Profile Publications No. 82 The Mitsubishi Ki-46

The challenge facing Tomio Kubo, who had been assigned the responsibility of leading Mitsubishi's design team, was tremendous, especially in regard to the maximum speed specified, which was to exceed that of the early Hurricane I, then just entering service, by some 55 m.p.h. and that of the Curtiss P-36A, about to be delivered to the squadrons of the U.S. Army Air Corps, by 60 m.p.h. Although no liquid-cooled engine of suitable power was then avail­able in Japan, Tomio Kubo was initially in favour of using this type of engine as opposed to the radial with its larger diameter and associated drag. However, as there was little or no prospect of obtaining a satis­factory liquid-cooled engine in the time available, it was decided to use the 15-cylinder radial Mitsubishi Ha-26 as it had the smallest diameter of the three types of engines recommended by the JAAF. To find a solution to the drag problem Tomio Kubo called upon facilities of the Aeronautical Research Institute of the University of Tokyo which conducted extensive wind tunnel tests. As a result of these tests close-fitting cowlings, minimising drag and improving the pilot's side vision while ensuring satisfactory engine cooling, were adopted. At the same time a thinner wing section than had been originally planned was selected and the fuselage diameter was kept to a minimum. To locate a large fuel tank in the fuselage close to the aircraft centre of gravity it was found necessary to separate the two crew members, the pilot being seated over the wing leading-edge whilst the radio-operator/gunner sat over the trailing-edge under a separate canopy. The Aeronautical Research Institute also recom­mended the use of constant speed propellers and conducted some studies of the retractable landing gear. FLIGHT TRIALS BEGIN The first prototype Ki-46 was completed at Mitsu­ bishi’s Nagoya aircraft plant in early November 1939, and the aircraft was transported to Kakumugahara airfield where flight testing began later in the month with Major Fujita, who had been the moving force behind the programme, at the controls. The aircraft was powered by two 875-h.p. 14-cylinder Mitsubishi Ha-26-I engines, each with a single-speed super­charger, driving constant-speed, three-blade pro­pellers. Provision was made for one 7-7-mm. Type 89 flexible machine gun with 216 rounds of ammunition manned by the radio-operator. Early in the flight test programme the aircraft attained a maximum speed of 335-5 m.p.h. at 13,125 ft. and few teething troubles were encountered. Even though the maximum speed The Australian Army discovered this Army Type 100 Mode! 2 o f the 76th Dokoritsu Dai Shijugo Chutai at Gasmata, New Britain. (Photo: Australian War Memorial) was some 40 m.p.h. below that specified, JA A F Head­quarters was still satisfied as the aircraft was faster than the A6M2 (331 m.p.h. at 14,930 ft.) and the Ki-43-I (308 m.p.h. at 13,125 ft.) then undergoing flight test evaluation. However, the JA A F was aware that the performance of the Ki-46 was insufficient to assure freedom of interception by Western fighters, such as the Spitfire IIA with its maximum speed of 370 m.p.h., and it instructed Mitsubishi to explore the possibilities of adapting more powerful engines to the Ki-46 airframe. Fortunately, Mitsubishi had underdevelopment an advanced version of the Ha-26, the Ha-102, which had the same overall diameter and was expected to develop 1,050 h.p. at take-off rating and 950 h.p. at 19,000 ft. Pending availability of the Mitsubishi Ha-102 engine the Ki-46 was placed in production with the Type 99 Model 1, the production version of the Ha-26-I, as the Army Type 100 Model 1 Command Reconnaissance Plane (Ki-46-I). These aircraft, which were identical to the prototypes, were used for pilot training and intensive service evaluation, most aircraft Undercarriage and engine de­tails visible on a captured 55th D.D .S.C .machine. (Photo: via the author) K i-4(-lI o f the 55th Dokuritsu Dai Shijugo Chutai. (Photo: via the author) Rear view o f the same machine. (Photo: via the author) 4
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