010

Royal Thai Air Force - Flew a single Ki-49 as a transport, during 1945-1946 (postwar)

Specifications (Ki-49-IIa)

Nakajima Ki-49 Donryū

Bron en licentie