Aichi D3A

In mid-1936, the Japanese Navy issued the 11-Shi specification for a monoplane carrier-based dive bomber to replace the existing D1A biplane then in service.

Aichi, Nakajima, and Mitsubishi all submitted designs, with the former two subsequently being 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 was used for simplicity.

The aircraft was to be powered by the 529 kW (709 hp) Nakajima Hikari 1 nine-cylinder radial engine.

The first prototype was completed in December 1937, and flight trials began a month later, after which it was designated as D3A1.

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 200 knots (370 km/h), and the Navy was already asking for a faster diving speed of 240 knots (440 km/h).

The second aircraft was extensively modified before delivery to try to address the problems.

Power was increased by replacing the Hikari with the 626 kW (839 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.

In December 1939, the Navy ordered the aircraft as the Navy Type 99 Carrier Bomber Model 11.

The production models featured slightly smaller wings and increased power in the form of the 746 kW (1,000 hp) Kinsei 43 or 798 kW (1,070 hp) Kinsei 44.

The directional instability problem was finally cured with the fitting of a long dorsal fin-strake which started midway down the rear fuselage, and the aircraft actually became highly maneuverable.

In June 1942, an improved version of D3A1, powered by a 969 kW (1,299 hp) Kinsei 54, was tested and designated as D3A2 or the Model 12.

The extra power reduced range, so the design was further modified with additional fuel tanks to give it the range needed to fight effectively over the Solomon Islands.

Known to the Navy as the Model 22, it began to replace the Model 11 in front-line units in autumn 1942, and most Model 11s were then sent to training units.

While some late production models of D3A1 were fitted with a propeller spinner, it became a standard with D3A2.

Specifications

Crew

2

Length

10.195 m (33 ft 5 in)

Wingspan

14.365 m (47 ft 2 in)

Height

3.847 m (12 ft 7 in)

Wing area

34.9 m2 (376 sq ft)

Empty weight

2,570 kg (5,666 lb)

D3A1

2,408 kg (5,309 lb)

Gross weight

3,800 kg (8,378 lb)

D3A1

3,650 kg (8,050 lb)

Powerplant

1 × Mitsubishi Kinsei 54 14-cylinder air-cooled radial piston engine

970 kW (1,300 hp) for take-off

1,200 hp (890 kW) at 3,000 m (9,800 ft)

1,100 hp (820 kW) at 6,200 m (20,300 ft)

Other engines

 1st prototype

710 hp (530 kW) Nakajima Hikari I 

2nd prototype

840 hp (630 kW) Mitsubishi Kinsei 3 

D3A1 Model 11 (early production)

1,000 hp (750 kW) Mitsubishi Kinsei 43  

D3A1 Model 11 (late production)

1,070 hp (800 kW) Mitsubishi Kinsei 44  

Propellers

3-bladed metal constant-speed propeller

Performance

Maximum speed

430 km/h (270 mph, 230 kn) at 6,200 m (20,300 ft)

D3A1

387 km/h (240 mph; 209 kn) at 3,000 m (9,800 ft)

Cruise speed

296 km/h (184 mph, 160 kn) at 3,000 m (9,800 ft)

Range

1,352 km (840 mi, 730 nmi)

D3A1

1,472 km (915 mi)

Service ceiling

10,500 m (34,400 ft)

D3A1

9,300 m (30,500 ft)

Time to altitude

3,000 m (9,800 ft) in 5 minutes 48 seconds

D3A1

3,000 m (9,800 ft) in 6 minutes 27 seconds

Wing loading

108.9 kg/m2 (22.3 lb/sq ft)

D3A1

104.6 kg/m2 (21.4 lb/sq ft)

Power/mass

3.9 kg/kW (6.4 lb/hp)

D3A1

4.9 kg/kW (8 lb/hp)

Armament

Guns

2 x forward-firing 7.7 mm (0.303 in) Type 97 aircraft machine guns in the forward fuselage upper decking &

1x 7.7 mm (0.303 in) Type 92 machine gun on a flexible mount in the rear cockpit

Bombs

1x 250 kg (550 lb) under the fuselage and 2x 60 kg (130 lb) bombs under the wings.

 

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