The Nakajima Ki-49 Donryu (Storm Dragon) 'Helen' was a somewhat disappointing Japanese Army bomber that served in China, New Guinea and the Philippines, but proved to be vulnerable to Allied fighters as the war progressed and to have disappointing speed and handling.
The Ki-49 was designed in response to an Army specification issued in 1938 for a new bomber to replace the Mitsubishi Ki-21 Army Type 97 Heavy Bomber, which was only just entering service.
The specification called for an aircraft with a top speed of 311mph, a range of 1,864 miles, a bomb load of 2,205lb, self sealing fuel tanks, some crew armour, a 20mm cannon in a dorsal turret and 7.7mm machine guns elsewhere. The new bomber was meant to be capable of operating without fighter escort, a constant concern for the Japanese Army Air Force as it operated over the vast distances of China.
Nakajima began work on the new design in the summer of 1938. T. Koyama led the design team. His team produced an all-metal aircraft with a smooth oval fuselage, with a raised section that ran from the pilot's cockpit to the rear gunner's position. The aircraft had a heavily glazed nose. It has a single tail with fairly tall vertical surfaces.
The mid-mounted wings had a slight dihedral. The leading edge was straight, the trailing edge tapered in, more sharply on the outer half of the wings. The centre section of the wings was thicker and had a bigger chord than the outer section and contained three self-sealing fuel tanks on each side. Two more self-sealing fuel tanks and self-sealing oil tank were located in the outer wing sections. The main undercarriage wheels retracted into the engine nacelles. The bombers were carried in an enclosed bomb bay carried between the wings. The aircraft was designed to be stable but manoeuvrable at low and medium altitudes.
The Ki-49 was armed with one flexibly mounted 20mm cannon that was carried on the left-hand side of a dorsal turret. It also ha the first tail turret on any Japanese army aircraft, carrying a single 7.7mm machine gun. 7.7mm machine guns were also carried in the nose, ventral, port and starboard positions.
The first prototype made its maiden flight in August 1939. It was followed by two further prototypes with more powerful engines and seven pre-production machines with constant speed propellers.
Ki-49-I Army Type 100 Heavy Bomber Model 1
The Ki-49 was accepted for production in March 1941. The Ki-49-I was identical to the pre-production machines. It was powered by two Nakajima Ha-41 engines, producing 1,250hp. The first production aircraft were completed in August 1941.
Nakajima produced 129 production Ki-49-I aircraft between August 1941 and August 1942.
Ki-49-II Army Type 100 Heavy Bomber Model 2
The Ki-49-I proved to be underpowered - it could carry a lighter bomb load over useful combat distances or a useful bomb load over short distances. In the spring of 1942 the Ki-49-II was developed. This saw the 1,250hp engines replaced with Nakajima Ha-109 Army Type 2 radial engines, producing 1,450hp each. Two prototypes were built, with extra armour and improved self-sealing fuel tanks.
Ki-49-IIa Army Type 100 Heavy Bomber Model 2A
The Ki-49-IIa Army Type 100 Heavy Bomber Model 2A was the first production version of the Ki-49-II. It carried the same guns as the -I, and the first aircraft were delivered to the Army in August 1942.
Nakajima produced 617 Ki-49-II aircraft of both types between September 1942 and the end of production in December 1944. Tachikawa Hikoki K.K produced another 50 aircraft.
Ki-49-IIb Army Type 100 Heavy Bomber Model 2B
The Ki-49-IIb saw the introduction of 12.7mm machine guns in place of the 7.7mm machine guns in the nose, ventral and tail positions. The aircraft still carried its single 20mm cannon and 7.7mm machine guns in the port and starboard positions.
The Ki-49-III was produced in an attempt to improve the speed of the aircraft. The two Ki-80 prototypes were used to test the 2,420hp Nakajima Ha-117 fourteen cylinder radial engines. Six pre-production Ki-49-IIIs were produced between March and December 1943 but efforts to increase the power of the engines failed and the Ki-49-III didn't enter production
The Ki-58 was a fighter-escort version of the Ki-49. It was produced in response to heavy losses of unescorted bombers in China, and carried five 20mm Ho-1 cannon and three 12.7mm machine guns. The Americans produced similar conversions of the B-17 Flying Fortress and B-24 Liberator, and in both cases the project was abandoned in favour of long range escort fighters. In Japan that role was filled by the Nakajima Ki-43 Army Type 1 Fighter Hayabusa. Three Ki-58s were built before the project was abandoned.
The Ki-80 was a version of the Ki-49 designed for use by formation leaders. Two prototypes were built but the type didn't enter production.
By the autumn of 1941 the 61st Sentai began to convert from the Ki-21 to the new Ki-49. Production was slow, and the last Ki-21s didn't go until February 1942.
Once enough aircraft were available the Ki-49 was introduced to combat in China.
The Ki-49-I entered combat against the Allies over New Britain and New Guinea. It was also used during Japan's raids against Australia.
The Ki-49-I was a disappointment in service. It was underpowered and wasn't fast enough to avoid Allied fighters. Its effective bomb load at combat ranges was lower than that of the Ki-21 and it was harder to fly. The armour and self-sealing fuel tanks did make it less vulnerable than earlier Japanese bombers, but the single 7.7mm machine guns weren't very effective. As a result the Ki-49-II was given more powerful engines and late production aircraft got 12.7mm machine guns.
The Ki-49-II saw service in New Guinea and in China. It was then used in the costly defensive battles in the Philippines, were it proved to be very vulnerable to the ever-increasing numbers of powerful Allied fighters.
Most of the surviving Ki-49s on the Philippines were used as kamikaze aircraft in attacks on the Allied fleet of Mindoro. For this role the guns were removed, the crew reduced to two and the bomb load raised to 3,527lb.
The Ki-49 was used for a number of special purposes. Some Ki-49-Is were given magnetic detection gear and other electronic kit and used as anti-submarine aircraft.
A number of Ki-49-IIs were used as troop transports, a sign of the low number of transport aircraft available to the Japanese Army.
Even more desperate was the attempt to use the Ki-49-II as a night fighter. They were used in pairs, one carrying a searchlight in the nose and the other a 75mm cannon. The idea was for the searchlight aircraft to find and illuminate the target and the cannon-armed aircraft to shoot it down, but the aircraft didn't have the performance required to intercept Allied bombers.
Engine: Two Nakajima Ha-109 radials
Span: 67ft 0in
Length: 54ft 1.5in
Height: 13ft 11.25in
Empty weight: 14,396lb
Maximum take-off weight: 25,133lb
Max speed: 306mph
Climb Rate: 13min 39sec to 16,405ft
Service ceiling: 30,150ft
Range: 1,833 miles maximum, 1,243 miles normally
Armament: One 20mm cannon and five 7.7mm machine guns
Bomb load: 2,205lb