Multi-role attack aircraft, capable of dive bombing, horizontal bombing and torpedo attacks. At the time, aircraft carriers carried dive bombers and torpedo bombers for anti-shipping operations. However, as both types of aircraft could be used in different situations, it was difficult to make use of the limited number of aircraft on board. The Ryusei was created to solve this problem.
Two-seater with all-metal monocoque structure. The main landing gear was of the retracted inward type with a tail wheel. The bomb bay is housed in the lower part of the fuselage (except for the aerial torpedo, which is carried externally). The wings are of the mid-wing monoplane type with inverted gull wings, which are a major feature of the aircraft’s looks.
According to the IJN’s definition, aircraft capable of dive bombing are classified as “bombers”, while those capable of torpedoing are classified as “attack aircraft” (horizontal bombing is possible for both types). However, as the abbreviation “B7A” indicates (Aichi Aircraft Company (A), 7th aircraft (B7)), the aircraft was classified as an “attack aircraft”. The Ginga, which was also a dive bomber and torpedo bomber, was classified as a “bomber”. Although it had outstanding performance compared with other single-engine bombers, it was difficult to operate as a carrier-based aircraft due to its excessive weight, and in fact it was operated as a land-based aircraft.
In order to obtain high speed performance, bombs that cause air resistance are carried in the bomb bay inside the fuselage. However, aerial torpedoes are loaded outside the bomb bay and suspended on the underside of the fuselage. Because the bomb bay is housed in the lower part of the fuselage, the main wings are mid-wing monoplane type with inverted gull wings. The main landing gear of the aircraft had to be strong enough to withstand the impact of landing on a carrier and to carry large and heavy bombs, but the normal mid-wing design would have made the main landing gear too long and structurally unstable for take-off and landing, as well as being too heavy. Therefore, the main landing gear is placed at the bend of the inverted gull wing and its length is shortened to secure the strength. In addition, the mid-wing monoplane design did not require fillets to connect wings to the fuselage, which also reduced weight. Semi-Fowler flaps on the trailing edge of the wings, developed for the earlier D4Y. The aileron flaps also lower the auxiliary flaps when the flaps are activated, improving not only the aircraft’s short takeoff and landing capability but also its manoeuvrability. While the B5N and Tenzan did not have protective equipment, this aircraft was the only IJN attack aircraft with such equipment at the time of development, but as mentioned below, it was later omitted to reduce weight. In addition, this plane is double-seated, whereas the Kate and Tenzan were triple-seated. The production version was equipped with engine Nakajima’s Homare Model 12 with a takeoff power of 1,825 horsepower and a 4-blade constant speed propeller developed by Sumitomo Metal Industries under license from VDM. However, the 2,000-horsepower engine, advanced aerodynamics, and movable flaps gave it outstanding high-speed performance for an attack aircraft, as well as excellent maneuverability. On the other hand, as described later, the aircraft could not be carried on aircraft carriers, a problem that fundamentally affected the reason for its existence.
From the First World War to the Second World War, each country’s warplanes were developed and designed for different purposes: fighting, bombing, torpedoing and reconnaissance. However, the capacity of conventional dive bombers was becoming inadequate against the increased defensive power of ships, and stronger aircraft were needed to carry larger bombs. On the other hand, torpedo bombers also needed more agile manoeuvrability and the strength to survive. As the performance requirements of the two types of aircraft were close to each other, the integration of the two types of aircraft began to be planned. The integration of the two aircraft types was also desirable from the point of view of carrier operations, which had a limited number of aircraft on board. In addition, the reconnaissance mission, which had previously been carried out by attackers, was to be carried out by a dedicated reconnaissance aircraft (i.e. Saiun). In 1941, in response to this trend, the Imperial Japanese Navy planned to integrate the dive bomber and attack aircraft. Aichi Aircraft, which had a proven track record in the development of carrier-based aircraft, was ordered to develop the B7A1 as the 16-Shi test shipboard attack aircraft based on the Practical Aircraft Test Project.
The main specification requirements were as follows.
