Aichi D3A - Design and Development

Design and Development

In mid-1936, the Japanese Navy issued the 11-Shi specification for a monoplane carrier-based dive bomber to replace the existing D1A biplane currently in service. Aichi, Nakajima and Mitsubishi all submitted designs, and Aichi and Nakajima were both asked for two prototypes each.

The Aichi design started with low-mounted elliptical wings inspired by the Heinkel He 70 Blitz. It flew slowly enough that the drag from the landing gear was not a serious issue, so fixed gear were used for simplicity. The aircraft was to be powered by the 529 kW (710 hp) Nakajima Hikari 1 nine-cylinder radial engine.

The first prototype was completed in December 1937, and flight trials began a month later. Initial tests were disappointing. The aircraft was underpowered and suffered from directional instability in wide turns, and in tighter turns, it tended to snap roll. The dive brakes vibrated heavily when extended at their design speed of 370 km/h (200 kn), and the Navy was already asking for a faster diving speed of 240 kn (440 km/h).

The second aircraft was extensively modified prior to delivery to try to address the problems. Power was increased by replacing the Hikari with the 626 kW (840 hp) Mitsubishi Kinsei 3 in a redesigned cowling, and the vertical tail was enlarged to help with the directional instability. The wings were slightly larger in span and the outer sections of the leading edges had wash-out to combat the snap rolls, and strengthened dive brakes were fitted. These changes cured all of the problems except the directional instability, and it was enough for the D3A1 to win over the Nakajima D3N1.