• bomber should be capable of horizontal bombing, dive bombing and torpedoing
• the maximum speed should be 555.6km/h or more at an altitude of 5000m with each bomb loaded.
• range, with 500kg bombs, must be at least 1852km in normal conditions and 3333.6km in overloaded conditions.
• takeoff capability is less than 100m (wind speed 12m/s) in overloaded condition with 800kg bomb.
• landing speed is less than 120.4km/h in bombed regular condition.
• can carry 1 x 800kg, 1 x 500kg, 2 x 250kg or 6 x 60kg bombs.
• the aircraft may be armed with either 1 x 850kg or 1 x 1000kg torpedo.
• armed with two 7.7mm machine guns in the wings and one 7.7mm gun in the rear cockpit (later changed to two 20mm cannons in the wings and one 13mm mg).
• its air combat performance exceeds that of the type 99 bomber.
• the structure should be robust, easy to maintain, easy to build and suitable for mass production.
The above text is from the memoirs of Norio Ozaki, the aircraft designer.
The requirements were severe, and in addition, Aichi Aircraft was busy with the mass production and improvement of the current aircraft, so the prototype work stalled. The first prototype, equipped with a NK9C Homare model 11 engine, was finally completed in December 1942 and made its maiden flight in April 1943. This was six months later than planned. However, the completed aircraft was judged by the Navy to be overweight. With a weight of over 3 tons and a regular bombing weight of over 5 tons, the Ryusei exceeded the launch capacity of the prototype Kawasaki catapult, and the conventional landing gear could not be used. Therefore, the weight of the Aichi was reduced by removing armour, air battle flaps, and other equipment, but at the same time, additional equipment such as in-wing tanks in the outer wings was required, and development went nowhere. And as the war changed from fleet air battle to intercepting battle from the land base, the Ryusei, which was a carrier-based attack aircraft, was driven into a state of being half forgotten.
However, a turning point came in the autumn of 1944, when the Ginga, a land bomber, was converted into a night fighter, and there was a shortage of land bombers. Thus, the Ryusei was used as a complementary land bomber to the Ginga, and saw the light of day again. Because of its excessive weight, insufficient strength, and the poor aerodynamic characteristics of the elliptical main wings, the main wings were redesigned as a tapered wing with a straight trailing edge from the second prototype, which was given the abbreviation B7A2, and is said by some to have been called the ” Ryusei Kai ” by those involved. However, engineer Norio Ozaki, who was the chief designer of the Ryusei, wrote in his memoirs that “it may have been mistakenly reported that no such major modifications were made, but that some designs were changed to reduce weight and that the style of the design drawings was changed in preparation for mass production”. In line with this, it was pointed out that “the abbreviation B7A2 for the mass-produced version of the Ryusei is wrong, the abbreviation for the Ryusei, including the mass-produced version, is B7A1, and B7A2 is the abbreviation for the performance-improved version with the engine changed to the Homare model 23”.
Mass production began in April 1944, but due to the high performance of the aircraft and the damage to the factory caused by B-29 bombing and the earthquake in the Tonankai area on 7 December, 1944, production was slow. To decentralise production, the production of the aircraft was shifted to the 21st Naval Air Arsenal at Omura, but this did not speed up production and the war ended. The final number of aircraft produced, including nine prototypes, was about 110. Some were used as experimental aircraft by the Yokosuka Naval Air Station, but by the end of the war, only the 1001st Naval Air Group and the 5th Attack Squadron ( a part of 131st Naval Air Group, 752nd Naval Air Group) operated the Ryusei in actual combat units. The 752nd Naval Air Group, Attack Squadron 5, equipped with the Ryusei, were deployed to Kisarazu Naval Air Station at Chiba Prefecture from May 1945 onwards A small number of aircraft attacked the US and British navy’s fast carrier task force, which was conducting air raids against various parts of the Japanese mainland (including a night torpedo attack that sortied as a second wave attack group at midnight on 25 July), but the results are unknown. On the day of the end of the war, from Kisarazu Naval Air Station, she made a special attack on the aircraft carrier Yorktown off the Boso Peninsula, becoming the “last suicide attack” in the Navy’s official records.